No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Destruction of cyanide by hydrogen peroxide, in tailings slurries from low bearing sulphidic gold ores
Abstract
The main objective of this work was to determine the effectiveness and kinetics of hydrogen peroxide in destroying cyanide in the tailings slurry from a gold mine with low sulphide and heavy metal content. The impacts of catalyst (Cu) and hydrogen peroxide concentrations, temperature and pH on the extent and rate of weak acid dissociable (WAD) cyanide destruction were investigated. Experiments were conducted using the variable-dose completely mixed batch reactor bottle-point method. Both the rate and extent of CNWAD destruction generally increased with increasing peroxide doses for either absence or presence of Cu catalyst. Catalyst addition was very effective in terms of not only enhancing the cyanide destruction rate but also significantly reducing the required peroxide dosages to achieve CNWAD concentrations of about 1 mg/l, independent of the temperatures tested (10, 20 and 30 °C). The initial cyanide destruction rates increased between 1.2 and 3 folds with the addition of 30 mg/l of Cu. Kinetic experiments showed that in most cases little CNWAD destruction occurred after a reaction time of 2–4 h. The impact of slurry pH on cyanide destruction varied depending upon the dosages of Cu catalyst. Relatively lower peroxide dose/CNWAD ratios required to achieve less than 1 mg/l of CNWAD may be due to lower heavy metals and sulphide content of the ore, resulting in lower peroxide requirement for metal bound cyanides. During cyanide destruction, nitrate was initially formed as a by-product and then possibly converted to other some volatile nitrogen-containing species, as supported by the mass balance calculations.
... The mining industry uses about 18% of the total CN -production [1] [2] [3] [4] [5] [6]. There are different processes to treat the effluents contaminated with CN -, such as biodegradation, alkaline chlorination, INCO process (SO2/air) (International Nickel Company), hydrogen peroxide, Caro's acid method (H2SO4/H2O2), ozonization, reverse osmosis, activated carbon, resins, among others [3] [6] [7] [8] [9] [10]. ...
... For the leaching of gold-containing ores using CN -, this may exist in three forms: total cyanide (CNT), weak acid dissociable cyanide or WAD and CNL [3][4][5][6][7][8][9][10][11]. The CNT includes the strong complexes such as iron cyanides ( . ...
... Peruvian regulations for water quality national standards; establishes the WAD CN in 0.1 mg/L and for CNL is established in 0.022 mg/L. Usually, the research to degrade the CN -ion is focused on the use of cyanide synthetic solutions to experience its destruction [4] [7] [9] [11] [16] [17]. In [7] when using vacuum ultraviolet and ultraviolet/persulfate UVC/(S2O8)2 -there was a complete destruction of 50 mg/L of cyanide in 15 min and 50 min respectively at a pH of 11; [4] when using Caro´s acid reduces the initial free cyanide concentration from 400 mg/L to 1 mg/L, after 10 min and at pH of 9 to 11 at 25°C; [9] when evaluating two non-thermal plasma reactors at atmospheric pressure, eliminates 99% of the CNL in both, from an initial concentration of 1 mg/L at a pH of 11, times of 15 and 3 minutes; [11] when reacting a molar ratio of (H2O2 + NaClO)/CN -= 2:1, oxidizes free cyanide by 98%, from an initial concentration of 100 mg/L, achieving a final concentration less than 0.2 mg/L in 20 minutes at a pH of 9°C and 25°C; [17] when increasing the molar ratio [H2O2]O/[CN -]O in the presence of activated carbon impregnated with copper, eliminates more than 90% of free cyanide in 20 minutes at a pH of 11. ...
Cyanide ion (CN-) is widely used in different industrial operations, such as jewelry, steel manufacture, gold and silver extraction and electroplating. However, industrial emissions containing the CN- ion have to be treated to comply with environmental regulations. This research aimed to degrade free cyanide (CNL) present in the tailing of a metallurgical plant that processes gold-bearing ores and uses sodium cyanide (NaCN) as a leaching reagent. Sodium metabisulfite (Na2S2O5) and sodium metabisulfite with hydrogen peroxide (Na2S2O5 + H2O2) were used as oxidizing agents. To evaluate the effect of the factors, we used a factorial design with three independent variables: stirring time, reagent excess percentage, type of reagent and a dependent variable: CNL degradation (mg/L). According to the analysis of variance (ANPVA), the variables influenced significantly CNL degradation, being the most relevant the reagent excess percentage and according to the results, the maximum CNL degradation was 97.67% when 400% of Na2S2P5 was added with 4 hours of stirring.
... Many studies have analyzed the use of homogeneous or heterogeneous catalysts for the removal of cyanide by treatment with hydrogen peroxide. For instance, catalyzed treatment has been investigated in the presence of Ru/MgO (Pak and Chang 1997), cadmium (Lee et al. 2004), activated carbon (Yeddou et al. 2010), copper (Sarla et al. 2004;Kitis et al. 2005a;Yazici et al. 2006;Chen et al. 2014), copper-impregnated pumice (Kitis et al. 2005b), and copper-impregnated activated carbon (Yeddou et al. 2011). The rate and extent of cyanide decomposition by hydrogen peroxide are dependent upon different factors including the pH, temperature, initial cyanide concentration, hydrogen peroxide concentration, absence or presence of catalyst, and type and concentration of catalyst (Lee et al. 2004;Kitis et al. 2005a;Yazici et al. 2006;Yeddou et al. 2010). ...
... For instance, catalyzed treatment has been investigated in the presence of Ru/MgO (Pak and Chang 1997), cadmium (Lee et al. 2004), activated carbon (Yeddou et al. 2010), copper (Sarla et al. 2004;Kitis et al. 2005a;Yazici et al. 2006;Chen et al. 2014), copper-impregnated pumice (Kitis et al. 2005b), and copper-impregnated activated carbon (Yeddou et al. 2011). The rate and extent of cyanide decomposition by hydrogen peroxide are dependent upon different factors including the pH, temperature, initial cyanide concentration, hydrogen peroxide concentration, absence or presence of catalyst, and type and concentration of catalyst (Lee et al. 2004;Kitis et al. 2005a;Yazici et al. 2006;Yeddou et al. 2010). Sarla et al. (2004) reported that with an initial cyanide concentration of 100 mg/L in an aqueous solution, 90 % of the cyanide was removed in 24 h with 88.2 mM H 2 O 2 at a pH of 10. ...
... Comparing the reaction rate constant for hydroperoxide radical with hydrogen peroxide and hydroxyl radical (k = 2.7 × 10 7 M −1 s −1 ) and the reaction rate constant for hydroxyl radical with cyanide (k = 4.5 × 10 9 M −1 s −1 ) (Gottschalk et al. 2000), it is possible to consider that an excess of hydrogen peroxide might react with the hydroxyl radicals competitively to form hydroperoxide radicals. Other studies have suggested that the cyanide removal increases when increasing the dosages of hydrogen peroxide both in aqueous solution (Yazici et al. 2006) and in industrial wastewater (Kitis et al. 2005a). The dosage of hydrogen peroxide that leads to the maximum cyanide removal in synthetic wastewater is 50 mg/L, representing a mass ratio of H 2 O 2 to CN − of 11.6. ...
This research work evaluates the use of hydrogen peroxide for the removal of cyanide from coking wastewater deriving from the washing of gases in coal combustion furnace. The effect of the presence or absence of suspended solids and organic micropollutants on the efficiency of the treatment is analyzed. Various dosages of hydrogen peroxide (6.5–200 mg/L) were added to both aqueous solution (at pH 10.5) and industrial wastewater (at pH 10.3) samples. The influence of suspended solids in coking wastewater was analyzed by applying a coagulation–flocculation–decantation process before the hydrogen peroxide treatment. The preliminary cyanide removal treatment in aqueous solution showed that the maximum cyanide removal did not exceed 14 % using a mass ratio of hydrogen peroxide to cyanide of 11.6. The maximum cyanide removal obtained in coking wastewater was 47 % with a mass ratio of hydrogen peroxide to cyanide of 12.2 provided that a coagulation–flocculation–decantation pretreatment was applied to remove the suspended solids composed mainly of coal, calcium carbonate, and magnesium carbonate. On the other hand, the cyanide removal treatment in coking wastewater with hydrogen peroxide showed promising results in the removing of different organic micropollutants formed mainly by polycyclic aromatic hydrocarbons and quinolines.
... They are among the most dangerous compounds and their toxicity is essentially due to their aptitude to release free hydrogen cyanide. Many processes are studied or used for the cyanide removal from solution and slurries, mainly oxidation with chlorine, oxidation with hydrogen peroxide (Knorre and Griffiths 1984;Kitis et al. 2005a;Yeddou et al. 2010;Chen et al. 2014), photooxidation (Barakat, Chen, and Huang. 2004), biological degradation (Kuyucak and Akcil 2013), electrochemical processes (Valiuniene, Margarian, and Valiunas 2015), and adsorption (Adams 1994;Adhoum and Monser 2002;Gupta, Balomajumder, and Agarwal 2012). ...
... Nevertheless, this process requires the use of a catalyst to increase the rate of cyanides removal. Soluble copper is in general used in this case (Knorre and Griffiths 1984;Sarla et al. 2004;Kitis et al. 2005a), but despite its effectiveness, being a heavy metal, it requires a downstream elimination. Therefore, heterogeneous catalysis would be more suitable in this case. ...
... The reached percentages of cyanide removal after 450 min are 37%, 41%, 67%, 70%, 81%, and 89%, respectively. Kitis et al. (2005a) and Yeddou et al. (2010) observed, in a previous study that the increase of the amount of catalyst improve the kinetics of cyanides oxidation by hydrogen peroxide. ...
This work is devoted to the removal of free cyanide from aqueous solution by oxidation with hydrogen peroxide H2O2 catalyzed by copper-impregnated activated carbon. Effects of initial molar ratio [H2O2]0/[CN−]0, copper-impregnated activated carbon amount, pH and the temperature on cyanide removal have been investigated.The presence of copper-impregnated activated carbon has increased the reaction rate showing thus a catalytic activity. The rate of cyanides removal increases with the raise of the initial molar ratio [H2O2]0/[CN−]0 and decreases with the increase in the pH from 8 to 12. The increase in the copper-impregnated activated carbon amount from 1.5 to 10g/L in reaction solution has a beneficial effect. Beyond this value, the impact of activated carbon amount is not anymore significant. The temperature does not have a significant effect between 20 and 35°C. The four successive times re-use of catalyst shows a good stability. The kinetics of cyanide removal has been found to be of pseudo-second-order with respect to cyanide and the rate constants have been determined. This process seems very interesting because the rate of cyanides removal is very fast, the reaction does not use soluble metal catalyst and it consumes only hydrogen peroxide as chemical product.
... The reaction between free cyanide and ferrous ions to form a complex is described by Equation (33). Iron-cyanide complexes that are not degraded by hydrogen peroxide are stable in effluents, but the reaction with copper ions increases the possibility of forming copper-iron-cyanide complex, which is insoluble and precipitates rapidly [40]. ...
... Some studies showed the catalytic role of copper in the simultaneous elimination of heavy metals from the effluent [40]. The relatively low decrease in nickel concentration compared to other metals may be in terms of the production of nickel-cyanide complexes that are soluble in the effluent, and the possibility of their removal is relatively low due to their relatively high stability. ...
One of the new methods used to remove the contaminants from effluent is the electrocoagulation method, which is sometimes combined with other methods to increase the removal efficiency of contaminants. To simultaneously remove nickel, cyanide, zinc, and copper, the combined method of photo-electrocoagulation was used along with an oxidizing agent, namely hydrogen peroxide (Hp). In addition, the effects of factors affecting the removal efficiency were studied, including pH, electrode arrangement, and current intensity. An electric current of 300 mA at a pH of 10 for 60 min, Fe-SS electrodes with a distance between them of 5 cm, and hydrogen peroxide at a rate of 4 mg/L were the ideal conditions needed to accomplish the photo-electrocoagulation-oxidation process. According to these study findings, when the combined method of photocatalyst-electrocoagulation-oxidation (Hp) was used, the highest removal efficiencies of nickel, cyanide, zinc, and copper were 85, 96, 94, and 98%, respectively. The results showed that using the combined photo-electrocoagulation-oxidation method increased the efficiency of simultaneous removal of pollutants by 10% compared to conventional electrocoagulation method. The reason for the increase in removal efficiency is the production of hydroxyl radicals simultaneously with the formation of coagulants produced by electrocoagulation process.
... The wafer was kept in a 500 mL, heated (65 °C) DMP solution for 15 min, but almost no improvement was seen. An alternative approach, i.e., applying Caros's acid, removed not only the burnt photoresist but also the underneath TiN layer, as it attacks some base metals (Al, Ti, Ni) in addition to organic materials [38,39]. ...
... The wafer was kept in a 500 mL, heated (65 • C) DMP solution for 15 min, but almost no improvement was seen. An alternative approach, i.e., applying Caros's acid, removed not only the burnt photoresist but also the underneath TiN layer, as it attacks some base metals (Al, Ti, Ni) in addition to organic materials [38,39]. ...
This paper presents a highly sensitive thermoelectric sensor for catalytic combustible gas detection. The sensor contains two low-stress (+176 MPa) membranes of a combination of stoichiometric and silicon-rich silicon nitride that makes them chemically and thermally stable. The complete fabrication process with details, especially the challenges and their solutions, is discussed elaborately. In addition, a comprehensive evaluation of design criteria and a comparative analysis of different sensor designs are performed with respect to the homogeneity of the temperature field on the membrane, power consumption, and thermal sensitivity. Evaluating the respective tradeoffs, the best design is selected. The selected sensor has a linear thermal characteristic with a sensitivity of 6.54 mV/K. Additionally, the temperature profile on the membrane is quite homogeneous (20% root mean standard deviation), which is important for the stability of the catalytic layer. Most importantly, the sensor with a ligand (p-Phenylenediamine (PDA))-linked platinum nanoparticles catalyst shows exceptionally high response to hydrogen gas, i.e., 752 mV at 2% concentration.
... Beberapa proses untuk menurunkan konsentrasi sianida bebas dalam air limbah telah banyak dikaji oleh para peneliti (4,5,6,7,8,9) . Prosesproses tersebut diantaranya adalah pengasaman (acidification) (4) , klorinasi basa (alkaline chlorination), oksidasi kimia, pertukaran ion, penguraian secara alami (natural degradation), penguraian menggunakan mikroorganisme, evaporasi, dan adsorpsi (2) . ...
... Spesi CN dari sianida akan dominan pada pH di atas 9,24 namun spesi HCN dari sianida akan dominan pada pH dibawah 9,24. Nilai pKa dari sianida bebas (CN dan HCN) adalah 9,24 (9) . ...
The processing of gold by cyanidation has an impact on the release of free cyanide into the environment contained in the tailings. Free cyanide is very dangerous because it has very high toxicity. The process to remove free cyanide from tailings is the oxidation-precipitation using a mixture of sulfur and oxygen catalyzed by copper (II). This process can reduce the concentration of free cyanide as well as heavy metals. Free cyanide is oxidized to cyanate and heavy metals are deposited as metal-hydroxide. The optimum parameter of these methods on tailing cyanidation from gold ore Lebak Situ Village-Lebak Gedong District-Lebak Regency-Banten province are the ratio of the weight of SO2/CN- is 7; the catalyst dose is 75 mg/L; pH is 9 and the processing time is 4 hours. Application tests of the optimum parameter were able to reduce free cyanide concentration from 95.8 mg/L to 0.25 mg/L. Wastewater from the processing with this process has fulfilled the specified Quality Standards. The wastewater pollution index value before the treatment process is 136.32, changing to 0.36 after processing. These changes indicate that the oxidation-precipitation process has been able to change the condition of cyanidation wastewater from heavily polluted to better conditions.Keywords: cyanidation, tailing, oxidation, optimum parameter, aplication test, pollution index ABSTRAKPengolahan emas dengan sianidasi berdampak pada pelepasan sianida bebas ke lingkungan yang terkandung di dalam tailing. Sianida bebas sangat berbahaya karena mempunyai toksisitas yang sangat tinggi. Salah satu proses untuk menghilangkan sianida bebas dari tailing adalah oksidasi-presipitasi menggunakan campuran gas sulfur dan oksigen terkatalisis tembaga (II). Proses ini mampu menurunkan konsentrasi sianida bebas sekaligus logam berat. Sianida bebas dioksidasi menjadi sianat dan logam berat diendapkan sebagai logam-hidroksida. Parameter optimum proses tersebut pada tailing sianidasi bijih emas Lebak Situ Kecamatan Lebak Gedong Kabupaten Lebak Provinsi Banten adalah rasio berat SO2/CN- 7; dosis katalis 75 mg/L; pH pengolahan 9 dan waktu pengolahan 4 jam. Uji aplikasi parameter optimum tersebut mampu menurunkan konsentrasi sianida bebas dari 95,8 mg/L menjadi 0,25 mg/L. Air limbah hasil pengolahan dengan proses tersebut telah memenuhi Baku Mutu yang ditetapkan. Nilai indeks pencemaran air limbah sebelum proses pengolahan adalah 136,32 berubah menjadi 0,36 setelah dilakukan proses pengolahan. Perubahan tersebut menunjukkan bahwa proses oksidasi-presipitasi telah mampu mengubah kondisi air limbah sianidasi dari tercemar berat menjadi kondisi lebih baik.Kata kunci: sianidasi, tailing, oksidasi, parameter optimum, uji aplikasi, indeks pencemaran
... The tailings and effluents from the CIP/CIL processes, containing gangue ore and spent solution, must be treated to destroy the cyanide to its less harmful form (i.e., cyanate) by an oxidation reaction (see Eq. 1) (Demopoulos and Cheng, 2004). The destruction process with H2O2 proves to be very effective, as it significantly reduces the concentrations of the complexes contained in the effluents and has been successfully employed for slurries with low sulfide and base metal contents (Kitis et al., 2005). Simulate the thermodynamics of the system will allow to evaluate the stability of the species as a function of pH and hydrogen peroxide concentration. ...
Cyanidation is the predominant process for the extraction of precious metals from their ores. However, given the toxic nature of cyanide, effluents from processing plants must be properly treated to avoid environmental damage. The present work shows a thermodynamic simulation for the identification of predominant species from the oxidation of free cyanide (i.e., HCN and CNˉ) and weak cyanide complexes (i.e., Ag(CN)2ˉ) by employing hydrogen peroxide (i.e., H2O2) at different concentrations (i.e., 1.4×10-2 , 2.1×10-2 , and 2.8×10-2 M). The thermodynamic analysis allowed to determine the stability of the cyanate (i.e., OCNˉ) in the range of alkaline pH values (i.e., 9-11) as a function of the hydrogen peroxide concentration. The results will serve as the basis for the thermodynamic analysis of the oxidation of weak and moderately strong metal-cyanide complexes since the effluents of the cyanidation process do not only contain free cyanide. Understanding the thermodynamics of the cyanide destruction process with hydrogen peroxide will help to adopt practices that will allow the correct disposal of effluents, pulps, or the recycling of water from hydrometallurgical processes, improving water use efficiency.
... La principal ventaja del peróxido de hidrógeno respecto al tratamiento de aguas residuales es el ser un producto químico "limpio", ya que no produce ni libera sustancias tóxicas que contaminen los efluentes (Griffiths et al., 1987;Kitis et al., 2005). ...
This research aims to compare two treatments for detoxification of cyanide mine tailings using hydrogen peroxide, the first one with a concentration of 50% and the second one with a concentration of 70%. The statistical tool ANOVA was used, together with the tukey method, to determine the differences and similarities of both treatments. The study was carried out in two trains composed of five tanks each, the treatment was randomized (DCA) for a period of 21 hours, obtaining a cyanide sample from each tank every hour. The results showed that the 70% peroxide treatment provides higher cyanide removal (<0.05 ppm), lower solvent consumption (975 kg) and lower consumption ratio (0.58 kg/m3), also, a solvent saving of 36% was obtained; the ANOVA analysis showed a significant influence between the peroxide concentration and cyanide removal, and also, that there is no relationship between the detoxification time and the final cyanide concentration for both treatments. In sum, the 70% peroxide treatment allows an effective cyanide removal, complying with the maximum permissible limits for its discharge, in accordance with the Peruvian legislation in force.
... Cyanide can be removed through physical, chemical and biological treatments [6][7][8], the most widely used of which are chemical methods including acidification [9], alkaline chloride oxidation [10], SO 2 -air oxidation [4], hydrogen peroxide oxidation [11] and ozone oxidation [12]. However, the above traditional treatments do not work satisfactorily for cyanide residues due to the high content of stable metal complex cyanides adsorbed on the ...
The toxic cyanides in gold cyanide residues produced in the cyanidation process of gold extraction threaten environmental safety and inhibit the recovery of valuable metals. In this study, the removal of cyanide through the persulfate-advanced oxidation process was investigated, and heat activation and ultrasonic activation were tested for cyanide removal. The results showed that cyanide in cyanide residue could be removed by 2.0 wt.% potassium persulfate at pH 10.0 after 60 min reaction with a removal efficiency of 53.47%. The removal efficiency increased to 62.18% at T = 60 °C for heat activation and 74.76% with an ultrasonic power of 100% for ultrasonic activation. The cyanide content in the toxic leaching solution of the residue after the ultrasonic-activated persulfate-advanced oxidation process (3.84 mg/L) reached the national standard of China. Two kinds of free radical scavengers, tert-butanol and methanol, were used to investigate the generation of free radicals. The results showed that both SO4•− and HO• were produced and accelerated the oxidation of cyanide, and HO• played a major role under alkaline conditions. According to XPS analysis, the oxidation of ultrasonic-activated persulfate focused on cyanide removal rather than pyrite in cyanide residue. More cyanides were transferred from the cyanide residue to the liquid phase, leading to the high efficiency of ultrasonic activation. The ultrasonic-activated persulfate-advanced oxidation process has potential application prospects for the treatment of gold cyanide residues.
... The tailings and effluents from the CIP/CIL processes, containing gangue ore and spent solution, must be treated to destroy the cyanide to its less harmful form (i.e., cyanate) by an oxidation reaction (see Eq. 1) (Demopoulos and Cheng, 2004). The destruction process with H2O2 proves to be very effective, as it significantly reduces the concentrations of the complexes contained in the effluents and has been successfully employed for slurries with low sulfide and base metal contents (Kitis et al., 2005). Simulate the thermodynamics of the system will allow to evaluate the stability of the species as a function of pH and hydrogen peroxide concentration. ...
A nivel mundial, la actividad ganadera genera impactos negativos en el medio ambiente. Se consumen 16,000 L por kg de carne producida y se liberan diversos compuestos contaminantes. Sinaloa es uno de los principales estados productores de alimentos de México. En el presente trabajo se evaluaron las características fisicoquímicas de un agua residual ganadera (ARG) real de la capital Sinaloense. Con base en dicha caracterización, se realizaron propuestas de tratamiento y reúso del ARG. Se tomaron muestras en época de lluvias y estiaje (2021-2021), en el efluente de una empresa productora de cárnicos. Se realizaron mediciones in situ de pH, conductividad, pOR y temperatura. Posteriormente, se realizó un pretratamiento basado en la eliminación de SST y turbidez para realizar las siguientes determinaciones: DQO, COT, NT, N-NO3- , PT, P inorgánico, Fe y Cu. También, se realizó la determinación de compuestos benzimidazoles (BZ) mediante un HPLC con detector UV-Vis. Los principales hallazgos fueron la detección de 50 mg/L de BZ y concentraciones de COT (1181.8 ± 90.79 mg/L). En época de estiaje se cuantificaron 0.65 y 4.55 mg/L de Fe y Cu, respectivamente. Con base en lo anterior, en las condiciones de los terrenos y en pruebas de tratabilidad, se propuso el tren de tratamiento. Este consiste en un pretratamiento de acidificación con control de variables, seguido de un proceso oxidación avanzada UV/H2O2. Esto permitiría, teóricamente, alcanzar niveles de tratamiento para el reúso del agua.
... As described in Fig. 2, the detoxification process consists of two stages of material mixing with different solutions, followed by filtration and drying. First, SPL was mixed with 3 M H 2 O 2 solution with cyanides been destroyed according to Eq. (1) [37]. Subsequently, 0.2 M NaOH solution was used for the decomposition and removal of fluoride salts in the form of sodium fluoride and sodiumaluminum hydroxide according to Eq. (2) [38]. ...
Spent potlining (SPL) consists of the carbon cathodes (1st cut), aluminosilicate refractories, and the insulation lining of Hall–Héroult cells (2nd cut) used in aluminum smelting. SPL is classified as hazardous material due to its high content in soluble fluoride salts and the presence of cyanides. The 1st cut contains considerable amount of carbon in graphitic form that can exceed 65 wt%; however, during cell’s dismantling process inevitable mixing with the 2nd cut occurs causing its contamination with undesirable aluminosilicates. The study investigates the selective recovery of graphite from SPL sample and its separation from mullite and quartz through flotation. Prior to this, SPL has been subjected to special chemical treatment to render it safe for use by minimizing cyanides and free fluorides content through leaching with H2O2 and NaOH, respectively. Flotation tests were carried out aiming at the maximization of carbon grade and recovery in the concentrate, while minimizing silicon content. The effect of pH, collector, and sodium silicate (depressant) dosage was investigated on two feeds of different granulometry (− 90 μm, 90–420 μm) and optimum conditions were determined. For pH 8 and kerosene dose of 500 g/t, carbon grade and recovery in the concentrate reached 85.6 wt% and 85.1% for the fine sample (− 90 μm), and 84 wt% and 94.9% for the sample with particle size 90–420 μm, respectively. The results clearly show that mullite and quartz were effectively separated since the silicon content was less than 1 wt% in both concentrates. Further grade improvement is possible through further size reduction of the concentrate and subsequent alkaline leaching towards elimination of fluoride salts and cryolite.
... In remote locations H 2 O 2 production from H 2 and O 2 (both H 2 and O 2 can be produced from water electrolysis using cheaper renewable electricity) would be economically viable alternative in the near future if direct H 2 O 2 process is developed successfully. [23][24][25][26] Chemical Synthesis As a powerful and environmentally benign oxidizing agent, H 2 O 2 has many applications in chemical industry [27][28][29][30][31][32][33][34][35][36][37] Cosmetics & Medicine H 2 O 2 is used in cosmetics and personal care products as an antimicrobial agent and as an oxidizing agent [38][39][40] Electronics H 2 O 2 is used for pickling of metal surfaces as well as for cleaning of silicon discs in the production of printed circuit boards [41][42][43][44] Environmental Applications Ecological friendliness properties of H 2 O 2 are utilized in a variety of environmental applications [45][46][47][48][49][50] Food Processing Due to its remarkable chemical properties and biological degradability, H 2 O 2 is often utilized in food processing applications [51][52][53][54][55] Mining H 2 O 2 is used as an oxidizing agent and oxygen source in various metallurgical process steps [56][57][58][59] Pulp & Paper In pulp & paper industry H 2 O 2 is employed as a versatile bleaching agent [60][61][62][63] Recycling In recycling of solid municipal waste H 2 O 2 is used as oxidant and bleaching agent [64][65][66][67][68] Textile Bleaching H 2 O 2 is used as bleaching agent for the treatment of natural and synthetic fibers [69][70][71][72][73] ...
21 st century global market place is moving towards subtainable development and without this approach our future would be at risk. Today's chemical industries need to give more focus for the planet through improving the environmental footprints of fuels and chemicals manufacturing processes. Oxidation and hydro-genation processes are widely used in the production of chemicals and fuels. Oxidation processes are especially important to convert petroleum-based materials to useful petrochemicals of higher oxidation state. Many existing oxidation processes, however , still rely on the use of stoichiometric oxidants, such as dichromate/sulfuric acid, permanganates, periodates, chromium oxides, osmium oxide etc., and remain a major source of environmental pollution. Therefore, oxidation processes using eco-friendly oxidizing agents such as molecular oxygen, ozone and hydrogen peroxide (H 2 O 2) are incresingly becoming important to improve the environmental sustainability. Hydrogen peroxide is especially attractive for the liquid-phase oxidation due to the presence of high percentage of active oxygen and the production of water as only by-product. As a result, H 2 O 2-based eco-friendly oxidation processes are gradually replacing some well-established processes such as production of propy-lene oxide, caprolactam, phenol etc. Moreover, recent advances in the area of oxidation catalysis is promoting H 2 O 2-based technologies to emerge as a frontline, eco-friendly sustainable processes. H 2 O 2 is also finding greater applications in pulp/paper industries and waste water treatment as a substitute of chlorine-based oxidizing agents. Herein, we have analyzed various reactions using H 2 O 2 as an oxidant and their recent advancement to bring important aspects of H 2 O 2-based oxidation processes and catalysis. Moreover, various aspects of using H 2 O 2 toward development of sustainable oxidation processes have been analyzed with respect to factors affecting the end uses in chemical industry such as efficiency, catalyst and reaction pathways. We have reviewed manufacturing trends of H 2 O 2 and emerging applications of H 2 O 2 in sustainable oxidation processes. Critical discussions have also been made on the opportunities and challenges with emerging H 2 O 2 based oxidation processes in the production of bulk as well as specialty chemicals.
... Conventional cyanide detoxification techniques predominantly involve separation or destruction, and may be grouped under physical, adsorption, complexation and/or oxidation methods, with the commonly used ones being the sulfur oxide/air, hydrogen peroxide and alkaline chlorination process (Akcil, 2003;Kitis et al., 2005;Kuyucak and Akcil, 2013). Degradation pathways are sensitive to the cyanide concentration and the physicochemical conditions such as oxygen concentration and pH of the media (Ebbs, 2004;Baxter and Cummings 2006;Kumar et al., 2017). ...
Cyanide, a carbon-nitrogen radical, is a major building block in many industries including pharmaceuticals, petrochemical and gold processing. In the gold extraction industry, cyanide has been the universal lixiviant for over a century due to better understood process chemistry, among others. Industries that discharge cyanide-laden effluents are mandated to keep concentrations below 0.2 mg/L to prevent death by cyanide-intoxification, which occurs when cyanide binds to key iron-containing enzymes and prevent them from supplying oxygen-containing blood to the tissues. Techniques used to attenuate cyanide in wastewater can broadly be grouped into chemical, physical and biological methods. In recent times, attention has been placed on biotechnological methods, which make use of cyanotrophic microorganisms to clean up cyanide-contaminated environments. This paper reports on studies set out to assess the ability of Phanerochaete chrysosporium to degrade cyanide under different conditions including changes in cyanide concentration, culture mass, time, closed system and open system. At the end of 24-hour contact in an open agitated system with initial pH of 11.5, a control experiment using 100 mg/L cyanide revealed a natural attenuation of 15% with pH decreasing to 9.88, while the best myco-detoxification of 85% was achieved by contacting 100 mg/L cyanide with 0.5 g culture mass, translating into degradation capacity of 17.2 mg/g (milligram of cyanide per gram of culture) with pH reducing to 8.4 in 24 hours. The degradation could be based on a number of mechanisms including hydrolysis to HCN, oxidation to cyanyl radical and cyanate due to natural attenuation through atmospheric contact, and secretion of organic acid, oxidative enzymes, and hydrogen peroxide by the fungus. Keywords: Cyanotrophic Organism, Myco-Detoxification, Cyanide-Laden Effluents, pH
... This result is based on the greater capability of dissociation of the complex, than on the oxidation of cyanide to cyanate. In that study, the use of hydrogen peroxide in the treatment of iron cyanide complex did not show a complex degradation (Young et al., 1995;Kitis et al., 2005). ...
Ferricyanide Fe(CN) 6 3- is one of the most stable cyanometallic complexes present in the gold mining effluents. This cyanocomplex is hard to degrade by natural attenuation and generates a negative impact on aquatic environments. Although free cyanide (CN-) can be obtained by acidifying the solution, the CN- is lethal for all forms of life. The oxidation of Fe(CN) 6 3- in a typical photocatalitic system was evaluated with the addition of H2O2. To verify the degradation, chemical parameters, such as free cyanide, the formation of ammonia, nitrate, and total iron were analyzed at the end of the process. Different parameters were evaluated to analyze the behavior of the degradation: 1. dark stage adsorption using the catalyst, 2. the TiO2 dosage, 3. Addition of H2O2, 4. UV radiation power (120 and 200W) and finally a test of TiO2 with solar radiation. The photolysis effect from a ferricyanide solution at 100 mg L-1 at alkaline pH 13, showed that the complex studied is highly stable since under UV irradiation conditions (l> 300 nm), a low rate of dissociation was observed. After 24h of irradiation, the cyanocomplex was under 20%, whereas degradations up to 70% were obtained in a heterogeneous photocatalysis system with TiO2. The best result was achieved with the H2O2 and TiO2 photocatalytic system, and the stoichiometric concentration was about 2.5 times less than the peroxide used in the gold mining industry, reaching 83% degradation. The photocatalytic process obtained less toxic byproducts than the original synthetic ferricyanide used as mining wastewater.
... The processes that are currently applied for the neutralization of cyanide, seek oxidation of the same. Among the most used processes to oxidize cyanide are: treatments with ozone, potassium permanganate, chlorine, sodium hypochlorite, Caro acid, titanium dioxide, quicklime, hydrogen peroxide, aeration, biological process, among many more (Dash et al., 2009;Gaviria and Meza, 2006; Jawale et al., Kitis et al., 2005;Potivichayanon et al., 2017). However, in the industrial environment the best technical procedures are those of alkaline chlorination (sodium hypochlorite), hydrogen peroxide and ozone. ...
Cyanide is one of the most used reagents in the precious metal extraction process; as well as the most efficient from the point of view of the dissolution process, but it is also a toxic product that requires a lot of care in handling. Likewise, the residual solutions of the process must be followed because they can be a risk of contamination of water, animals and human health. In the artisanal processes of obtaining gold and silver, neutralization of the residual solutions is used to passivate the present cyanide. During this process ammonium cyanate is formed which decomposes rapidly in the presence of air and sunlight in carbon dioxide and ammonia gas, contributing to the greenhouse effect. In this work, the use of the ammonium cyanate obtained in the process of neutralization of the cyanide solutions as a reagent to obtain urea is proposed. Urea was obtained indirectly through the use of the reagent kit UREA/BUN-COLOR. The process is effective at pH ≤ 4.5 with a rapid increase in solution temperature and the addition of hydrogen peroxide. The urea crystals begin to form at 50°C. The cyanide/urea ratio obtained was 1/7.5.
... There are a number of cyanide treatment processes, e.g., biological treatment, adsorption by activated carbon, oxidation by various oxidants such as sulfur dioxide/air, hydrogen peroxide, Caro's acid and alkaline chlorination [1][2][3][4][5]. The applicability of biological process for the treatment of cyanide water is somewhat limited due to its extreme environment. ...
A novel dielectric-barrier-discharge (DBD) loop reactor was designed for the efficient degradation of cyanide anion (CN⁻) in water. The circulation of cyanide water as a falling film through plasma gas discharge zone enhanced gas–liquid mass and energy transfer and induced formation of H2O2 which was associated with the efficient destruction of CN⁻. It was observed that among different discharge gases, the CN⁻ degradation rate decreased in the order of Ar > air > H2/air mixture. Depending on discharge voltage, the treatment time for complete removal of 100 ppm CN⁻ in this DBD loop reactor is in the range 120–300 min. The dose of Cu²⁺ catalyst in combination with in situ production of H2O2 enhanced the destruction of CN⁻ apparently in this DBD loop reactor. The treatment time for complete degradation of 100 ppm CN⁻ decreased from 180 min with Ar DBD discharge alone to 40 min with 40 mg/L dose of Cu²⁺ ion in water, making it an efficient means to degrade cyanide water.
... Photocatalytic degradation of cyanide in wastewater using a nano-thin film photocatalyst is also reported (Pala et al., 2015). Although the chemical methods are well established, they generally suffer from some serious shortcomings such as their inability to degrade stable CN-metal complexes, requirement of expensive reagents and equipment (Patil & Paknikar, 1999), maintenance and royalty payments and generation of chlorinated compounds as byproducts (Akcil & Mudder, 2003;Khamar, Makhdoumi-Kakhki, & Mahmudy Gharaie, 2015;Kitis, Akcil, Karakaya, & Yigit, 2005). In such a scenario, the remediation of cyanide contaminated sites such as solid mine tailings, abandoned mining areas, and former gas manufacturing plants (MGP) using biological agents (micro-organisms or plants) is a potential solution. ...
Mining industry has been using cyanide for more than ten decades to recover precious metals such as gold and silver. The presence of cyanide in the environment has long been a matter of concern due to its high toxicity to human, animal, and aquatic life. The available treatment processes either physical or chemical are suffered with issues such as operating conditions, generation of secondary pollution, and lack of cost effectiveness. A number of micro-organisms are capable to consume cyanide as a source of carbon and nitrogen, and convert it into ammonia and carbonate. Some plants are also efficient in cyanide attenuation process. Bioremediation of cyanide might be an efficient, cost-effective, eco-friendly, and an attractive alternative to the conventional physical and chemical processes. This paper reviews the recent advances in remediation of cyanide contaminated tailings via micro-organisms and plants. Aspects such as speciation, toxicity, source, and degradation mechanisms of cyanide are discussed. Factors affecting functioning of micro-organisms and plants as bioremediation agents are also highlighted.
... Several biological, physical and chemical techniques have been developed for the treatment of CN − solutions (Kitis et al. 2005;Kuyucak and Akcil 2013;Sarla et al. 2004). Biological treatments are a feasible alternative and environmental friendly; however, these techniques are mostly used for polishing applications because they cannot treat a highly concentrated CN − waste (Dash et al. 2009a). ...
In this work, the removal of cyanide from aqueous solutions was accomplished by using the synergetic effect of activated carbon and an oxidizing agent. A basic-character coconut shell activated carbon (CAC) was used; experiments were conducted in a semi-batch reactor, at 25 °C, initial pH of 11.5, and using cyanide solutions with initial concentration up to 1200 mg/mL. In particular, the beneficial effect of an oxidizing agent such as air, oxygen or ozone on the removal of cyanide by CAC was evaluated. At the optimum operating conditions found in this study, 1200 mg/mL of cyanide were totally decomposed in about 3 h, by using 1 g of CAC and about 2 mgO3/min. The experimental results were rationalized based on different mechanisms reported in the literature. The findings provide the basis to optimize the removal of cyanide from aqueous solutions in mining or metallurgical effluents by using the synergetic effect of CAC and ozone.
... The cyanide is exceptionally stable and difficultly degraded in the environment, and liquid effluent from plants employing cyanides industrially must be effectively treated. Numerous conventional treatment methods, such as alkaline chlorination [7], hydrogen peroxide [8], ozonation [9,10], air oxidation [11], ion exchange [12,13], sulphur-based technologies and biological processes [14,15], have been used in treatment process of containing cyanide wastewater. The operating costs for destruction of cyanide by some chemical and physical technologies are typically expensive. ...
This work was to investigate the electrolytic oxidation of cyanide solution with the Ti/SnO 2 -Sb-Ce anode under different conditions, such as initial pH, current density and flow rate. The results show that the destruction of cyanide on the anode is more favorably and completely conducted in strong alkaline solution. The conversion of cyanide and COD removal are 98.2 % and 84.2 % at initial pH 13 at reaction time of 4 h, but 69.5% and 48.2 % at initial pH 6, respectively. The conversion of cyanide, COD removal and current efficiency (CE) increase as the flow rate and applied current density increase, respectively, but the higher flow rate, the smaller is the increment extent of conversion of cyanide, COD removal and CE. The CE for destruction of cyanide was proved to be inversely proportional to the applied current density.
... The efficacy of hydrogen peroxide as oxidant for gold dissolution during the cyanidation of pyritic ore has been evaluated (Stoychevski and Williams, 1993). Oxidation by Hydrogen peroxide was selected as the most appropriate route during an investigation into a means of detoxifying cyanide in tailings slurry from a gold mine (Castrantas et al., 1988;Kitis et al., 2005). ...
... Although cyanide degradation with those oxidants is adequately fast and efficient for various types (compositions) of effluents, there are cases in which a high dosage of the oxidant may be necessary to achieve a higher reaction speed and cyanide removal efficiency level -for example, in the detoxification of slurry effluents (Kitis et al., 2005 ). In such cases, although it is possible to enhance the oxidation reaction by simply increasing the oxidant dose, other (more powerful) oxidants may be considered in order to attain the legal discharge limits while aiming at minimizing operating costs. ...
... This is due to the fact that it undergoes natural oxidation converting the cyanide to CO 2 and N 2 . Based on this process, there are currently a number of commercially available processes, both chemical and biological, to treat cyanide solution effluents and decontaminate concentrates from cyanide leaching operations (Akcil, 2002(Akcil, , 2003Barriga-Ordonez et al., 2006;Dash et al., 2009;Fatma et al., 2009;Gupta and Mukherjee, 1990;Kitis et al., 2005;Ozel et al., 2010;Parga et al., 2003;Patil and Paknikar, 2000;Yeddou et al., 2010). Aside from this, waste effluents can be treated using physical methods such as carbon sorption and the use of membrane technology (Deveci et al., 2006;Gonen et al., 2004;Lien, 2008). ...
This research proposes a new conceptual process to economically extract platinum group metals (PGMs), and as a secondary aim, base metals (BMs) from a low-grade concentrate originating from typical PGM concentrator plants. Slurry made from the concentrate was coated onto granite pebbles and packed into a column, in which it was bioleached with a mixed culture of thermophiles and mesophiles at 65 °C. After 30 days the extractions achieved were 52% copper, 95% nickel and 85% cobalt. The residual concentrate material was subsequently subjected to a cyanide leach also in a packed column operating at a room temperature of 23 °C. After 21 days 20.3% Pt, 87% Pd and 46% Rh were extracted. Using these results and projected extractions over longer operating times, a conceptual flowsheet was proposed for a possible process route to recover PGM values circumventing the problematic smelter route for this material.
... Attempts have been made for removal of cyanide from water by several methods like biological treatments, INCO process (by SO 2 =air), Caro's acid, ozonation, electrolytic oxidation, ion exchange, AVR (acidification, volatilization, and reneutralization) process, reverse osmosis, activated carbon adsorption, biological treatments, photocatalytic and catalytic oxidation (5,6,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). However, plants based on these methods have often failed in successful removal of cyanide and the other major pollutants from wastewater and the drawbacks are well documented (3,5,22,23). ...
Investigations on separation of cyanide from coke wastewater were carried out in a cross flow nanofiltration membrane module following microfiltration of real industrial wastewater. Different composite polyamide nanofiltration membranes were used in the system while studying their effectiveness in cyanide separation under different operating conditions. Transmembrane pressure, pH and cross flow velocity exhibited strong influence on percentage removal of cyanide. 94% cyanide rejection with a permeate flux of 79 liters per hour at a transmembrane pressure of 13 kg/cm and at a volumetric cross flow rate of 700 liters per hour was achieved. The membrane module with a composite membrane having high negative charge was successfully operated without any significant loss in flux even after 72 hours operation. These encouraging results show that microfiltration and nanofiltration with properly selected membranes in an appropriate module could lead to a practical solution to a longstanding problem of cyanide removal from industrial wastewater.
The toxic cyanides in cyanide residues produced from cyanidation process for gold extraction are harmful to the environment. Pyrite is one of the main minerals existing in cyanide residues. In this work, the interaction of cyanide with pyrite and the decyanation of pyrite cyanide residue were analyzed. Results revealed that high pH value, high cyanide concentration, and high pyrite dosage promoted the interaction of cyanide with pyrite. The cyanidation of pyrite was pseudo-second-order with respect to cyanide. The decyanation of pyrite cyanide residue by Na2SO3/air oxidation was performed. The cyanide removal efficiency was 83.9% after 1 h of reaction time under the optimal conditions of pH value of 11.2, dosage of 22 mg·g−1, and air flow rate of 1.46 L·min−1. X-ray photoelectron spectroscopy analysis of the pyrite samples showed the formation of Fe(III) and FeSO4 during the cyanidation process. The cyanide that adsorbed on the pyrite surface after cyanidation mainly existed in the forms of free cyanide (CN−) and ferrocyanide (Fe(CN) 4−6 ), which were effectively removed by Na2SO3/air oxidation. During the decyanation process, air intake promoted pyrite oxidation and weakened cyanide adsorption on the pyrite surface. This study has practical significance for gold enterprises aiming to mitigate the environmental impact related to cyanide residues.
This work is concerned with the cyanide removal from aqueous solution by oxidation with hydrogen peroxide H2O2 catalyzed by copper zinc oxide (CuO-ZnO) nanoparticles prepared by co-precipitation method. The influences of catalyst dose, hydrogen peroxide concentration, temperature, and catalyst stability on cyanide removal were examined. The use of CuO-ZnO nanoparticles made it possible to increase the reaction rate, thus showing good catalytic activity. The cyanide removal percentage was increased after 75 minutes of reaction time from 70% to 100% by raising the catalyst dose from 0.25 g/L to 1.0 g/L. Increasing the temperature from 24 °C to 35 °C enhanced cyanide removal rate, the apparent activation energy was then found to be equal to 48 KJ/mol. The nanocatalyst was used again for four successive times and exhibited good stability. The kinetics of cyanide elimination was found to be pseudo-first order with respect to cyanide.
Cyanide tailings are the bulk solid waste generated by the production processes of gold mines. Since the highly toxicity of cyanide affects its disposal and comprehensive utilization, a decyanation treatment is needed. However, wide-ranging industrial uses of the current decyanation methods are restricted due to the treatment effects and costs. Based on the natural degradation method, the cyanide treatment effect was enhanced by raising the treatment temperature, increasing the ultraviolet (UV) irradiation and turning the pile periodically. Using the Arrhenius equation, the activation energies of the cyanide hydrolysis reactions were calculated as 52.22 kJ/mol and 34.59 kJ/mol for heating alone and for heating combined with UV irradiation, respectively. At 60 ℃, the cyanide tailings reached the discharge standard (leachate, total cyanide (CNt)< 5 mg/L) after 8 h of treatment. Moreover, after adding UV irradiation (with an intensity of 120 μW/cm2) and a hydrogen peroxide spray (spraying intensity, 2 mL/kg) to the above conditions and shortening the treatment time to 7 h, the cyanide tailings reached the standard for use in building materials (leachate, CNt <0.5 mg/L). Based on these results, UV irradiation, ventilation, spraying and pile-turning were integrated into the solar drying room to form an enhanced natural degradation system, which was applied in the semi-industrial scale treatment of the cyanide tailings. The results showed that the cyanide tailings consistently met the standards for discharge and use in building materials, successfully verified the conditions and effects of the laboratory treatment, and reduced the treatment cost by more than 50 %.
In this study, the solid–liquid separation washing wastewater from cyanide tailings was used as the research object, and the acidification iron salt precipitation process was used to purify the cyanide in the wastewater. The results show that the total cyanide content of the wastewater is greatly reduced after acidification stripping treatment. After acidification, ferrous sulfate is added to the filtrate for precipitation treatment, and the total cyanide content in the wastewater can be reduced to less than 50 mg/L. the treated wastewater can be used in the washing process of cyanide tailings. Therefore, acidification iron salt precipitation process can realize the recycling of wastewater after solid–liquid separation and washing.KeywordsAcidificationIron salt precipitationCyanide containing wastewaterWashing and purification
Synthesis of nanoparticles through physical and chemical processes for several applications is common, but it is often expensive and involves inorganic chemicals. For the first time, in this study, a simple and novel approach for producing a CuO-loaded Alocasia macrorrhizos stem biomass (ASB–CuO) nanocomposite that is effective in cyanide degradation has been presented. The CuO nanoparticles (CuO NPs) synthesis was revealed by UV spectroscopy at a wavelength of 247 nm. The CuO NPs on the dried ASB surface were well scattered and mostly spherical, as revealed by SEM/EDX analysis. The crystalline structure of ASB–CuO was established by XRD investigations. For the elimination of cyanide from aqueous systems, it was shown that the nanocomposite of ASB–CuO had a higher removal performance than the raw ASB. A catalytic test on the efficacy of ASB–CuO in removing cyanide (100 mg/L) from wastewater revealed a removal efficiency of 90% within 60 min. Different factors, such as contact time, dosage, initial concentration, and temperature were examined. The cyanide removal followed pseudo-second-order kinetics with the ASB–CuO having higher rate constant than the raw ASB. Furthermore, the produced nanocomposite was able to remove 90% of cyanide from real wastewater samples, as demonstrated by removal studies on the tailings water samples of a gold cyanidation operation.
Because of the highly toxic cyanide in the gold cyanide residues, cyanide must be removed for environmental protection. The process mineralogy of residues was studied firstly, and then cyanide removal was carried out by three chemical methods. The results showed that the residue mainly contained Si, S and Fe. Pyrite was the main metallic mineral, and the iron-complex cyanides make cyanide removal difficult. The minerals in residues were in ultrafine particle size with high monomer dissociation degrees. In H2O2 oxidation process, the self-decomposition and side reactions resulted in high consumption of H2O2. In Na2S2O5-air oxidation process, the time for complete process was long because of the reactions between Na2S2O5 and O2. Na2SO3 oxidation method was found to be a new method for cyanide removal without air inflation device. The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na2SO3 dose of 2.0 g/L.
Cyanide tailings are the major hazardous wastes generated in the production process of the gold industry, which not only contain highly toxic cyanide, but also contain heavy metals with recycling value and other substances suitable for building materials or filling. These tailings are in urgent need of purification treatment and safe utilization. In this study, the impacts of treatment methods, types and combinations of reagents on decyanation effect were researched. Gold in cyanide tailings was recovered by flotation, and flotation tailings were used for filling after identifying the properties of solid waste. Results are as follows: (1) INCO method and 5 reagents (sodium sulfite, sodium persulfate, copper sulfate, ferrous sulfate and zinc sulfate) were selected for synergistic decyanation treatment, and cyanide concents in slurry and leaching solution were decreased to the minimum. (2) The gold recovery rate of the tailings through flotation was increased by 27.8% than without detoxification. (3) Flotation tailings were identified as general industrial solid wastes by leaching toxicity and toxic substance content analysis. (4) As filling aggregate, under the conditions of slurry concentration of 63% and cement-sand ratio of 1:6, the strength filling body of flotation tailings reached 1.32 Mpa after 28 days of maintenance. (5) This process and combined reagents were applied to engineering. The cyanide content in the leaching solution and the flotation recovery rate of gold were kept below 0.2 mg/L and above 60% respectively, and the strength of the filling body was stable to meet the requirements of underground filling.
At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution method developed in this research was extended for engineering. Results showed that the optimum elution conditions were determined to be: stirring elution, tailings/water ratio (M/V; 1:1) and operating time (10-20 min). Besides, 4 reagents (sodium dodecyl benzene sulfonate, cyclodextrin, sodium silicate and calcium hydroxide) were selected from four categories of 21 reagents for further composite elution. The cyanide elution rate was the highest (90.7%±0.1%) while the molar ratio of these 4 reagents was 5:2:2:1. Moreover, the combination of reagent elution and positive pressure filtration improved the elution efficiency of cyanide (92.6%±0.8%). And the cyanide content in the toxic leaching solution was lower than the standard value (5.0 mg/L). Furthermore, the composite elution method developed in this study was also extended for engineering. The concentration of cyanide in the leachate was < 5.0 mg/L, and was stable during 189 days of detection. Notably, the effluent can be reused directly, or reused after further treatment. The zero discharge of effluents and solid wastes was realized in the processes. The above results provided supports for the engineering treatment of cyanide tailings.
Given that mining is considered to be an essential activity for Mexico’s industrial development, cyanide has been increasingly used to recover precious metals such as gold and silver. Along with that arises the need to develop new technologies to treat the wastes (mining tailings). In addition to their high cyanide content, metal and other contaminants that are found in tailings also present a problem. As a result, conventional (physicochemical) strategies have been developed to reduce contamination from tailings, nonetheless, these have high operating costs and generate unwanted by-products. For this reason, studies have begun to focus on non-conventional strategies to treat free cyanide and cyanide complexes such as fungi, bacterial consortia, and pure bacteria. These are important because of the mechanisms involved in degrading or modifying contaminants at neutral to high pH levels, which convert contaminants into non-hazardous products. The ability of microorganisms to grow at an alkaline pH prevents HCN volatilization. These studies have been performed at the laboratory level using two types of microbial binding: suspended biomass and immobilized biomass. They have used both natural (granite rock, citrus peels, cellulose, gravel) and synthetic (stainless steel, geotextiles, alginate, plastics) packing material, as well as reactors with different types of flow, namely, batch and continuous.
Over the past century, many problems have been focused on the problems of low leaching rate of gold and methods have been developed to intensify the leaching of gold. Among these methods, the use of hydrogen peroxide to accelerate the leaching of gold is known. In order to intensify the leaching process, the indicators of cyanide leaching of gold from ore using hydrogen peroxide were studied. This article presents the results of assay-gravimetric, chemical, and mineralogical analyses of gold-bearing ore from the Sari Gunay Deposit (Iran). The content of sulfide sulfur ore belongs to the category of low-sulphide, by oxidation of sulphur (50.70%) to the category of oxidized ores. Thermodynamic analysis of possible reactions of ore components with hydrogen peroxide is carried out. Laboratory studies on cyanide leaching of gold have shown that the maximum recovery of gold is 52.92% at a concentration of hydrogen peroxide of 0.5%, the recovery of gold without ore treatment is 52.03%. The results of laboratory and column tests with and without treatment with hydrogen peroxide (H2O2–0.5%) were compared. Treatment of gold-bearing ore with hydrogen peroxide during heap leaching of gold increases gold recovery by 1.2% and amounts to 55.89%, without treatment - 54.69%. This increases the consumption of sodium cyanide by 0.04 kg/t.
In this work, the cyanide tailings were treated with slurry electrolysis technology. The removal of cyanide and the regularity of the oxidative dissolution of the main minerals in tailings during direct electrolysis (ET), air electrolysis (ETA), and NaCl electrolysis (ETC) were compared and analyzed. X ray diffraction, backscattered electron analysis, mineral liberation analysis, and other analytical methods were performed to analyze and characterize the mineral composition and interlocking relationship of cyanide tailings. Results indicated that cyanides and typical minerals, such as pyrite and pyrrhotite, in cyanide tailings would undergo a certain degree of oxidation and dissolution in the ET, ETA, and ETC systems, and the processing effect of the ETC system was more obvious than that of other systems. After the treatment, the mass loss of cyanide tailings could reach 8.62%, which was 5.10% and 1.36% higher than the mass loss in ET and ETA, respectively. The removal rates of CNT, CN⁻, Cu, Zn, and Fe were 92.07%, 97.17%, 86.31%, 98.24%, and 93.03%, respectively. The relative contents of pyrite and pyrrhotite decreased by 8.82% and 4.65%, respectively. The particle size occupancy rates of pyrite greater than 50μm and pyrrhotite greater than 15μm were 0.24% and 3.36%, respectively. The mineral liberation degrees of typical minerals increased significantly, and the mineral liberation degrees of pyrite and pyrrhotite increased by 16.46% and 13.20%, respectively. The oxidation of cyanides and minerals in cyanide tailings under the ETC system mainly involved electrochemical indirect oxidation. Cl⁻ migrated to the anode through electrogeneration to generate Cl2/ClO⁻ in situ. CN⁻ and metal cyanide ions that migrated near the anode were oxidized by Cl2/ClO⁻ to produce CO2, N2, and metal cations. Metal cations returned to the cathode where they were reduced and deposited. Pyrite, pyrrhotite, and other minerals in cyanide tailings could also be oxidized and dissolved by ClO⁻. Therefore, the particle size of minerals decreased, and the degree of mineral liberation increased. As electrolysis proceeded, the interlocking relationship between the minerals was destroyed, and more minerals were exposed in the form of monomers. These phenomena provided favorable conditions for the subsequent comprehensive recovery of valuable metals from cyanide tailings.
Protein-specific glycoform analysis is essential for the thorough understanding of cellular chemistry and signaling but presents a significant assay challenge for small-sized, free-floating exosomes, ubiquitous regulators of cellular physiological functions and mediators of intercellular communication. We report herein a quantitative localized analysis (QLA) method for the first-time achievement of protein-specific glycosignature assay on these important extracellular vesicles. The integration of localized chemical remodeling and quantitative electrochemistry allows the proof-of-concept QLA examination of exosomal mucin 1 (MUC1)-specific terminal galactose/N-acetylgalactosamine (Gal/GalNAc). In combination with sialic acid (Sia) cleavage manipulation for the exposure of originally capped Gal/GalNAc, QLA has revealed distinct MUC1-specific sialylation capping ratios for MCF-7 and MDA-MB-231 exosomes, as well as when compared to parent cells. These findings suggest a useful non-invasive indicator for subtyping cancer cells and exosome secretion as a likely venue for the preservation of cellular compositional and functional integrity. The QLA method also permits dynamic monitoring of changes in the exosomal MUC1-specific sialylation capping ratio, enabling the distinction of biogenesis pathways of exosomes.
A regioselective cyanation of heteroaromatic N‐oxides with trimethylsilyl cyanide has been developed to obtain 2‐substituted N‐heteroaromatic nitrile without the requirement of any external activator‐, metal‐, base‐, and solvent. The present protocol is a straightforward, one‐pot heteroaromatic C−H cyanation process, and proceeds smoothly in conventional heating but also under microwave irradiation with shorter reaction times. This approach now allows access to a broad class of quinoline N‐oxides and other heteroarene N‐oxides with high to good yields and can also be scaled up to obtain gram quantities. Further application of this process was observed and utilized in late‐stage cyanation of the anti‐malarial drug quinine as well as transformation of the 2‐cyanoazines to a series of biologically important molecules. Based on the experimental observations, a plausible mechanism has also been proposed highlighting the dual role of trimethylsilyl cyanide as a nitrile source and as an activating agent.
image
چکیده
به دلیل اهمیت مدیریت آب و بازیافت پساب صنایع، شناخت آلایندههای خطرناک و راهکار مؤثر حذف آنها بسیار حائز اهمیت است. سیانید یکی از ترکیبات شیمیایی سمی است که به طور گسترده در صنعت کاربرد دارد و بخش گستردهای از فاضلاب صنایع حاوی این ماده خطرناک است. سالانه حدود 4/1 میلیون تن سیانید در سراسر دنیا تولید و از طریق پساب صنایع، وارد محیط زیست میشود. این پساب با نفوذ در آب های سطحی و زیرزمینی، منابع محدود آب را آلوده میکند و زندگی بسیاری از جانداران را به خطر میاندازد.
TiO2/Fe2O3 در این پژوهش به بررسی حذف سیانید با استفاده از فرایند اکسیداسیون پیشرفته در حضور کاتالیست
بر پایه زئولیت طبیعی و اشعه فرابنفش و هیدروژن پراکسید پرداخته شده است. این روش نسبت به روشهای فیزیکی و زیستی
دارای راندمان حذف بالاتر، آلایندههای ثانویه کمتر و هزینههای کل پایینتر است. در این آزمایش غلظت های 150، 300 و 450
میلیگرم بر لیتر سیانید
pHدر
های 10، 11 و 12 و در زمان ماندهای 1، 2 و 3 ساعت، برای بدست آوردن شرایط بهینه، مورد آزمایش قرار گرفتند و راندمان حذف سیانید در شرایط بهینه 90 درصد بدست آمد.
سيانيد مولكولي با پيوند سهگانه کربن و نيتروژن ميباشد که کاربردهای زیادی در صنایع مختلفي
همچون دارویي ٬ متالورژی ٬ خودروسازی ٬ پلاستيک ٬ نقاشي ٬ عكاسي و در استخراج فلزات بویزه طلا و نقره دارد. سالانه یک
ميليون تن سيانيد در جهان توليد و وارد محيطزیست ميشود و به آبهای سطحي و زیرزميني نفوذ ميکند و با توجه به
سمي بودن سيانيد و مشتقات آن، تهدیدی جدی برای موجودات زنده ميباشد. بنابراین ضروری است که قبل از تخليه به
محيطزیست غلظت آلاینده های موجود در آن به حد مجاز استاندارد کاهش یابد.در سالهای اخير روشهای فتوکاتاليستي
برای حذف سيانيد از آبهای آلوده صورت گرفتهاند که بيشترین راندمان حذف آلاینده را دارند. . در این پژوهش به بررسي
پارامترهای موثر همچون pH ، زمان ماند ٬دما، غلظت آلاینده و فوتوکاتاليست بر عملكرد حذف سيانيد از آبهای آلوده،
پرداخته شده است.
It is known that the presence of sulphidic minerals in the cyanidation of gold ores may cause significant consumption of oxygen supplied in the injected air. This may result in dissolved oxygen starvation for the oxidative leaching of the gold, and ultimately it will reduce the maximum attainable recovery of gold from the ore. In addition, the presence of sulphides leads to extra consumption of the cyanide-leaching agent, NaCN, due to the formation of thiocyanate, therefore increasing costs. These types of gold sulphidic ores may be pre-treated prior to cyanidation by means of an oxidation step, converting the sulphides into oxides or sulphates. This treatment leads to a reduction in the consumption of dissolved oxygen and of cyanide in the cyanidation step and to an improvement in the metallurgical recovery. In the current work we present the results of a five month full-scale trial carried out in a gold extraction plant in Brazil, which normally operated with three tanks in series carrying out an alkaline pre-oxidation step using compressed air only, followed by a train of fourteen aerated and mechanically-agitated tanks for the cyanidation. The ore feeding the leaching circuit averages 1.70 g Au/t, with about 2.5% of pyrrhotite (FeS) as the main sulphide constituent. The addition of 60 L/h of concentrated hydrogen peroxide, H2O2, 50% w/w (density = 1.19 g/mL) for pre-oxidation of a slurry of 60% solids at a rate of 150 t/h (dry ore) resulted in a marked increase in dissolved oxygen (DO). This addition corresponds to a dosing rate of 0.24 kg 100% H2O2 per ton of dry ore and increased the dissolved oxygen level from an average of about 1.0 to 7.2 mg/L in the pre-oxidation tanks. It also led to an overall reduction of NaCN consumption from an average of 0.52 to 0.40 kg/t of ore, and an increase in metallurgical Au recovery from an average of 91.3% to 92.5%.
The enrichment of copper from copper–cyanide wastewater by solvent extraction was investigated using a quaternary ammonium salt as an extractant. The influences of important parameters, e.g., organic-phase components, aqueous pH values, temperature, inorganic anion impurities, CN/Cu molar ratio, and stripping reagents, were examined systematically, and the optimal conditions were determined. The results indicated that copper was effectively concentrated from low-concentration solutions using Aliquat 336 and that the extraction efficiency increased linearly with increasing temperature. The aqueous pH value and concentrations of inorganic anion impurities only weakly affected the extraction process when varied in appropriate ranges. The CN/Cu molar ratio affected the extraction efficiency by changing the distribution of copper–cyanide complexes. The difference in gold leaching efficiency between using raffinate and fresh water was negligible.
In this work, a combination process was developed in lab-scale for the purpose of removing pollutants in electroplating wastewater with high cyanide and metal loadings. Most of heavy metal ions were removed by Fe2+ reduction (for Cr6+) and subsequent precipitation (for Cr3+, Cu2+ and Ni2+ ions), and cyanide was efficiently removed by the formation of insoluble complex compounds with Fe2+ ions. During the following chemical oxidation process, the residual cyanide was mainly transformed to low-toxic cyanate, and Cu2+ and Ni2+ ions were released due to degradation of organic compounds and then removed by precipitation.
For the sterilisation of aseptic food packages it is taken advantage of the microbicidal properties of hydrogen peroxide (H2O2). Especially, when applied in vapour phase, it has shown high potential of microbial inactivation. In addition, it offers a high environmental compatibility compared to other chemical sterilisation agents, as it decomposes into oxygen and water, respectively. Due to a lack in sensory detection possibilities, a continuous monitoring of the H2O2 concentration was recently not available. Instead, the sterilisation efficacy is validated using microbiological tests. However, progresses in the development of calorimetric gas sensors during the last 7 years have made it possible to monitor the H2O2 concentration during operation. This chapter deals with the fundamentals of calorimetric gas sensing with special focus on the detection of gaseous hydrogen peroxide. A sensor principle based on a calorimetric differential set-up is described. Special emphasis is given to the sensor design with respect to the operational requirements under field conditions. The state-of-the-art regarding a sensor set-up for the on-line monitoring and secondly, a miniaturised sensor for in-line monitoring are summarised. Furthermore, alternative detection methods and a novel multi-sensor system for the characterisation of aseptic sterilisation processes are described.
Oxidation of Cu(CN)(3)(2-) in water by H2O2 is less documented. The present study investigated the effects of pH, H2O2 dose and CN-/Cu(I) on oxidation of cu(CN)(3)(2-). Furthermore, oxidation of Cu(CN)(3)(2-) by H2O2 was investigated in the presence of ethylenediaminetetraacetate (EDTA) or pyrophosphate. The results indicated that Cu(CN)(3)(2-) oxidation was more favored at pH 9.5 and 11.0 than at pH 12.0. With the increase of H2O2 dose, rate of cu(cN)(3)(2-) oxidation was accelerated. Oxidation of Cu(CN)(3)(2-) was accelerated with CN-/Cu(I) decreasing from 4.0 to 2.8. In the presence of EDTA or pyrophosphate, oxidation of Cu(CN)(3)(2-) was significantly enhanced. 4.0 mM cyanide was nearly oxidized by 4.8 mM H2O2 in the presence of 1.0 mM EDTA. According to UV-Visible spectra variation of Cu(CN)(3)(2-) solutions, it was found that H2O2 firstly oxidized Cu(CN)(3)(2-) to Cu(CN)(2)(-). The successive oxidation of cyanide from Cu(CN)(2)(-) led to liberation of Cu(I). Cu(I) was oxidized into Cu(II) with formation of hydroxyl radicals (HO) or Cu(III). H2O2 was decomposed of into O-2 in the process. The strong bonding of Cu(II) to EDTA suppressed decomposition of H2O2 into O-2 and enhanced the effective utilization of H2O2 for cyanide destruction. By contrast, complexation of Cu(II) with pyrophosphate enhanced the catalytic redox reaction (Cu(I)/Cu(II) or Cu(I)/Cu(III)), improving cyanide oxidation. The results provide a possible way to improve treatment of Cu(CN)(3)(2-) wastewater by H2O2.
Removal of cyanides by the pulsed discharge plasma using a needle-plate reactor has been investigated. Effects of some factors were studied, including treatment modes, pH values, treatment time, and bubbling gases. The results of experiment indicate that the removal efficiency of cyanide increased greatly when air or nitrogen was injected into the reaction region during the discharge process, and was higher with the addition of air than the addition of nitrogen. The pH value was an important factor that affected the removal rate of cyanide. At a pH of 9, a highest removal rate of 99% was achieved after discharge 120 min. The specific energy consumption for the discharge reactor is 31.25kWh/m3.
The main objective of this work was to investigate the recovery of silver from mining wastewaters using a hybrid cyanidation and high-pressure membrane process. The tested hybrid process in lab-scale experiments includes the concentration and recovery of silver by nanofiltration (NF) or reverse osmosis (RO) after the silver is taken into solution as AgCN employing re-cyanidation and subsequent sedimentation and/or pre-filtration of wastewaters. Synthetic water experiments were conducted in this work. In synthetic water experiments (in distilled and deionized water), the soluble AgCN complex was formed after cyanidation of low-soluble AgCl particles which were added to the leach tank. Two different NF membranes and one RO membrane were tested in a lab-scale flat-sheet configuration test unit. The results indicated that although a significant amount of silver was lost on the RO membrane due to irreversible sorption, RO membrane performed better than NF membranes based on higher silver rejections, thus higher mass recoveries. Therefore, RO membrane was found to be more effective in terms of precious metal recovery and production of high quality permeate that can be reused in the leaching process. The tested hybrid cyanidation (leaching) and high-pressure membrane process in this work may be an effective approach in recovering precious metals and producing reusable water from wastes or wastewaters of mining industry.
The year 1987 marks the centennial of the beginning of modern hydrometallurgy. On October 19, 1887, British Patent No. 14174 entitled Process of Obtaining Gold and Silver from Ores was issued. The discovery was made by John Steward MacArthur. This article describes the background to the discovery and modern developments since that time.
Cyanide is the reagent of choice for gold and silver extraction, but also a toxic chemical that may cause
severe environmental pollution problems. Vascular plants possess an enzyme system that detoxifies
cyanide by converting it to the amino acid asparagine. The phytotoxicity of cyanide is indirectly connected
to the efficiency of this enzyme system: Plants only survive cyanide exposure up to a dosage they can
metabolize. Cyanide phyto-toxicity was measured for the subtropical grass Sorghum bicolor. Potassium
cyanide was not toxic when added to the irrigation water at up to 125mg KCN/l (50mg CN/l). In a
degradation test, cyanide was efficiently degraded by sorghum roots and leaves. Cyanide elimination using
plants seems to be a feasible option for gold and silver mine waste and wastewater. Theoretical estimates
indicate that a large area of land is needed. But the process is cost effective, sustainable, and has less critical
emissions than any competing technology. Until now, phytotreatment of gold mining wastewater has only
been tested on a lab scale. With the current knowledge, a pilot-scale demonstration could be implemented
immediately
Summary Cadmium and zinc biosorption, alone or in combination, was investigated with sodium alginate immobilizedChlorella homosphaera cells. Concentrations ranging from 20.0 to 41.0mg/l cadmium, 75.0 and 720.0mg/l zinc were tested and, in all cases, the metal removal achieved values near 100%. When these metals were put in combination a decrease in the rate of absorption was detected. Gold was also tested in the immobilized system and 90% of the initial metal added was recovered in a solution containing 213.0mg/l of the metal, the alginic matrix being responsible for 40% gold uptake.
The photocatalytic oxidation of free cyanide ions was carried out in aqueous aerated suspensions containing polycrystalline TiO2 (anatase) irradiated by sunlight. The influence of the presence of an organic compound (phenol) or of a strong oxidant (H2O2) on the photoprocess was also studied. The dependence of cyanide photo-oxidation rate on the following parameters: (1) cyanide concentration; (2) catalyst amount; and (3) phenol concentration was investigated. At the used experimental conditions, the kinetics of cyanide photo-oxidation is independent of the initial cyanide concentration and of the catalyst amount while it is affected by the phenol concentration and by the presence of H2O2. The Langmuir–Hinshelwood kinetic model has been used for phenomenologically describing the photoreactivity results. The reaction pathway was also investigated: cyanate, nitrite, nitrate and carbonate were found to be the main oxidation products. The mass balance of nitrogen was achieved only in strongly oxidant conditions; this insight suggests that some volatile nitrogen-containing species are formed at mild oxidation conditions.
The photocatalytic oxidation of free cyanides in aqueous suspensions containing polycrystalline TiO2(anatase) powders irradiated in the near-UV region has been investigated. The rate of cyanide photooxidation has been studied by varying the following operative parameters: (i) initial cyanide concentration; (ii) catalyst concentration; (iii) initial pH; (iv) power of irradiation; and (v) chloride ion concentration in the reacting mixture. Under the used experimental conditions the photoreaction proceeded at a measurable rate until the complete disappearance of cyanides. The kinetics of cyanide photooxidation is affected by the catalyst concentration, the chloride ion concentration, and the power of irradiation while it is independent of the initial cyanide concentration and the pH. The detrimental effect of chloride ions on cyanide photooxidation rate is not determined by a competition mechanism of chloride ions with cyanide ions or oxygen molecules for adsorption on active sites. Chloride ions affect the photoreaction rate by lowering the concentration of dissolved oxygen to values for which oxygen may become a rate limiting reactant. The Langmuir–Hinshelwood kinetic model well fits all the photoreactivity results. The reaction pathway was also investigated; cyanate, nitrate, and carbonate were found to be the main oxidation products. A mass balance on nitrogen was also successfully carried out. Specific experiments were carried out in a particular setup for measuring both the photon flow absorbed by the reacting suspension and the cyanide photoreaction rate; for these particular conditions the quantum yield value was calculated.
Applications of biotechnology are in use or have been proposed for almost all sectors of the mining and minerals industries for metal extraction, metal recovery, and environmental control. A recently completed study in Canada reviewed the status of biotechnological process development in different sectors of the industry and by commodity. This paper provides an overview of the findings of the study including a discussion of the sectors of the industry in which biotechnology enjoys commercial success and those for which future applications are indicated. Special emphasis is given to the commercial metal extraction processes and to applications for environmental control for which future technical and economic advantages are likely as environmental regulations become more stringent.
Heavy metals, depending on their oxidation states, can be highly reactive and, as a consequence, toxic to most organisms. They are produced by an expanding variety of anthropogenic sources suggesting an increasingly important role for this form of pollution. The toxic effect of heavy metals appears to be related to production of reactive oxygen species (ROS) and the resulting unbalanced cellular redox status. Algae respond to heavy metals by induction of several antioxidants, including diverse enzymes such as superoxide dismutase, catalase, glutathione peroxidase and ascorbate peroxidase, and the synthesis of low molecular weight compounds such as carotenoids and glutathione. At high, or acute, levels of metal pollutants, damage to algal cells occurs because ROS levels exceed the capacity of the cell to cope. At lower, or chronic, levels algae accumulate heavy metals and can pass them on to organisms of other trophic levels such as mollusks, crustaceans, and fishes. We review here the evidence linking metal accumulation, cellular toxicity, and the generation of ROS in aquatic environments.
Cladosporium cladosporioides biomass was a highly efficient biosorbent of copper cyanide and nickel cyanide from aqueous solutions. A 32–38 fold concentration of initial 0.5mM metal cyanides could be achieved when biosorption process was carried out under standardised conditions. Residual, unrecoverable metal cyanide could be completely biodegraded in 5–6h. The solution treated with the combined biosorption-biodegradation process was fit for discharge in the environment.
Biosorbent materials are a potential alternative to conventional processes of metal recovery from industrial solutions. Algal biomass ofSargassum natans andAscophyllum nodosum outperformed ion exchange resins in sequestering respectively gold and cobalt from solutions. Non-living biomass ofSaccharomyces cerevisiae andRhizopus arrhizus exhibited higher metal-uptake capacity than the living biomass for the uptake of copper, zinc, cadmium, uranium. The solution pH affected the metal-uptake capacity of the biomass whereas the equilibrium biosorption isotherms were independent of the initial concentration of the metal in the solution. Desorption of the metal from the biosorbent and recycle of the biosorbent have also been demonstrated.
Cyanide hydratase, which converts cyanide to formamide, was induced in mycelia of Stemphylium loti by growth in the presence of low concentrations of cyanide. Mycelia were immobilised by several methods. The most useful system was found to be treatment with flocculating agents. This technique is applicable to a wide range of easily isolated fungi that contain cyanide hydratase.
Cyanidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
This review concentrates on the uncertainties that dominated the mining industry throughout 1993. Recession, political upheaval and balancing supply and demand are the major factors discussed. Developments and trends in mineral exploration, surface and underground mining and mineral and coal processing are included as technical articles. Regional and national mining trends in 153 separate countries are covered in detail. Indexes include buyers, manufacturers, mines and companies. -S.E.Long
Cydnidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
Cyanide is commonly used to leach precious metals from ore, in many cases producing tailings with elevated concentrations of cyanides. If tailings treatment to reduce cyanide concentration is required, the overall cost of handling cyanide in a leaching circuit may be increased. This paper analyzes estimated capital and operating costs associated with several commonly employed cyanide recovery and destruction processes and gives details of some applications of the Cynaniorb process.
Chemical replacements for cyanide have been investigated for decades; however cyanide remains the exclusive lixiviant of choice in the mining industry due to a combination of its availability, effectiveness, economics and ability to use it with acceptable risk to humans and the environment. About 90% of the significant gold producing operations worldwide currently utilize cyanide for gold and silver extraction. Despite the number of cyanide-related mining operations, there have been no documented accounts during the previous three decades of the death of humans due to cyanide as a direct consequence of major mining-related environmental incidents. Major mining-related environmental incidents have not been concentrated in any geographic location, may occur regardless of the size of the company and do not occur more frequently with a specific type of mining activity. The main aspects of cyanide management that should be addressed at mining operations include transportation of cyanide to site, process solution conveyance, worker health and safety training, water management and treatment, emergency response and preparedness, workplace and environmental monitoring, and community relations. If these aspects of cyanide management are integrated into an overall cyanide management plan, dramatic reductions in risk and potential incidents at mine sites will be realized.
The Ovacik Gold Mine is the first gold mine using the cyanide leaching method in Turkey and has been operating since early June, 2001. The process plant comprises a conventional carbon-in-pulp (CIP) process with a treatment capacity of 300,000tpy ore. Sodium cyanide consumption is approximately 0.5kg/t ore treated. Process tailings are treated in a three-stage chemical destruction circuit using the Inco SO 2 /AIR process before being discharged to a lined tailings pond in order to achieve the limits for cyanide and heavy metals set by the Turkish Ministry of Environment. The limit for cyanide in the chemical destruction effluent is 1mg/l, as weak acid dissociable (WAD) cyanide. The circuit was commissioned successfully, under the control of Inco experts, and has since been operating in compliance with all the regulatory environmental requirements.
Cyanide (CN -) is a toxic species that is found predominantly in industrial effluents generated by metallurgical operations. Cyanide's strong affinity for metals makes it favorable as an agent for metal finishing and treatment and as a lixivant for metal leaching, particularly gold. These technologies are environmentally sound but require safeguards to prevent accidental spills from contaminating soils as well as surface and ground waters. Various methods of cyanide remediation by separation and oxidation are therefore reviewed. Reaction mechanisms are given throughout. The methods are compared in regard to their effectiveness in treating various cyanide species: free cyanide, thiocyanate, weak-acid dissociables and strong-acid dissociables.
Cyanidation tailings which are disposed in a surface impoundment experience a loss of cyanide due to natural attenuation, frequently reducing the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed solution chemistry has been largely empirical though in many cases mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a more quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared against data collected for a North American tailings impoundment during 1998.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The potential of sewage sludge for decomposition of cyanide has been investigated at different temperatures, ratio sewage sludge to cyanide, pH and also at prolonged and at four cycle repeated processes. Along with the kinetics of cyanide decomposition, the consumption of reagents necessary to maintain pH of the biosystem and the releasing of volatile cyanide have been examined. The positive effect of the activation of sewage sludge by means of aeration and its correlation to the kinetics of the bacterial growth have been also studied. Along with aeration, “carrier biology” has been employed to improve the characteristics of sewage sludge, using wood peels as a carrier material.
A series of pumice supported nickel catalysts used in the CO hydrogénation reaction were characterised by X-ray photoelectron spectroscopy. Qualitative and quantitative analysis of the XPS peaks have shown the effect of the calcination conditions on the chemical state of the nickel before hydrogenation and the particle size of the metal after reduction. Calcination at high temperature determined enrichment of sodium ions on the surface of the support and also on the metal particles. After exposure to the gas mixture CO/H2, formation of nickel carbides and other carbon species was checked. The correlation found between the surface atomic ratio Na/Si and the activity and selectivity of the catalysts in the hydrogenation of CO substantiated the role of the alkali ions naturally present in the pumice support.
Three identical anaerobic fluidized bed reactors containing different biomass support media were fed a distillery wastewater at various hydraulic retention times and COD loadings. The support media used were sepiolite, pumice stone and sand; particle diameter was around 0.5 mm in all cases. Start-up of the reactors was achieved within 63 days using a regime that included stepped increases in influent COD concentration and substitution of methanol for part of the wastewater COD. No significant differences in performance between reactors were observed during this period. Six different steady states at hydraulic retention times between 0.5 and 2.48 days were studied. Results obtained at these steady states showed similar performances in all three reactors except at HRT of 0.5 days, when the reactors containing sepiolite and pumice stone achieved better COD removal efficiencies and higher methane yields than the sand-containing reactor. It was concluded that sepiolite and pumice stone would be excellent solid supports in biological fluidized bed processes and have a lower energy consumption than the one demanded when using a sand support.
This chapter provides an overview of the microbial treatment of industrial wastes. Biochemical wastes treatment with activated sludge as a major agent is effective for the detoxification of domestic wastes. Industrial wastes differ from domestic ones because they have an unstable composition and contain many compounds including those that are oxidized with difficulty. In those conditions, the oxidizing activity of the microorganisms of sludge is repressed and the screening of active destructors is necessary. More than 50 active strains of microorganisms were isolated from activated sludge and waste waters that were capable of destroying the toxic compounds of these industries: methylatyrols, crotonic aldehyde, and toluol. The strains belong to the genus Pseudomonas and Bacillus. Almost all isolated strains of pseudomonads utilize substances, such as toluol, biphenyl, naphtalin and are resistant to high concentration of Hg. Many of these strains contain plasmida of biodegradation that determine their growth on the aromatic compounds.
Experiments were carried out to develop the technological basis for the integrated biodegradation of cyanide and formamide. The ability of both Fusarium oxysporum CCMI 876 and Methylobacterium sp. RXM CCMI 908 to transform cyanide and formamide was analysed and characterised. The Kmi for cyanide hydratase in the immobilised Fusarium oxysporum CCMI 876 was 19±4mM of cyanide and the Vmaxi was 21±5μmolmin−1g−1 (DW) cells. For the entrapped Methylobacterium sp. RXM CCMI 908 the values of the apparent reaction kinetics were Kmi=1.7±0.3mM of cyanide and the Vmaxi=20±2μmolmin−1g−1 (DW) cells. These data were used to design and operate a two-catalyst system to balance cyanide and formamide transformations and assess the system stability. The cyanide was degraded by Fusarium oxysporum CCMI 876 at a rate of 0.059mMh−1 leading to 96% cyanide conversion and leaving a residual 0.21mM. Average 3.76mM of formamide and 0.34mM of formate were formed. This effluent is contacted with Methylobacterium sp. RXM CCMI 908 which used 84% of formamide. Then this compound drops to an average value of 0.62mM. In parallel, formate builds up to nearly 12-fold the initial concentration, correlating with the amount of formamide used. The two systems were merged in a single system which design involved a scale-up criterion and the degradation profiles along the system were determined.
Former gasworks sites are sometimes be heavily contaminated with spent oxide which contains cyanide complexed to metals (especially iron). In this study, mixed fungal cultures have been isolated from acidic gasworks soil by their ability to utilize iron or nickel cyanide as the sole source of nitrogen at acidic or neutral pH, respectively. A mixed culture comprising Fusarium solani and Trichoderma polysporum was obtained by enrichment on tetracyanonickelate [K2Ni(CN)4] at pH 4. A second mixed culture consisting of Fusarium oxysporum, Scytalidium thermophilum, and Penicillium miczynski was isolated on hexacyanoferrate [K4Fe(CN)6] also at pH 4. Both consortia were able to grow on K4Fe(CN)6 as the sole source of nitrogen under acidic conditions. Growth was associated with progressive removal of cyanide from the culture supernatant. After the termination of growth, at least 50% of the total cyanide had been degraded. Growth of the fungi on K2Ni(14CN)4 as a source of nitrogen at pH 7 yielded 14C-labelled carbon dioxide. Growth of the Fusarium isolates on K2Ni(CN)4 at pH 7, associated with the removal of cyanide, required 5 days as compared to 28 days on K4Fe(CN)6 at pH 4. Cyanide uptake by the fungi on K4Fe(CN)6 at pH 4 occurred simultaneously with removal of iron from the biomass-free medium. Pure cultures of F. solani and F. oxysporum were grown on K2Ni(CN)4 or K4Fe(CN)6 in pure culture at pH 7 or 4, respectively.
Two series of pumice-supported palladium catalysts (W = washed, U = unwashed) were prepared by the reaction of [Pd(CâHâ)â] with the support, followed by reduction using Hâ. W catalysts were washed before reduction to eliminate unreacted [Pd(CâHâ)â]. U catalysts did not undergo this treatment. Microstructural characterization of the catalysts was performed by small-angle X-ray scattering (SAXS), wide-angle X-ray line broadening, and transmission electron microscopy (TEM). Line-broadening analysis revealed the presence of lattice imperfections, such as growth stacking faults and microstrains in the fcc structure of palladium. The average particle size values determined by SAXS were confirmed by TEM analysis and were employed to calculate the percentage of palladium exposed (catalyst dispersion). W catalysts showed well-dispersed spheroidal particles, whereas the U series displayed agglomerates. 38 refs., 9 figs., 2 tabs.
Porous lavas, more precisely pumice stone, are promising supports for TiO2 used as a photocatalyst. TiO2 deeply penetrates into pores that favours its retention. Its deposition is convenient and facile and the photocatalytic activity is not significantly affected by the erosion of the surface. The immobilization of TiO2 on pumice stone gave better results for the photocatalytic degradation of 3-nitrobenzenesulfonic acid than conventional sol–gel dip-coating on cement and red brick. A layer of pumice stone as pellets, fixed on a cement layer and impregnated with TiO2 is used in a thin film fixed bed reactor, for the photocatalytic treatment of water.
Water-soluble iron cyanide compounds are widely used as anticaking agents in road salt, which creates potential contamination of surface and groundwater with these compounds when the salt dissolves and is washed off roads in runoff. This paper presents a summary of available information on iron cyanide use in road salt and its potential effects on water quality. Also, estimates of total cyanide concentrations in snow-melt runoff from roadways are presented as simple mass-balance calculations. Although available information does not indicate a widespread problem, it also is clear that the water-quality effects of cyanide in road salt have not been examined much. Considering the large, and increasing, volume of road salt used for deicing, studies are needed to determine levels of total and free cyanide in surface and groundwater adjacent to salt storage facilities and along roads with open drainage ditches. Results could be combined with current knowledge of the fate and transport of cyanide to assess water-quality effects of iron cyanide anticaking agents used in road salt.
Biological treatment of a synthetic leachate containing cyanide was accomplished in a sequencing batch biofilm reactor (SBBR). A mixed culture of organisms growing on silicone tubing were provided with cyanide as a sole carbon and nitrogen source. Organisms consumed cyanide (20 mg/liter CN−WAD) and produced ammonia in an approximate 1:1 molar yield. The SBBR was operated on a 24-h cycle. Over the course of each cycle, 20 mg/liter of cyanide was degraded to below 0.5 mg/liter. Results from four track studies are presented. It was demonstrated that, when supplied with glucose, the organisms would readily consume excess ammonia. For each mole of glucose added, 10 moles of NH3-N were removed from solution. The SBBR can be used as a mobile system for treatment of leachate from gold-mining operations. Large volumes of low concentration wastewater can be treated in the SBBR since it is not necessary to maintain a consortium of settling organisms. © 1998 Elsevier Science Ltd. All rights reserved
There are several water and tailings treatment processes that have been successfully used worldwide for cyanide removal at mining operations. The key to successful implementation of these processes involves consideration of the following:•Site water and cyanide balances under both average and extreme climate conditions.•Goals to be adopted for cyanide levels in treated effluent, including the form of cyanide to be regulated (free vs. WAD vs. total cyanide).•The range of cyanide treatment processes available and their ability to be used individually or in combination to achieve treatment objectives.•Proper treatability testing, design, construction, maintenance and monitoring of both water- and cyanide-management facilities.By carefully considering these aspects of water and cyanide management before, during and after mine operation, operators can reduce the potential for environmental impacts associated with the use of cyanide. Another aspect of cyanide treatment to be considered is the potential environmental impact of the cyanide-related compounds - cyanate, thiocyanate, ammonia, nitrate and nitrite. These compounds may be present in mining solutions to varying extents and may require treatment if water is to be discharged. Each of these cyanide-related compounds is affected differently in the treatment processes discussed, and this should be considered when evaluating cyanide-treatment alternatives for a given site. Table 13 provides a simplified summary of the general applications of various treatment technologies for the removal of iron cyanide and WAD cyanide. This table represents a very simplified summary, but can be used as a conceptual screening tool when evaluating cyanide-treatment processes.
Ecological and toxicological aspects of molybdenum (Mo) in the environment are briefly reviewed, with emphasis on fish and wildlife. Subtopics include sources and uses, chemical properties, mode of action, background concentrations in biological and nonbiological samples, and lethal and sublethal effects on terrestrial plants and invertebrates, aquatic organisms, birds, and mammals. Current recommendations for Mo and the protection of sensitive living resources are presented.
The oxidation of aqueous cyanide solution using hydrogen peroxide in the presence of heterogeneous catalyst, Ru/MgO, was tested in a batch reactor at room temperature. The cyanide oxidation using hydrogen peroxide was markedly enhanced in the presence of Ru/MgO catalyst with compared to the control, aqueous cyanide solution containing hydrogen peroxide in the absence of the catalyst. The rate of catalytic cyanide oxidation was observed to be function of the reaction conditions such as pH, temperature and H2O2/CN ratio. The optimum pH for the catalytic cyanide oxidation was between 6 and 8. The conversion rate of catalytic cyanide oxidation was increased with increasing temperature. H2O2/CN ratio was observed to determine the conversion rate. The optimum H2O2/CN ratio was between 1.2 and 1.6 at room temperature (18°C).
Gold mining is attracting increasing attention in many countries of the world, although it has a major impact on the environment. Large quantities of hazardous chemicals such as mercury or sodium cyanide are consumed to recover gold from its ores. Therefore, this activity should be carefully regulated by means of global directives based on an up-to-date knowledge of ecotoxicity principles and modern environmental standards. This article summarizes the basic information on past and present environmental impacts of gold production. Novel methods, possibly with reduced environmental risks, are briefly mentioned. Global regulatory criteria for minimization of the ecological and human health risks in mining, production, and processing facilities are proposed. Articles from different scientific disciplines distilled from the experiences of actual gold mining operations are cited. The most recent information gathered during the last 10 years of discussions regarding gold prospecting and recovery in Turkey has been added to them. gold mining environmental impacts of gold mining amalgamation cyanide leach process wastes global directives for gold mining
Pumice-supported copperpalladium catalysts prepared from organometallic precursor have been tested in the hydrogenation of phenylacetylene and in the hydrogenation/isomerization of the but-1-ene. The structure and catalytic behaviour of the bimetallic catalysts depended on the different temperatures of reduction. The presence of CuO or Cu metal in an alloyed state with Pd influenced the two reactions. The system containing CuO is the most active and selective towards the formation of the monoalkene in the hydrogenation of the highly unsaturated hydrocarbon. The system containing Cu partially alloyed with Pd is more active and selective towards the isomerization of the but-1-ene. The performance in the two reactions is discussed in terms of the electronic effect prevailing when CuO is present and in terms of the geometric ensemble size variation prevailing with the CuPd system.Copyright 1999 Academic Press.
Tests were conducted at the Ryan Lode Mine near Fairbanks, Alaska, to determine the comparative costs of chemical and biological destruction of cyanide in mine wastewater. The main body of pond and rinse water was treated by the patented, INCO Air-SO2 process. A 250 ton test heap was built and inoculated with a cyanide-reducing bacterium Pseudomonas pseudoalcaligenes (UA7). The capital and operating costs for both processes were carefully recorded during the treatment. These costs were used as the basis for an analysis of the comparative costs of rinsing and detoxifying a hypothetical, two-million ton heap using each method. Four scenarios were analyzed. The biological method had a higher capital cost, but a significantly lower operating cost, so that the present-worth cost was significantly lower for the biological method.
The aim of this study was to obtain a catalyst or support material from a natural pumice that could then be used in the hydroisomerization of n-pentane. Acid treatment of the raw material with HCl was found to extract a larger amount of cations than NH4Ac (Ac = acetate), yielding a product with a better developed texture and structure. The total number of protons present in the solution affects potassium extraction, while sodium is affected by both factors of concentration and volume of dissolution independently. The specific area of the material (meters squared per gram) obtained depends on the treatment conditions, and it value can be calculated by means of the treatment condition variables or by the total number of moles of the cations extracted. The treatments could be carried out by working at and above ambient temperatures and with and without fresh acid replacements. The optimum treatment for obtaining a catalytic support was 10 mL/g of pumice of 3 M HCl for 10 h with three replacements of fresh acid working at 70 °C.
The presence of cyanide in industrial effluent waste presents a major environmental and ecological hazard. Although chemical methods of treating this compound are known, bacterial detoxification of cyanide is of interest both in order to understand how cyanide may be dealt with in the environment and to evaluate the economic viability of bacterial systems for cyanide detoxification. The enzyme rhodanese, which catalyzes the formation of thiocyanate and sulfite from cyanide and thiosulfate, has been found in various organisms including Bacillus subtilis and E. coli. Thiobacillus denitrificans was shown to have the highest levels of this enzyme, but growth conditions in continuous culture on defined media have recently been developed for the production of equally high rhodanese levels in the thermophile Bacillus stearothermophilus. Purified rhodanese from this latter organism has already proved to be of value as an antidote in experimental cyanide poisoning in small mammals. This communication reports on the use of a culture of B. stearothermophilus in a small chemical reactor for the continuous removal of cyanide in the form of thiocyanate. The capacity of B. stearothermophilus to remove cyanide in the form of thiocyanate in the process described is high (5 to 8 g NaCN/l culture/hr at 27°C); furthermore, both the rate of cyanide removal and the half life of the process were unaffected by the presence of 5x10-5M Zn2+, Cu2+, Ni2+, or Al3+ over a 12 day period. By running the process at temperatures at which B. stearothermophilus is capable of growth in normal media (i.e. above 35°C) higher rates of cyanide detoxification are possible (14 to 25 g NaCN/l culture/hr at 50°C), although preliminary evidence indicates a reduction in half life at higher temperature.