Article

Destruction of cyanide by hydrogen peroxide in tailings slurries from low bearing sulphidic gold ores

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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.

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... Soluble copper catalysts generally increase cyanide destruction rates significantly. The copper catalyst can be either copper present in solution (from gold/silver cyanidation processes) or can be added as a reagent copper solution (Botz, 2001;Mudder et al., 2001;Kitis et al., 2005). ...
... Similar to results presented in Fig. 2, adsorption with pumice doses of 30 or 1000 mg/L removed up to 15% cyanide. Peroxide (150 mg/L) alone removed about 43% free cyanide (from 97 to 55 mg/L CN WAD ) through oxidation, consistent with the results in the literature obtained from experiments for tailings slurry or low-solid containing solution samples from gold mining wastewaters ( Knorre and Griffiths, 1984;Botz, 2001;Mudder et al., 2001;Kitis et al., 2005). Peroxide and original pumice added together were also ineffective in removing cyanide. ...
... These results overall indicate that the impregnation of copper into natural pumice particles used as heterogeneous supports significantly catalyzes the degradation of cyanide and also enhances the ultimate removals through peroxide oxidation. As employed in industrial treatment applications (i.e., for gold mining wastewaters), soluble copper catalyst, either added as a reagent copper solution or as copper naturally present in the ore, also significantly increase both the rate and extent of cyanide destruction (Botz, 2001;Mudder et al., 2001;Kitis et al., 2005). However, the addition of soluble copper introduces another contaminant and creates new problems in terms of downstream metals removal. ...
Article
The main objective of this research was to investigate the oxidative destruction of free cyanide with hydrogen peroxide and copper-impregnated pumice as a heterogeneous catalyst. Original or copper-impregnated pumices added alone were not effective adsorbents of negatively charged cyanide ions due to incompatible surface interactions. Peroxide and original pumices added together were also ineffective in removing cyanide. However, for all of the three natural pumices tested with various particle size fractions, the use of copper-impregnated pumices and peroxide together significantly enhanced both the initial rate and extent of cyanide removal. Although copper-impregnated specific surface area was the major factor affecting the rate and extent of cyanide destruction for a particular pumice source with similar surface chemistries, the type of surface chemistry (i.e., specific functional groups) within different pumice sources also appears to be a very important factor. Lower rates and extents of cyanide removals were observed at pH 11 compared to pH 8 probably because of the negative impacts of alkaline conditions in terms of scavenging peroxide and forming more negatively charged pumice surfaces. Both the initial rate and ultimate extent of cyanide removals were generally higher at a temperature of 20 degrees C compared with those found at 10 degrees C. The use of copper-impregnated pumice as a light, cheap, readily available, natural, and porous heterogeneous catalyst either in completely mixed/suspended or fixed-bed reactor configurations may be an effective treatment technology for cyanide removal from solution. This new approach may minimize downstream metal removal problems experienced in conventional cyanide oxidation technologies.
... 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. ...
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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.
... In all the studies related to the oxidation of cyanides and even of other pollutants by hydrogen peroxide, it has been proved that the use of catalysts is necessary whatever the type of catalysis is homogeneous or heterogeneous (Sarla et al., 2004;Kitis et al., 2005a,b). Knorre and Griffiths (1984), Sarla et al. (2004) and Kitis et al. (2005a) have demonstrated the effectiveness of Cu ++ . Although interesting, the homogeneous catalysis requires in certain industries, as those of plating effluents, the elimination of the catalysts after treatment which are in general heavy metals. ...
... It can be observed on Fig. 2 that the initial removal rate of cyanide (determinated from Fig. 1) (Table 2), the initial rates of cyanide removal are 0.024, 0.066, 0.11, 0.12 and 0.24 mmol/L min, respectively, in absence of AC-OS and 0.048, 0.12, 0.19, 0.33, 0.49 mmol/L min, respectively, in presence of AC-OS. The same effect of molar ratio H 2 O 2 /CN À was reported in the literature for homogeneous (Sarla et al., 2004;Kitis et al., 2005a) and heterogeneous catalysis (Pak and Chang, 1997). Fig. 3 shows the evolution of residual cyanides and produced cyanate concentrations and the sum of them during the oxidation of cyanides by hydrogen peroxide in presence of AC-OS. ...
... The rate and the extend of the cyanide elimination increase with the concentration of catalyst. Kitis et al. (2005a) observed that the increase of the amount of catalyst improve the kinetics of oxidation of cyanides. The linear plots of K app (min À1 ) versus concentration of AC-OS (R 2 > 98%) (Fig. 9) shows that the variation of apparent rate constant with the concentration Cm (g/L) of AC-OS can be described by Eq. (8): ...
Article
This work is dedicated to the removal of the very toxic free cyanide from aqueous solution by oxidation with hydrogen peroxide H2O2 in the presence of activated carbon prepared from olive stones. Effects of the initial molar ratio [H2O2]0/[CN−]0, the initial cyanide concentration, the activated carbon concentration and the temperature on cyanide removal have been examined. The removal of free cyanide in absence of activated carbon showed very slow kinetics. The presence of activated carbon has increased the reaction rate showing thus a catalytic activity. The kinetics of cyanide removal has been found to be of pseudo-first-order with respect to cyanide and the rate constants have been determined for different values of the aforementioned parameters. The apparent activation energy has been determined from tests carried out at three different temperatures. It was found equal to 46.2 kJ/mol in the presence of activated carbon, which is about half of the 82.7 kJ/mol found for the oxidation in absence of the activated carbon.This process can be interesting for the cyanide removal from processed solutions because it does not use soluble metal catalyst and it consumes only hydrogen peroxide as chemical product.
... 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. ...
Article
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 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. ...
Article
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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.
... 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]. ...
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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) . ...
Article
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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
... 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). ...
Article
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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. ...
Article
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.
... 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. ...
... 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). ...
... 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. ...
Article
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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.
... 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). ...
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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). ...
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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.
... Hydrogen peroxide is an effective oxidant industrially used for the destruction of cyanide species [Eq. (6)] present in the effluents of gold/silver leaching and metal finishing operations [24,36]. Fig. 8 illustrates the effect of the intensity of ultrasonic irradiation on the removal of cyanide (20 mg/l) at 30°C. ...
Article
The generation of hydrogen peroxide and the decomposition of free cyanide by ultrasonic waves were studied and the statistical analysis of the results for significance was performed using Ergun's test (essentially One-way Analysis of Variance (ANOVA) for gradients). Effects of the ultrasonic intensity, the external addition of hydrogen peroxide, aeration, temperature and pH on the rate and extent of formation/accumulation of hydrogen peroxide were demonstrated. The generation of H2O2 was found to increase with increasing the ultrasonic intensity (9–114 W/cm2), which also controls the accumulation of H2O2 in solution (400 ml). External addition of H2O2 or high temperatures (>30–50°C) appeared to suppress the production of H2O2 in water. Formation of H2O2 tends to be adversely affected by the increase in alkalinity (pH 4–10.5) whilst effects of air-saturation prior to the ultrasonic irradiation and aeration during the ultrasonic irradiation were shown to be statistically insignificant. The results have also shown that a high ultrasonic power input is required for the degradation of cyanide ([CN]0: 20 mg/l, 200 ml) to become significant (i.e. 25% reduction in cyanide level at 114 W/cm2). The removal of cyanide by ultrasonic irradiation appeared to be substantially enhanced with the aid of additives (NaCl and CCl4) with the complete removal of cyanide in the presence of 24 g/l CCl4. These findings suggest that ultrasonic treatment could be used more suitably for the treatment of the effluents containing low concentrations of cyanide and the addition of NaCl and CCl4 is essential to improve its effectiveness.
... The commonly used methods, such as ion-exchange, adsorption or foam floatation only can separate and transfer CN from one matrix to another. Various oxidants such as chlorine, hypochlorite, hydrogen peroxide, ozone and etc., are often used to degrade CN (Kitis et al., 2005). ...
Article
Ferrate(VI) was employed for the oxidation of cyanide (CN) and simultaneous removal of copper or nickel in the mixed/complexed systems of CN-Cu, CN-Ni, or CN-Cu-Ni. The degradation of CN (1.00 mmol/L) and removal of Cu (0.095 mmol/L) were investigated as a function of Fe(VI) doses from 0.3-2.00 mmol/L at pH 10.0. It was found that Fe(VI) could readily oxidize CN and the reduction of Fe(VI) into Fe(III) might serve efficiently for the removal of free copper ions. The increase in Fe(VI) dose apparently favoured the CN oxidation as well as Cu removal. Moreover, the pH dependence study (pH 10.0-13.0) revealed that the oxidation of CN was almost unaffected in the studied pH range (10.0-13.0), however, the maximum removal efficiency of Cu was obtained at pH 13.0. Similarly, treatment was carried out for CN-Ni system having the initial Ni concentration of 0.170 mmol/L and CN concentration of 1.00 mmol with Fe(VI) dose 2.00 mmol at various pH values (10.0-12.0). Results showed a partial oxidation of CN and partial removal of Ni. It can be observed that Fe(VI) can partially degrade the CN-Ni complex in this pH range. Further, Fe(VI) was applied for the treatment of simulated industrial waste/effluent waters treatment containing CN, Cu, and Ni.
... 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. ...
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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.
... 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]. ...
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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.
... 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. ...
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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.
... 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] ...
Article
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.
... 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). ...
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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.
... 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). ...
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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
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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%.
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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.
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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.
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Nitrogen-doped carbon nanotube (N-CNT) mat electrodes exhibit high catalytic activity toward O(2) reduction, which can be exploited for the remediation of free cyanide (CN(-)). During the electrochemical O(2) reduction process, the hydroperoxide anion (HO(2)(-)) is formed and then reacts to chemically oxidize cyanide (CN(-)) to form cyanate (OCN(-)). The proposed electrochemical-chemical (EC) mechanism for CN(-) remediation at N-CNTs is supported by cyclic voltammetry and bulk electrolysis, and the formation of OCN(-) is confirmed via spectroscopic methods and electrochemical simulations. Our results indicate that by exploiting their catalytic behavior for O(2) reduction, N-CNTs can efficiently convert toxic CN(-) to the nontoxic OCN(-).
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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.
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Results of voltammetry and spectrophotometry analyses revealed that upon sunlight exposure, the conversion of ferricyanide to ferrocyanide, and the reverse reaction, in the absence and in the presence of TiO2 catalyst depends strongly on pH. Thus, the pH of the solution dictates whether the redox reactions will proceed under illumination. In addition, the extent of the heterogeneous photocatalytic degradation of ferricyanide was influenced by pH. The initial concentration of ferricyanide did not affect its degradation.
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The electrochemical oxidation of cyanide, with the simultaneous recovery of cadmium present in a typical plating rinse wastewater, was conducted in a bipolar capillary gap disc stack electrochemical reactor under batch recirculation mode. The concentrations of cyanide and cadmium present in the reservoir of the batch recirculation system were measured as a function of electrolysis time at various flow rates, pH values, and applied cell potentials. The objective of this work was to explore the feasibility of using a bipolar disc electrochemical reactor that consisted of graphite as the electrodes to remove cyanide and Cd ions from the plating industry effluent using batch continuous recirculation modes. Experimental results showed that the reactor was able to reduce (from rinse water with a cyanide concentration of 240 mg/L and cadmium concentration of 50 mg/L) the content of toxic species by more than 99%, so that the treated water can be reused for further operations.
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In this study, the decomposition of free cyanide by hydrogen peroxide was studied. The results have shown that the rate and extent of cyanide removal ([CN]0: 100 mg/l) improve with increasing the concentration of hydrogen peroxide, cyanide and copper as catalyst. At a fixed ratio of [H 2O2]0/[CN]0: 8 over 95% of CN - could be removed by maintaining a [CuSO4]0 level of ≥40 mg/l (i.e. [H2O2]0/[CuSO4]0 ≥20) over 180 min. Kinetics of cyanide removal was found to be consistent with the first-order kinetic model. The efficiency of the removal of cyanide by hydrogen peroxide was observed to deteriorate with increasing pH whilst the increase in temperature exerted a positive effect on the rate of cyanide destruction. The current findings suggest that hydrogen peroxide may be used more effectively for the treatment of the effluents containing high concentrations of cyanide since at low cyanide levels the decomposition of hydrogen peroxide by side reactions would probably become significant.
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The main objective of this work was to investigate the oxidative destruction of free cyanide with hydrogen peroxide and copper-impregnated pumice as the heterogeneous catalyst. Original or copper- impregnated pumices added alone were not effective adsorbents of negatively charged cyanide ions due to incompatible surface interactions. Peroxide and original pumices added together were also ineffective in removing cyanide. However, the use of copper-impreg nated pumices and peroxide together significantly enhanced both the initial rate and extent of cyanide removal. Although copper-impregnated specific surface area was the major factor affecting the rate and extent of cyanide destruction for a particular pumice source with similar surface chemistries, the type of surface chemistry (i.e., specific functional groups) within different pumice sources also appears to be a very important factor. Lower rates and extents of cyanide removals were observed at pH of 11 compared to pH of 8 probably because of the negative impacts of alkaline conditions in terms of scavenging peroxide and forming more negatively charged pumice surfaces. The use of light, cheap, readily available, natural, and porous heterogeneous supports (i.e., pumice) impregnated with copper either in completely mixed/suspended or fixed-bed reactor configurations may be an effective treatment technology for cyanide removal in solutions. This new approach may minimize downstream metal removal problems experienced in conventional cyanide oxidation technologies.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
Chapter
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.
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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.
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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).
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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
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Pumice-supported copper–palladium 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 Cu–Pd system.Copyright 1999 Academic Press.
Article
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.
Article
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.
Article
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.
Article
Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined-cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi-batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo-first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H2O2 and/or UV is faster at pH 9.5. The optimum concentration of H2O2 was 20.58 × 10−2M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O3/H2O2(20.58 × 10−2M) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O3/UV or O3/H2O2/UV was about 75%, while in the processes with H2O2 and/or O3/H2O2 was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry
Article
Pumice-supported nickel catalysts, prepared by the method of slow homogeneous precipitation with urea, were analysed by x-ray photoelectron spectroscopy (XPS). By comparison with similarly prepared silica- and alumina-supported nickel catalysts, a preferential interaction of Ni2+ with Al3+ of the support has been determined. A quantitative XPS analysis indicated large segregation of nickel to the surface. The treatment with H2 at 673 K and 1073 K produced a partial reduction of Ni+2 to Ni0. The extent of the reduction was largest at 1073 K and in this case the reduced Ni in the metallic phase was detectable by x-ray diffraction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in the lower temperature H2-treated catalysts was attributed to diffusion of nickel as Ni2+, as a consequence of a solid-state reaction between nickel ions and support oxides, whereas the decrease of the intensity ratio in the high-temperature reduced catalysts was attributed to sintering of the nickel particles and to diffusion of nickel atoms interacting with oxygen vacancies of the support.
Article
Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the pH of the solution by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at recognizing the chemical relations between the cyanide and metals during distillation. The regeneration of cyanide from gold processing proved to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved.
Article
Accumulation of UO 22 + by Scenedesmus obliquus 34 was rapid and energy-independent and the biosorption of UO 22 + could be described by the Freundlich adsorption isotherm below the maximum adsorption capacity (75 mg g-1 dry wt). The optimum pH for uranium uptake was between 5.0_8.5.0.1_2.0 M NaCl enhanced uranyl, while Cu2+, Ni2+, Zn2+, Cd2+ and Mn2+ competed slightly with uranyl. Pretreatment had an unexpected effect on biosorption. After being killed by 0.1 M HCl, S. Obliquus 34 showed 45% of the uptake capacity of the control in which fresh cells were suspended directly in uranyl solution, while the pretreatment of cells by 0.1 M NaOH, 2.0 M NaCl, ethanol or heating decreased uptake slightly. Fresh S. obliquus 34 at 1.2_2.4 mg dry wt mL-1 was able to decrease U from 5.0 to 0.05 mg L-1 after 4_6 equilibrium stages with batch adsorption. Deposited U could be desorbed by pH 4.0 buffer. It is suggested that U was captured by effective groups or by capillary action in the cell wall in the form of [UO2OH]+.
Article
The removal of Sr, Cs, U and Th ions from aqueous solution by means of natural pumice stone was studied using energy dispersive X-ray fluorescence spectroscopy (EDXRF) as an analytical tool. The results indicate the usefulness of pumice powder and the removal efficiency was found to be in order of Th>Sr>Cs ions, which is altered by the pH of the solution.
Article
A bacterial coculture capable of growing on thiocyanate has been isolated from thiocyanate adapted bacterial suspension of urban sewage treatment plant. The coculture is composed of two bacteria identified as species Acinetobacter johnsonii and Pseudomonas diminuta. The two end products of thiocyanate conversion are ammonia and sulfate. The thiosulfate has been identified as the sulfur intermediate product of the conversion of thiocyanate to sulfate.