Article

Experimental process analysis and mathematical modeling for selective gold leaching from slag through wet chlorination

Authors:
  • Institutul National de Cercetare Dezvoltare pentru Metale si Resurse Radioactive (R&D National INstitute for Metals and Radioactive Resources)
  • National Institute of Research - Development for Metals and Radioactive Resources
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Abstract

The aim of this paper consists in defining optimal conditions of controlled and selective gold leaching contained in copper - gold slag, by wet chlorination. Studies were conducted on three types of copper - gold slag, resulting as by-products from pyrometallurgical processing of non-ferrous raw materials. Due to high levels of copper in slag, an oxidative pre-treatment is necessary to separate gold from accompanying elements and also for copper recovery. After nitric acid pre-treatment, nearly 87% Cu were readily extracted, and lead and silver content in the all three types of solid samples has been reduced by 91.34% and 96.29% respectively. Selective leaching of the solid phase resulting after HNO3 pre-treatment was done by wet chlorination, using nascent chlorine (Cl2) as leaching agent, in presence of hydrochloric acid (HCl). The chlorine was obtained «in situ» by the reaction of sodium hypochlorite (NaOCl, 5% Cl2) and HCl. In this study, the effect of nitric acid pre-treatment, redox potential (Eh) given by sodium hypochlorite (NaOCl) consumption, hydrochloric acid concentration, temperature and leaching time have been studied. The potential required for a rapid leaching rate and for avoiding the reduction of gold is 950 mV (vs AgCl/Ag(KCl sat)).The 5% NaOCl consumption required for gold leaching from pre-treated samples was lower than NaOCl consumption necessary for original samples leaching. The highest gold extraction yield (98%) was obtained after 6 hours at ambient temperature, solid/liquid ratio (w/v) 1:2 and 4M HCl. In order to explain experimental results a mathematical model of the simultaneous gold, copper, lead and silver dissolving has been developed. It considers at particle level, the competition between surface reaction and the diffusion of the active species by a gel coating that covers the dissolving particle.

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... Therefore, it is predictable, raising Clconcentration increases the affinity of AuCl − 4 dissolution. Olteanu et al. [33] also reported a similar result for the gold dissolution rate so that the hydrochloric acid concentrations lower than 2.74 M had an effective kinetic dissolution model. gram that enhances the Au leaching rate [34]. ...
... Based on Eq.(1), changing the pulp density changes the reactant (Cl 2 and Au) ratio, influencing the reaction rate. On the other hand, increasing pulp density affects the fluid flow through the solid particles, and mass transfer of lixiviate around the particle was decreased [33]. However, after 120 min, Au recovery was equaled with 50 and 80 g/L, approximately. ...
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... Fig. 7. Comparing by means of X-ray diffraction spectra humic substances obtained using different amounts of potassium hydroxide It can be observed from Fig. 6b that humic substance content carried to the solution increased along with the increase in the stirring time in the optimal stirring time experiments. These results explained that the possibility of chemical reactions providing dissolution increased as the contact time increased (Abbruzzese et al., 1995;Nan et al., 2005, Olteanu et al., 2014, Bas et al., 2015. However, the 24-h stirring time that produced best results was considered as too long in terms of industrial application. ...
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The more restrictive regulations for controlling the environmental pollution by cyanide bearing streams and materials have given an impetus to the researches aiming the discovery of some new, more ecological methods for gold leaching. This paper presents an alternative lixiviant system for the recovery of gold from secondary sources such as gravitational concentrates from alluvial sands. The gold leaching using nascent chlorine resulted from NaClO decomposition in hydrochloric acid medium was experimented. Also, the influence of the main parameters: solid: liquid ratio, temperature, chlorine and chloride ion concentration; redox potential is presented. A mathematical model for lixiviation time computing was proposed, using as parameters the initial radius of gold particle (R(in)) and molar fraction of chlorine in solution (y(Cl2 center dot)): tau(s) = rho(Au)/M(Au) R(in)(2)/D(Cl2) CT(ln(1-y(Cl2 center dot))
Article
Mintek has developed a process called iGoli Mercury-free Gold Extraction Process that can be used to extract gold from 0.1 % gold concentrate to produce 99.90 percent gold product. The process uses a mixture of pool acid (dilute hydrochloric acid), bleach (sodium hypochlorite) and sodium metabisulphate to leach and recover gold. Artisanal and small-scale miners concentrate their gold using sluice boxes followed by panning as a final physical separating method. The gold produced in this manner is extracted from the concentrate by a chlorine solution produced from a mixture of pool acid and bleach. The leach liquor contains gold and other metals that are soluble in chlorine media such as base metals and ferrous iron. During leaching excess gas that is produced is redirected to a separate vessel where it is scrubbed using caustic soda to form water and sodium chloride (salt). The slurry from the leaching process is filtered to separate the gold bearing leach liquor and the solid residue. This gold pregnant solution is treated with sulphur dioxide, introduced in the form of sodium metabisulphate, to reduce gold ions in solution to a metallic gold powder. The solid waste produced from iGoli process is rich in silicate with effluent and is neutralized using lime/ limestone with an addition of apatite where necessary to destroy or precipitate all base metals and ferrometals available. The development of this process was mainly driven by the need to ensure reduction in mercury use and subsequent alleviation on the entire biophysical environment. There is an array of mitigating measures that could be used as treatment methods for the safe use of iGoli leaching process. The process wastes which are significantly less toxic are characterized as follows: → Waste solids Feed → → Waste solution (effluent) → Waste heat → Waste gases Any potentially hazardous gases released from the gold leaching process are monitored and controlled by neutralization below the legislative requirements. The tailings produced have a high percentage of silica and iron with low levels of base metals. The process is very important to artisanal and small-scale miners as it lowers the risk of mercury poisoning on the miners themselves and mercury pollution into the environment. The process also offers economic benefits because of its high recoveries and product purity coupled with its simple way of waste management. Lastly the process recovers refractory gold which is very difficult to recover using other conventional ASM extraction methods.
Article
A review is presented summarising the leaching of gold with ammoniacal thiosulfate solutions, and evaluating the current use and development of ion exchange resins for the recovery of gold and silver from such leach liquors. Comparisons are also made with other recovery processes, including carbon adsorption, solvent extraction, electrowinning and precipitation. Thiosulfate leaching chemistry is compared with cyanide leaching, and the problems associated with obtaining a high yield of recovered gold using the former process are discussed. The present limitations of using Resin-in-Pulp (RIP) and Resin-in-Leach (RIL) systems with thiosulfate liquors are indicated and possible solutions discussed.
Article
The thiourea leaching of silver from a tetrahedrite concentrate mechanically activated in a planetary mill or an attritor was studied. It was found that the two types of equipment gave rise to different rates of new surface formation and of crystal structure disordering. The rate of thiourea leaching of silver from tetrahedrite (Cu,Ag)lo(Zn,Fe)E(Sb,As)4S 13 is a structure-sensitive quantity, while the dependence of the rate constant of leaching on the empirical coefficient Sg/(l-R) (S A = specific surface, R = disordering of tetrahedrite structure) exhibits a linear character with equal slope for both types of mills. The results are also of prognostic character because they enable us to propose suitable equipment for intensive grinding depending on the demand for fineness or reactivity of the solid substances.
Article
During the last 15 years about 700 t of gold have been consumed in the manufacture of low voltage electrical contactors, which, over a period of time, have become redundant and thus the gold component has become candidate for recovery. The results of laboratory and batch pilot experimentation, reported in this article, have demonstrated an average gold recovery rate of 95 per cent from used contactors by means of mechanical and chemical processing.
Article
This study investigates the biooxidation of a refractory gold concentrate using a mixed culture of acidophilic mesophiles, moderate thermophiles and extreme thermophiles and their effect on the subsequent cyanidation and gold recovery. The experiments with high % solids using mixed mesophiles showed better oxidation potential compared to moderate thermophiles and extreme thermophiles. However, the extreme thermophiles performed better than mesophiles and moderate thermophiles during the biooxidation with
Article
The effect of pyrite on gold dissolution was investigated in the ammoniacal thiosulphate leaching system using pure gold foils. Special emphasis was placed on gold leaching in association with pyrite dissolution, thiosulphate decomposition and gold leaching passivation. The presence of pyrite retarded gold dissolution and this detrimental effect became more pronounced at higher pyrite contents. Pyrite catalysed the decomposition of thiosulphate to trithionate. The addition of sulphate enhanced gold leaching by retarding the dissolution of pyrite in ammoniacal thiosulphate solutions. XPS analysis indicated the presence of iron hydroxide species at the gold surfaces in the presence of pyrite, which was likely responsible for the reduced gold dissolution. SEM analysis indicated a lesser extent of gold dissolution occurring in the presence of pyrite.
Article
Thiosulfate leaching appears to be the most promising alternative to cyanidation for the recovery of gold from ores. The current paper presents a fundamental study on the gold oxidation half reaction in the solutions containing thiosulfate. It will be shown that this electrochemical reaction is unusual, as the presence of the heavier inert cations such as potassium, calcium, and caesium enhance the oxidation of gold in thiosulfate solutions. The use of sulfur-containing species such as thiourea (TU) and potassium ethyl xanthate (PEX) as additives was also studied. It will be shown that in the presence of thiourea, the gold oxidation half reaction is dramatically improved, with a typical Tafel-like polarisation curve being obtained in the presence of thiourea. However, the presence of low concentrations of xanthate were shown to completely block the gold surface and prevent its oxidation in thiosulfate solutions.
Article
The thiourea leaching of silver from a tetrahedrite concentrate mechanically activated in a planetary mill or an attritor was studied. It was found that the two types of equipment gave rise to different rates of new surface formation and of crystal structure disordering. The rate of thiourea leaching of silver from tetrahedrite (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13 is a structure-sensitive quantity, while the dependence of the rate constant of leaching on the empirical coefficient SA(1 − R) (SA = specific surface, R = disordering of tetrahedrite structure) exhibits a linear character with equal slope for both types of mills. The results are also of prognostic character because they enable us to propose suitable equipment for intensive grinding depending on the demand for fineness or reactivity of the solid substances.
Article
An oxide gold ore was subjected to chloride/hypochlorite leaching at room temperature. The effects of three factors, including Ca(OCl)2 vs. NaOCl, OCl− concentration, and HCl concentration on gold leaching performance were investigated. Due to formation of CaOCl+ complex in solution and hence less reactivity, calcium hypochlorite produces a sluggish gold leaching kinetics, taking twice the time (46 h) to achieve maximum gold recovery of 58% compared to sodium hypochlorite. 10 g/L of total initial hypochlorite species in solution produces reasonable gold recoveries. The amount of added HCl and hence the initial pH was found to have a major effect on gold leaching kinetics and maximum gold recovery. A high level of 9 g/L of added HCl causes HClO to be very reactive, producing very fast kinetics, reaching 67% gold extraction in 4 h. It also causes a faster consumption of hypochlorous acid, through catalytic decomposition (by NiO and CuO) and disproportionation. Hypochlorous acid reactions with sulfide and ferrous content of ore proceed very slowly in the pH range of 4–11. Gold–chloro complexes are strongly adsorbed on quartz component of ore. To minimize this undesirable adsorption of gold–chloro species, the aging time must be limited to a few hours only.
Article
This study was carried out on a finely disseminated gold-bearing ore from Kaymaz, Turkey. The main objective was to determine the mechanism of reaction between thiourea and Fe3+ in the thiourea leaching of gold. Thiourea consumption levels were also examined during the leaching operations for different leaching parameters, i.e., molar ratio of ferric sulfate/thiourea, pH, and temperature. The leaching using the thiourea process was compared with cyanidation. In optimum leach conditions, 85.8% gold extraction was obtained with feed of −53 μm particle size in 6 h.
Article
The demand for metals is ever increasing with the advancement of the industrialized world. On the other hand, worldwide reserves of high grade ores are close to depletion. However, there exists a large reserve of metals in low and lean grade ores and other secondary sources. Metal recovery from low and lean grade ores using conventional techniques such as pyrometallurgy, etc. requires high energy and capital inputs which often result in the secondary environmental pollution. Thus, there is a need to utilize more efficient technologies to recover metals. Biohydrometallurgy, which exploits microbiological processes to recover metal ions, is regarded as one of the most promising and revolutionary biotechnologies. The products of such processes are dissolved in aqueous solution, thereby rendering them more amenable to containment, treatment and recovery. On top of this, biohydrometallurgy can be conducted under mild conditions, usually without the use of any toxic chemicals. Consequently, the application of biohydrometallurgy in the recovery of metals from lean grade ores and wastes has made it an eco-friendly technology for enhanced metal production. This paper reviews the current status of biohydrometallurgy of low grade ores around the world. Particular attention is focused on the bioleaching of black shale ore and its metallogenic diversity in the world. The review assesses the status of bioprocesssing of metals to evaluate promising developments. Bioleaching of metals is comprehensively reviewed with the emphasis on the contribution of microbial community, especially fungal bioleaching coupled with ultrasound treatment. In this manuscript, the principles of bioleaching, their mechanisms, and commercial applications are presented. The case studies and future technology directions are also reviewed
Article
The use of ammonium thiosulphate as leaching agent for gold from a flotation concentrate has been studied. The gold content in the concentrate was 95 g/t, whereas the main mineralogical species were chalcopyrite, pyrite, pyrrhotite, tennantite and sphalerite. The experimental variables studied were: (i) Cu(II) concentration (0–6.5 g Cu(II) (added) per liter of leaching solution), (ii) thiosulphate concentration (0.1–0.7 M), (iii) pH (9–10) and (iv) pulp density (10–40%). Best gold dissolution (94%) was obtained at 0.05 M Cu(II), 0.3 M S2O32−, pH 10 and 10% pulp density after 15 h, whereas cyanidation gives the same yield but after about 46 h of reaction.
Article
The extraction of gold, silver, copper, zinc, and nickel present in thiosulfate solutions with or without the presence of ammonia was studied. Results show that neither a primary amine nor the mixed extractants of a primary amine with tributyl phosphate or trialkyl amine oxide can separate gold from other metals in the absence of ammonia in aqueous solutions. In the case of ammonium thiosulfate solutions, the percent extraction of gold is increased tremendously in comparison with other metals, and thus gold can be separated from them. The pH50 of gold extraction for a mixed solvent of primary amine with amine oxide is about 9.0, which is very close to the pH of the actual leaching solutions. By using the mixed solvent to extract gold in the solutions from leaching of gold-containing sulfide concentrate, the separation factors of Au to Ag and Au to Cu could reach as high as 15 and 1695, respectively, for a pH less than 8.
Article
Zinc exists as smithsonite and hemimorphite in the lead flotation tailings from the Dandi mineral processing plant in north western Iran. In this research, zinc-rich tailings produced in the Dandi plant were characterized mineralogically and a leaching study was carried out to assess the effect of several parameters on the kinetics of zinc dissolution. Parameters studied included: sulfuric acid concentration, reaction time, temperature and slurry density. It was found that leaching is controlled by a single rate-controlling step with an activation energy of 23.5 kJ/mol. To overcome some of the filtration problems associated with polymerization of silicic acid, lime was added as a coagulant. The optimum pH, holding time and temperature required to maximize the filtration rate were determined.
Article
Elemental gold on non-metallic secondary raw materials is easy to dissolve by leaching with sulphuric acid solutions of thiourea in the presence of an oxidant such as iron(III) sulphate or hydrogen peroxide. Leaching time is highly dependent upon oxidant concentration and the thickness of the gold coating. The gold goes into solution as the Au[SC(NH2)2]2+ complex and can be removed almost completely using cationites, the gold residues being not greater than 6 μM. The gold-free leaching solution may be reused for leaching; the completely-loaded cationite resin (with a gold content of about 30–60 g/l) is burnt to recover the gold.A study of the adsorption of Au and Fe by cationites indicates that the adsorption of gold takes place purely by means of an ion-exchange mechanism, the bond of the gold complex being considerably stronger than that of the iron compounds.
Article
The leaching of gold, silver and base metals from a sulfidic gold ore in the presence of an oxidant (peroxomonosulfate (HSO5−) or iron(III)) and leaching agent (thiourea, chloride, bromide or iodide) is compared in 1-butyl-3-methylimidazolium hydrogen sulfate (bmimHSO4) and chloride (bmimCl) ionic liquids, as well as in aqueous saturated K2SO4 as the solvent medium. Over 85% of gold and silver was recovered in the presence of HSO5−/ thiourea at 25–50 °C in both bmimHSO4 and bmimCl, with silver recovery significantly enhanced compared with that from aqueous sulfate medium. The leaching efficiency with HSO5− was similar to that with Fe(III) as oxidant in bmimHSO4 and was far superior in bmimCl. With HSO5− /halide ion (Cl−, Br−, I−) as leaching agent, gold and silver recovery in bmimHSO4, bmimCl or saturated aqueous K2SO4 improved from Cl− to Br− to I−, but only I− gave a high recovery in the bmimCl ionic liquid due to the particular stability of the iodo complex anion in this medium. However, recovery was significantly higher than in an aqueous medium. Negligible recovery of base metals occurred in the ionic liquid medium, making it highly selective for Au and Ag. Concentration dependence studies with respect to halide and oxidant have defined optimum conditions for gold and silver recovery.
Article
a b s t r a c t Waste of electric–electronic equipment (WEEE) with an annual growth rate of about 3–5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydromet-allurgical processes were reviewed in this study. With their relatively low capital cost, reduced environ-mental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treat-ment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes.
Article
In this study, competitive adsorption of metal chloro complexes on the polymer adsorbent XAD-7 has been investigated. Au(III), Fe(III) and Te(IV) dissolved in HCl and alkali metal chloride solutions were used as the model compounds. Adsorption equilibria were measured for individual elements as well as for binary pairs and the data were correlated in terms of activities of the adsorbable complexes. Finally, the equilibrium model together with the experimentally determined apparent diffusion coefficients was utilized in simulation of break-through curves of multicomponent mixtures.Adsorption of gold and iron can be explained satisfactorily by taking into account the formation equilibria of the tetrachloro complexes and the difference in their acid strengths. The uptake of the weakly acidic HAuCl4 depends only slightly on the HCl concentration and adsorption was substantially stronger in NaCl solutions. The opposite trends observed for iron were due to the lower stability and higher degree of dissociation of HFeCl4. The adsorbable complex of Te(IV), HTe(OH)Cl4, has lower affinity for the adsorbent, but at high concentrations it can reduce substantially the adsorption capacity for Au(III) and Fe(III). This effect was confirmed with the adsorption column runs, and the change in the break-through behavior of Au(III) and Fe(III) can be explained quantitatively by the simulation model.
Article
The intensification of the thiosulfate leaching of silver, gold and bismuth from sulfide concentrates using mechanical activation and mechanochemical pretreatment step was investigated. The physico-chemical changes in a complex sulfide concentrate (Casapalca, Peru) as a consequence of mechanochemical pretreatment had a pronounced influence on the subsequent silver extraction. The optimum results from mechanochemical pretreatment and subsequent leaching of the concentrate with ammonium thiosulfate were achieved with 99% recovery of Ag after only 3 min of leaching. The leaching of gold from a mechanically activated complex sulfide concentrate (Banská Hodruša, Slovakia) using ammonium thiosulfate was studied as follows. Physico-chemical transformations in the concentrate due to mechanical activation have an influence on the rate of extraction and the recovery of gold. It was possible to achieve 99% Au recovery within 45 min for a sample mechanically activated. Mechanical activation proved to be an appropriate pretreatment for this concentrate before extraction of gold into thiosulfate leaching solution. The selective leaching of a bismuth from the lead concentrate (Atacocha, Peru) by using of sodium thiosulfate and mechanical activation as the pretreatment step was examined as the last example. It is possible to achieve more than 90% recovery of a bismuth in leachate even in three minutes for mechanically activated samples.
Article
Thiosulphate leaching of precious metals has been developed as an alternative and non-toxic technique to the conventional cyanidation. This process has advantages over cyanide in a decreased interference from foreign cations and a lower environmental impact. Ammoniacal thiosulphate solution allows the solubilization of gold as stable anionic complex. Leaching of gold occurs at appreciable dissolution rates.The aim of this work is devoted to a preliminary evaluation of the feasibility of thiosulphate leaching for the extraction of gold from precious metals ores on a laboratory scale. The experimental work has allowed the authors to point out the influence of temperature, thiosulphate concentration, ammonia concentration and copper sulphate concentration on the gold dissolution from an ore (51.6 g/t Au) that originated from the Dominican Republic.Gold was recovered from the leach liquors by adsorption onto activated carbon or by electrowinning. With the optimisation of the process parameters about 80% gold recovery has been attained, as in the case of conventional cyanidation.
Article
An investigation has been carried out to identify the parameters of importance in the dissolution of gold and silver values from an ore using ammoniacal thiosulfate solutions containing copper. The chemistry of the dissolution process has been analyzed through the construction of EH −pH diagrams. The experimental results show that it is possible to solubilize about 70% of silver and 90% of gold values in one hour. The leaching process is quite sensitive to thiosulfate and ammonia concentrations. Maintenance of proper Eh and pH conditions is necessary to prevent precipitation of copper as Cu2S with concomitant loss of silver values from solution.
Article
Previous researchers have rationalized the thiosulfate oxidation by ammoniacal copper(II) on the basis of the rate equation −d[Cu(II)]/dt = k[Cu(II)][S2O32−]/[NH3] for the decomposition of the reaction intermediate Cu(NH3)3(S2O3)0, but no such detailed analysis has been made in the case of gold. This work revisits literature data to show that the oxidation of thiosulfate takes place via mixed complexes Cu(NH3)2(S2O3)n−(2n−2) (n = 1 or 2). The oxidation can be considered as a first-order decomposition of these complexes, with a rate constant kCu(1) = 4×10−4 s−1, to produce S2O3− which undergoes dimerization to S4O62−. It can also be treated as a second-order decomposition of Cu(NH3)3(S2O3)0 or Cu(NH3)2(S2O3)0 with rate constants kCu(2) = 0.2 and 0.1 L mol−1 s−1, respectively, which produce S4O62− in one step.The literature data reported for gold dissolution in the copper(II)–ammonia–thiosulfate system show first-order dependence with respect to copper(II) and thiosulfate concentration, but it is relatively less affected by ammonia and hydroxide concentrations. At higher concentrations of copper(II) and thiosulfate, the rate becomes zero order with respect to these reagents. The leaching data obey a shrinking core model for both gold powder and carbonaceous or roasted ore with an apparent rate constant ksc≈10−5 s−1, but the ksc also shows a first-order dependence with respect to the measured copper(II) concentration in solution. The copper(II) sepeciation analysis shows Cu(NH3)2(S2O3)22−, Cu(NH3)2(S2O3)0 and Cu(NH3)3(S2O3)0 as the predominant species in ammoniacal copper(II)–thiosulfate solutions. Thus, gold oxidation can be represented by a sequence of equations representing adsorption and redox reactions.
Article
The rudimentary nature of small-scale gold mining activities often generates a legacy of extensive degradation and deplorable social conditions, both during and after activities have ceased. Small-scale mining usually involves the extraction of secondary gold from placer deposits (alluvial, colluvial or elluvial), which can be liberated and treated using gravity methods. In the Guianas, the most popular form of small-scale gold mining is referred to as “land dredging”, a combination of hydraulicking and suction dredging. This method requires application of large volumes of water for both mining and mineral processing; in most cases, there are no containment structures for the waste tailings generated. Mercury, a dangerous pollutant, is the preferred method employed by small-scale miners for gold recovery. Gold extraction using mercury is comprised of the following four stages: (1) amalgamation, (2) separation of amalgamation, (3) removal of excess mercury, and (4) burning of the remaining amalgam to produce a gold sponge. Mercury can be released into the environment at each stage, which makes the promotion of mercury-free alternatives imperative.Technical alternatives for small-scale gold mining, however, must be thoroughly evaluated, pre-tested, modified accordingly and successfully transferred. Moreover, technology must be inexpensive, relatively simple and easy to adapt, while allowing a rapid rate of return. WWF-Guianas is working with the regulatory agencies and other relevant stakeholders of the Guianas to reduce the environmental footprints caused by small-scale mining. The major aspects of this program are to develop the capacity and regulatory mechanisms within the local government, to promote mercury-free technology, and monitor mercury in the environment. This paper reviews the alternative technologies being investigated by the WWF-Guianas for use in the small-scale gold mining industry.
Article
The leaching behaviour of three Fe-containing sphalerite minerals (0.45, 11.40, and 12.90 wt.% Fe) was investigated at pH 1 in O2-purged HClO4 from 25 to 85 °C. For all three sphalerite samples, the leach data closely fitted a rate expression which incorporates both a shrinking sphere term and rate control via diffusion through a reacted surface layer. The leach rate increased with increasing Fe content of the sphalerite. At 85 °C after 168 h of leaching, 0.89 of the Zn had been leached from the 12.90 wt.% Fe-containing sphalerite while, over the same period of time, 0.49 of the Zn had leached from the 0.45 wt.% Fe-containing sphalerite.The activation energies for leaching decreased with increasing Fe content of the sphalerite (i.e. for Zn leaching 63±6, 50±7 and 39±2 kJ mol−1 for the 0.45, 11.40 and 12.90 wt.% Fe-containing sphalerite samples, respectively). The activation energy of leaching of Fe and Zn was within experimental error for the 11.40 and 12.90 wt.% sphalerite samples. The solution Fe content was not measured reliably for the 0.45 wt.% Fe-containing sphalerite.The leaching mechanisms have been interpreted as a function of surface speciation, which was analysed using time of flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) for samples leached at 85 °C. The decrease in Zn dissolution rate on leaching is attributed to the formation and growth of a polysulfide surface layer, which forms during the initial rapid leach period. The formation of elemental sulfur during the subsequent slow leach period does not further affect the leach rates. The concentrations of polysulfide and elemental sulfur that form increase with increasing Fe concentration as expected from the higher leach rates. The formation of polysulfide and elemental sulfur on the ZnS surface consumes H+ (via conversion to H2O) thus decreasing solution acidity.
Article
The effects of the particle geometry and size, stirring speed, pH, chlorine and chloride concentrations and temperature on the kinetics of the aqueous chlorination of gold were studied. Surface examinations of gold samples leached in different conditions were carried out by SEM/EDS and XPS.The kinetics appear to be chemically controlled in conditions of full suspension of the particles. The dependence of pH and the chlorine and chloride concentrations indicate that the rates were essentially determined by the concentration of the trichloride ion. The expression obtained for the specific rate was: Rate (mol cm−2 min−1) = 4.25 105 [Cl3−] exp () A discussion of the possible mechanism is included, based on the kinetic dependence, previously reported electrochemical studies and mixed potential measurements.
Article
A new mathematical model was developed for leaching of zinc ores containing silicates such as hemimorphite which produce a gel during leaching with sulfuric acid. This model is based on the shrinking core model in which the particle size and the reacting core shrink simultaneously. It was shown that the actual dissolution time of the ore particles is longer than the time corresponding to the dissolution of chemical zinc oxide itself. It was suggested that because of the existence of silicates in the ore, a gelatinous layer was formed around the reacting core. Since the gel product is soft, it breaks apart when the particles collide and as a result, the particles shrink. However, a thin gelatinous layer always covers the reacting core which increases the mass transfer resistance and increases the leaching time. This model was applied to leaching of a zinc-rich tailing containing hemimorphite and the thickness of the gelatinous layer as well as the diffusion coefficient in this layer was determined.
Article
Crosslinked polyacrylamide and polyvinylpyrrolidone gels have been used to subcutaneously implant (125)I-labeled immunoglobulin, (125)I-labeled luteinizing hormone, (125)I-labeled bovine serum albumin, (125)I-labeled insulin, [(3)H]prostaglandin F(2alpha), and Na(125)I into hamsters. From the rates of absorption of the solutes, their diffusion coefficients were determined. The diffusion coefficients showed a logarithmic dependence on implant polymer concentration and solute molecular weight. Release of the solutes from gel preparations incubated 10 mM phosphate buffer (pH 7.2) at 37 degrees revealed a similar relationship between solute diffusion coefficient, molecular weight, and the concentration of polymer. A general equation was derived that gives the expected diffusion coefficient of a substance in a polymer gel from its molecular weight, diffusion coefficient in solvent, and polymer concentration of the gel.
Gold recovery from powdered ores by iodide redox leaching with chemical regeneration, World Patent WO 9805569 AI
  • J Leibovitz
Leibovitz, J., 1998, Gold recovery from powdered ores by iodide redox leaching with chemical regeneration, World Patent WO 9805569 AI, pp. 46.
Highly Efficient Processes for Gold Separation from Solid and Liquid Media
  • A Filcenco Olteanu
Filcenco Olteanu, A., 2010. Highly Efficient Processes for Gold Separation from Solid and Liquid Media. PhD Thesis Politehnica University of Bucharest.
The effect of nascent chlorine and multivalent chloride salts in the dissolution of gold by chlorine
  • C C Nesbitt
  • J L Hendrix
  • J H Nelson
Nesbitt, C.C., Hendrix, J.L., Nelson, J.H., 1992. The effect of nascent chlorine and multivalent chloride salts in the dissolution of gold by chlorine. In: Hager, J.P. (Ed.), EPD Congress. TMS, Warrendasle, P.A, pp. 313-326.
Gold and silver recovery from chlorous mud
  • R Radulescu
  • Gh Filip
Radulescu, R., Filip, Gh., 2004. Gold and silver recovery from chlorous mud. RO118664.
Gold recovery from computer circuit boards with acidic thiourea
  • P P Sheng
  • T H Etsell
  • S R Rao
  • L M Aamaratunga
  • G G Richards
Sheng, P.P., Etsell, T.H., 1988. Gold recovery from computer circuit boards with acidic thiourea. In: Rao, S.R., Aamaratunga, L.M., Richards, G.G., Kondos, P.D. (Eds.), Waste Processing and Recycling in Mineral and Metallurgical Industries III. The Metallurgical Society of CIM, Montreal, Canada, pp. 559-566.
Study of the thiosulphate leaching of gold from carbonaceous ore and the quantitative determination of thiosulphate in the leached solution
  • M Hemmati
  • J L Hendrix
  • J H Nelson
  • E B Milosavljevic
Hemmati, M., Hendrix, J.L., Nelson, J.H., Milosavljevic, E.B., 1989. Study of the thiosulphate leaching of gold from carbonaceous ore and the quantitative determination of thiosulphate in the leached solution. Extraction Metallurgy Symposium, 89. IMM, London, UK, pp. 665-678.
Recovery of Au and Ag from material containing non-ferous metals and Fe including leaching by KCNO method, Russian Patent, RU 2109826 CI, pp2 Hydrometallurgical extraction of gold from electronic waste
  • A M Khalemskii
  • S A Payvsov
  • S A Kadnikov
  • A G Talanov
  • Y S Tumashov
  • D Kristofova
  • T Karnik
Khalemskii, A.M., Payvsov, S.A, Kadnikov, S.A, Talanov, A.G., Tumashov, Y.S, 1998, Recovery of Au and Ag from material containing non-ferous metals and Fe including leaching by KCNO method, Russian Patent, RU 2109826 CI, pp2; Kristofova, D., Karnik, T., 1996. Hydrometallurgical extraction of gold from electronic waste. Miner.Slov. 28 (5), 429–430.