Cyanide Leach Solutions Research Articles

Sulfur speciation analysis in cyanide leach solutions with liquid chramotography

Sulfur speciation analysis in cyanide leach solutions with liquid chramotography

Novel approach for removing iron-cyanide complex ions and cesium ions from solutions using hydrogel-like beads

In the process of recycling cyanide leaching solutions, the presence of iron-cyanide complex ions in gold leaching solutions leads to increased cyanide consumption and competition with gold for adsorption onto activated carbon. Consequently, the removal of iron- cyanide complex ions from cyanide leaching solutions is crucial. This study presents a novel strategy for the treatment of metal ions in leaching solutions, achieving effective waste treatment using hydrogel-like beads. To remove iron-cyanide complex ions from cyanide leaching solutions, we synthesized carboxymethyl cellulose‑iron (CMCFe) hydrogel through a crosslinking method. The adsorbent, carboxymethyl cellulose-Prussian blue (CMC-PB) hydrogel, obtained after iron-cyanide complex ion adsorption, can directly remove Cs+ ions from solution without the need for desorption and regeneration. Notably, the CMC-Fe hydrogel exhibits exceptional adsorption performance and high selectivity toward iron-cyanide complex ions. The adsorption process of the CMC-Fe hydrogel follows a pseudo-second-order kinetic model, while the Freundlich isotherm model is more suitable for describing the adsorption equilibrium. Additionally, the CMC-PB hydrogel efficiently adsorbs 83.1% of Cs+ ions at a dosage of 86.5 μg, and desorption and regeneration studies reveal that its adsorption efficiency remains high even after three cycles. Furthermore, the proposed adsorption mechanism of CMC-PB for Cs+ ions involves a combination of chemisorption (K+/Na+ exchange) and physisorption (hole channels of hydrogels).

Effect of metal ions on gold adsorption onto activated carbon in the acidic thiourea solution: Experiment study and DFT calculation

Thiourea leaching has been regarded as a promising method to substitute cyanidation for gold recovery from ores or concentrates. Activated carbon used in traditional cyanide leaching solution can also be used for gold recovery from thiourea leaching solution. In this paper, the effect of metal ions including Cu2+, Ag+, Pb2+ and Zn2+ on gold adsorption onto activated carbon from acidic thiourea solution was studied for the first time. Results showed that the adsorption process of activated carbon for gold can be well described by the Freundlich isotherm model, and followed the Pseudo-second kinetic model. The adsorption of gold onto activated carbon in thiourea solution may be a ligand exchange reaction. The S of the activated carbon is the electron-accepting atoms, which can form the bond of Au-S with Au in Au[CS(NH2)2]2+. The presence of Pb2+ and Zn2+ did not interfere gold adsorption at gold concentration of 5 mg/L, but hindered gold adsorption at gold concentration of 100 mg/L. When Cu2+ and Ag+ were added in the whole studied concentration range, the gold adsorption could be significantly declined. The adsorption capacity of gold onto activated carbon in the presence of metal ions followed the sequence of Cu2+ < Ag+ < Pb2+ < Zn2+ < no addition of metal ions. Meanwhile, metal ions also adsorbed onto activated carbon, and their adsorption capacity on activated carbon obeyed the descending order of Cu2+ > Ag+ > Pb2+ > Zn2+, consistent with the complexing ability of metal ions with thiourea. The decrease of active site of activated carbon occupied by metal ions was responsible for the decrease of gold adsorption. Based on the DFT analysis, it can be inferred that the ability of metal ions to lose electrons caused the different influence of metal ions on gold adsorption.

A new strategy for extraction of copper cyanide complex ions from cyanide leach solutions by ionic liquids

Copper cyanide complexes in cyanide leach solutions deteriorate the recoveries of gold. Herein, five phosphonate-based [P204]− ionic liquids were synthesized, which were pioneered to apply to extraction of copper cyanide complex ions in cyanide leach solutions. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the aqueous-organic phase interface, which was driven by self-assembly of ionic liquids. Notably, the layered solids can be obtained by simple filtration. The extraction behaviors were systematically studied in the present work. The results show that the extraction efficiency in excess of 90 % can be achieved at higher pH (13.16) and enriched as self-assembly solids in the process of one-step extraction and solidification, based on the self-assembly extraction systems of [P4444][P204] IL. It is worthy of note that no self-assembly sample was observed when the extraction systems is applied to extraction zinc and iron cyanide complex ions. It indicates that the present self-assembly extraction systems could be applied in separation copper and zinc/iron cyanide complex ions. Meanwhile, the coordination mechanism was investigated detaily, and the covalent nature played a leading role in the binding interaction. Remarkably, [P4444][P204] can be repeatedly used without obvious loss in extraction capacity of copper cyanide complex ions after two cycles, indicating that the IL has a good recycling ability. In conclusion, it is possible to employ the self-assembly extraction systems to separate and recover various valuable metals from aqueous solutions by designing and developing ILs extractants in the future.

Removal of mercury from cyanide leach solution using potassium amyl xanthate (PAX)

The dissolution of mercury during cyanide leaching of Hg-containing gold ores and amalgamation tailings cause many environmental, health and operational problems. For this reason, mercury removal is a very important factor in the economic and environmental selection of the separation method.In this study, the use of potassium amyl xanthate (PAX) as precipitation reagents in the removal of mercury-cyanide complexes from synthetic solutions containing gold, silver and mercury has been investigated. The effect of reaction time, PAX:Hg molar ratio, pH, temperature, CN concentration and Cu concentration on the precipitation of mercury was explored using synthetic mercury-cyanide solutions. Detailed characterization of precipitates was performed using SEM EDS, XRD, FT-IR and particle size analysis.The results of this study illustrate that the precipitant dosage, initial concentrations, pH and temperature were quite effective on the Hg removal efficiency. The best Hg removal efficiency was obtained of 99.2 % at 44.7 °C. The Hg concentration was reduced from 10000 ppb to 72 ppb. As a result of characterization tests, it has been determined that highly stable metacinnabar (β-HgS) is formed as precipitate. The findings showed that PAX is an effective reagent for the selective precipitation of mercury from cyanide leaching solutions.

Опыт развития, внедрения и стандартизации BIM (ТИМ)-проектирования в горнодобывающей отрасли

The modern metals industry is characterised by a downward trend in the quality of ores involved in processing, and conventional methods of extracting useful components are inefficient for raw materials with complex composition. To maintain the growing level of metal production it is required to introduce new efficient technologies for processing of low-grade and refractory ores as well as man-made deposits. The article describes processing methods of refractory raw materials with high cyanide content using copper-gold ores as an example, where gold is the primary commodity, and copper is the accompanying useful component. The most common method of processing copper-gold ores is preconcentration followed by selective leaching of copper and gold. In some cases, technologies involving copper by-products and cyanide recovery from the cyanide leaching solutions offer equally effective options for processing of the copper-gold ores and concentrates. Copper-gold ores are processed at gold mines using the cyanide procedures, supplemented if required by gravity and flotation concentration. In all variations of the cyanide treatment, most of copper minerals actively react with cyanides of alkali metals, binding the CN– ions into the copper complex of [Cu(CN3)]2–. This reaction results in an increased solvent consumption, as well as in number of challenges related to cleaning tailings and slurries from highly toxic cyanide compounds and dissolved copper. In addition to technological complications associated with the need to meet strict requirements for the maximum permissible concentrations, copper accumulated in the cycling solutions also causes a decrease in gold extraction from the processed ores.

Comparison of ion-exchange resins and activated carbon in recovering gold from cyanide leach solutions with low level of copper.

This study was conducted to determine the effectiveness of three different adsorbents for the adsorption of gold from a real cyanide leach liquor. An activated carbon (NORIT GAC 1240), strong base (Purogold A194), and weak base (Purogold S992) resins were tested as the adsorbents. The pregnant leach solution (PLS) was derived from cyanide leaching (1.5 g/L NaCN, 25% w/w solids ratio, 1.5 L/min air flow rate, pH 10.5 – 11, 24 h) of the roasted copper-rich refractory gold ore pretreated with H2SO4. Gold and copper concentrations in the PLS were analysed to be 26.1 mg/L Au and 62.4 mg/L Cu, respectively. Activated carbon was found to be the best performing adsorbent as it achieved the highest gold loading. Purogold A194 loaded the highest amount of copper amongst the adsorbents tested. Despite the fact that activated carbon loaded a high amount of gold, it was less selective than Purogold S992. Purogold A194 exhibited the lowest selectivity, which was defined as the distribution ratio of gold to copper, compared with Purogold S992 and activated carbon. Therefore, the order of selectivity of the adsorbents tested was as follows: Purogold S992 > Activated carbon > Purogold A194.

Reducing preg-robbing in carbonaceous gold ores using passivative or blanking agents

Carbonaceous materials found in gold ores often exhibits strong preg-robbing properties which adversely affect gold recovery during the cyanidation due to its ability to adsorb, or preg-rob gold from the cyanide leach solution. Treatments of carbonaceous ores with chemical surfactants as blinding agents to limit preg-robbing have shown promising results however, if not properly used, could have a strong detrimental effect on the gold recovery process. The present study investigated the effectiveness of using commercially available surfactants (Dextrin, naphthalene sulphonate and Triton X-100) as blanking agents to minimize the preg-robbing capacity of various carbonaceous materials (activated carbon, anthracite and bituminous) and carbonaceous gold ore through adsorption and leaching studies. Chemical analysis of ore sample used for the study showed that the gold (Au) content was 17.2 g/t. The organic carbon content of the ore sample was 0.95%. Mineralogical composition of the ore sample determined with X-ray diffraction (XRD) showed that pyrite (24.8%), Quartz (21.5%) and Muscovite (21.8%) were the main mineral in the ore. Gold adsorption studies performed revealed that the treatment of the carbonaceous materials (activated carbon, anthracite and bituminous) with the blanking reagents significantly decrease gold adsorption by the carbonaceous materials. However, the blanking ability for the surfactant varied for the various carbonaceous materials. Application adsorption studies to gold leaching test confirmed that the three surfactants, especially naphthalene sulphonate could be used as blanking agents for carbonaceous gold ores during cyanidation. Gold recovery from CIL studies increased from 46.0% to 67.7%, 52.3% and 49.0% after treatment with naphthalene sulphonate, dextrin and triton X-100 (49.0%) respectively.

Precipitation of copper from cyanide leach solutions using sodium dimethyldithiocarbamate (SDDC)

Production of gold from copper-rich gold ores has received particular attention due to some technical and economic challenges associated with the ready dissolution of most copper minerals during cyanide leaching. This leads to excessive consumption of cyanide by forming copper cyanide complexes, which adversely affect downstream recovery and cyanide detoxification processes. In this study, a novel method is proposed to precipitate copper from cyanide solutions using sodium dimethyldithiocarbamate (C3H6NNaS2; SDDC). The influence of various parameters (i.e., reaction period (0–360 min.), concentration of SDDC (165–992 mM), [CN−]/[Cu] ratio (3–8), pH (10–12.5) and temperature (20–60 °C) on the precipitation of copper were investigated using synthetic copper-cyanide solutions. Increasing reaction time, concentration of SDDC and temperature were found to significantly improve the precipitation of copper. Increasing the ratio of [CN−]/[Cu] adversely affected the precipitation of copper with no precipitation being occurred at ratios of ≥6. Strong alkaline conditions appeared to have a slightly negative impact on the process. In the light of these findings, the response surface methodology (i.e., central composite design; CCD) was adopted to reveal the influence and interactions of [SDDC]/[Cu] ratio (21.0–126), initial concentration of copper (50–950 mg/L) and reaction period (15–360 min.) on the precipitation of copper. The analysis of the data confirmed that statistically significant parameters affecting the process were reaction time and [SDDC]/[Cu] ratio. It was also found that initial copper concentration did not significantly influence the process. Tests on real cyanide leach solutions derived from gold ores/concentrates demonstrated that the SDDC could selectively precipitate copper (as well as zinc and silver) from gold-bearing solutions. The activation energy (i.e., ≈67 kJ/mol) calculated by Arrhenius equation has indicated that the precipitation of copper is a chemically controlled reaction. Detailed characterisation of Cu-DDC precipitates was performed using SEM-EDS, FT-IR and particle size analysis. The precipitates (d80 = 16 μm) are thin, rod-like particles in brownish colour. The recovery of copper from Cu-DDC precipitates using acid solutions (HCl, H2SO4 and HNO3) was also investigated. Complete recovery of copper was achieved using HCl and HNO3 solutions at high concentrations. The findings have suggested that SDDC is an effective reagent for selective precipitation of copper from cyanide leach solutions.

Gold deportment and leaching study from a pressure oxidation residue of chalcopyrite concentrate

Pressure oxidation (POX) is an effective method for base metal extraction and a pretreatment of refractory gold ores. A residue from pressure leaching of chalcopyrite concentrate was collected and investigated for gold recovery and deportment of metals. A comprehensive mineralogical analysis and gold deportment study were conducted using techniques including X-ray diffraction (XRD), optical microscope, scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX), and dynamic secondary ion mass spectrometry (D-SIMS). Gold leaching tests were performed using cyanide and glycine as lixiviants. The gold grade is 3.1 g/t, with 0.31% residual copper in the sample. Hematite was a dominant iron oxide (31.5%), and iron sulfate salts (45.4%) existed in various minerals phases. The gold deportment study revealed that 32.3% of the total gold was present as a visible gold, and the remainder was sub-microscopic gold. The visible gold was native gold with an average particle size of less than 20 μm. Colloidal gold, the dominant existence of invisible gold, was found in hematite, jarosite, and iron sulfate. Hematite was the major sub-microscopic gold carrier, forming a nonporous rimmed structure and locking gangue minerals randomly. Gold in arsenopyrite was found as solid-solution, accounting for 7.2%. Gold extraction of 84% was achieved by 500 mg/L NaCN, while only 35% of gold was extracted by 100 mg/L NaCN. A significant synergistic effect of cyanide and glycine was observed. The addition of glycine in cyanide leaching solution boosted the gold leaching kinetics and recovery. Gold recovery of 85% was observed with 100 mg/L NaCN and 0.3 M glycine in 24 h. In the hybrid leaching system, copper was stabilized by glycine and further utilized as a catalyst for gold leaching. To achieve higher gold extraction and lower lime consumption, a product with high sulfur oxidation degree and low iron sulfate content is preferable in pressure oxidation operation. Hematite is a stable product and does not impair gold leaching.

Comparison of Adsorption Properties of Activated Carbons with Different Crops Residues as Precursors for Gold Cyanide Recovery: An Iranian Gold Industry Guide

Adsorption of gold cyanide on three types of Activated Carbons (ACs) has been investigated in batch and column adsorption conditions. Applied ACs have been derived from different crops precursors i.e., coconut shell (CAC), peach stone (PAC), and walnut shell (WAC). As peach stone and walnut shells are abundant agricultural residues in Iran, the activated carbons produced from these precursors are economically preferable for the gold recovery process. The ACs were characterized using FTIR, SEM, BET, and Wet-Bed Compaction Hardness analyses. Batch equilibrium adsorption data were analyzed using the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. Freundlich isotherm was in better agreement with the equilibrium data and the maximum adsorption capacity (40.8 mg/g) was tabulated for CAC. Adsorption kinetics was also modeled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The PAC recorded the highest removal rate in the light of better agreement of the pseudo-second-order model. Fixed-bed column experiments were carried out at different initial gold concentrations (30, 50 mg/L) to determine the characteristics of the breakthrough curves. The maximum bed capacity (37.55 mg/g) was obtained for CAC. Three dynamic adsorption models including, Thomas, Yoon–Nelson, and Adam–Bohart,were applied to describe the breakthrough curves. Both Thomas and Yoon–Nelson models were in appropriate agreement with the experimental column adsorption data. This research introduces peach stone as a promising precursor considering availability, technical features, and economical aspects for the production of AC for gold recovery from cyanide leach solutions. Results are also conducive for gold mining industries to select the appropriate activated carbon.

Adsorption of Mercury from a Cyanide Leaching Solution Using Various Activation Rates of Granular Activated Carbon: A Laboratory- and Industrial-Scale Study

The use of granular activated carbon (GAC) is a typical and sustainable technique for recovering precious metals from a cyanide leaching solution (CLS). The level of GAC activity is a fundamental factor in assessing the rate of precious metal adsorption; thus, it is essential to determine the efficiency of carbon elution for reproducing GACs. Since mercury (Hg) adsorption plays a critical role, economically and environmentally, in GAC efficiency, we conducted various laboratory and industrial experiments to explore the effect of different rates of GAC activation (10%, 35%, 70% and 100%) on Hg adsorption from CLS. Assessments of laboratory test results showed a direct relationship between the Hg adsorption and GAC activity; by increasing the GAC activity from 10% to 100%, the recovery of Hg was increased from 20% to 41%. Kinetic modeling results indicated that the Hg adsorption for all GAC activities followed chemisorption mechanisms. There was good agreement between the laboratory test results and the results of experiments on the industrial scale (that used a continuous circuit). These outcomes indicate that by increasing the frequency of carbon reactivation and using GAC with a high level of activity in the first tank, Hg desorption was meaningfully decreased and recovery was improved (for 10% GAC activity vs. 35% GAC activity, recovery was 40% vs. 90%, respectively).

Gold extraction via cyanide leaching using alkaline-based empty fruit bunch activated carbon

This research is carried out to extend the knowledge on the modernized method of modifying the physical and structural properties of empty fruit bunches (EFB), a low-cost, highly accessible and abundant agricultural waste in Malaysia, for gold adsorption process. To complete this aim, EFB was modified by using an alkaline-based chemical to improve the surface area, porosity volume and surface chemistry of sorbents. The structure of the empty fruit bunch is characterized by using characterization techniques such as Thermogravimetric analysis (TGA) and Energy-Dispersive X-ray spectroscopy. The gold solution was prepared by mixing gold with a sodium cyanide solution to undergo a leaching process for 24 hours. The solution was then used for the adsorption experiment. The performance of the alkaline-based EFB-AC to separate gold from the cyanide leaching solution was further studied on the effect of contact time, pH and agitation rate. The gold adsorption capacity achieved by the alkaline-based EFB-AC was measured by calculating the difference between the initial and final gold concentrations using Atomic Absorption Spectrometry (AAS). The maximum gold adsorption capacity findings of contact time, pH, and agitation rate were found to be 2.5 hours, pH of 10 and 60 rpm, respectively. This study reveals that the alkaline-based EFB-AC has the potential to extract gold as an alternative activated carbon in the gold adsorption process.

Precipitation of zinc from cyanide leach solutions using Trimercapto-s-triazine (TMT)

Cyanide leach solutions produced from gold/silver ores can be contaminated with zinc due to the gold/silver cementation in Merrill-Crowe process and/or the dissolution of zinc minerals present in the ore. Zinc levels in cyanide solutions should be controlled to avoid potential problems in leaching and downstream processes associated with the accumulation of zinc. In this study, the application of a novel method was demonstrated for the precipitation of zinc from synthetic/real cyanide solutions using Trimercapto-s-triazine (TMT), a non-toxic organic reagent. Experimental studies have shown that precipitation of zinc with TMT is a fast process occurring in a short period of time i.e., ≤15 min. Increasing the concentration of TMT (33–90 mM) and pH (10–12.5) was found to improve the precipitation of zinc, which was unaffected by increasing the temperature (20–60 °C). Response surface methodology was adopted for detailed investigation of the effect of [TMT]/[Zn] ratio (2.70–16.25), [CN−]/[Zn] ratio (3.00–8.00) and initial concentration of Zn (50–950 mg/L) on the precipitation of zinc. High recoveries (≤95.4%) were obtained under suitable conditions. Precipitation tests were also performed using synthetic multi-metal and real leach solutions. The complete recovery/dissolution of zinc from the precipitates was also demonstrated using different acids (HCl and H2SO4). The findings have shown that TMT can be effectively used as an environmentally friendly reagent for removal of zinc from cyanide leach solutions.

Destruction of Cyanide and Removal of Copper from Waste Printed Circuit Boards Leach Solution Using Electro-Generated Hypochlorite Followed by Magnetite Adsorption

The removal of the cyanide and copper (Cu) from the waste printed circuit boards (WPCBs) cyanide leach solution through the alkaline chlorination using electro-generated hypochlorite (NaOCl) followed by magnetite (Fe3O4) adsorption is investigated. The efficiency of the destruction of cyanide and precipitation of Cu was increased with increasing the concentration of free available chlorine in NaOCl. More than 99% of free cyanide and 76% of Cu were removed under the following conditions: concentration of chlorine in electro-generated NaOCl, 5.2 g/L; volume ratio of NaOCl/leach solution, 1; pH, ~9.8; ambient temperature for 12 h. Then, magnetite adsorption for selective removal of remaining Cu (50.5 mg/L) was selected and more than 99% of copper ion was successfully removed with dosage 10g/100mL, shaking speed 150 rpm within 30 min. The results revealed that the alkaline chlorination using electro-generated NaOCl followed by magnetite adsorption could completely remove the cyanide and Cu, remaining Au in the final solution.

Exploring relationships between various activations of granular activated carbon on silver and gold adsorption: A kinetic and equilibrium study

ABSTRACTThis investigation examined various kinetic and equilibrium models for gold (Au) and silver (Ag) adsorption from cyanide leach solution, onto surface of granular activated carbon (GAC) with 10, 35, 70 and 100% activities. Results indicated that the initial rate for Au and Ag adsorption is similar and increases by increasing the GAC activities. Outcomes showed that the adsorption for low activity GAC is proportional to the number of adsorption sites while the rate-limiting can be chemisorption for GAC with high activity. Thus, even low amount of contaminations on the fresh GAC can significantly decrease the capacity of precious metals adsorption.

Thiosulphate leaching of silver from an arsenical refractory ore

Thiosulphate leaching has received particular attention in recent years as an environmentally benign alternative to cyanide leaching. In this study, thiosulphate leaching combined with ultra-fine grinding (UFG) was studied for silver extraction from an arsenical refractory ore. Direct cyanidation of the ore (d80: 50 µm) led to a low silver extraction of ≤ 70% over 24 h. leaching period. Extraction of silver in cyanide leaching was improved to 85% after ultra-fine grinding. In comparison, up to 98% of silver extraction was achieved in thiosulphate leaching system after ultra-fine grinding of the ore down to 5 μm (d80) in a stirred mill. Furthermore, thiosulphate leaching is more selective than cyanide leaching with only negligible leaching of arsenic, antimony and other metals observed in this study. This is of particular importance considering the environmental concern for the presence of arsenic in cyanide leaching solutions and effluents. Effects of thiosulphate (0.2–0.6 M Na2S2O3), ammonia (0.04–0.52 M NH3) and copper (0.02–0.11 M CuSO4) on the extraction of silver were investigated using a Box-Behnken design. Statistical analysis of the experimental data (%Ag extraction at 8 h.) confirmed that all the parameters have quadratic effects in that the extraction of silver tends to improve with increasing their concentration up to a critical level above which a reverse trend occurs. The addition of a small amount (0.1 M EDTA, 50 mg/L CMC) of ethylenediaminetetraacetic acid (EDTA) and carboxymethyl cellulose (CMC) improved (by ∼20–30%) silver extraction and reduced thiosulphate consumption by ∼20%. Using nickel sulphate in place of CuSO4 also improved silver extraction with concurrent decrease in thiosulphate consumption. Recovery of silver from real pregnant leach solutions using sodium borohydride (NaBH4) as the precipitating agent was also investigated in detail. A high silver recovery of ≥98% was achieved under suitable conditions. These findings highlight that ammoniacal thiosulphate leaching in combination with ultra-fine grinding can be used as a suitable and environmentally sound alternative to cyanide leaching and the additives such as EDTA and CMC, and nickel in place of copper can improve the extraction of silver from refractory silver ores.

Recovery of silver from cyanide leach solutions by precipitation using Trimercapto-s-triazine (TMT)

Cyanide leaching is the most common method used for production of silver from gold/silver ores. Silver (and gold) can be recovered from pregnant leach solutions (PLSs) using Merrill-Crowe process (zinc cementation) and activated carbon adsorption. Due to their inherent limitations and paucity of selectivity, development of alternative processes for selective recovery of silver from PLSs is of great interest. In the current study, selective recovery of silver by precipitation from cyanide solutions using an environmentally friendly organic reagent i.e. Trimercapto-s-triazine (C3N3S3; TMT) was investigated. The results have shown that precipitation of silver by TMT is a rapid process in that 87.9% of silver could be precipitated at the initial period of 5min. Response surface methodology (i.e. central composite design) was adopted to examine the main and interaction effects of [TMT]/[Ag] ratio (0.09–36.52), [CN]/[Ag] ratio (3−10) and initial concentration of silver (1–40mg/L Ag) on the precipitation of silver in five levels. The statistical analysis of the experimental data revealed that ratio of [TMT]/[Ag] (i.e. concentration of TMT) was the key parameter exerting a profound effect on the precipitation of silver. However, effects of [CN]/[Ag] ratio and Ag concentration appeared to be statistically insignificant. Complete precipitation of silver was found to be readily achieved under suitable conditions. The precipitation process was proved to be highly selective for silver over gold and copper as also confirmed by the tests on real pregnant leach solutions. It was found that the presence of TMT had no discernible effect on adsorption of gold by activated carbon, which was observed to even improve from copper containing solutions. Silver-TMT precipitates were characterised using SEM/EDS, FT-IR and other techniques. The current findings demonstrate that this precipitation process can be exploited as a potent alternative for selective recovery of silver from cyanide leach solutions of silver and gold/silver ores or purified/concentrated solutions ahead of gold electro-winning.

Adsorption of gold from cyanide leaching solution onto activated carbon originating from coconut shell—Optimization, kinetics and equilibrium studies

This study investigates the behavior of gold adsorption from cyanide leaching solution onto activated coconut shell carbon. The experimental was designed according to CCD implemented with RSM and a quadratic model was developed for regression analysis. The effects of important parameters including pH, agitation rate, adsorbent concentration and adsorption time were studied to find the best operating conditions, and the optimized value of pH, agitation rate, activated carbon concentration and adsorption time was found to be 11, 40 rpm, 1.25 g/L and 3 h, respectively. Under these conditions, the adsorption rate was found to be about 87.11%. Also, the optimal conditions were established on industrial cyanide leaching solution and the results demonstrated that adsorption rate of gold could be obtained about 89.25%. Adsorption behavior was kinetically investigated using pseudo first-order and pseudo second-order models among which data were mostly correlated to pseudo first-order model. The further analysis of kinetics indicated that intra-particle diffusion was the rate-limiting step. Adsorbate–adsorbent interactions at 298 k was assessed by Langmuir, Freundlich, and Temkin isotherm models from which Freundlich model had the highest consistency with the experimental data.

The extraction of platinum and palladium from a synthetic cyanide heap leach solution with strong base anion exchange resins

The use of ion exchange resins for the extraction of platinum and palladium from a synthetic cyanide leach solution is described in this paper. An increase in the concentrations of both platinum and palladium cyanide in solution from 0.15 to 0.45mg/L and from 0.40 to 1.2mg/L respectively resulted in higher equilibrium loadings while the first order constants remained constant. The solution pH did not have a significant effect on the equilibrium loading of platinum cyanide and palladium cyanide in the ranges 9 to 11. However, improvements in the loading kinetics of both these complexes were noticed with an increase in solution temperature from 30 to 60°C. Changes in zinc cyanide and nickel cyanide concentrations in the range 5 to 20mg/L did not have a significant effect on the adsorption of platinum cyanide and palladium cyanide. It was concluded that strong base anion exchange resins could effectively recover platinum and palladium cyanides from dilute synthetic cyanide solutions and that the exchange capacity and functionality of these ion exchange resins might have played an important role in their affinity for different metal anions in solutions.