Cyanide Leaching Research Articles

Ore treatment hydrogen peroxide during heap leaching of gold

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.

Green Treatment of Cyanide Tailings Using a “Filter Press BackWash–Chemical Precipitation–Gaseous Membrane Absorption” Method

Based on a “filter press backwash–chemical precipitation–gaseous membrane absorption” process, treatment of harmless cyanide tailings was conducted using cyanide tailings from a gold smelting enterprises (Yunnan Province, China) as the research object. The effects of air-drying time, backwash water parameters, initial pH of acidification, NaHS dosage, cyanide-containing water flow rate, and gaseous membrane stages on the process were investigated. Chemical composition, X-ray diffraction, and X-ray photoelectron spectroscopy analyses of the copper products were carried out. Results showed that the copper content in the copper product was 54.56%, and the chemical composition was mainly CuSCN, CuS, Cu2S, and CaSO4. Five cycles of experiments were carried out under optimal conditions; the results showed that the process can make the treated cyanide tailings meet the requirements of the technical specification for pollution control of cyanide leaching residue in the gold industry (TSPC) standard for storage in a tailings pond and a have certain stability. The average recovery rate of copper and total cyanide in elution water was 97.8% and 99.89%, respectively, and the average removal rate of thiocyanate was 94.09%.

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.

Silver Metal Extraction from Refractory Silver Ore Using Chloride-Hypochlorite and Hydrochloric Acid Media Under High Pressure

The mobility of gold and silver metals from refractory ores is very low due to free metal ions in their bodies that bind the transportable and free metal molecules or they are encapsulated in minerals such as sulfides, arsenosulfides, carbonaceous, and clayey materials which make it difficult to extract them. As known from the literature, the enrichment of oxide refractory gold, silver ores, Ag, and Au-rich flotation concentrated from sulfur refractory ores can be leached in the chloride-hypochlorite solutions. In this work, the leaching approach was studied to extract silver ions from refractory ores in the presence of hypochlorite media under high pressure. The mineralogical and scanning electron microscopy analysis of the sample indicated that the silver was encapsulated in barite and quartz minerals in fine sizes. In order to obtain the optimum leaching conditions for the silver ore, the effects of several parameters, namely, temperature, leaching time, NaCl and NaOCl concentration, solid ratio, and particle size on the leaching recovery were investigated in detail. The leaching experiments showed that the highest silver recovery of 62.35% was obtained under the following conditions: temperature of 150 °C, oxygen pressure of 1800 kPa, leaching time of 2 h, concentrations of 2 mol/dm3 and 0.4 mol/dm3 for NaCl and NaOCl, respectively, the solid ratio of 30%, and particle size (d80) 15 μm. The results obtained from this study indicated that the enrichment of refractory silver ores to extract the silver encapsulated in barite and quartz minerals could be possible in the chlorite-hypochlorite under high pressure, a relatively shorter leaching time compared to conventional cyanide leaching.

Roasting temperature effect on the recovery of refractory gold and silver in pyrite concentrates

Pyrite concentrates with refractory gold and silver were roasted at different temperatures to improve the recovery of the metals by cyanide leaching. Scanning Electron Microscope characterization of the calcine revealed that the gold occluded in the pyrite less than one micron, and roasting produced channels in the concentrate, exposing the gold particles to the leaching solution. Gold and silver recoveries were maximum in the temperature range of 500-600?C due to the calcine high surface area and porosity. The Au and Ag recovery improved from 25 to 86% and 50 to 73%, respectively. The Au secondary encapsulation due to the sintering, the formation of the Ag-Fe-S species (Fe1?xS + Ag2S + Ag) and Ag ferrite in higher roasting temperatures hence Au and Ag recoveries decreased.

Experimental study on thiosulfate leaching of gold from a high copper gold concentrate

The conventional cyanide leaching process is used to extract gold from a high copper gold concentrate. Because the copper associated minerals consume sodium cyanide in large quantities, the cost of the reagents is high and the economic benefit is not ideal. At the same time, a large number of cyanide tail slag are produced, which brings a series of environmental problems. In order to solve the environmental problems caused by excessive sodium cyanide consumption and cyanogen slag, the feasibility of leaching gold by thiosulfate in copper ammonia system was studied. The gold leaching rate of thiosulfate was increased to more than 90% by using the direct thiosulfate leaching process and pretreatment thiosulfate leaching process, which was close to the gold leaching index of sodium cyanide at the production site.

Surface processes at a polymetallic (Mn-Fe-Pb) sulfide subject to cyanide leaching under sonication conditions and with an alkaline pretreatment: Understanding differences in silver extraction with X-ray photoelectron spectroscopy (XPS)

Leaching of polymetallic sulfides is often challenging due to the complexity of these systems. The main issues are related to the formation of surface by-products or to the presence of different metals that require a greater consumption of chemicals compared to that needed to extract the target metal during leaching. This latter case is followed in the present work using X-ray photoelectron spectroscopy (XPS) during the leaching of a silver-containing polymetallic (Mn-Fe-Pb) sulfide under three different cyanidation procedures: (1) conventional leaching, (2) ultrasound-assisted leaching, and (3) leaching of a sample pretreated in alkaline media. In all cases, leaching results in the build-up of Pb compounds (oxides/hydroxides) on the surface of the minerals, suggesting a mechanism in which Pb is first leached by hydroxide and cyanide and later is re-adsorbed as an external layer on the minerals. On the other hand, the effect of each process on Mn was quite distinct: 1) Conventional leaching leads to the oxidation of the sulfide (pyrite) surface and a slight increase of surface Mn species; 2) Ultrasound-assisted leaching decreases surface Mn by dissolving oxidized species, which exposes fresh sulfide surfaces and increases Ag extraction; and 3) An alkaline pretreatment at high temperature exposed fresh sulfide surfaces and decreased the surface concentration of Mn. The fact that ultrasound-assisted leaching and leaching after an alkaline pretreatment allow for a higher Ag extraction (60% and 75% of total Ag, respectively, as opposed to the 25% extracted via conventional leaching), indicates that leaching is more efficient if the surface is not oxidized and if Mn is removed from the samples, either before or during leaching.

INVESTIGATION OF THE AMENABILITY OF A COPPER-RICH REFRACTORY GOLD ORE TO CYANIDE LEACHING

The production of gold from refractory gold ores has been increasing due to the exhaustion of free milling gold ores. The presence of cyanicides (e.g., copper minerals) and encapsulation of gold in minerals such as pyrite and arsenopyrite are common reasons for refractoriness of gold ores. In this study, the amenability of a copper-rich gold ore (108 g/t Au, 1.60% Cu) to cyanide leaching was investigated. Direct cyanide leaching of the ore showed that the gold extraction was very low by 18.4% over 24 h., indicating that the ore is highly refractory. Sulphuric acid pretreatment for the removal of acid-soluble copper was found to be not effective to achieve high gold extractions at the subsequent cyanide leaching. Leaching at high NaCN concentrations (1-8 g/L) yielded limited Au extractions of ≤47.2%. Ultra-fine grinding (UFG) (d80: 8-73 μm) as a pretreatment route followed by cyanide leaching also could provide Au recoveries of just below 54.1%. The findings showed that the ore is double-refractory and needs the employment of more effective pretreatment process(es) to achieve acceptable gold extractions (>90%) in subsequent cyanidation stage.

Effective density concentration in refractory gold ore for characterization purposes

This article evaluates the efficiency, benefits and limitations of pre-concentration by density separation for process mineralogy studies of low-grade gold ore. The pre-concentration by density aims to generate a product with a high content of gold and to maximize the number of gold-bearing particles characterized, thereby increasing the representativity and reducing the number of polished sections to be analyzed. Pre-concentration by density was carried out for a low-grade sulfide gold ore (0.96 ppm) from the north of Brazil. The sample was ground to below 1.7 mm, sieved down to 0.037 mm and subjected to density separation, amalgamation of the heavy product and cyanide leaching of all products. Gold was assessed in each product to evaluate the separation recovery and distribution. The finer the particle size, the higher the gold distribution in the heavy product, due to a higher degree of liberation of gold and sulfides; these values varied from 65% to 84% in fractions below 0.60 mm and decreased from 40% to 13% in the coarser fractions. Regarding gold distribution, fractions finer than 0.84 mm indicates a notable increase on gold recovery by amalgamation, indication higher surface exposure.

Multi‐stage economic model predictive control for a gold cyanidation leaching process under uncertainty

ABSTRACTIn order to dynamically operate the gold cyanidation leaching process (GCLP) under uncertainty, a multi‐stage economic model predictive control (EMPC) is proposed for GCLP for the transient and steady‐state economic optimization. The proposed multi‐stage EMPC is composed of two steps. In the first step, the unmeasurable uncertain parameters are estimated by using Tikhonov regularization based method, so as to avoid amplification and propagation of the noise measurements into the estimation. Based on the estimated results, the scenario tree for multi‐stage EMPC is generated from the historical data using a data‐driven approach, and the control inputs are obtained from solving the resulting large nonlinear programming problem (NLP) at each sampling point. The resulting uncertainty model and the probability of each scenario are more consistent with the actual industrial GCLP, and the solutions are less conservative. The efficiency of the proposed multi‐stage EMPC is verified through a simulated industrial GCLP. Compared with other EMPC methods, including classic EMPC and multi‐stage EMPC with box uncertainty region, the proposed method can reduce the economic cost while accounting for the constraints at the same time.

An alternative to cyanide leaching of waste activated carbon ash for gold and silver recovery via synergistic dual-lixiviant treatment

This study reports the development of a hydrometallurgical treatment for activated carbon ash (ACA); a waste product of the carbon-in-pulp (CIP) process used in the gold mining industry, rich in adsorbed precious metals. After an initial screening of known leaching chemistries, the research focusses on dual-lixiviant (thiourea and thiocyanate) and thiourea systems, both of which have lower environmental impact than traditional cyanide leaches. Comparing ferric sulfate and hydrogen peroxide as oxidants showed that a thiourea leach is more suited to ferric sulfate whereas the dual-lixiviant leach achieved greater extraction with hydrogen peroxide. This was believed to be due to a more favourable effective [thiourea]:[thiocyanate] molar ratio in solution. The latter demonstrated faster kinetics and improved efficiency for dissolution of gold and silver. However, both leaches had issues with silver extraction due to formation of passivating layers on the surface of the silver nanoparticles. Kinetic modelling showed both systems tended towards a mixed-controlled process. Gold extraction of 89%, with leaching reaching equilibrium within 100min, using the dual-lixiviant process demonstrated that there is an alternative to cyanide leaches employed in gold recovery.

Effect of hydrogen peroxide and lead(II) nitrate on gold cyanide leaching of Malaysian mesothermal deposit gold ore

Effect of hydrogen peroxide and lead(II) nitrate on gold cyanide leaching of Malaysian mesothermal deposit gold ore

Superabsorbent dewatering of refractory gold concentrate slurries

In this paper, superabsorbent polymer (SAB) dewatering behaviour of selected mineral pulps comprising low-grade, refractory gold flotation concentrate, bio-oxidation product and cyanide leach residue was investigated as an alternative to conventional, gravity thickening. The shear rheology of the resulting sediments was also investigated for pulp handleability. All slurries displayed better SAB-mediated dewatering performance, in terms of reduced processing time, volume minimization and greater water recovery for recycle, in comparison with gravity thickening. Specifically, SAB absorbed >94 wt.% water from the dilute slurries within 30 min of contact time. 45–76 wt.% more water was recovered after 60 min at high supernatant clarity using the SAB dewatering approach compared with gravity settling. The observed non-Newtonian, shear thinning rheological behaviour of SAB-dewatered consolidated slurries, reflecting low to moderate yield stresses in the range 1–40 Pa and shear thinning viscosities (<10 mPa⋅s), indicate their “handleability” in hydro-transport. The cost effectiveness of the SAB dewatering process engendered by its significantly greater water recovery and SAB polymer recovery, regeneration and multiple reuse capacity.

Bioprocessing of oxidized platinum group element (PGE) ores as pre-treatment for efficient chemical extraction of PGE

Platinum-group elements (PGE) are relevant for many high technology applications, prompting the search for potential alternative resources and environmentally friendly processing technologies. The largest deposit of PGE worldwide is the Bushveld Complex in South Africa. The pristine sulfide-bearing ore is mined using conventional metallurgical methods, while the near-surface oxidized PGE ore is currently stockpiled. Economic extraction of PGE from these stockpiles using conventional technologies is not feasible to date. Hence, biohydrometallurgical approaches to recover valuable transition metals and liberate platinum-group minerals for subsequent chemical PGE extraction have been considered. The four stockpile samples taken from a heap of oxidized PGE ores from the Platreef formation showed a similar mineralogical composition with >90 wt% silicates and minor amounts of Fe-(oxy)/hydroxides, both associated with Ni, Mn and Cu. Platinum-group minerals were present as sperrylite (PtAs2), cooperite (PtS low Pd), native platinum and Pd‑bismuthotellurides and mostly associated with silicates. Stirred tank bioleaching under various conditions was proven to be most feasible for an oxidative process at moderately-high temperatures using a consortium of iron- and sulfur-oxidizing acidophiles dominated by Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. Bioleaching achieved up to 86% total metal recovery (including Co, Cu, Mn and Ni) and led to a liberation of platinum-group minerals. The bioleach residues were subsequently chemically leached by a HNO3/NaCl and a cyanide leach, allowing for the enhanced extraction of up to 89% Pt and 96% Pd after bioleaching. Chemical and mineralogical analysis validated the potential of oxidative bioleaching as a promising processing option for a pre-treatment of oxidized PGE ore, allowing separate and efficient recovery of valuable base metals and enhancing the subsequent chemical PGE extraction.

Hydrometallurgical recovery of manganese, gold and silver from refractory Au-Ag ore by two-stage reductive acid and cyanidation leaching

In this study, a refractory Au-Ag ore from Beiya (Yunnan, China) was characterised and the occurrence states of low-grade gold and silver were clarified. The results revealed that the gold in the ore mainly occurred as visible native gold, which can be leached easily via cyanidation, whereas the visible silver minerals occurred as native silver, acanthite, chlorargyrite, acanthite, pyrargyrite, andorite and polybasite. Nevertheless, most of the silver occured as invisible silver in manganese oxide ore with the form of isomorphs and could not be leached via direct cyanidation. A pretreatment of reductive acid leaching using sodium sulphite as a reductant successfully leached the manganese and liberated the silver, which was very beneficial for the cyanidation of silver. The manganese was enriched in the leaching solution at a concentration of 16.51 g/L with an average leaching percentage of 70.27% after five-stage cyclic reductive acid leaching under optimised conditions of 1.0 mol/L of H2SO4, 20 g/L of Na2SO3, a liquid-solid ratio of 5:1, and stirring speed of 300 r/min at room temperature (28 ± 1 °C) for 1.0 h. We could easily recover 99.90% copper and 99.80% manganese from the leaching solution via iron powder reduction and sodium carbonate precipitation. Following the leaching of manganese, the cyanidation leaching percentages of gold and silver were to 87.37% and 80.19% respectively. In summary, we developed a novel process for the hydrometallurgical recovery of manganese, gold, and silver from refractory Au-Ag ore.

Environmentally friendly process instead of cyanide leaching on recycling of gold and silver from jewellery scraps and wastes.

Nowadays, the production and exploration of gold has an increased importance all over the world. Recycling is a significant source for the supply of gold and has a pronounced effect on its price. The flotation method, which is more economical and more environmentally friendly than cyanide leaching, has been investigated for recycling gold and silver from jewellery slag. A jewellery slag sample containing 28.3 ppm Au and 42.0 ppm Ag was obtained from a refinery in Turkey. Flotation concentrate assaying 614.6 ppm Au and 511 ppm Ag was achieved with recoveries of 89.0% and 83.2%, respectively. On the other hand, 87.8% Au and 81.5% Ag extractions were obtained by cyanide leaching tests. Based on these results, flotation is suggested, considering its environmental and economic benefits.

Differences of cyanide leaching between calcine and dust from refractory gold concentrates

Abstract Differences of cyanide leaching between the calcine and the dust from a refractory gold concentrate were investigated by comparative method. Results showed that gold leaching efficiencies of the calcine and the dust were 85.31% and 54.30%, respectively, with direct cyanidation. Contents and existing forms of arsenic and carbon were the main reasons for those differences. The maximum gold leaching efficiencies of the calcine and the dust were 87.70% and 58.60%, respectively, with cyanidation after NaOH pre-leaching. Harmful elements removal, gold loss in NaOH pre-leaching and iron oxides hindrance codetermined gold leaching efficiencies of the calcine and the dust. After H2SO4 pre-leaching, the maximum gold leaching efficiencies of the calcine and the dust achieved 94.96% and 80.40%, respectively. The effect of carbonaceous matter was the main reason for differences for leaching efficiencies of the calcine and the dust. Based on those differences, two proper gold extraction processes were put forward, and gold leaching efficiencies for the calcine and the dust achieved 94.91% and 91.90%, respectively.

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.

Studies on Hydrometallurgical Treatment of Oxydized Gold-Bearing Copper Ore

Inherent problems of oxidized gold-bearing copper ores processing and a comparison of hydrometallurgical methods, applied for such materials, are discussed in this article. Studies on sulfuric acid and cyanide leaching have been carried out, using the following sample of oxidized ore from one of the copper deposits (Kyrgyzstan), %: 15 Mg O, 45.6 SiO2, 0.1 S, 20 Ca O, 12.1 Fe2O3, 0.86 Cu, 1.78 Au, 9.61 Ag. Studies have been carried out. Agitation sulfuric acid leaching able to extract up to 29.9% of copper. At the same time, column sulfuric acid leaching able to extract up to 78.5% of total copper and 85.23% of copper presented by acid-soluble compounds. In case of precious metals, the agitation cyanide leaching is able to extract up to 97.6% of gold in 24 h. Increasing the grinding fineness up to 90% - 74 μm reduces cyanidation duration down to 12 h. The consumption of sodium cyanide is 4.8 kg/t of ore. At the same time, column cyanide allows to extract 73.5% Au and 81.9% Ag during 111 days, whereas 52.4% of gold is recovered in the first 10 days. Consumption of sodium cyanide is 5.45 kg/t. The most efficient ways for processing of such materials are proposed.

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).