Refractory Gold Concentrate Research Articles

Thermodynamic Behavior of Pyrite and Arsenopyrite in Preoxidation for Chlorination Leaching of Refractory Gold Concentrate

Recently, preoxidation is an effective pretreatment method of refractory gold ore, which has been widely used due to the high desulfurization, arsenic removal, low environmental pollution, and rapid reaction rate. In this paper, we describe the thermodynamic considerations of preoxidation of pyrite and arsenopyrite, the main minerals of the refractory gold ore, and the effect of the pressure oxidation, one of the preoxidation processes on the chlorination leaching. The thermodynamic results indicated that arsenopyrite under acidic conditions is easier to oxidize compared to pyrite and the oxidation decomposition of pyrite and arsenopyrite-type gold ore can be considered mainly for pyrite. The experiment has shown that the arsenic removal rate was higher than the desulfurization rate; it is confirmed that the thermodynamic conclusion of the oxidation of pyrite and arsenopyrite was correct. Comparing the XRD, SEM, and EDX analyses of gold concentrate and pressurized oxidation residue, it can be seen that the surface of pressurized oxidation residue is a fine porous structure and the dense and durable structure of sulfide ore is mainly destroyed.

Combined Bacterial and Pressure Oxidation for Processing High-Sulfur Refractory Gold Concentrate

Microbially assisted bio-oxidation of sulfide concentrates in stirred-tank reactors (stirred-tank reactor bio-oxidation (STRB)) and acid pressure oxidation (POX) are widely used to pretreat refractory sulfide concentrates and increase gold extraction via cyanidation. Continuous STRB requires a comparatively long residence time; however, in some cases, it cannot effectively oxidize some sulfide minerals. POX enables oxidation in a short residence time. At the same time, if a processed concentrate contains a large amount of sulfur, it decreases the ratio of the solid mineral phase to liquid (pulp density) during POX and limits its economic attractiveness. In the present work, experiments were performed to investigate the problems associated with both processing methods for refractory sulfide concentrates. The experiments combined both treatments (STRB and POX) based on the example of a pyrite–arsenopyrite gold-bearing concentrate. The gold recovery from the untreated concentrate via cyanidation reached 58%. Continuous STRB for 2, 4, and 6 days oxidized 43, 74, and 79% of the sulfide sulfur (Ss), respectively. The gold recovery rates from the bio-oxidation residues were 68, 82, and 88%, respectively. The pressure oxidation of both the concentrate and STRB residues increased Ss oxidation by 97–99% and gold recovery by 96–97%. For 2 days, STRB decreased the Ss content and increased the possible liquid-to-solid ratio for POX. The combined processes result in a new promising direction because the POX stage allows high gold recovery, whereas combining STRB and POX provides products for further POX in terms of Ss content and increases POX productivity.

Research on Gold Leaching from a Refractory Gold Concentrate in Copper-Malic Acid-Thiosulfate Solutions

Research on Gold Leaching from a Refractory Gold Concentrate in Copper-Malic Acid-Thiosulfate Solutions

Transfer Pricing Methodology for Refractory Gold Concentrates

In March 2022, to bring clarity to the tax valuation of transactions with gold concentrates, Kazakhstan’s government enacted a new transfer pricing methodology. The methodology applies to export sales transactions with concentrates with defined physical properties and contents of deleterious elements, such as arsenic, sulphur, and carbon. This article examines the new rules to clarify their scope and application.

Comparative Study on Refractory Gold Concentrate Kinetics and Mechanisms by Pilot Scale Batch and Continuous Bio-Oxidation

Most studies conducted have focused on the pulp density, Fe3+ concentration and sulfuric acid concentration, etc., of bio-oxidation, and few have reported on the influence of different bio-oxidation methods on kinetics. In this study, a comparative investigation on refractory gold concentrate by batch and continuous bio-oxidation was conducted, with the purpose of revealing the kinetics influence. The results showed that improving the removal rates of the gold-bearing pyrite (FeS2) and arsenopyrite (FeAsS) yielded the best results for increasing gold recovery. The removal rates of S, Fe and relative gold recovery linearly increased when compared to the second-order equation increase of the As removal rate in both batch and continuous bio-oxidation processes. The removal kinetics of S and Fe by continuous bio-oxidation was 12.02% and 12.17% per 24 h day, approximately 86.64% and 51.18% higher than batch bio-oxidation, respectively. The higher removal kinetics of continuous bio-oxidation resulted from a stepwise increase in microbe growth, a larger population and higher dissolved Fe3+ and H2SO4 concentration compared to a linear increase by batch bio-oxidation. The cyanidation gold recovery was as high as 94.71% after seven days of continuous bio-oxidation, with the gold concentrate sulfur removal rates of 83.83%; similar results will be achieved after 13 days by batch bio-oxidation. The 16sRNA sequencing showed seven more microbe cultures in the initial residue than Acid Mine Drainage (AMD) at genus level. The quantitative real-time Polymerase Chain Reaction (PCR) test showed the four main functional average microbe populations of Acidithiobacillus, Leptospirillum, Ferroplasma and Sulfobacillus in continuous bio-oxidation residue as 1.08 × 103 higher than in solution. The multi-microbes used in this study have higher bio-oxidation activity and performance in a highly acidic environment since some archaea co-exist and co-contribute.

Cyanide-free recovery of metals from polymetallic and refractory gold concentrates by the KellGold process

A patented hydrometallurgical approach (KellGold) for high-yield, cyanide-free recovery of metals from refractory gold and polymetallic concentrates is summarized. Drivers include elimination of atmospheric emissions of SO2, As2O3 and Hg produced by smelters and roasters, as well as cyanide risks arising from transportation, operations and detoxification activities.The Kell process comprises several commercially proven unit operations. Sulphur and other soluble metals are first selectively removed by use of a pressure oxidation leaching step during which the dissolution of precious metals such as Au, Ag and platinum group metals (PGM) is minimized. The residue from pressure oxidation may be subjected to further conditioning by HCl leaching and/or thermal treatment to ensure efficient precious metals recovery by subsequent chlorination leaching from a clean leachate. Subsequent metal recovery steps provide marketable end products close to the mine site.Testwork on a range of concentrate types typically shows >95% recovery of gold, silver, copper, cobalt, zinc, lead, antimony, and, if present in economic quantities, other value elements, including PGM (Pt, Pd, Rh, Ir, Ru). Engineering studies have been successfully completed for two KellGold applications, while KellPGM studies have been completed to definitive feasibility level. Centralized concentrate processing plants are under active consideration in several countries. KellPGM has been demonstrated in a nine-week integrated pilot campaign at 1:1000 scale, supporting a bankable feasibility study for a ~ 1110 ktpa plant now at the financing stage, treating a PGM concentrate at a South African PGM mine site.

Recovery of Gold from the Refractory Gold Concentrate Using Microwave Assisted Leaching

Microwave technology has been confirmed to be suitable for use in a wide range of mineral leaching processes. Compared to conventional leaching, microwave-assisted leaching has significant advantages. It is a proven process, because of its short processing time and reduced energy. The purpose of this study was to enhance the gold content in a refractory gold concentrate using microwave-assisted leaching. The leaching efficiencies of metal ions (As, Cu, Zn, Fe, and Pb) and recovery of gold from refractory gold concentrate were investigated via nitric acid leaching followed by microwave treatment. As the acid concentration increased, metal ion leaching increased. In the refractory gold concentrate leaching experiments, nitric acid leaching at high temperatures could limit the decomposition of sulfide minerals, because of the passive layer in the refractory gold concentrate. Microwave-assisted leaching experiments for gold recovery were conducted for the refractory gold concentrate. More extreme reaction conditions (nitric acid concentration > 1.0 M) facilitated the decomposition of passivation species derived from metal ion dissolution and the liberation of gangue minerals on the sulfide surface. The recovery rate of gold in the leach residue was improved with microwave-assisted leaching, with a gold recovery of ~132.55 g/t after 20 min of the leaching experiment (2.0 M nitric acid), according to fire assays.

Study on Pre-oxidation of a High-Arsenic and High-Sulfur Refractory Gold Concentrate with Potassium Permanganate and Hydrogen Peroxide

For arsenic-containing refractory gold concentrate, gold recovery by leaching is extremely difficult due to the encapsulation of gold in arsenopyrite and pyrite. In this work, the pre-oxidation of a high-arsenic and high-sulfur refractory gold concentrate in the acidic potassium permanganate or hydrogen peroxide solutions has been investigated. The studied parameters include pre-oxidation time, acidity, pre-oxidation temperature, ethylene glycol addition and oxidant concentration. When potassium permanganate of 0.25 mol/L is used as oxidant, 61.4% of arsenic and 51.8% of iron can be removed, respectively. The results of kinetics analysis indicate that the oxidative dissolution of arsenopyrite during the pre-oxidation process is controlled by the product layer diffusion, with an activation energy of 7.92 kJ/mol. The stability of hydrogen peroxide can be significantly improved by increasing both sulfuric acid concentration and ethylene glycol addition when hydrogen peroxide is used as oxidant. Under optimum conditions, arsenic removal ratio of 57.2% and iron removal ratio of 51.9% have been achieved with hydrogen peroxide of 2.5 mol/L, sulfuric acid of 0.75 mol/L and ethylene glycol of 30 mL/L. The gold extraction of refractory concentrate is only 11.5% in the copper–ammonia–thiosulfate leaching solutions without pre-oxidation. A gold extraction of 71.8% and significant decrease in thiosulfate consumption from 28.2 to 5.7% have been observed for the concentrate after pre-oxidation.

Enrichment of Gold in Antimony Matte by Direct Smelting of Refractory Gold Concentrate

Conventional cyanidation technology achieves low gold recovery when used to process refractory gold concentrate. Based on the geochemical characteristics of gold deposit mineralization, a new method is proposed herein for gold enrichment in antimony matte by smelting of refractory gold concentrate. The effects of the FeO/SiO2 and CaO/SiO2 ratios, smelting temperature, and smelting time on the gold recovery were investigated in detail. The optimum conditions were determined to be FeO/SiO2 ratio of 1.2, CaO/SiO2 ratio of 0.4, smelting temperature of 1200°C, and smelting time of 45 min. The gold content in antimony matte and smelting slag was 96.68 and 1.13 g/t, respectively. The gold, antimony, and arsenic recovery was 97.72%, 26.89%, and 6.56%, respectively, with most of the antimony and arsenic volatilized into dust. Mineral liberation analyzer results showed that the antimony matte mainly consisted of FeS and FeO, with three phases, viz. FeAs, SbAs, and AuSb, embedded between them, indicating that gold was easily enriched with antimony and arsenic during smelting of refractory gold concentrate.

Improvement of Gold Leaching from a Refractory Gold Concentrate Calcine by Separate Pretreatment of Coarse and Fine Size Fractions

A total gold extraction of 70.2% could only be reached via direct cyanidation from a refractory As-, S- and C-bearing gold concentrate calcine, and the gold extraction varied noticeably with different size fractions. The reasons for unsatisfactory gold extraction from the calcine were studied through analyses of chemical composition, chemical phase and SEM-EDS of different sizes of particles. It was found that a significant segregation of compositions occurred during the grinding of gold ore before flotation. As a result, for the calcine obtained after oxidative roasting, the encapsulation of gold by iron oxides was easily engendered in finer particles, whilst in coarser particles the gold encapsulation by silicates was inclined to occur likely due to melted silicates blocking the porosity of particles. The improvement of gold leaching from different size fractions was further investigated through pretreatments with alkali washing, acid pickling or sulfuric acid curing-water leaching. Finally, a novel process was recommended and the total gold extraction from the calcine could be increased substantially to 93.6% by the purposeful pretreatment with alkali washing for the relatively coarse size fraction (+37 μm) and sulfuric acid curing–water leaching for the fine size fraction (−37 μm).

Factors Affecting the Selection of BIOX<sup>®</sup> as the Preferred Technology for the Treatment of a Refractory Gold Concentrate

The BIOX®process was developed in the late 1980’s for the treatment of refractory gold concentrates. The process has since developed into a commercially proven process with 12 successful installations of which 6 are currently still in operation. During this time development of the technology continued to improve the efficiency of the process, improve the reliability of the equipment used and to reduce the capital and operating cost for the implementation and operation of the process.This paper will look at some critical aspects in the selection of the BIOX as the preferred technology for the treatment of a refractory gold. Process selection will include technical criteria, for example the amenability of a concentrate to biooxidation and process design criteria, but will also include the overall project economic evaluation, a study of the project risks, the impact of the project and technology on the environment and local communities, operability of the process and implementation strategy.It is important that these aspects be taken into consideration in the design of any testwork program, be it fundamental research in the biooxidation field or in the development of a specific project. The impact of decisions taken during the execution of the program must also be tested continuously to gauge the impact on the overall process viability.The selection of biooxidation as the preferred process route for any project, be it gold, copper or any other mineral, will in most cases be based on the overall project economics compared to other processes, rather than technical considerations.

Comparison of Cyanide and Chloride-Hypochlorite Leaching of a Ball Milled Refractory Gold Concentrate with Ultra-Fine Particles

In this research, cyanide and chloride–hypochlorite leaching of gold from a pyritic concentrate (particle size: −75+53 µm, gold content: 27.15 g/t) were compared. It was shown that only 13.6 % of gold was extracted after 24 h leaching by cyanide, as compared to 37.2 % after 8 h by chloride–hypochlorite. Effect of ultra–fine milling of the concentrate on the leaching was investigated using a high–energy planetary ball mill at different milling times. It was found that the leaching rate of gold by both leachants could be substantially enhanced after the milling of the particles to sub–micron dimensions. This was attributed to the increase of specific surface area and the accumulation of energy in the pyrite particles. After 480 min milling (air atmosphere, 300 rpm, sample/ball:1/20), 96.1 % of gold was extracted by 24 h cyanide leaching, while 100 % extraction could be achieved after only 45 min milling and 30 min chloride–hypochlorite leaching. This was attributed to the oxidation of pyrite by the hypochlorite oxidant and the complete liberation of gold encapsulated in the pyrite particles.

A Study on Extraction of Gold-silver from Refractory Gold Concentrate by Using Thiourea Solution

A Study on Extraction of Gold-silver from Refractory Gold Concentrate by Using Thiourea Solution

Catalytic Oxidation Pretreatment of Sulfide-Rich Arsenic-Bearing Refractory Gold Concentrate by Hydrogen Peroxide in Sulfuric Acid in Tongling, China

This paper summarizes the result of experiment that was fourced on investigation of oxidation pretreatment on sulfide mineral for leaching of refractory gold concentrate by hydrogen peroxide in sulfuric acid. For a viable option, extraction rate of Fe, Cu was low, but extraction rate of arsenic reached nearly 100%. As the result of oxidation, elemental sulfur was not produced.

Catalytic Oxidation Pretreatment of Sulfide-Rich Arsenic-Bearing Refractory Gold Concentrate by Hydrogen Peroxide in Sulfuric Acid in Tongling, China

This paper summarizes the result of experiment that was fourced on investigation of oxidation pretreatment on sulfide mineral for leaching of refractory gold concentrate by hydrogen peroxide in sulfuric acid. For a viable option, extraction rate of Fe, Cu was low, but extraction rate of arsenic reached nearly 100%. As the result of oxidation, elemental sulfur was not produced.

Prediction of pre-oxidation efficiency of refractory gold concentrate by ozone in ferric sulfate solution using artificial neural networks

An artificial neural network model was developed to predict the oxidation of refractory gold concentrate (RGC) by ozone and ferric ions. The concentration of ozone and ferric ions, pulp density, oxygen amount, leaching time and temperature were employed as inputs to the network; the output of the network was the percentage of the ferric extraction iron from RGC. The multilayered feed-forward networks were trained by 33 sets of input-output patterns using a back propagation algorithm; a three-layer network with 8 neurons in the hidden layer gave optimal results. The model gave good predictions of high correlation coefficient ( R 2=0.966). The predictions by ANN are more accurate when compared with conventional multivariate regression analysis (MVRA). In addition, calculation with ANN model indicates that temperature is the predominant parameter and ozone concentration is the lesser influential parameter in the pre-oxidation process of refractory gold ore. The ANN neural network model accurately estimates the ferric extraction during pretreatment process of RGC in gold smelter plants and can be used to optimize the process parameters.

Experimental Study on Microwave Pretreatment with some Refractory Flotation Gold Concentrate

The microwave pretreatment of a typically refractory flotation gold concentrate was investigated. The results demonstrated that a maximum gold recovery of 97% was achieved, and that gold recoveries of the refractory gold concentrate quickly increased to the maximum with microwave heating time. Adding additives during microwave heating process was helpful to improve the leaching rate of gold, and the effect of microwave heating with single NaOH on the leaching rate of gold is not better than that of NaOH combined with other additives.

Development of Gold Extraction Technology from Refractory Gold Concentrates Based on Fine Grinding

The problem of in-site treatment of refractory gold and silver flotation concentrates is urgent in Russia at present, because the cost of concentrate treatment at copper smelters raises the cost of the recovered gold up to 30%. Sorption leaching with ultrafine pre-grinding of concentrates to a particle size of 0.010-0.020 mm has emerged as one of the perspective methods of handling this problem. A peculiarity of the devised technology is that ultrafine grinding is performed in standard ball mills loaded with different particle size material, thus providing a maximum contact surface. Typical low-coned hydrocyclones with 75 mm, 50 mm, and 35 mm diameters assembled in a multi-cyclone battery are used as classifying equipment. The proposed grinding scheme produces a final product of 98-99% minus 0.020 mm. Pilot plant tests on pyrite and arsenopyrite concentrates from various deposits of Zabaikalie were carried out. The refractory nature of these concentrates is due to the presence of finely disseminated gold....