Refractory Gold Ores Research Articles

Performance Evaluation of Fe-Al Bimetallic Particles for the Removal of Potentially Toxic Elements from Combined Acid Mine Drainage-Effluents from Refractory Gold Ore Processing

Acid mine drainage (AMD) is a serious environmental issue associated with mining due to its acidic pH and potentially toxic elements (PTE) content. This study investigated the performance of the Fe-Al bimetallic particles for the treatment of combined AMD-gold processing effluents. Batch experiments were conducted in order to eliminate potentially toxic elements (including Hg, As, Cu, Pb, Ni, Zn, and Mn) from a simulated waste solution at various bimetal dosages (5, 10, and 20 g/L) and time intervals (0 to 90 min). The findings show that metal ions with greater electrode potentials than Fe and Al have higher affinities for electrons released from the bimetal. Therefore, a high removal (>95%) was obtained for Hg, As, Cu, and Pb using 20 g/L bimetal in 90 min. Higher uptakes of Hg, As, Cu, and Pb than Ni, Zn, and Mn also suggest that electrochemical reduction and adsorption by Fe-Al (oxy) hydroxides as the primary and secondary removal mechanisms, respectively. The total Al3+ dissolution in the experiments with a higher bimetal content (10 and 20 g/L) were insignificant, while a high release of Fe ions was recorded for various bimetal dosages. Although the secondary Fe pollution can be considered as a drawback of using the Fe-Al bimetal, this issue can be tackled by a simple neutralization and Fe precipitation process. A rapid increase in the solution pH (initial pH 2 to >5 in 90 min) was also observed, which means that bimetallic particles can act as a neutralizing agent in AMD treatment system and promote the precipitation of the dissolved metals. The presence of chloride ions in the system may cause akaganeite formation, which has shown a high removal capacity for PTE. Moreover, nitrate ions may affect the process by competing for the released electrons from the bimetal owing to their higher electrode potential than the metals. Finally, the Fe-Al bimetallic material showed promising results for AMD remediation by electrochemical reduction of PTE content, as well as acid-neutralization/metal precipitation.

Arsenic removal strategy in the processing of an arsenopyritic refractory gold ore

In the gold mining industry, the exploitation of low-grade refractory deposits generates effluents with high arsenic concentrations. In this study, an additional stage in the processing of an arsenopyritic refractory gold ore was studied. Arsenic extraction in an alkaline pretreatment was evaluated to avoid metalloid release in the subsequent gold thiosulfate leaching stage, without affecting precious metal extraction. Experiments were conducted with different extracting agents (citric acid, sodium bicarbonate, oxalic acid, deionized water); contact time in the alkaline pretreatment stage (6 and 13 days) was also assessed; furthermore, the effect of arsenic extraction time (4 h, 6 days and 12 days), concentration of oxalic acid (0.02, 0.1, 0.5 M) and temperature (25, 70 °C), was studied. The results showed that it is possible to remove arsenic without altering the subsequent release of gold (80%). The best conditions were: 0.1 M oxalic acid for 1 h and at 70 °C. Finally, it was observed that the concentration of As released into the subsequent thiosulfate leach decreases by 97.7% (from 640 to 15 mg/l), thereby conserving its ability to eventually be recycled after gold recovery.

Arsenic removal from industrial effluent: In-situ ferric sulfate production and arsenic partitioning in the residues

Ferric sulfate solution was producedin situby sulfating arsenic-bearing, hematite-rich calcines (56–62% Fe2O3) with sulfuric acid, both produced by roasting refractory gold ore. The solution was then used for arsenic precipitation in the treatment of effluents from the cyanidation plant. The conversion of hematite to ferric sulfate increased as the acid/calcine ratio increased and reached 60.7%, with 0.87 of the stoichiometric acid amounts. An iron sulfate solution (13.4 g.L−1 Fe and 2.32 g.L−1 As) was produced at the end of the calcine sulfation/dissolution. Arsenic removal varied between 99.4 and 99.8%. Arsenic concentration dropped from 1583.4 mg.L−1 to 5.31 mg.L−1 As, which is far less than the industrial circuit's typical concentration (15 mg.L−1). Hydrated calcium sulfates were the principal constituents in the arsenical residues (i.e., 42–50%). Its removal allowed the identification of ferric arsenate/arsenite coprecipitates, arsenical ferrihydrite, and hydrated calcium-iron hydroxy-arsenate and hydrated calcium using X-ray diffraction analyses and Raman spectroscopy. The sequential extraction protocol and microscope automatic system confirmed the arsenic carriers. These are ferric (aluminum) or calcium arsenate/arsenites, accounting for 71.2 and 72.8% total As, and minor arsenic adsorbed on iron oxyhydroxides. Arsenic was primarily found (63.3%) in the Fe,Al-AsOx coprecipitates in the industrial residue. A 17% As-richer sludge, as achieved here (4.18% As), would result in a lower sludge volume for disposal. Transportation and disposal costs would then drop. These benefits were confirmed along one year of industrial operation. The projected reduction in effluent treatment costs reaches 60%.

Identification of elements hindering gold leaching from gold-bearing dust and selection of gold extraction process

The gold-bearing dust generated during the roasting process of refractory gold concentrates is valuable as a secondary gold resource. In this study, the effects of different pre-treatment methods on the removal of harmful elements and gold extraction from gold-bearing dust by cyanidation after pre-treatment were studied based on mineralogical analysis. The results showed that the dust belonged to refractory gold ore category, and the detrimental effects of arsenic, carbon and iron on gold extraction could be responsible for the low gold extraction. The removal efficiencies of arsenic and carbon were 99.7 and 60.6%, respectively, at a NaOH concentration of 6 mol L−1; moreover, gold extraction was 58.9% and increased by only 4.60% compared to direct cyanidation. The removal efficiencies of iron, arsenic, and carbon were 33.7, 80.4, and 12.6% at a 15 wt% H2SO4 concentration, respectively, and gold extraction reached 80.4%. After roasting at 650 °C with an airflow rate of 0.2 m3 h−1 for 4 h, the removal efficiencies of arsenic and carbon were 54.7 and 95.0%, respectively, and gold extraction reached 84.5%. Through 6 mol L−1 NaOH leaching after roasting, the removal efficiencies of arsenic and carbon were 99.5 and 95.5%, respectively, and gold extraction reached 86.1%. Through 50 wt% H2SO4 leaching after roasting, the removal efficiencies of iron, arsenic, and carbon were 99.5, 99.6, and 99.0%, respectively, and gold extraction reached 95.5%. These findings indicated that carbon had the greatest influence on gold leaching from the dust, followed by iron and arsenic. Through the comparison of different gold leaching processes, a proper process for gold extraction from the dust was developed. Under the most suitable condition, gold extraction improved by 41.2% compared to that of direct cyanidation.

Recovery of gold from refractory gold ores: Effect of pyrite on the stability of the thiourea leaching system

The extraction of gold from refractory gold ores (RGOs) without side reactions is an extremely promising endeavor. However, most RGOs contain large amounts of sulfide, such as pyrite. Thus, investigation of the influence of sulfide on the gold leaching process is important to maximize the utilization of RGOs. In this work, the effects of pyrite on the stability of the thiourea system were systematically investigated under different conditions. Results showed that the decomposition rate of thiourea was accelerated sharply in the presence of pyrite. The effect of pyrite on gold recovery in thiourea leaching systems was then confirmed via a series of experiments. The decomposition efficiency of thiourea decreased by 40% and the recovery efficiency of gold increased by 56% after the removal of sulfide by roasting. Under optimal conditions, the efficiency of the gold recovery system increased to 83.69% and only 57.92% of thiourea decomposition was observed. The high consumption of thiourea by the leaching system may be attributed to not only adsorption by mineral particles but also catalytic decomposition by some impurities in the ores, such as pyrite and soluble ferric oxide.

Recovery of gold from sulfide refractory gold ore: Oxidation roasting pretreatment and gold extraction

Recovering gold from sulfide refractory gold ore has been an important guarantee for the sustainable development of gold industry, while there are many challenges in the treatment of sulfide refractory gold ore, such as environmental pollution and low gold recovery. In this study, A novel method for gold recovery from refractory gold ore was proposed with the purpose of improving recovery efficiency of gold and reducing environmental pollution. The method consisted of two stages roasting for arsenic and sulfur removal, gold recovery by thiourea leaching, followed by an enhanced chlorination roasting for gold recovery in the presence of pyrite. In the two-stage roasting process, the phase transition of FeAsS and FeS2 during the roasting process was analyzed. In the first stage roasting process, the removal efficiency of arsenic reached 96.98% with only 43.07% sulfur was removed. We achieved removal efficiency of 97.19% for sulfur and 84.11% of gold was exposed during the second stage roasting process. The thiourea leaching combined with pyrite enhanced chlorination roasting was first proposed to effectively extract gold from the second stage roasting slag, and the pyrite shown a great role in promoting gold extraction during chlorination roasting. In this process, gold could be effectively recovered from the sulfide refractory gold ore with a recovery efficiency of 98.06%.

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.

The mechanism of ultrasound oxidation effect on the pyrite for refractory gold ore pretreatment

The effect of ultrasonic cavitation on the oxidation of the crystal pyrite in deionized water has been discussed. The effect of solution alkalinity, ultrasonic power and temperature on the surface morphology of pyrite and the chemical forms of sulfur and iron was discussed. The surface of pyrite is severely corroded under ultrasound. The sulfur in the pyrite is oxidized to S2O32- and SO42-. Most of the iron is in the form of Fe2+, few of it is in the form of Fe3+. With the increase of alkalinity, ultrasonic power and temperature, the surface corrosion of pyrite becomes more and more obvious. With the increase of the NaOH concentration, the Fe(II) concentration in solution decreases and the deposition of iron oxides on the pyrite surface prevents pyrite oxidation. With the increase of the ultrasonic power, the Fe(II) concentration in solution increase. The effect of the NaOH concentration on the SO42- and S2O32- concentration indicates pyrite oxidation is in mild alkalinity under ultrasound. The concentration of SO42- and S2O32- increases along with increase of the ultrasonic power and decreases tremendously with increase of the temperature. The pyrite oxidation is initiated by hydroxyl radical and promoted by Fe3+.

Optimization Process of the Refractory Gold Ore Extraction by Hypochlorite Oxidative Leaching

Optimization Process of the Refractory Gold Ore Extraction by Hypochlorite Oxidative Leaching

Technological innovation in Córrego do Sítio Mineração - A study of technical and economic aspects by using sensor-based sorting for refractory gold ore

Technological innovation in Córrego do Sítio Mineração - A study of technical and economic aspects by using sensor-based sorting for refractory gold ore

Depositional environment - The original control on gold processing

SYNOPSIS Methods for treating and processing refractory gold ores are well established. However, what is less well understood is how the formation of the gold-bearing deposits affects gold processing and extraction. In order to evaluate the effect of ore genesis on gold extraction a number of South African gold deposits were studied. These included complex Pilgrim's Rest samples as well as refractory Fairview, Barbrook, and Consolidated Murchison samples. We found the refractory nature of gold ores is controlled by a limited number of well-understood mineralogical factors. Solid solution gold is linked to low temperature and pressure conditions in fine-grained sedimentary lithologies, while reactive pyrrhotite can form from hydrothermal fluids associated with mafic magmatic rocks. These formational controls can be used to identify and avoid complex deposits at a desktop study phase, or address and reduce complications further along the pipeline using early mineralogical studies. Keywords: gold processing, refractory gold, ore mineralogy.

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.

Eco-friendly and economical extraction of gold from a refractory gold ore in iodide solution using persulfate as the oxidant

Iodine–iodide leaching is an effective and environmentally friendly gold extraction method that is expected to replace cyanidation. However, as the price of iodine is relatively high, for the industrial application of iodine–iodide leaching, decreasing the required amount of iodine is important to reduce production costs. In this study, persulfate was used to replace iodine as the oxidant for the extraction of gold from refractory gold ore. Using single-factor tests, the optimal leaching conditions were determined as a solid–liquid ratio of 1:3, a stirring speed of 350 rpm, 0.02 mol/L ammonium persulfate, and 0.1 mol/L potassium iodide. At pH 5, the gold extraction rate reached 83.69% after stirring for 1.5 h at room temperature. Even under neutral conditions, a gold extraction rate of more than 80% could be achieved. Using the activated carbon adsorption method to recover the gold from the leaching solution, a high gold recovery rate was obtained without solid–liquid separation. Compared with cyanidation, the S2O82− – I− – H2O system has the advantages of nontoxicity, eco-friendly, a fast leaching speed, and a high gold extraction rate. Thus, this system was a promising alternative method for gold extraction from refractory ore.

Leaching Kinetics of Antimony from Refractory Gold Ore in Alkaline Sodium Sulfide under Ultrasound

The leaching kinetics of antimony from refractory gold ore in alkaline sodium sulfide was investigated under ultrasound. The influence of factors such as stirring speed, temperature, the concentration of sodium hydroxide and sodium sulfide and particle size, was studied. The leaching kinetics has also been studied under convention and ultrasound. The experimental data are consistent with the shrinkage core model and the leaching rate is controlled by surface chemical reaction for both ultrasonic and the conventional method. Ultrasound increases the leaching rate of antimony from 81.2% to 93.1%. It can be seen that the rate constant kr of ultrasonic method at various temperatures is larger than that of the conventional method. The ultrasound reduces the apparent activation energy from 48.39kJ/mol to 33.88kJ/mol and reduces the apparent response series of sodium sulfide concentration from1.3 to 1.1. Comparing with conventional method, the ultrasound can greatly improve the antimony leaching rate, accelerate the leaching process and lower temperature and the concentration of sodium hydroxide and sodium sulfide. These advantages of ultrasonic method were also confirmed by the SEM analysis of the leached solid.

Bio-Oxidation of a Double Refractory Gold Ore and Investigation of Preg-Robbing of Gold from Thiourea Solution

Carbonaceous sulfidic gold ores are commonly double refractory and thus require pretreatment before gold extraction. In this paper, the capacity of pre-bio-oxidation can simultaneously decompose sulfides or deactivate carbonaceous matters (CM) from a double refractory gold ore (DRGO) using pure cultures of A. ferrooxidans or L. ferrooxidans, and a mixed culture containing A. ferrooxidans and L. ferrooxidans was investigated. The results showed that direct thiourea leaching of the as-received DRGO yielded only 28.7% gold extraction, which was due to the encapsulation of sulfides on gold and the gold adsorption of CM. After bio-oxidation, thiourea leaching of the DRGO resulted in gold extraction of over 75–80%. Moreover, bio-oxidation can effectively reduce the adsorption of carbon to gold. XRD, SEM-EDS and FTIR analysis showed that many oxygen-containing groups were introduced on the surface of DRGO during bio-oxidation, while the C=C bond was cleaved and the O–C–O and C–N bonds were degraded, causing a decrease in active sites for gold adsorption. Moreover, passivation materials such as jarosite were formed on the surface of DRGO, which might reduce the affinity of CM for gold in solutions. In addition, the cleavage of the S–S band indicated that sulfides were oxidized by bacteria. This work allows us to explain the applicability of pre-bio-oxidation for degrading both sulfides and CM and increasing gold recovery from DRGO in the thiourea system.

Destabilisation of gold cyanide complex by sulphur species: A computational perspective

The interaction of gold cyanide complex with elemental sulphur and all metastable sulphur species has been studied using Density Functional Theory (DFT). The elemental sulphur and sulphide species formed during pre-treatment of refractory gold ores or dissolution of sulphide minerals form a series of metastable species including hydrosulphide, polysulphide, thionates, sulphite and finally sulphates which are known to have a detrimental effect on gold cyanidation. Previous researchers have attributed this effect mainly to passivation of the gold surface. However, interaction of dissolved aurocyanide with sulphur species has received almost no attention. Here, DFT molecular modelling has been used for the first time to describe the interaction of dissolved gold cyanide and sulphur species, and to explain the reduction and destabilisation potential of sulphur species in gold cyanidation.Computational modelling shows that sulphur species can have a significant negative effect on the stability of gold cyanide complex. Elemental sulphur and sulphide ion with −446.6 and − 198.4 kJ.mol−1 interaction energies have the most negative effect. S0 and S2− contribute to the destabilisation of gold cyanide via two different mechanisms of precipitation of AuCN and thiocyanate formation as well as reduction of gold by formation of sulphite and sulphates respectively. The effect of elemental sulphur can be neutralised by excess free cyanide in solution, while sulphide ion can still stay reactive toward gold cyanide in the presence of free cyanide. Addition of lead salt can decrease the inhibiting effect of sulphide ions by formation of lead sulphide. However, lead cannot eliminate the negative effect of elemental sulphur. It is concluded that oxidation of sulphur species can significantly overcome the adverse impact of sulphur species on the stability of gold cyanide complex. The destabilisation of gold cyanide complex by sulphur metastable species is introduced as one of the main mechanisms for loss of gold in sulphide gold ores.

Biological pretreatment of carbonaceous matter in double refractory gold ores: A review and some future considerations

The pretreatment of carbonaceous material in double refractory gold ores (DRGO) is necessary to decrease preg-robbing of gold and maximize gold recovery. DRGO contains of carbonaceous matter and gold grains encapsulated in sulfide minerals, which typically results in very poor gold recovery. However, there is growing interest in DRGO because some estimates show that it makes up about a third of the total available gold for production by mining. This can be achieved by chemical and biological techniques, however, the chemical techniques like flotation, surface passivation and chemical oxidation have received more extensive study and either have to be retooled or modified to be applied to the carbonaceous matter in the DRGO. In comparison, the biological techniques are relatively unknown with significant gaps in the knowledge about the bio-treatment mechanism, byproducts and avenues for scaling up like bioreactor design. This study reviews the enzymatic pretreatment of DRGO to facilitate gold recovery and minimize reagent consumption. It focuses on the potential for application of oxidative enzymes like lignin peroxidase, manganese peroxidase and laccase to pretreat carbonaceous matter in DRGO with or without an additional step of sulfide oxidation and addresses characterization of byproducts of the enzymatic decomposition. Further, potential bioreactor configurations for the enzymatic decomposition without direct contact of ore with microorganisms are considered, both in terms of understanding the mechanisms within the pretreatment and in terms of application.

Adsorption studies of sulphidic refractory gold ore

A high auriferous arsenopyrite floatability is desirable to maximise gold recovery in sulphidic refractory gold ore flotation. This study examines the adsorption properties of sulphidic refractory gold ore (2.58 g/t Au) in the presence of sodium isobutyl xanthate (SIBX) collector, under different pH and CuSO4 additions for maximum arsenopyrite and gold floatability. The SIBX adsorption studies showed that pH greatly influences SIBX adsorption on to the surface of sulphidic refractory gold ore. Very little effect of CuSO4 on SIBX adsorption in acidic environment (pH 5–5.5) was observed due to low copper ions adsorption. Better flotation recoveries of arsenopyrite (86%) and gold (91%) were achieved at the ore's natural pH (8–8.5) than under acidic or basic environments. Pyrite floated poorly (<20% recovery) for all pH conditions. Based on the studies, conditions for maximum collector adsorption, arsenopyrite and gold flotation recovery for the ore were established.

Kinetics of cupric leaching of pyrite in 4 M NaCl solutions

ABSTRACT Cupric chloride leaching is an attractive alternative for the treatment of pyritic refractory gold ores. In this context, the kinetics of pyrite dissolution was studied in cupric chloride solutions containing 4 M NaCl. Pyrite leaching experiments were conducted in a stirred tank reactor for 250 h. The effect of temperature was evaluated at 45°C, 60°C and 75°C, while the effect of [Cu (II)] was evaluated with solutions containing 0.054, 0.252 and 0.512 M. The results showed that the increase in temperature and [Cu (II)] improved the rate of pyrite dissolution. The fraction of pyrite oxidised to sulphate ranged from 52% to 75%. Sulphate formation correlated well with the number of holes and cracks formed on leached pyrite particles. The kinetics of pyrite dissolution fitted well to the shrinking core model with chemical reaction control (T ≤ 60°C and [Cu (II)] ≤ 0.054 M) or mixed control (T > 60°C and [Cu (II)] > 0.054 M). The activation energy was 73.102 kJ/mol and the dependence of [Cu (II)] was proportional to .