Low-grade Refractory Gold Ores Research Articles

Characterizing low-grade refractory gold ores using automated mineralogy coupled with LA ICP-MS

Researchers have made notable progress in quantifying refractory components causing gold losses in traditional extraction methods. The potential for improving gold recoveries lies in targeted re-treatment of the 'invisible' gold fraction hosted within various ore minerals, even at low concentrations. This study presents a methodology for analysing the refractory components that cause gold losses in traditional extraction methods. The approach utilizes automated mineralogical techniques in conjunction with in-situ laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to characterize low-grade refractory ores and assess gold deportment. The methodology combines pre-concentration gravity separation, traditional chemical and mineral techniques, and LA ICP-MS to generate comprehensive datasets. To demonstrate the practical application of the methodology, a case study was conducted on historical tailings material from Witwatersrand's Evander Goldfield in South Africa. The case study aimed to determine the mineralogical distribution of gold that cannot be extracted through cyanidation. The results indicated that invisible gold is primarily hosted in pyrite (with an average concentration of 10.21 ppm representing 32 % of total gold), other sulphides (with an average concentration of 1.29 ppm representing 0.42 % of total gold), and oxides (with an average concentration of 0.50 ppm representing 1 % of total gold). The remaining gold is present in discrete fine cyanide amenable phases (with 28 % deportment) and silicate-hosted phases (with 39 % deportment). Environmental monitoring of the Witwatersrand tailings material revealed a net “acid-producing” nature, with high concentrations of heavy metals (such as As, Cu, Pb, Mn, Hg, and Ni) associated with sulphides (with over 78 % deportment). The deportment information obtained through this approach can optimize ore processing strategies and provide valuable insights for future remediation plans. By characterizing the refractory components causing gold losses and understanding the distribution of gold within the ore, this methodology offers the potential to enhance gold recovery and improve the efficiency of ore processing operations.

Application of Phanerochaete chrysosporium for enhancing gold recovery via bio-oxidation of refractory sulfidic ores in a circumneutral environment

Regardless of the effectiveness of the industrial process design for gold recovery encompassing acidic bio-oxidation and cyanidation, the substantial neutralization of effluents required after bio-oxidation results in a considerable generation of waste streams. Conducting a bio-oxidation at circumneutral pH with in-situ neutralization is a novel technological opportunity for strengthening environmental protection and safety. For the first time, this research reports the capacity of Phanerochaete chrysosporium to oxidize a low-grade refractory gold ore at circumneutral pH. The fungal treatment was evaluated in five culture media regarding pH variation, enzyme activity, and sulfide oxidation. Thereafter, optimal conditions were investigated and then scaled up in a bioreactor. Results indicated that pH > 5.0 decreased the enzyme concentration released by P. chrysosporium, reducing sulfide oxidation. An initial pH of 5.8 led to a 24.4 ± 2.2% sulfide oxidation after 14 days, comparatively better to reported studies in the same pH range. A higher efficiency was attained by replenishing the fungal culture for three cycles, reaching 47.6 ± 2.3% sulfide oxidation and 49.5 ± 2.4% gold recovery. The results were confirmed by UV–visible, C/S detector, SEM and gold fire assay. Overall, this study opens a possibility to explore a bio-oxidation at higher pH, contributing to the vision of a net-zero target.

Selective alkaline leaching of antimony from Low-grade refractory gold ores and process optimization

To eliminate the adverse effect of antimony on extracting of gold in matte smelting process from Sb-bearing refractory gold ores, the sodium sulfide leaching method was proposed to selectively remove antimony in advance. On the basis of the analysis and characterization of raw materials (XRD, SEM-EDS, mineralogical phase analysis, etc.), it can be detected that the antimony in refractory gold ores is mainly in form of stibnite with small quantities of oxides, and the gold is mainly wrapped up in sulfides and silicates. The effects of sodium sulfide and sodium hydroxide concentration, temperature, leaching time and liquid–solid ratio on the extraction rate of antimony and gold were discussed. Furthermore, the response surface method was applied to distinguish the interaction influence of process parameters on the antimony and gold extraction rate. It is detected that the polysulfides and thiosulfates are the main cause of associated leaching of gold. Furthermore, the regression equation model is established adopting the antimony extraction rate as response value, and it can be deduced that the relevance degree is Na2S concentration > temperature > NaOH concentration. Accordingly, the optimized process results are determined as follows: the extraction rates of antimony and gold reach 94.15% and 3.37%, respectively, under Na2S concentration of 85.66 g/L, NaOH concentration of 45.5 g/L, liquid–solid ratio of 1.5, leaching at 90 °C for 5 min, which are very consistent with the predicted values of the regression equation, proving the feasibility of the proposed optimization model.

Two-stage chemical-biological oxidation process for low-grade refractory gold concentrate with high arsenic and sulfur

In order to cost-effectively exploit and utilize the low-grade refractory gold ore resource with high arsenic and sulfur and reuse the ferric iron resources remained in the bio-oxidation waste solution, a two-stage oxidation process combining secondary high-temperature oxidation of the bio-oxidation solution with subsequent bio-oxidation was proposed for treating such resource. Scanning electron microscopy and laser particle sizer were used to analyze the oxidized residue, and the results demonstrated that the material surface was destroyed and the particle specific surface area was increased accordingly. Moreover, chemical analysis revealed that the nitrogen element content in concentrate was also increased greatly after oxidation. As a result, microbial adsorption behavior and growth rate were significantly improved and accelerated in the bio-oxidation stage. Specifically, 16S rRNA gene analysis indicated that the activity and proportion of iron-oxidized microorganism Leptospirillum genus in community was improved obviously after chemical oxidation. Therefore, the bio-oxidation efficiency of the concentrate was significantly increased in this stage. Consequently, the extraction levels of As, Fe and S elements in this process were 97.9 ± 0.9 %, 71.5 ± 4.8 % and 64.3 ± 1.6 % respectively, which were significant increased by 30.8 ± 0.8 %, 40.2 ± 1.6 % and 35.6 ± 3.8 % compared to the values in one-stage bio-oxidation. In the meantime, the gold and silver extraction yields by cyanidation in this process were increased from 61.5 ± 1.0 % and 58.1 ± 1.2 % of one-stage bio-oxidation process to 92.2 ± 1.2 % and 89.8 ± 2.8 %, respectively.

Mineralogical characteristics and recovery process optimization analysis of a refractory gold ore with gold particles mainly encapsulated in pyrite and Arsenopyrite

To interpret the leaching rules, select suitable treatment methods, or optimize the treatment process of refractory gold ores, an in-depth analysis of ore characteristics using ore mineralogy is required. In this study, the mineralogical characteristics of a low-grade refractory gold ore were analyzed by a variety of analytical techniques and methods. The ore composition was obtained by chemical analysis, and the main minerals include gold, pyrite, arsenopyrite, feldspar, mica, and quartz. Gold exists in the form of sub-microscopic gold with a particle size of fewer than 1.7 μm, of which 56.90 % is encapsulated gold, 16.97 % is semi-coated gold, and 26.13 % is fractured gold. The content, classification, shape, grain distribution, and occurrence state of the main minerals in the gold ore were obtained by microscopic observation and statistical analysis. Based on the results, the leaching rules of the gold ore were predicted, and suggestions for optimizing the pretreatment process were put forward. These results can accurately guide the pretreatment and leaching process of the gold ore and lay a foundation for the effective utilization of comparable gold ores.

Comparative studies of novel biooxidation process to low-grade sulphide gold ores

ABSTRACT The Sand Farming is one of novel biooxidation processes suitable for sulphide oxidation of low-grade refractory gold ores. It has been previously proven to be feasible and more efficient compared to other conventional sulphide oxidation processes. In this study, the Sand Farming was compared with conventional tank biooxidation to investigate biooxidation behaviors on ores with different mineralogy and compare the ultimate gold recovery. Ore samples were tested for Sand Farming biooxidation. Conventional tank biooxidation was also compared as the baseline. After each biooxidation was completed, cyanidation was conducted for gold extraction. The Sand Farming achieved the gold recovery of 75% from high grade with higher sulphur content sample (Sample A) and 68% from low grade with lower sulphur content sample (Sample B), slightly lower than tank biooxidation of 83% and 85%, respectively. Sand Farming can be an alternative to several sulphide oxidation processes with better overall economics.

Kinetic limitations of gold leaching in ferric chloride media Part I: Batch reactor studies

The global gold industry is under increasing pressure to search for alternative technologies to replace cyanidation due to the inefficiency of cyanide in treating low grade refractory gold ores and increased public scrutiny on the use of cyanide in gold mining. Chloride has been identified as a promising candidate to replace cyanide. Despite extensive efforts to investigate gold leaching in chloride media, gold leaching in ferric chloride media at moderate temperatures relevant to heap leaching has not been well studied. Sponsored by Barrick Gold Corporation, we investigated the thermodynamics and kinetics of gold dissolution in ferric chloride media at moderate temperatures using batch leaching and electrochemical techniques. The Part I of this study reports the effects of four key process variables, initial ferric concentration, total chloride concentration, redox potential of the leaching solution, and the type of chloride salts, on the rate and extent of gold dissolution in ferric chloride media. A series of batch reactor leaching tests was carried out using pure gold as the model mineral. The experimental results showed that the leaching process was either under thermodynamic or kinetic control depending on the leaching conditions. The gold extraction increased with the initial ferric concentration up to 0.3 M, after which a negative effect was observed. This was thought to be caused by the transition from cathodic reduction of the oxidant controlling the kinetics to anodic oxidation of gold controlling the kinetics. Increasing total chloride concentration and the redox potential of the leaching solution also increased the gold extraction. Gold extraction was higher in the presence of the monovalent salts than in the presence of the divalent salts.

Column bio-oxidation of low-grade refractory gold ore containing high-arsenic and high-sulfur: Insight on change in microbial community structure and sulfide surface corrosion

Currently, there is a lack of research on column bio-oxidation for low-grade refractory gold ore with high arsenic and sulfur content. Therefore, it is essential and significative to investigate column bio-oxidation for this type of gold ore. The column bio-oxidation process of refractory gold ore was characterized by a variety of analytical methods, including X-ray diffraction, 16S rRNA gene analysis, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy and 3D confocal laser scanning microscopy. The evolution of the microbial community structure was analyzed. Simultaneously, the process of passive film formation and the behavior of the dynamic corrosion on the sulfide surfaces were described in detail. The results showed that the cyanidation of gold yielded 81 ± 2% after column bio-oxidation. The oxidation extent for As, Fe and S were 57 ± 1%, 38 ± 1% and 44 ± 1%, respectively. The community structure of attached and planktonic microorganisms was different and changed with the oxidation time. Importantly, the Sulfur film was observed on the arsenopyrite surface under scanning electron microscope, yet it was not found on the pyrite surface. This finding revealed that the inhibitory effect generated by the passive film of arsenopyrite was significantly higher than that of pyrite. Furthermore, the average corrosion pit volume per unit area of pyrite and arsenopyrite were 161 ± 6 μm3/μm2 and 65 ± 3 μm3/μm2. This indicated that arsenopyrite was more easily oxidized during the column bio-oxidation.

Mineralogical Characteristics of a Micro-Fine and Low Grade Refractory Gold Ore

Detailed characterization of a micro-fine, low-grade refractory gold ore from a beneficiation plant in Yunnan Province, China, was investigated. Different analytical techniques, such as videlicet size analysis, scanning electron microscopy, and mineral analysis by a Mineral Liberation Analyser, were used for mineralogical characterization of the ore. The results show that the most valuable metal is gold. Grain size of pyrites and arsenian pyrites, which are main gold carrying minerals, are mostly 1 ~ 30 μ m. The gangue mineral is composed of quartz, mica, dolomite and feldspar, while the content of easy-to-float and clay gangue minerals is up to 33%.

Mineralogical Characteristics of a Micro-Fine and Low Grade Refractory Gold Ore

Mineralogical Characteristics of a Micro-Fine and Low Grade Refractory Gold Ore

Beneficiation and leaching study of a muti-Au carrier and low grade refractory gold ore

Detailed mineralogy and beneficiation and leaching study of a muti-Au carrier, low grade refractory gold ore from a beneficiation plant in Henan Province, China, was investigated. Mineral liberation analysis, scanning electron microscopy, element phase analysis and etc. by a mineral liberation analyser were used for mineralogical characterization study of this ore. The present work describes an experimental study on the effect of traditional parameters (such as grinding fineness and reagent regimes), middling processing method and flowsheet construction on the total recovery and the assay of the floatation concentrate. Two-step floatation and part of middling combined to the floatation tailing for gold leaching process resulted in high gold grade (g.t-1) and gold recovery (%) for this refractory gold ore. This process opens the possibilities of maximizing Au grade and recoveries in a muti-Au carrier and low grade refractory gold ore where low recoveries are common.

Improved recovery of a low-grade refractory gold ore using flotation–preoxidation–cyanidation methods

In this work, different flotation–preoxidation–cyanidation methods are considered for treating a low-grade refractory gold ore. On the one hand, the results of selective flotation show that 22% and 31.1% of total Sb and As, respectively, remained in the final tailings and only about 28% of the total Au remained for further cyanidation processes. On the other hand, in bulk method of flotation the maximum Au recovery of 90.6% achieved after 60min of flotation at the grind size with K80 of 146micron. In addition, the bulk flotation method resulted in the concentrate with low concentrations of Sb and As elements. To improve the recovery of low-grade refractory gold ores, flotation should be followed by roasting, biological, or pressure oxidation processes so that the gold could be liberated prior to cyanidation processes. It is also found that the pressure oxidation pre-treatment of the concentrates prior to cyanidation may yield high gold recoveries of over than 83%. In these processes, recoveries are controlled by the temperature and the oxygen partial pressure in the solvent. However, by utilizing the bio-oxidation technique, the oxidation of sulfur to sulfate cannot be completed and, consequently, the gold recovery may be limited to only 72.2%.

Extraction of gold from an Indian low-grade refractory gold ore through physical beneficiation and thiourea leaching

The work carried out on the processing of a low-grade and refractory gold ore using thiourea is presented. Direct leaching of the “as-received” ore with thiourea has yielded only 16% gold extraction. Starting with ore containing 1.4 g/t of gold, it has been possible to generate a sulphide concentrate with 6.1 g/t of gold by physical beneficiation of the ore through froth flotation. Thiourea leaching of this flotation concentrate after pressure, pre-oxidation has resulted in gold extraction of 98%, with an overall gold recovery of 74%. Pressure oxidation was found to be slightly superior to roasting for the pre-oxidation of the refractory gold ore/concentrate.

Investigations of accelerating parameters for the biooxidation of low-grade refractory gold ores

This research was designed to accelerate the biological oxidation rate of low-grade suphidic gold ores. The biological oxidation by tamed Thiobacillus ferrooxidans bacteria with a mixed low-grade refractory gold ore was investigated. These bacteria could well tolerate up to 18.0 g/L of arsenic (III). The effect on the oxidation rate due to the presence of a magnetic field on the culture medium was examined as well as the influence of surfactants (tween-80, tween-20 and emulsifier-OP) and selected ionic metals such as Ag +, Bi 3+, Co 2+ and Hg 2+. The results showed that, based on a 60% oxidation rate for arsenic, the oxidation time was shortened by 83 hours, 90 hours, 98 hours and 100 hours under the optimal conditions of tamed bacteria, magnetized water, concentrations of tween-80 and Ag + respectively. Under the combination of the above parameters, the biooxidation rate was shortened by 120 hours to achieve a 60% oxidation rate for arsenic. However it did not produce a simple additive effect on the biooxidation.

Aeration pretreatment of low grade refractory gold ores

Aeration curing, over a long duration in wetted stockpiles, shows promise as an affordable pretreatment method for oxidizing gold encapsulating sulfide minerals, and possibly organic matter, in low grade refractory ores. Following aeration pretreatment, the ore is reclaimed, neutralized, and cyanide leached by conventional practices. Large tonnages of subeconomic material, including mine stripping waste, may be converted into ore by this new technology. The results presented show that a successful application of this technology will likely require crushing to about −2 cm (−3/4 in.), followed by aeration in a wet stockpile for long periods, up to three years. Natural convection may be inadequate, but forced air ventilation, at modest pressures and power consumption, is affordable.