Low-grade Sulfide Research Articles

Hydrometallurgical Processing of a Low-Grade Sulfide Copper–Nickel Ore Containing Pt and Pd

The goal of the present work was to study the recovery of copper, nickel, and platinum group metals (PGMs) (Pt and Pd) from low-grade copper–nickel ore containing pyrrhotite, pentlandite, and chalcopyrite by column bioleaching followed by cyanidation. The ore sample contained the following: Ni—0.74%, Cu—0.23%, Fe—14.8%, Stotal—8.1%, and Ssulfide—7.8%. The Pt and Pd contents in the ore sample were 0.2535 and 0.515 g/t, respectively. Biological leaching in columns was carried out at 25, 35, and 45 °C for 140 days. A mixed culture of acidophilic microorganisms was used as an inoculum. Cu and Ni extraction depended on temperature, and at 45 °C, copper and nickel recovery was the highest, being 2.1 and 1.8 times higher than that at 25 °C, respectively. As a result, up to 35% of nickel and up to 10% of copper were recovered by bioleaching within 140 days. Bioleaching resulted in an increase in Pt and Pd recovery by cyanidation, but the effect on Pd recovery was insignificant. Pt recovery varied in the range of 3–40% depending on process conditions; Pd recovery was 44–55%.

The deleterious role of gangue mineralogy in copper extraction: A case study of poor recovery in leaching low-grade Cu ores

In a series of four extended industrial column leach experiments spanning 542 days, aimed at examining Cu-recovery from low-grade sulfide ores, all instances yielded suboptimal Cu recovery rates (<27%). Through a nuanced analysis integrating time-resolved chemical data on leachate with detailed mineralogical investigations, we highlight that the dissolution of aluminosilicate gangue minerals is a pivotal factor constraining Cu recovery. The source materials, extracted from a low-grade segment of a Cu–Au porphyry deposit (∼0.32–0.36 wt% Cu), underwent diverse leaching conditions employing various lixiviants, curing phases, redox conditions, and particle size distributions. Notably, poor Cu recovery is closely tied to gangue mineralogy. The ammonia leach column experienced limited Cu leaching due to an inert gangue shielding chalcopyrite from the lixiviant. In acid columns, swift precipitation of silica-rich phases impeded effective Cu leaching at multiple scales, from large-scale-column to molecular levels. Identifying gangue mineralogy and considering their impact during acid leaching are crucial for formulating effective lixiviant strategies for Cu recovery from low-grade primary sulfide ores. The curing phase, requiring high acid concentrations (∼50 g/L H2SO4), emerges as a critical aspect for promoting effective gangue dissolution while preventing refractory silica-rich phase precipitation.

Process Optimization of an In-Situ Bioleaching Section with Associated Membrane Filtration in a Field Test Laboratory

The winning of critical raw materials from secondary resources, e.g., from abandoned mines, mining residues, electronic waste or low-grade ores, is a potential source with promising outcomes due to innovative and more efficient extraction methods. The research and education mine “Reiche Zeche” at the TU Bergakademie Freiberg, Germany offers a scientific lab in a real application environment for an in-situ bioleaching section from a low-grade sulfide ore vein with on-site associated membrane downstream processing. The evaluation and resumption of previous research activities showed both the feasibility and the potential for further up-scaling. But there was also potential evaluated for improving the effectiveness, especially in terms of individual process elements within the leaching and membrane cycle as well as regarding microbiology. Based on this, further optimization was carried out and effectiveness was evaluated and compared to the prior state. The results regarding the leaching outcome proved that process optimization leads to stable and continuous leaching process operations as well as to improved and more favorable conditions for the microorganisms due to the implementation of a bioreactor and changing the whole leaching operation from a direct into an indirect process. Furthermore, cleaning in place (CIP) resulted in the maintenance of selectivity despite discontinuous membrane process operation.

Full factorial design model applied for understanding the dissolution kinetics of iron being a part of arsenopyrite

Current concentration plants are dealing with great amounts of low-grade sulphide ores containing gold and other noble metals. Because noble metals are often found encapsulated in the main sulphide minerals (such as pyrite and arsenopyrite), such ores cannot be processed using conventional processes (e.g. cyaniding). Nitric acid leaching offers one of the innovative techniques for loosening sulphide minerals. That&rsquo;s why one believes it to be of relevance to look at the dissolution kinetics of sulphide minerals in nitric acid solutions. The authors consider using the full factorial design model to study the leaching kinetics of iron being a part of arsenopyrite. The process involves the use of a rotating disk in HNO3 solutions with the concentrations of 3 and 5 mol/dm3 at the temperatures of 303 and 333 K and the rotary speeds of 3.3 and 10 RPS. The kinetic equations obtained describe the dissolution process with a high degree of accuracy. Temperature and HNO3 concentration were found to produce the most positive effect on the iron dissolution rate when iron comes as part of arsenopyrite. Agitation does not appear to produce any noticeable effect. This is confirmed by low orders of reaction with respect to the disk rotation frequency, which vary in the range of &ndash;0.13 to 0.20. The high apparent activation energy (60.8&ndash;69.6 kJ/mol) calculated can be attributed to a significant influence of the temperature on the iron dissolution rate when iron comes as part of arsenopyrite. High reaction orders with respect to the concentration of nitric acid for iron (3.9&ndash;4.7) were observed when a sample arsenopyrite disk was dissolved. It may be attributed to a passivating film that formed on the disk surface, the presence of which is indicative of a possible transition into a state in which internal diffusion serves as a limiting stage.Support for this research was provided by the Ministry of Science and Higher Education&nbsp;of the Russian Federation under the Development Programme of the Ural&nbsp;Federal University named after the First President of Russia B. N. Yeltsin and&nbsp;in line with the Strategic Academic Leadership Programme Prioritet-2030.

Research progress in intensified bioleaching of chalcopyrite: A review

Chalcopyrite (CuFeS2) as one of the most abundant copper sulfide minerals, is refractory to conventional hydrometallurgical and pyrometallurgical processes. Bioleaching is a practice of extracting valuable metals by using acidophilic bacteria to catalyse the dissolution of sulfide/iron-containing ores. It has been widely adopted in copper ores processing due to environmental and economic performance over the conventional methods, especially its use in low-grade sulfide minerals. To date, low copper extraction is a common problem during chalcopyrite bioleaching, which limits its industrial application. Hence, it is of particular importance to find methods to enhance the leaching rate. Chalcopyrite dissolution is a complex process with the participation of microorganisms, minerals and gas and liquid phases. All these physicochemical, microbiological, mineralogical and processing parameters have influences on the rate and efficiency at which bioleaching proceeds. High copper yield can be achieved by optimizing leaching conditions in an optimum range. A number of researches has been conducted to explore the influence of leaching parameters on bioleaching rate. This review intends to briefly describe the effect of some parameters on the bioleaching of chalcopyrite. And it lays the emphasis on the presentation of methods to promote the efficiency of bioleaching and the strengthening mechanisms.

Attempts to Stimulate Leaching Activity of Acidithiobacillus ferrooxidans Strain TFBk

Autotrophic acidophilic bacteria Acidithiobacillus ferrooxidans is a model species for studying metal bioleaching from low-grade sulfide ores and concentrates. Arsenopyrite gold-bearing concentrates are refractory and often processed using biohydrometallurgical approaches; therefore, it is important to develop methods to improve arsenopyrite bioleaching. In the present work, we have studied the possibility of improving arsenopyrite concentrate bioleaching by the strain of A. ferrooxidans. For this purpose, we have analyzed the genome of the strain A. ferrooxidans TFBk to reveal the genes potentially important in the bioleaching process. Genes determining resistance to arsenic, as well genes involved in the utilization of C1-compounds and resistance to oxidative stress, were revealed. Therefore, the possibility of increasing the rate of arsenopyrite concentrate bioleaching using C1-compounds (methanol and formate) was studied. Formate was able to increase both the biomass yield of the strain A. ferrooxidans TFBk as well as the bioleaching rate. In addition, the effect of redox potential increase by means of the addition of sodium persulfate in the medium on arsenopyrite concentrate bioleaching was studied. It was shown that the addition of 0.1% sodium persulfate stimulated strain growth, while a higher concentration inhibited it. Despite this, the rate of concentrate bioleaching increased in the presence of 0.5–1.0% of persulfate, which may be explained by the interactions of added oxidizer with concentrate components.

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.

Reuse and stabilization of sulphide mine tailings as fine aggregate for construction mortar

The processing of low-grade sulphide gold ores generates a significant volume of tailings which impacts the environment. The reuse of sulphide mine tailings as a substitute for sand in construction mortar offers the advantages of reducing costly tailings management whilst promoting sustainable construction. However, the acceptance of mine tailings as alternative sand for construction depends on its effective stabilization during use. In this study, hardened mortar cubes have been prepared by varying the substitution of river sand with sulphide mine tailings. The stabilization effects of cement, cement-lime and cement-pozzolana on sulphide mine tailings have been investigated. The water demand, slump behaviour, bulk density, water absorption, compressive strength, and X-ray diffraction (XRD) were examined to observe the physical and mechanical properties of the mortars. The water demand and bulk density decreased whilst the slump value and water absorption increased with increased tailings replacement. The highest 28-day compressive strength of 12.2 MPa was achieved at 25% tailing replacement with a cement binder. Cement proved to be the best binder for the stabilization of the tailings which was followed by cement-pozzolana and cement-lime respectively.

Stirred-tank bioleaching of copper and cobalt from mine tailings in Chile

Metals from low-grade sulfide ores, electronic waste and mine tailings can be recovered using biohydrometallurgy. In this study, acidophilic microbial consortia of mesophiles and moderate thermophiles were applied in shake flasks as well as in stirred tank reactors (STR) to bioleach cobalt and copper from mine tailings in Chile. The mine tailings near Taltal contained considerable amounts of copper (∼5000 ppm) and cobalt (∼115 ppm). After adaptation of the mesophilic consortium, 38% of Co and 86% of Cu were recovered in 2-L STR at 10% solid load after 12 days bioleaching at 30 °C. In a mini-pilot test in 20-L STR at 15% solid load, Co and Cu extraction reached 49% and 83%, respectively. Improved metal recovery was obtained by using a moderate thermophilic microbial consortium at 42 °C, reaching 74% of Co and almost 100 % Cu in 2-L STR at 10% solid load. Low Fe dissolution below 14% for all tests was observed which may favor the downstream processing of Cu and Co. Together with the results from chemical leaching, the data indicated that Cu was mainly leached by sulfuric acid (acid leaching) while a high Co extraction required Fe(II)-oxidizing microbial activity (bioleaching).

Intensification of Nickel Bioleaching with Neutrophilic Bacteria Guyparkeria halophila as an Approach to Limitation of Sulfuric Acid Pollution.

Hydrometallurgical production of valuable and non-ferrous metals is traditionally accompanied with acid waste effluents/acid mine drainage leading to acidification of the mining areas. The traditional cause of this pollution is the well-known technology based on the recovery of metals with acid solutions and the application of strong acidophilic leaching bacteria for the oxidation of sulfide ores. In our experiments, we used neutrophilic autotrophic bacteria (NAB) stimulated with formic acid or coupled with acidophilic bacteria. The first approach was based on using formic acid as an energetic substrate by autotrophic bacteria. In the second case, the NAB provided initial biogenic acidification for the following growth of the inoculated acidophilic bacteria. Our experiments resulted in increased nickel recovery from the low-grade sulfide ores, which was provided by the NAB in a medium supplemented with formic acid. Bioleaching resulted in 1116 mg Ni/L (69.75%) in the medium with formate and only 35.4 mg Ni/L without formate in 43 days. As a whole, our bench scale experiments showed that the stimulated NAB can be effective at pH 7–5. Partially replacing sulfuric acid with formic acid could also give benefits via the following natural degradation of acid wastes. As a whole, this approach is more environmentally friendly than conventional bioleaching techniques.

The Effect of Hydrodynamic Conditions on the Selective Flotation of Fully Liberated Low Grade Copper-Nickel Ore

Low grade sulfide ores are difficult to process due to their composite mineralogy and their fine grained dissemination with gangue minerals. Therefore, fine grinding of such ores becomes essential to liberate valuable minerals. In this research, selective flotation was carried out using two pitched blade turbine impellers with diameters of 6 cm and 7 cm to float copper and nickel. The main focus of this research was to generate optimum hydrodynamic conditions that can effectively separate nickel and copper from gangue minerals. In addition, we investigated the effects of superficial gas velocity, impeller speed, bubble size distribution, and bubble surface area flux on the flotation recovery and rate constant. The results demonstrated that a 7 cm impeller comparatively produced optimum hydrodynamic conditions that improved Cu-Ni recovery and the rate constant. The maximum copper and nickel recoveries in the 7 cm impeller tests were observed at 93.1% and 72.5%, respectively. However, a significant decrease in the flotation rate of nickel was observed, due to entrainment of nickel in copper concentrate and the slime coating of gangue minerals on the nickel particle surfaces.

Influence of organic acids on pentlandite bioleaching by Acidithiobacillus ferrooxidans LR.

Bioleaching is a bio-hydrometallurgical process of solubilizing metals from low-grade sulfide ores by microbial action employing chemolithoautotrophic microorganisms capable of promoting redox reactions. Organic acids have been applied in bioleaching once can act in two different ways; providing hydrogen ions for mineral acidolysis and complexing metals due to their chelating capacity. This study investigates the synergy of different organic acids (acetic, ascorbic, citric, lactic, and oxalic) and Acidithiobacillus ferrooxidans LR pentlandite bioleaching. The addition of oxalic acid had a positive effect on the Ni extraction during pentlandite biological-chemical leaching after 15days, and the yields observed were 45.6% (26.5mg Ni/g ore). The yields for Co extraction were meager, and Co extraction values were found to only 2.8% (1.6mg Co/g ore) in the presence of citric acid. A design of experiments with mixtures was used to evaluate the interaction of organic acids in bioleaching. According to simplex-centroid experiments, only citric acid presented a statistically significant effect and has contributed in a synergistic form in pentlandite biological-chemical leaching in the presence of A. ferrooxidans. This study provides a new synergistic bioleaching system to improve Ni and Co extraction from sulfide ores.

Interaction effects of flotation reagents for SAG mill reject of copper sulphide ore using response surface methodology

Flotation reagents have a complex behaviour in the beneficiation of base minerals in clayey ores. Interaction effects of reagents on the efficiency of copper flotation for a highly clayey low-grade sulphide ore were investigated using a central composite design. Preliminary results showed that sodium-isopropyl-xanthate (SIPX) and O-isopropyl-N-ethyl-thionocarbamate (IPETC) were found to be the most efficient collectors in the presence of lime as the pH regulator. The effects of dosage of collectors (SIPX and IPETC) and the dosage of methyl-isobutyl-carbonyl (MIBC) as frother on the separation efficiency were evaluated at different pH levels. Based on the analysis of variance (ANOVA), the interaction effects of the collector−pH and collector−frother were significant for the separation efficiency. At the low level of collector dosage, increasing pH from 9 to 11 enhanced copper separation efficiency from 81% to 86% for IPETC and from 77% to 86% for SIPX. Results of ANOVA showed that the maximum copper separation efficiency (88.7%) was obtained at the dosages of 8.6 g/t SIPX, 7 g/t IPETC and 20 g/t MIBC at pH 11. Finally, it was concluded that a mixture of SIPX and IPETC collectors was more suitable to treat highly clayey sulphide ores.

Biological and acid leaching of low-grade sulfide concentrate containing Cu and Ni at different temperatures

In this study, the bioleaching of low-grade nickel-copper concentrate was carried out using the nutrient medium containing yeast extract (YE) at temperature range of from 40 to 60°C in order to study the dependence of biooxidation rate and Cu and Ni extraction levels on the temperature and the presence of organic compounds. Mixed culture of the strains Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus, and Acidiplasma sp., moderately-thermophilic acidophiles, which oxidize sulfide minerals, was used in the experiments. Temperature and organic carbon source were shown to affect bioleaching. At 40−50°C, the influence of YE addition was insignificant. At 55 and 60°C bioleaching depended on YE presence. Nevertheless, microbial activity affected mainly iron leaching and allowed maintaining comparatively low pH of medium. Both Cu and Ni extraction rates almost was not affected by biooxidation activity. Thus, the leaching of the base metals form the concentrate was mainly determined by abiotic factors (acidity and temperature). Regardless of this fact, bioleaching may play a significant role for processing of similar sulfide concentrates, since to maintain favourable pH, abiotic acid leaching could require a large amounts of H2SO4, while biooxidation provides sulfuric acid generation.

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.

Cations stress on low-grade nickel sulfide ore oxidation leaching

The effects of cations stress of magnesium ion and sodium ion on the low-grade nickel sulfide ore oxidative leaching in simulated sulfuric acid solutions were investigated. This study was performed in two courses, including the effect of the cations on the valuable metals leaching efficiencies of the nickel ore and its influences on the electrochemical oxidation behavior of the nickel ore. The leaching results present that parts of magnesium-containing gangues and ferrous sulfide are preferentially dissolved into lixivium, and the leaching efficiencies of Ni and Cu decreased much related to the leached concentrations of Mg2+ increased. The results of electrochemical measurements show that the oxidation leaching of the low-grade nickel sulfide ore is controlled by the intermediates oxidative diffusion. Mg2+, as well as Na+, affects the transformations of the Fe3+/Fe2+ couple and sulfur-containing species, and those cations are apt to be attracted by the anions and directionally adhere to the negative active site of the metal sulfide surface, causing an increase in the electrochemical activities, which facilitates the electron transfer between the ore and leaching mediums. By comparative study of the role of Mg2+ and Na+, it is found that Mg2+ negatively affects the oxidative diffusion of the intermediates through promoting the generation of a compact film, which lowers the metals leached efficiencies, and the unfavorable effect of Na+ tends to be the coupled effect of the leached Mg2+ and Fe3+.

Effect of pretreatment prior to leaching on a chalcopyrite mineral in acid media using NaCl and KNO3

Chalcopyrite is the most abundant copper ore mined in Chile. Hydrometallurgical plants are currently changing to concentration by flotation-matte smelting deposits when oxide minerals run out and chalcopyrite appears in deposits. The change from hydrometallurgical processing to flotation is mainly dependent on whether comminution costs can be absorbed given the copper grade. It is important to develop alternative technologies to work profitably with low-grade copper sulphide ores. One alternative that has been recently studied is the pretreatment of low copper grade sulphide minerals, especially chalcopyrite, to improve leaching efficiency. The curing time, as pretreatment, improves dissolution kinetics and shortens leaching time. This study used a pure sample of chalcopyrite mineral with 28.5% copper. Chalcanthite (copper sulphate) represented 9% of total copper in the sample. The effect of curing time as a function of copper extraction prior to leaching was evaluated using different concentrations of sodium chloride (NaCl), potassium nitrate (KNO3) and sulphuric acid (H2SO4). A 23% copper dissolution was obtained prior to leaching using 25kg/t NaCl, 15kg/t H2SO4 and 15 days of curing time. The ANOVA analysis reported that curing time was the most important variable (56.4 and 54.7% of contribution) in tests with NaCl and KNO3. According to the results, KNO3 does not have a significant effect on copper extraction prior to leaching.

Efficient Synchronous Extraction of Nickel, Copper, and Cobalt from Low\u2013Nickel Matte by Sulfation Roasting\u2012Water Leaching Process

Considering that the low recovery efficiency and the massive loss of valuable metals by the traditional pyrometallurgical process smelting low‒nickel matte. Therefore, this paper focuses on studying the optimal process parameters and the mechanism of sulphation roasting followed by water leaching achieving efficient synchronous extraction of nickel (Ni), copper (Cu), and cobalt (Co) from low‒nickel matte with sodium sulfate as the sulfating addictive. Under optimal conditions, the recovery efficiency of Ni, Cu, and Co metals can achieve 95%, 99%, and 94%, respectively, whereas the recovery efficiency of Fe metal is less than 1%. The results revealed that the mechanism of the sulfating roasting pretreatment could form a liquidus eutectic compound sulfates [Na2Me(SO4)2] (Me = Ni, Cu, Co) at the solid–solid interface, which plays a significant role in promoting the leaching efficiency of valuable metals. Not only enhance the reaction kinetics of sulfation, but improve the utilization efficiency of SO2/SO3. Thus, the sulfation roasting‒water leaching process developing an efficient and eco-friendly pathway to simultaneous extraction of Ni, Cu, and Co valuable metals from low grade sulfide ores.

The High Temperature Co-Processing of Nickel Sulfide and Nickel Laterite Sources

The pressure oxidation of low-grade nickel sulfide concentrate with high iron sulfides content generates significant amounts of sulfuric acid that must be neutralized. This acid can be utilized to leach metal values from ores such as nickel laterites. The present study demonstrates the use of a low-grade nickel concentrate generated from Poseidon Nickel Mt Windarra ore to enable additional nickel and cobalt extraction from a Bulong Nickel Operation nickel laterite blend. The co-processing of these materials at 250 °C, with oxygen overpressure, using total pulp densities of 30% or 40% w/w, and a range of nickel concentrate to nickel laterite mass ratios between 0.30–0.53, yielded base metal extractions of 95% or greater. The final free acid range was between 21.5–58.5 g/L, which indicates that enough in situ sulfuric acid was generated during co-processing. The acid was shown from mineralogical analysis to be efficiently utilized to dissolve the laterite ore, which indicates that the primary iron hydrolysis product was hematite, while the aluminum-rich sodium alunite/jarosite phase that formed hosts approximately 5% of the hydrolyzed iron.

Effects of Fe3+ and Ag+ on Column Bioleaching of a Low-grade Sulfide Copper Ore

Effects of Fe3+ and Ag+ on Column Bioleaching of a Low-grade Sulfide Copper Ore