Copper Solubilization Research Articles

Hydroxy-Carboxylic Acids as Green and Abundant Ligands for Sustainable Recovery of Copper from a Multimetallic Powder: A Proof of Concept.

The recovery of copper and other valuable metals had become increasingly strategic for the future of the global economy, particularly in regions lacking abundant mineral resources, such as most European countries. In this study, we investigated the viability of utilizing environmentally friendly, cost-effective, abundant and bio-based ligands, specifically carboxylic acids and their derivatives, for copper leaching in a low-temperature hydrometallurgical process. Our investigation focused on elucidating the impact of substituents in the α position of hydroxy-carboxylic acids on copper solubilization efficacy. Notably, hydroxy-carboxylic acids, like malic acid and lactic acid, were evidenced as particularly promising ligands for leaching copper from a custom-made multimetallic powder. By thoroughly characterizing the obtained complexes (Raman, UV-Vis) and by supporting the experimental efforts by a Design of Experiment (DoE) approach, we optimized the leaching process. The influence of experimental parameters such as pH, temperature, leaching time, and Cu/ligand molar ratio on process yield (determined through Inductively Coupled Plasma - Optical Emission Spectroscopy, ICP-OES, analysis) was thoroughly investigated. Additionally, we developed a subsequent copper recovery step by precipitating copper (II) hydroxide in an alkaline environment, guided by speciation diagrams tailored for each copper-ligand system.

Effect of a pre-treatment with hydrochloric acid on the copper solubilization of a bornite concentrate with posterior leaching in chloride medium

The formation of soluble species from a bornite flotation concentrate pre-treated with hydrochloric acid was studied. Copper recovery after a leaching in a H2SO4-NaCl solution was determined. The influence of acid concentration and ore particle size were evaluated. Chemical and morphological characterization of the samples before and after the leaching were carried out by XRD and SEM to evaluate changes in the bornite. It was revealed that increasing acid concentration during the pre-treatment dramatically enhances the formation of soluble species, reaching in one case 49.0% of copper dissolution after 15 d of pretreatment and 24 h of leaching, both at 25 °C, without reducing the particle size of the concentrate. It was also revealed that the ore particle size did not affect the transformation rate into soluble species, due to the corrosive effect of HCl, which fractured and generated micro-pores on the surface of the particles studied.

Multi-Metal Mining from Waste Cell Phone Printed Circuit Boards using Lixiviant Produced by a Consortium of Acidophilic Iron Oxidizers

Recently electronic waste (e-waste) includes the fastest growing waste stream in the world. Nevertheless, it also contains about 40 different elements of the periodic table; hence it is a significant metal source. Generally, e-waste recycling is done by the pyrometallurgy and/or hydrometallurgy method. However, the use of microorganisms in hydrometallurgy called bioleaching is a good alternative for eco-friendly and cost-effective recycling of e-waste and recover metals. Leptospirillum-dominated consortium was used to generate ferric iron lixiviant by oxidizing ferrous iron. The resulting lixiviant was used for bioleaching of metals from waste cell phone printed circuit boards (WPCBs). The pretreatment of pulverized WPCB (p-WPCB) and unpulverized WPCB (up-WPCB) was done using 2 M NaOH to see the effect of pretreatment on metal extraction. Moreover, the effect of maintenance of pH of the system was also checked. The controlling of pH of the system to 2.0 ± 0.1 showed enhancement of Cu, Zn, and Ni solubilization. The highest solubilization of copper was 96.86%, which was achieved with pretreated up-WPCB; zinc was 90.69% with pretreated p-WPCB, whereas nickel was 93.65% with untreated up-WPCB. Ours is the first report for extraction of copper, zinc, and nickel from unpulverized mobile phone WPCBs at high pulp density. The solubilization of metals achieved with 100 g/L pulp density provides a promising indication to scale up the process.

Effect of inoculum history, growth substrates and yeast extract addition on inhibition of Sulfobacillus thermosulfidooxidans by NaCl

This study reports on the effect of inoculum history, growth substrates, and yeast extract on sodium chloride tolerance of Sulfobacillus thermosulfidooxidans DSM 9293T. The concentrations of NaCl for complete inhibition of Fe2+ oxidation by cells initially grown with ferrous iron sulfate, or tetrathionate, or pyrite as energy sources were 525 mM, 725 mM, and 800 mM, respectively. Noticeably, regardless of NaCl concentrations, oxygen consumption rates of S. thermosulfidooxidans with 20 mM tetrathionate were higher than with 50 mM FeSO4. NaCl concentrations of higher than 400 mM strongly inhibited the iron respiration of S. thermosulfidooxidans. In contrast, the presence of NaCl was shown to stimulate tetrathionate oxidation. This trend was especially pronounced in NaCl-adapted cells where respiration rates at 200 mM NaCl were threefold of those in the absence of NaCl. In NaCl-adapted cultures greater respiration rates for tetrathionate were observed than in non-NaCl-adapted cultures, especially at concentrations ≥ 200 mM NaCl. At concentrations of ≤ 200 mM NaCl, cell growth and iron oxidation were enhanced with the addition of increasing concentrations of yeast extract. Thus, cell numbers in cultures with 0.05% yeast extract were ∼5 times higher than without yeast extract addition. At NaCl concentration as high as 400 mM, however, iron oxidation rates improved compared to control assays without yeast extract, but there was no clear dependence on yeast extract concentrations. The initial growth of bacteria with and without yeast extract in the presence of different NaCl concentrations was shown to impact leaching of copper from chalcopyrite. Copper dissolution was enhanced in the presence of 200 mM NaCl and absence of yeast extract, while the addition of 0.02% yeast extract was shown to promote copper solubilization in the presence of 500 mM NaCl.

Extremely Thermoacidophilic Metallosphaera Species Mediate Mobilization and Oxidation of Vanadium and Molybdenum Oxides.

Certain species from the extremely thermoacidophilic genus Metallosphaera directly oxidize Fe(II) to Fe(III), which in turn catalyzes abiotic solubilization of copper from chalcopyrite to facilitate recovery of this valuable metal. In this process, the redox status of copper does not change as it is mobilized. Metallosphaera species can also catalyze the release of metals from ores with a change in the metal's redox state. For example, Metallosphaera sedula catalyzes the mobilization of uranium from the solid oxide U3O8, concomitant with the generation of soluble U(VI). Here, the mobilization of metals from solid oxides (V2O3, Cu2O, FeO, MnO, CoO, SnO, MoO2, Cr2O3, Ti2O3, and Rh2O3) was examined for M. sedula and M. prunae at 70°C and pH 2.0. Of these oxides, only V and Mo were solubilized, a process accelerated in the presence of FeCl3 However, it was not clear whether the solubilization and oxidation of these metals could be attributed entirely to an Fe-mediated indirect mechanism. Transcriptomic analysis for growth on molybdenum and vanadium oxides revealed transcriptional patterns not previously observed for growth on other energetic substrates (i.e., iron, chalcopyrite, organic compounds, reduced sulfur compounds, and molecular hydrogen). Of particular interest was the upregulation of Msed_1191, which encodes a Rieske cytochrome b6 fusion protein (Rcbf, referred to here as V/MoxA) that was not transcriptomically responsive during iron biooxidation. These results suggest that direct oxidation of V and Mo occurs, in addition to Fe-mediated oxidation, such that both direct and indirect mechanisms are involved in the mobilization of redox-active metals by Metallosphaera species.IMPORTANCE In order to effectively leverage extremely thermoacidophilic archaea for the microbially based solubilization of solid-phase metal substrates (e.g., sulfides and oxides), understanding the mechanisms by which these archaea solubilize metals is important. Physiological analysis of Metallosphaera species growth in the presence of molybdenum and vanadium oxides revealed an indirect mode of metal mobilization, catalyzed by iron cycling. However, since the mobilized metals exist in more than one oxidation state, they could potentially serve directly as energetic substrates. Transcriptomic response to molybdenum and vanadium oxides provided evidence for new biomolecules participating in direct metal biooxidation. The findings expand the knowledge on the physiological versatility of these extremely thermoacidophilic archaea.

Interaction of British Anti-Lewisite (BAL) with Copper(I) and Copper(II) compounds in conjunction with Wilson’s disease

The chemistry of British Anti-Lewisite (BAL) and copper in relation to the therapeutic action for the treatment of Wilson's disease was studied by reacting selected Cu(I) and Cu(II) compounds with a range of thiol compounds. Optimum conditions for the preparation of cuprous mercaptides, CuI-SR, from thiophenol, 3-mercapto-1,2-propanediol (MPDH), cysteine (CysH), and glutathione (GSH), were established. BAL displaced Cu(I) from CuI-MPD giving CuI2-BAL irrespective of stoichiometry, while from CuI-cys and CuI-SG, Cu-BAL were obtained. BAL passivated CuI-SPh. The direct reaction of BAL with either Cu(II) or Cu(I) gave insoluble amorphous solids assumed to be CuI2-(oxidized dimeric BAL) or CuI2-BAL, respectively, that could not be completely analyzed or solubilized under various conditions. Thus, the detection of elevated copper in the urine ofWilson's disease patients treated with BAL may not be directly due to the solubilization of endogenous copper by BAL. Cuprous mercaptides are easily autoxidized by attack ofO2 to CuI to give CuII probably as peroxo complexes.

Microbial oxidation of refractory gold sulfide concentrate by a native consortium

A defined mesophilic consortium including an iron oxidizing bacterium and a sulfur oxidizing bacterium was constructed to evaluate its ability for bioleaching a flotation concentrate from Andacollo mine in Neuquén, Argentina. Experiments were performed in shake flasks with a pulp density of 10% (w/v), using a basal salt medium containing ferrous iron at pH 1.8. The leaching solutions were analyzed for pH, redox potential (using specifics electrodes), ferrous iron (by UV-Vis spectrophotometry) and metal concentrations (by atomic absorption spectroscopy). The results showed that the consortium was able to reduce the refractory behavior of the concentrate, allowing 91.6% of gold recovery; at the same time, high dissolution of copper and zinc was reached. These dissolutions followed a shrinking core kinetic model. According to this model, the copper solubilization was controlled by diffusion through a product layer (mainly jarosite), while zinc dissolution did not show a defined control step. This designed consortium, composed of bacterial strains with specific physiological abilities, could be useful not only to optimize gold recovery but also to decrease the leachates metallic charge, which would be an environmental advantage.

Genomic and metagenomic challenges and opportunities for bioleaching: a mini-review

High-throughput genomic technologies are accelerating progress in understanding the diversity of microbial life in many environments. Here we highlight advances in genomics and metagenomics of microorganisms from bioleaching heaps and related acidic mining environments. Bioleaching heaps used for copper recovery provide significant opportunities to study the processes and mechanisms underlying microbial successions and the influence of community composition on ecosystem functioning. Obtaining quantitative and process-level knowledge of these dynamics is pivotal for understanding how microorganisms contribute to the solubilization of copper for industrial recovery. Advances in DNA sequencing technology provide unprecedented opportunities to obtain information about the genomes of bioleaching microorganisms, allowing predictive models of metabolic potential and ecosystem-level interactions to be constructed. These approaches are enabling predictive phenotyping of organisms many of which are recalcitrant to genetic approaches or are unculturable. This mini-review describes current bioleaching genomic and metagenomic projects and addresses the use of genome information to: (i) build metabolic models; (ii) predict microbial interactions; (iii) estimate genetic diversity; and (iv) study microbial evolution. Key challenges and perspectives of bioleaching genomics/metagenomics are addressed.

Some Characteristics of Free Cell Population in the Airways of Rats after Intratracheal Instillation of Copper-Containing Nano-Scale Particles

We used stable water suspensions of copper oxide particles with mean diameter 20 nm and of particles containing copper oxide and element copper with mean diameter 340 nm to assess the pulmonary phagocytosis response of rats to a single intratracheal instillation of these suspensions using optical, transmission electron, and semi-contact atomic force microscopy and biochemical indices measured in the bronchoalveolar lavage fluid. Although both nano and submicron ultrafine particles were adversely bioactive, the former were found to be more toxic for lungs as compared with the latter while evoking more pronounced defense recruitment of alveolar macrophages and especially of neutrophil leukocytes and more active phagocytosis. Based on our results and literature data, we consider both copper solubilization and direct contact with cellular organelles (mainly, mitochondria) of persistent particles internalized by phagocytes as probable mechanisms of their cytotoxicity.

Investigation of the Effect of pH Operating Conditions on Bioleaching of Low-Grade Chalcopyrite in Column Reactors

Bioleaching of low-grade sulphide minerals is now an established process, with much interest in chalcopyrite. However few studies have been carried out on ores containing silicates gangue materials. Chalcopyrite has been reported to be refractory at ambient temperature. Several factors that influence bioleaching kinetics are well documented such as particle size, pH, temperature, galvanic interaction and microbial activity. The purpose of this research was to investigated the effect of pH as well as pre-leaching on bioleaching of silicate rich and low-grade chalcopyrite using mixed thermophilic cultures, with a view to maximize copper solubilization rate in a column reactor operated at 70°C. The column was packed with low-grade chalcopyrite of the size range -20+15 mm. Leaching was monitored at specific time intervals (3 days) by measuring the pH, the redox potential, the copper and iron concentration in the solution. The results of the investigation have shown that copper extracted was highest at pH 1.3 and at moderately low redox potential (410 – 430 mV) using Ag/AgCl electrode, and that pre-leaching contributed insignificantly to the leaching rate. At pH 2.5, the copper extraction was low due to the jarosite. Furthermore, the analysis XRD of leached residues has indicated that the main passivating products were gypsum, jarosite, hexahydrite, and silica. However, although low pH resulted to high copper recovery, the results also showed that the pregnant leach solution (PLS) contained high concentrations of dissolved ions which might have inhibited the microbial activities.

Reaction pathways over copper and cerium oxide catalysts for direct synthesis of imines from amines under aerobic conditions

Copper(II) oxide, cerium oxide, and several copper(II) oxide supported on cerium oxide catalysts are explored in the aerobic oxidative homocoupling of benzylamine to form N-benzylidenebenzylamine in DMSO at 110°C. Although both CuO and CeO2 alone are shown to catalyze the reaction, CuOCeO2 catalysts are shown to most efficiently catalyze the reaction, providing higher rates (per g Cu) due to the presence of both copper and ceria species in the reactor. Catalysts with lower copper loadings and increased ceria content reduce the product yield, as ceria domains can catalyze the decomposition of the desired product as well. The amine conversion occurs with a significant induction period, associated with the putative formation of an initial benzylimine intermediate in the case of catalysis with CeO2 alone or from slow copper solubilization in cases where supported or unsupported copper catalysts are used, followed by rapid conversion to the N-benzylidenebenzylamine product. Copper leaching studies clearly demonstrate that catalysis using copper-containing catalysts is primarily associated with turnover by soluble copper species. A series of experiments targeted at elucidating the reaction pathway suggests that copper oxide domains promote the coupling of the initial intermediate, benzylimine, with benzylamine to produce the N-benzylidenebenzylamine product (path A), with a maximum production rate of 888μmol/m2h (13.3mmol/gCuh) over the pure CuO catalyst or 22.9μmol/m2h (26.1mmol/gCuh) over the CuOCeO2 catalyst. In contrast, cerium oxide domains are suggested to primarily convert the benzylimine to benzaldehyde, followed by condensation of the benzaldehyde with benzylamine in a rapid step to yield the N-benzylidenebenzylamine product (path B), with a maximum amine production rate of 2.74μmol/m2h. Both ceria and copper(II) oxide domains promote the initial benzylimine formation at comparable rates. Although the CuOCeO2 catalyst leaches about 11% of the copper during the reaction, and these soluble copper species are largely responsible for the catalytic turnover, the recovered solid can be recycled until the copper is depleted, catalyzing the reaction with an identical rate per g Cu in a second cycle, after calcination. The copper–ceria family of catalysts offers an alternative, potentially lower cost composition for the target oxidative homocoupling reaction than previously studied precious metal catalysts, although copper leaching is a distinct drawback to the catalyst composition.

Fungal Bioleaching of Metals From Mine Tailing

The present study was undertaken to develop an economically feasible and environmental-friendly technique to recover metals (Ni, Cu, Co, Zn, Mg) from mine tailing by employing Penicillium chrysogenum strain KBS3. The potential of Penicillium chrysogenum in generating a variety of organic acids was studied and the effect of different organic wastes as substrates was evaluated. Maximum solubilization of nickel (55%), copper (67%), magnesium (69%), cobalt (60%), and zinc (65%) was achieved in the media containing glucose, tea leaves, molasses, and waste winery grapes as substrates.

Effects of Synthetic Chelators and Low-Molecular-Weight Organic Acids on Chromium, Copper, and Arsenic Uptake and Translocation in Maize (Zea mays L.)

Chelate-assisted phytoextraction is a promising technique to remediate metal-contaminated soil. Batch and greenhouse experiments were conducted to assess the effects of synthetic chelators (ethylenediaminetetraacetic acid [EDTA], ethylenediaminedisuccinic acid [EDDS], and nitrilotriacetic acid) and low-molecular-weight organic acids (oxalic and citric acids) on the solubilization of copper, chromium, and arsenic (Cu, Cr, and As, respectively) in chromated Cu arsenate (CCA)-contaminated soil and on metal uptake and translocation in maize (Zea mays L.). Chelators significantly enhanced the solubilization of Cr, Cu, and As in the soil and markedly increased their accumulation in plant tissues. Applying 5 and 10 mmol kg EDDS increased plant Cu uptake by 2.8- and 3.5-fold greater than that in control soil (without chelate applications), respectively. EDTA and citric acid were more efficient for increasing Cr uptake by plant shoots, resulting in 5.0- and 5.5-fold increases, respectively, compared with that in the control. Maximum As uptake was observed in response to a treatment of 10 mmol kg citric acid, which was 1.9-fold greater than that in control soil. However, translocation factors, phytoextraction efficiencies, and remediation factors indicated that metal uptake was not high enough for successful phytoremediation of CCA–contaminated soil. Our results suggest that EDDS and citric acid as alternatives to EDTA may facilitate phytoextraction of contaminated soil.

Investigation of copper solubilization and reaction in micronized copper treated wood by electron paramagnetic resonance (EPR) spectroscopy

Abstract The purpose of this study was to compare the reaction chemistry of micronized copper and alkaline copper treatments with wood and to determine how fast copper is solubilized during the reaction between the acidic functionality in wood and the basic copper carbonate (CuCO3). Copper species produced in wood by various treatment methods were analyzed by electron paramagnetic resonance (EPR) spectroscopy. The effects of time and solution concentration on the spectral parameters of copper complexes in sawdust treated with copper sulfate solutions were examined, followed by study on the structure and the rate of formation of the copper complexes in sawdust treated with basic CuCO3 suspension. The study further attempted to identify the soluble copper species formed in wood during treatment with micronized copper preservatives. Comparisons were made among the fixed copper complexes in wood treated with micronized copper preservatives, copper sulfate solutions, basic CuCO3 suspensions and alkaline copper solution. The results showed rapid formation of fixed copper complexes in wood treated with aqueous suspensions of basic CuCO3. These complexes can resist leaching, and they have similar stereochemistry to those formed between wood and copper sulfate. This finding supports the premises that soluble copper is generated during the treatment of sawdust with basic CuCO3, and it can bond to wood cell components by migrating into the cell wall in a manner similar to other soluble copper species. Such copper complexes formed are different from those of alkaline copper treated wood, which can be easily distinguished by EPR.

Optimization of Copper Removal from ACQ-, CA-, and MCQ-Treated Wood Using an Experimental Design Methodology

AbstractThe development of appropriate disposal options for copper-based treated wood waste has been encouraged owing to stringent regulations regarding solid-waste landfilling or burning. Previous studies identified an efficient chemical process for removing metals from wood treated with chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), copper azole (CA), and micronized copper quaternary (MCQ). The objective of this research was to identify optimal leaching parameters for removing copper from ACQ-, CA-, and MCQ-treated wood in terms of efficiency and operating costs. A 24 Box-Behnken design was used for determining influential parameters (sulfuric acid concentration, temperature, retention time, and number of leaching steps) on the copper removal and for identifying optimal leaching conditions. The results obtained showed that sulfuric acid concentration and number of leaching steps were the main influential parameters on copper solubilization from alternatively treated wood. The values ...

Effects of aging on the digestive solubilization of Cu from sediments

Solubilization of particulate Cu by different solutions, mimicking digestive fluids of deposit-feeders, was quantified in stable isotope 65Cu-spiked sediments (with 3 days-2 months Cu-sediment contact time or aging). Copper solubilization generally decreased with prolonged aging. However, such decrease became less evident after 1 month and equilibrium of Cu in sediments could be reached after 2 months. Aging effects on Cu solubilization can be explained by the changes in Cu geochemical fractionation with aging: Cu generally transferred from more mobile phases (carbonate and Fe–Mn associated) to more refractory phases (organic associated and residual phase). Besides Cu geochemical fractionation, digestive fluid composition and different Cu solubilization pathways involved, as well as sedimentary organic content, could all affect the digestive solubilization of Cu and its change with aging. Our results emphasize the necessity of considering Cu aging in laboratory sediment toxicity experiments, and in risk assessment of Cu contaminated sediments.

Operationally defined solubilization of copper and iron in human saliva and implications for metallic flavor perception

Metals such as copper and iron cause unpleasant taste perceptions. Metallic compounds come in contact with saliva before delivery to taste receptors. Therefore, it is assumed that interactions between saliva and metallic compounds affect the perceptions of metals. The aim of this study was to determine the solubilization of metals in saliva and to examine whether or not perceptions of metallic flavor are influenced by metal solubility in saliva. Ten trained panelists evaluated the sourness, bitterness, astringency, electric sensation, and rusty nail-like retronasal aroma of copper sulfate (CuSO4·5H2O, Cu) and ferrous sulfate (FeSO4·7H2O, Fe) dissolved in ultrapure water at different concentrations. Total and soluble metals were measured in the subjects’ saliva collected after tasting the samples using an inductively coupled plasma spectrometer. Approximately, 4.5–6.4% of Fe and 4.0–6.6% of Cu were retained in the saliva after expectoration. The proportion of soluble metal to total metal retained in saliva decreased from 0.68 to 0.29 for Cu and 0.019 to 0.0016 for Fe, as the metal concentration increased. In particular, Fe was solubilized in saliva at a maximum level of 4.5–4.6 μM, regardless of the metal concentration of the solution. The perceived intensities of sensory attributes showed positive linear relationships with log concentrations of total Cu, soluble Cu, and total Fe, but they did not have any relationship with soluble Fe. These results indicate that sensory perceptions of Fe were influenced mainly by the total Fe retained in saliva, whereas the perception of Cu was affected by soluble Cu as well as total Cu.

The aggressive influence of lead-free solders and the protection of soldering devices against damage

The article presents the influence of lead-free solders on SnAg3.8Cu0.7 and SnCu0.7 tin matrices, as well as SnPb37 solder on the solubilization of copper under various conditions during dip soldering. The influence of lead-free solders, higher soldering temperatures and mobile soldering baths on the intensified effects of copper solubilization is demonstrated. Elements of soldering facilities coming into contact with SnCu3 solder-filled soldering bath are subject to solubilization and damage as a result. Protection of these elements and increase of their resistance by covering them with a ceramic layer based on Al2O3–TiO2 oxides was suggested.

Effect of multiple metal resistant bacteria from contaminated lake sediments on metal accumulation and plant growth

Naturally occurring bacteria play an important role in bioremediation of heavy metal pollutants in soil and wastewater. This study identified high levels of resistance to zinc, cesium, lead, arsenate and mercury in eight copper resistant Pseudomonas strains previously isolated from Torch Lake sediment. These strains showed variable susceptibility to different antibiotics. Furthermore, these metal resistant strains were capable of bioaccumulation of multiple metals and solubilization of copper. Bacterial strains TLC 3-3.5-1 and TLC 6-6.5-1 showed high bioaccumulation ability of Zn (up to 15.9 mg/g dry cell) and Pb (80.7 mg/g dry cell), respectively. All the strains produced plant growth promoting indole-3-acetic acid (IAA), iron chelating siderophore and solubilized mineral phosphate and metals. The effect of bacterial inoculation on plant growth and copper uptake by maize ( Zea mays) and sunflower ( Helianthus annuus) was investigated using one of the isolates ( Pseudomonas sp. TLC 6-6.5-4) with higher IAA production and phosphate and metal soubilization, which resulted in a significant increase in copper accumulation in maize and sunflower, and an increase in the total biomass of maize. The multiple metal-resistant bacterial isolates characterized in our study have potential applications for remediation of metal contaminated soils in combination with plants and metal contaminated water.

Leaching of metal ions from black shale by organic acids produced by Aspergillus niger

The main concern of the present study is to find a more feasible and economical method to extract metal ions from low grade discarded ores like black shale by Aspergillus niger. A. niger exhibited a good potential in generating varieties of organic acids effective for metal ions solubilization. The effectiveness of organic acids was enhanced when sulphuric acid was added to the medium. Different agricultural wastes as substrates were evaluated. Maximum solubilization of copper (68.5%), zinc (49.0%) and cobalt (60.4%) was achieved in the media containing mango peel, rice bran and glucose as substrates. The extraction of low concentrations of metal ions from this ore indicated that this low grade discarded ore may be a potential source for metal ions in the future.