Microbial leaching of zinc concentrate in fresh‐water microcosms: Comparison between aerobic and oxygen‐limited conditions

Microbially mediated leaching and solubilization of zinc ore concentrate by native aquatic microbial communities incubated under aerobic and oxygen‐limited conditions were examined in static microcosms consisting of stream sediment and water. Sterile controls provided information on abiotic sulfide oxidation and leaching of zinc, lead, cadmium, and copper. The flux of these heavy metals from the sediments to the water column was greatest under biotic oxygen‐limited conditions. When calculated as the percentage of total metal available in zinc concentrate‐amended microcosms, the order of metal solubilization under oxygen‐limited conditions was lead, copper, zinc, and cadmium. Under biotic aerobic conditions, the order of solubilization was zinc, lead, cadmium, and copper. This study indicates that aquatic heterotrophs are capable of leaching and solubilizing metallic sulfides under conditions of neutral to slightly acidic pH and are effective in releasing heavy metals to the water column under oxygen‐limited conditions.     

The Sociedad Minera Pudahuel bacterial thin-layer leaching process at Lo Aguirre

The thin-layer leaching process originally conceived and developed for leaching oxide ores has been successfully adapted to bacterial leaching of mixed and secondary sulphide ores. The process is currently being applied at the Socicdad Minera Pudahuel Lo Aguirre Plant. About 3000 ton of ore per day are being processed to produce 14000 ton of high-grade copper cathodes per year, in a closed circuit integrated with SX-EW. Changes in the soluble copper grade of the ore from about 1.8C4 to (I.6% have occurred during the last years, which have been compensated by an equivalent increase in the insoluble copper grade. In addition, ore from satellite ore bodies has resulted in acid consumption variations ranging from 611 to 120 kg H₂SO₄ per ton of ore. The main sulphide mineralogical species are chatcocite and bornite, with small amounts of chalcopyrite and covellite. An intensive research program in columns and large-scale heaps has been carried out to define the operating conditions which assure adequate bacterial growth and bacterial activity towards the sulphides. Agglomerated ores with 1.7 2.5% Cur and (I.3-0.6%: Cus, with the insoluble copper mainly present as chalcocite bornite, were leached at a flow rate of 0.2 1 min¹ mu² with a SX-Raffinate solution containing (in g^-1) 5–10 H₂SO₄, 2–4 Fe_T, 1–3 Fe⁺³, 0.5 Cu, as well as impurities resulting from a closed circuit operation. Copper recoveries of 75 85% Cu_T were obtained after 180–250 days of total leaching time, depending on the copper grade, the mineralogical composition, and the acid consumption of the ore. Important bacterial activity was detected. About 10 ³−10⁵ bacteria ml⁻¹ were measured in effluent solutions. Iron oxidation rates of 7–100μg Fe²⁺ h⁻¹ g⁻¹, measured from respirometric tests on agglomerated ore, suggest that an adsorbed biomass of about 10⁷-10⁸ bacteria g⁻¹ must also be present. Further applications of the bacterial thin-layer leaching process to Cerro Colorado and Qucbrada Blanca ores in North Chile are being studied.     

Microbiological Leaching of Metallic Sulfides

The percentage of chalcopyrite leached in percolators by Thiobacillus ferrooxidans was dependent on the surface area of the ore but not on the amount. Typical examples of ore leaching, which demonstrate the role of the bacteria, are presented. In stationary fermentations, changes in KH(2)PO(4) concentration above or below 0.1% decreased copper leaching as did reduction in the MgSO(4).7H(2)O and increase in the (NH(4))(2)SO(4) concentration. Bacterial leaching of chalcopyrite was more effective than nonbiological leaching with ferric sulfate; ferric sulfate appeared to retard biological leaching, but this effect was likely caused by formation of an insoluble copper-iron complex. Ferrous sulfate and sodium chloride singly accentuated both bacterial and nonbiological leaching of chalcocite but jointly depressed bacterial action. Sodium chloride appeared to block bacterial iron oxidation without interfering with sulfide oxidation. Bacterial leaching of millerite, bornite, and chalcocite was greatest at pH 2.5. The economics of leaching a number of British Columbia ore bodies was discussed.     

Bacterial leaching of uranium ore from Figueira—PR, Brazil, at laboratory and pilot scale

Abstract: A bacterial leaching program was carried out in order to evaluate the potential of applying this process to leach uranium from the ore of Figueira-PR, Brazil. The experiments were carried out in shake flasks, column percolation (laboratory and scmipilot scale)and in heap leaching. In shake flasks and in column percolation experiments at laboratory scale, bacterial activity on Ihe ore was confirmed: approximately 60% of uranium was leached, against around 30% in sterilized controls. Colunm percolation experiments at semipilot scale and heap leaching (850 tons of ore) showed uranium extractions of approximately 50%. In both experiments, a complementary sulfuric acid attack, after the bacterial leaching phase, was neccssaw to reach this level of uranium extraction.     

The Blue Water Footprint of Primary Copper Production in Northern Chile

Water consumption related to the life cycle of metals is seldom reported, even though mines are often situated in very dry regions. In this study we quantified the life cycle consumption of groundwater and fresh surface water (blue water footprint [WF_blue]) for the extraction and production of high‐grade copper refined from both a copper sulfide ore and a copper oxide ore in the Atacama Desert of northern Chile. Where possible, we used company‐specific data. The processes for extracting copper from the two types of ore are quite different from each other, and the WF_blue of the sulfide ore refining process is 2.4 times higher than that of the oxide ore refining process (i.e., 96 cubic meters per metric ton [tonne] of copper versus 40 cubic meters per tonne of copper). Most of the water consumption (59% of WF_blue) in the sulfide ore process occurred at the concentrator plant, via seepage, accumulation, and also by evaporation. In the oxide ore process, the main user of water is the heap‐leaching process, with 45% of WF_blue. The crushing and agglomeration operations, electrowinning cells, and solution pools are also significant contributors to the total consumption of water in the oxide ore process. Most of the water consumed in the oxide ore process was lost to evaporation. The WF_blue of the oxide ore process can be reduced by preventing water evaporation and using more sophisticated devices during irrigation of the leaching heaps. The WF_blue of the sulfide ore refining process can be reduced by improving water recovery (i.e., reducing seepage, accumulation, and evaporation) from the tailings dam at the concentrator plant. Using seawater in the production of copper is also a promising option to reduce the WF_blue by up to 62%.     

Integrated biological process for the treatment of a Chilean complex gold ore

Abstract: A process for gold recovery from a complex Chilean ore from Burladora (IV Region) which integrates concentration by flotation, bacterial leaching and cyanidation was studied at a laboratory scale. The chemical composition of the ore is 8.2% Fe, 0.78% Cu, 0.88% As and 3.5 g/t Au, with pyrite, hematite, covelite, arsenopyrite and chalcopyrite as the main metal-bearing minerals. The initial gold recovery by conventional cyanidation on a crushed ore sample was only 54%. The ore was ground and concentrated by flotation with a gold recovery of only 56%. The gold content of the concentrate is 17 g/I Au. Concentrate samples were leached in 1.5 l stirred reactors at 10% pulp density in 1000 ml of acid medium (pH 1.8). Some experiments were inoculated with harvested bacteria previously isolated from mining solutions. Dissolved metals, pH and bacteria concentration in the leaching solutions were periodically determined. In the presence of bacteria, oxidation of the ferrous ion produced by acid dissolution of the concentrate was observed, and after 4 days of leaching 100% of the dissolved iron was present as ferric ion. Gold recovery by cyanidation increased from 13% for the initial concentrate to 34% after 10 days of chemical acid leaching and 97% after 10 days of bacterial leaching. To increase the total gold recovery, the flotation tailings were submitted to cyanidation. A complete flowsheet of the process and a first economical evalualion are proposed. As a possible alternative process, heap bacterial leaching and further cyanidation of the ore are suggested.     

Mineralogical controls on the bacterial oxidation of refractory Barberton gold ores

Abstract: The effect of mineralogical characteristics of gold ore minerals on the nature of sulphide oxidation during a bacterial leaching process was investigated. Three different ore types from the South African goldmines were used, i.e. an arsenopyritic-pyritic ore (Sheba goldmine), a pyritic ore (Agnes goldmine) and a loellingitic-arsenopyritic ore (New Consort goldmine). Detailed mineralogical characterization of each ore was performed. Thereafter, polished sections of the sulphides were suspended in a bacterial leach pulp in an air-stirred vessel for various periods of time. The effect of bacterial oxidation on the sulphides was monitored. Different types of gold-bearing arsenopyrite exist, each type having its own characteristic behaviour during the bacterial oxidation process. The rate of oxidation is controlled by the amount of defects in the crystal structure, and the amount of defects is again controlled by the composition of the arsenopyrite crystal. The distribution of refractory gold in the sulphide minerals can be correlated with the presence of compositional zones and structural deviations. These same mineralogical features also control the sites and rates of bacterial oxidation. Thus. refractory gold occurs at sites which are preferentially leached by the bacteria. The rate of gold liberation from sulphides is therefore being enhanced during the early stages of bacterial oxidation. Defects in a crystal structure influence the rate of bio-oxidation, and can be related directly to the crystal structure of the sulphide mineral, the crystallographic orientation of the exposed surfaces, and differences in chemical compositional and mechanical deviations in the crytals. A combination of all of these mineralogical factors influences the bacterial oxidation process. To optimize and to understand the leaching of an individual ore it is important to establish its controlling factors.     

Selective extraction of metals from zinc concentrate by association of chemolithotrophic bacteria

Ability for selective extraction of copper and zinc from zinc concentrate using association of chemolithotrophic bacteria was investigated. In the presence of bacterial association, the rate of leaching of zinc, copper, and iron was increased 3-fold, 4–5-fold, and 2-fold, respectively. The results indicate the maximum dissolution rate for zinc, then followed by copperand iron. It was revealed that addition of Fe³⁺ 2 g/l resulted in reduction of iron leaching and in 3-fold increase of leaching rate of copper at constant dissolution rate of mineral zinc. It is suggested that the intensification of copper leaching is connected with the activity of sulfur-oxidizing bacteria able to activate the mineral surface via elimination of passivation layer of elemental sulfur. It was concluded that sulfur-oxidizing bacteria play a significant role in copper leaching from zinc concentrate. A unique strain of mesophile sulfur-oxidizing bacteria was isolated from leaching pulp of zinc concentrate; in the perspective, it may serve as efficient candidate for performing of selective extraction of copper from zinc concentrate.     

Effect of anions on selective solubilization of zinc and copper in bacterial leaching of sulfide ores

Bacterial leaching of sulfide ores using Thiobacillus ferrooxidans, Thiobacillus thiooxidans, or a combination of the two was studied at various concentrations of specific anions. Selective zinc and copper solubilization was obtained by inhibiting iron oxidation without affecting sulfur/sulfide oxidation. Phosphate reduced iron solubilization from a pyrite (FeS(2))-sphalerite (ZnS) mixture without significantly affecting zinc solubilization. Copper leaching from a chalcopyrite (CuFeS(2))-sphalerite mixture was stimulated by phosphate, whereas chloride accelerated zinc extraction. In a complex sulfide ore containing pyrite, chalcopyrite, and sphalerite, both phosphate and chloride reduced iron solubilization and increased copper extraction, whereas only chloride stimulated zinc extraction. Maximum leaching obtained was 100% zinc and 50% copper. Time-course studies of copper and zinc solubilization suggest the possibility of selective metal recovery following treatment with specific anions.     

废弃铅锌矿石和钨矿砂中可培养细菌多样性分析

为了了解废弃铅锌矿石和钨矿砂中可培养细菌的多样性,发掘其中的微生物新资源,采用3种培养基(R2A、无磷R2A、无磷R2A+Cd2+)分别对其中的可培养细菌进行分离纯化和培养。再通过16S rRNA基因测序获取相关的分类学信息,并进行系统进化分析。从2种材料中共分离到可培养细菌152株。其中,废弃铅锌矿石中的可培养细菌涵盖了5个门、7个分支,分属于Alphaproteobacteria、Betaproteobacteria、Gammaproteobacteria、Deinococcus-Thermus、Actinobacteria、Bacteroidetes和Firmicutes,以Massilia、Methylobacterium、Deinococcus和Sphingomonas为主要类群;而钨矿砂中的可培养细菌涵盖了3个门、4个分支,分属于Alphaproteobacteria、Betaproteobacteria、Actinobacteria和Firmicutes,以Methylobacterium、Massilia、Ralstonia和Microbacterium为主要类群。废弃铅锌矿石中可培养细菌的多样性和新分类单元发现率均大于钨矿砂,且两者的可培养细菌类群组成存在较大差异。此外,向培养基中添加重金属Cd2+降低了可培养细菌的多样性。研究分离到的Cd2+耐受菌株主要属于3个属：Methylobacterium、Herbaspirillum和Ralstonia,其能耐受2 mmol/L Cd2+,是金属尾矿中重金属耐受菌的优势种群。研究结果为金属尾矿中微生物新资源的深入发掘提供了依据。     

Effect of temperature on the microbiological leaching of sulfide ore material in percolators containing chalcopyrite,pentlandite, sphalerite and pyrrhotite as main minerals

Summary Microbiological leaching of complex sulfide ore material was evaluated in percolators at 4, 10, and 20°C. The onset of leaching was associated with an increase in redox potential and a decrease in pH. Copper from chalcopyrite was leached at a slow rate at each test temperature compared with the leaching of zinc from sphalerite and nickel from pentlandite.     

Chemical constituents and antibacterial activity of the leaf essential oil of <Emphasis Type="Italic">Feronia limonia</Emphasis>

Bioleaching of uranium was carried out with Turamdih ore sample procured from Uranium Corporation of India Limited, Jaduguda. The bacterial strain that was used in the leaching experiments was isolated from the Jaduguda mine water sample. Efficiency of bioleaching was studied by varying parameters like pulp density and initial ferrous concentration as source of energy. It is observed that the efficiency of bioleaching was 49% at 10% pulp density (w/v) and initial pH 2.0. Addition of external has no effect on efficiency of bioleaching showing domination of direct leaching mechanism over indirect.     

Bioindicators and accumulators in geobotanical and biogeochemical prospecting of metals

Results of geobotanical and biogeochemical studies carried out on the known lead-zinc deposits of Zawar Mines and Khetri Copper Deposits, India, are discussed. A wild variety of Impatiens balsamina was found to be the most characteristic species on lead-zinc metal dumps, which can be regarded as a local 'bioindicator' for these metals. A number of 'accumulators' for lead, zinc, copper with high BAC values, as well as some 'excluders' are also discussed.     

Bioleaching of zinc sulfide concentrate by Thiobacillus ferrooxidans

The kinetics of the bioleaching of ZnS concentrate by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experimental studies were made at 30 degrees C and pH 2.2 on adsorption of the bacteria to the mineral, ferric iron leaching, and bacterial leaching. The adsorption rate of the bacteria was fairly rapid in comparison with the bioleaching rate, indicating that the bacterial adsorption is at equilibrium during the leaching process. The adsorption equilibrium data were correlated by the Langmuir isotherm, which is a useful means for predicting the number of bacteria adsorbed on the mineral surface. The rate of chemical leaching varied with the concentration of ferric iron, and the first-order reaction rate constant was determined. Bioleaching in an iron-containing medium was found to take place by both direct bacterial attack on the sulfide mineral and indirect attack via ferric iron. In this case, the ferric iron was formed from the reaction product (ferrous iron) through the biological oxidation reaction. To develop rate expressions for the kinetics of bacterial growth and zinc leaching, the two bacterial actions were considered. The key parameters appearing in the rate equations, the growth yield and specific growth rate of adsorbed bacteria, were evaluated by curve fitting using the experimental data. This kinetic model allowed us to predict the liquid-phase concentrations of the leached zinc and free cells during the batch bioleaching process.     

The Accumulation of Zinc by the Mosquito

The zinc content of mosquitoes in various developmental stages was determined by spectrographic and microchemical analysis and use of zinc⁶⁵ and found to be five to ten times higher than other trace elements. Also the concentration of zinc in the mosquito was much greater than in other insects of different biological orders. Over 90 per cent of this element was localized in the Malpighian tubules at a concentration of 32 µg zinc per mg dry weight. The non-dialyzable form of zinc is loosely bound, for it was dissociated upon dialysis against ethylenediamine tetraacetate. The uptake of this trace element was correlated during larval growth with weight increase and required the presence of food particles. Furthermore, this uptake was different from that of cobalt which was not accumulated when offered as an inorganic salt or as vitamin B₁₂. Zinc was not detectable in pooled egg masses, and once embodied by the larvae, was retained under fasting conditions and at a constant level throughout the pupal stage and as long as 14 days' adult life. Supplementation of the media with EDTA caused a marked inhibition of growth that could be completely reversed by the addition of zinc or zinc plus lead. The resultant pupae, however, contained less than 5 per cent of the normal amount of zinc and were essentially zinc-free; yet their rate of growth and gross appearance were normal.     

Optimization of staged bioleaching of low-grade chalcopyrite ore in the presence and absence of chloride in the irrigating lixiviant: ANFIS simulation

In this investigation, copper was bioleached from a low-grade chalcopyrite ore using a chloride-containing lixiviant. In this regard, firstly, the composition of the bacterial culture media was designed to control the cost in commercial application. The bacterial culture used in this process was acclimated to the presence of chloride in the lixiviant. Practically speaking, the modified culture helped the bio-heap-leaching system operate in the chloridic media. Compared to the copper recovery from the low-grade chalcopyrite by bioleaching in the absence of chloride, bioleaching in the presence of chloride resulted in improved copper recovery. The composition of the lixiviant used in this study was a modification with respect to the basal salts in 9 K medium to optimize the leaching process. When leaching the ore in columns, 76.81 % Cu (based on solid residues of bioleaching operation) was recovered by staged leaching with lixiviant containing 34.22 mM NaCl. The quantitative findings were supported by SEM/EDS observations, X-ray elemental mapping, and mineralogical analysis of the ore before and after leaching. Finally, Adaptive neuro-fuzzy inference system (ANFIS) was used to simulate the operational parameters affecting the bioleaching operation in chloride–sulfate system.     

Interactive effects of cadmium,lead and zinc on root growth of two metal tolerant genotypes ofHolcus lanatus L.

Lead and zinc tolerant genotypes ofHolcus lanatus L. were grown in culture solution at different cadmium, lead and zinc concentrations, and combinations. In all treatments, an increased inhibition of root length with increasing concentrations of heavy metals was observed. Growth of genotype 1 was better than that of genotype 2 in all treatments, suggesting that genotype 1 is more tolerant. The better root growth of genotype 1, at different cadmium concentrations, than that of genotype 2, indicated the existence of a co-tolerance or greater tolerance of genotype 1 to cadmium. Heavy metal combinations resulted in increased lead or zinc uptake by plants, while cadmium was decreased. In a lead-zinc combination, decreased lead and increased zinc uptake were detected. The different interactive effects of heavy metals on root growth of genotype 1 (additive or synergistic) and genotype 2 (additive or antagonistic) may suggest their differential susceptibility to the above metals.     

Fungal biotransformation of zinc silicate and sulfide mineral ores

In this work, several fungi with geoactive properties, including Aspergillus niger, Beauveria caledonica and Serpula himantioides, were used to investigate their potential bioweathering effects on zinc silicate and zinc sulfide ores used in zinc extraction and smelting, to gain understanding of the roles that fungi may play in transformations of such minerals in the soil, and effects on metal mobility. Despite the recalcitrance of these minerals, new biominerals resulted from fungal interactions with both the silicate and the sulfide, largely resulting from organic acid excretion. Zinc oxalate dihydrate was formed through oxalate excretion by the test fungi and the mineral surfaces showed varying patterns of bioweathering and biomineral formation. In addition, calcium oxalate was formed from the calcium present in the mineral ore fractions, as well as calcite. Such metal immobilization may indicate that the significance of fungi in effecting metal mobilization from mineral ores such as zinc silicate and zinc sulfide is rather limited, especially if compared with bacterial sulfide leaching. Nevertheless, important bioweathering activities of fungi are confirmed which could be of local significance in soils polluted by such materials, as well as in the mycorrhizosphere.     

Chemical and biological leaching of enargite

Enargite (Cu 3 AsS 4 ) was leached faster by bacteria in sulfuric acid medium (pH 1.6) with added ferric sulfate than by chemical leaching at the same or higher iron concentration. During chemical leaching with ferric iron, the copper dissolution rate decreased from an initial value of 0.03% per hour to a value of 0.002% per hour. Enargite is oxidized to elemental sulfur and dissolved arsenic (As 3+ and As 5+ ). Less than 10% of sulfur is oxidized to sulfate. The arsenic and copper dissolutions observed in bacterial leaching experiments suggest the existence of a specific bacterial action on the leaching of enargite, demonstrated by the ability of bacteria to oxidize enargite at very low concentration of dissolved iron and by the higher dissolution rate obtained in bacterial leaching compared to chemical ferric leaching.     

Biological leaching of sulfide minerals with the use of shake flask,aerated column,air-lift reactor,and percolation techniques

Four different experimental approaches were used to evaluate the microbiological leaching of ore material containing metal sulfides (Fe, Zn, Ni, Cu, Co) and aluminum silicates. A shake flask technique required the shortest contact time for the complete solubilization of the most readily leachable metals (Ni and Zn). Air-lift reactors and aerated column reactors required longer contact times and complete solubilization of either zinc or nickel was not achieved. The air-lift reactor approach was somewhat more effective than the aerated slurry technique. A percolation system was the least effective and yielded the lowest recoveries. Shake flasks (easily autoclavable) offered the advantage of comparison of the microbiological and solely chemical leaching. Aseptic conditions could not be maintained with the air-lift and aerated column reactors because of contamination via aerosol formation. In a relative scale the leaching patterns were similar in that the precipitation of Fe(III) occurred regardless of the technique; zinc and nickel sulfides were solubilized more quantitatively than those of copper and cobalt; aluminum concentrations, although high, indicated low leaching yields relative to aluminum silicates in the ore material; and the pH reached similar final values in the presence of bacteria.