Microbial leaching of metals from solid industrial wastes

Biotechnological applications for metal recovery have played a greater role in recovery of valuable metals from low grade sulfide minerals from the beginning of the middle era till the end of the twentieth century. With depletion of ore/minerals and implementation of stricter environmental rules, microbiological applications for metal recovery have been shifted towards solid industrial wastes. Due to certain restrictions in conventional processes, use of microbes has garnered increased attention. The process is environmentally-friendly, economical and cost-effective. The major microorganisms in recovery of heavy metals are acidophiles that thrive at acidic pH ranging from 2.0–4.0. These microbes aid in dissolving metals by secreting inorganic and organic acids into aqueous media. Some of the well-known acidophilic bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Sulfolobus spp. are well-studied for bioleaching activity, whereas, fungal species like Penicillium spp. and Aspergillus niger have been thoroughly studied for the same process. This mini-review focuses on the acidophilic microbial diversity and application of those microorganisms toward solid industrial wastes.     

Microbiological leaching of sulfide minerals with different percolation regimes

Summary The microbiological leaching of Fe, Al, Zn, Cu, Ni and Co from sulfide ore material was evaluated with four percolation regimes involving trickle and flood leaching. Continuous circulation of the leach solution associated with flood leaching resulted in the highest rates of leaching of Ni (44% recovery), Zn (25%), Co (18%), and Cu (8%) over a period of about half a year. Iron and aluminum recoveries remained low because of their precipitation. Bacterial counts increased from 3.2×10⁶ to 4.8×10⁷ iron-oxidizers and from 6.6×10⁶ to 1.8×10⁷ glucose-oxidizers per ml leach solution. Microscopic counts reached a maximum of 4.9×10⁸ cells per ml. Neither microscopic nor viable counts reflected the time course and the progress of the leaching. However, both the microscopic and viable counts were highest with the continuous flooding technique which also yielded the fastest rates of metal solubilization.     

A new look at microbial leaching patterns on sulfide minerals

Leaching patterns on sulfide minerals were investigated by high-resolution scanning electron microscopy (SEM). Our goal was to evaluate the relative contributions of inorganic surface reactions and reactions localized by attached cells to surface morphology evolution. Experiments utilized pyrite (FeS(2)), marcasite (FeS(2)) and arsenopyrite (FeAsS), and two iron-oxidizing prokaryotes in order to determine the importance of cell type, crystal structure, and mineral dissolution rate in microbially induced pit formation. Pyrite surfaces were reacted with the iron-oxidizing bacterium Acidithiobacillus ferrooxidans (at 25 degrees C), the iron-oxidizing archaeon 'Ferroplasma acidarmanus' (at 37 degrees C), and abiotically in the presence of Fe(3+) ions. In all three experiments, discrete bacillus-sized (1-2 μm) and -shaped (elliptical) pits developed on pyrite surfaces within 1 week of reaction. Results show that attaching cells are not necessary for pit formation on pyrite. Marcasite and arsenopyrite surfaces were reacted with A. ferrooxidans (at 25 degrees C) and 'F. acidarmanus' (at 37 degrees C). Cell-sized and cell-shaped dissolution pits were not observed on marcasite or arsenopyrite at any point during reaction with A. ferrooxidans, or on marcasite surfaces reacted with 'F. acidarmanus'. However, individual 'F. acidarmanus' cells were found within individual shallow (<0.5 μm deep) pits. The size and shape (round rather than elliptical) of the pits conformed closely to the shape of F. acidarmanus (cells) pits on arsenopyrite. We infer these pits to be cell-induced. We attribute the formation of pits readily detectable (by SEM) to the higher reactivity of arsenopyrite compared to pyrite and marcasite under the conditions the experiment was conducted. These pits contributed little to the overall surface topographical evolution, and most likely did not significantly increase surface area during reaction. Our results suggest that overall sulfide mineral dissolution may be dominated by surface reactions with Fe(3+) rather than by reactions at the cell-mineral interface.     

Bacterial leaching of metals from sewage sludge

Summary Thiobacillus thiooxidans is capable of oxidizing sulfur in digested sludge, while decreasing the pH value from about 5.5 to, say, 1.0 to 1.5. Insoluble metal sulfides can be solubilized through this acidification. Thiobacillus ferrooxidans oxidises pyritic ore in the presence of 6% centrifuged sludge if the pH value is adjusted to about 2.5. When mixing T. thiooxidans and T. ferrooxidans with sludge and 1% sulfur, the former acidifies the sludge and the latter oxidizes metal sulfides; together they solubilize more metal than T. thiooxidans alone. The following metals solubilized from their sulfides have been investigated so far: iron, copper, zinc, nickel, and cadmium. The possibility of recycling metals from sewage sludge with this method is discussed.     

Alterations in surfaces and textures of minerals during the bacterial leaching of a complex sulfide ore

Abstract

The purpose of the work was to characterize changes in surface textures of minerals during the biological leaching of a complex sulfide ore. The ore contained pyrrhotite (Fe_I__xS), pyrite (FeS₂), sphalerite (ZnS), pentlandite [(Ni,Fe,Co)₉S₈], and chalcopyrite (CuFeS₂). Several mixed cultures were initially screened using the ore material as the sole substrate. Shake flask leaching experiments showed no major differences among test cultures, which were all derived by enrichment techniques using environmental samples collected from a mine site. Leached pyrrhotite surfaces were invariably surrounded by a dark rim of elemental S. A reaction zone was also associated with leached sphalerite grains. Chemical analyses of leach solutions indicated that the relative ranking of biological leaching of the sulfide minerals was Zn > Ni > Co > Cu. Microscopic observations were in keeping with this rankin     

Microbiological leaching of a zinc sulfide concentrate

The microbiological extraction of zinc from a high-grade zinc sulfide concentrate has been investigated, using a pure strain of Thiobacillus ferrooxidans. Conditions such as temperature, pH, pulp density, nutrient, concentration, and specific surface of solids have been studied in terms of their effects on zinc extraction rate and in some instances on final zinc concentration in solution. Where appropriate, optimum conditions for leaching have been specified.     

Microbial leaching of lateritic nickel ore

Lateritic nickel ore from the Sukinda Mines, Orissa, India, was leached using Thiobacillus ferrooxidans, Bacillus circulans, Bacillus licheniformis and Aspergillus niger at 5% (w/v) solid: liquid ratio for 5–20 days. Maximum leaching of Ni was achieved with B. circulans (85%) and Aspergillus niger (92%) after 20 days. Bacillus circulans showed significantly higher rate of leaching than the other organisms giving 80% Ni extraction after 15 days. The importance and usefulness of heterotrophic organisms in metal extraction are discussed.     

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.     

Bacterial leaching of two Swedish zinc sulfide ores

Abstract: Two Swedish zinc sulfide ores, from Saxberget (S-ore) and Kristineberg (K-ore), respectively, were compared for bacterial leachability with respect to grain size, and additions of ammonia, iron and phosphate. 87 days of column leaching resulted in 2.4–3.2 g Zn/I in solution and 1.5–1.9 g Cu/I from the K-ore and 1.2–5.3 g Zn/l and 0–0.3 g Cu/l from the S-ore. The highest values were achieved for grain sizes between 16 and 64 mm. Ammonium showed a stimulating effect on bacterial leaching, increasing leached Zn in the K-ore from 27% to 35% and from 7% up to 70% Zn in the S-ore after 53 days of batch leaching. Phosphate additions showed negative effects. Iron additions had a positive effect for the K-ore, increasing the leaching from 48% to 78% Zn at an addition of 6 mg Fe²⁺.     

Microbial ore leaching in developing countries

Microbial leaching processes are being considered as an economical and technically viable alternative for processing low-grade ores and wastes in developing countries. The research and development programs in developing countries aim to design appropriate technologies for the large scale exploitation of local mines. In most cases mining companies, universities, research institutes and governmental and international agencies are all involved, demonstrating a widespread confidence in the application of this technology.     

Microbial asymmetric oxygenation of an organometallic sulfide

Summary Penicillium frequentans IFO 5692 oxidized enantioselectively (methylthiomethyl)ferrocene (1) to (R)-(–)-(methylsulfinylmethyl)ferrocene (2) (98 %e.e.) andCorynebacterium equi IFO 3730 to (S)-(+)-2 (69 %e.e.).     

Thermophilic microbial leaching of heavy metals from municipal sludge using indigenous sulphur-oxidizing microbiota

 It was demonstrated in shake-flask experiments that the sulphur-oxidizing microbiota of municipal sludges can be used at 53°C for heavy-metal leaching. Five sludges were tested and the average final pH, oxidation/reduction potential and SO^2- ₄ concentration after 30 days were 2.8, 237 mV and 5668 mg/l respectively. Ferric chloride was added to enhance the redox potential and to lower pH, which resulted in average values of 409 mV and 1.86 respectively. The average solubilisation of Cd, Cu, Cr, Mn, Ni, Pb, Zn, K and P after ferric chloride addition was 35.6±20.6%, 65.9±15.1%, 28.5±13.5%, 74.0±10.0%, 60.3± 13.1%, 33.7±27.6%, 83.9±6.2%, 39.0±16.6 and 18.2±15.8% respectively. The present process enhanced the sludge dewaterability compared to the conventional thermophilic digestion. During the leaching batch process, the volatile and volatile suspended solids were degraded to the same level as observed when the conventional thermophilic digestion was used as control. Received: 7 June 1995/Received revision: 8 September 1995/Accepted: 29 September 1995     

Microbial reduction of metals and radionuclides

The microbial reduction of metals has attracted recent interest as these transformations can play crucial roles in the cycling of both inorganic and organic species in a range of environments and, if harnessed, may offer the basis for a wide range of innovative biotechnological processes. Under certain conditions, however, microbial metal reduction can also mobilise toxic metals with potentially calamitous effects on human health. This review focuses on recent research on the reduction of a wide range of metals including Fe(III), Mn(IV) and other more toxic metals such as Cr(VI), Hg(II), Co(III), Pd(II), Au(III), Ag(I), Mo(VI) and V(V). The reduction of metalloids including As(V) and Se(VI) and radionuclides including U(VI), Np(V) and Tc(VII) is also reviewed. Rapid advances over the last decade have resulted in a detailed understanding of some of these transformations at a molecular level. Where known, the mechanisms of metal reduction are discussed, alongside the environmental impact of such transformations and possible biotechnological applications that could utilise these activities.     

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.