Use of biotechnology in mining and metallurgy.

Biotechnology continued to gain importance in the mineral industry during the past four years. This upsurge of interest is especially expressed in the areas of biodesulfurization of coal, recovery of precious metals from pyrite- and arsenopyrite- containing minerals, biosorption processes and biogenetic engineering.

Biotechnology applied to mining of metals.

The present review describes the advances achieved during the last two years in the application of biotechnological principles in the extraction of metals from ores and minerals. Despite the fact that this branch of science is very young and many details are yet to be understood, the microbes are applied at commercial levels especially for the extraction of copper and uranium from low-grade ores. The technique is far from being developed to its full potential and it is generally recognized to be a technology of the future. The studies involved are complex and multidisciplinary in nature.

Oxidation of gallium sulfides by Thiobacillus ferrooxidans.

The bacterial oxidation of naturally occurring gallium-bearing chalcopyrite concentrate and a pure synthetic gallium (III) sulfide has been investigated at pH 1.8 and 35 degree C, using an active culture of Thiobacillus ferrooxidans. This oxidation process may proceed by direct or by indirect bacterial action. The highest dissolved gallium and copper concentrations were about 2.2 and 40.2 g/l, respectively. The order of the specific rate of oxygen uptake by T. ferrooxidans in approximately CuFES2 greater than or equal to gallium-bearing CuFeS2 greater than FeS2 greater than Cu2S greater than Cu2S greater than Ga2S3.

Ferrous iron oxidation and uranium extraction by Thiobacillus ferrooxidans.

The microbiological oxidation of ferrous iron in batch and continuous systems has been investigated in relation to uranium extraction from a low-grade ore by Thiobacillus ferrooxidans. The influence of the parameters, agitation, and aeration on oxygen saturation concentration, rate of oxygen mass transfer, and rate of ferrous iron oxidation was demonstrated. The kinetic values, Vmax and K were determined using an adapted Monod equation for different dilution rates and initial concentrations of ferrous iron. The power requirements for initial leaching conditions were also calculated. Uranium extraction as high as 68% has been realized during nine days of treatment. Regrinding the leach residue and its subsequent leaching yielded 87% uranium solubilization.

Oxidation of stibnite by Thiobacillus ferrooxidans.

Optimum pH, temperature and pulp density for microbiological leaching of museum-grade stibnite mineral has been investigated using a stibnite-adapted strain of Thiobacillus ferrooxidans. Optimum conditions were found to be pH 1.75, 35 C and 12g solid substrate per 100 ml of basal salts medium as the initial dose. The energy of activation was determined to be 16.8 kcal per mole, and the temperature coefficient 2.2. The highest total dissolved antimony concentration, [Sbt] = [Sb+3] + [sb+5] + I1SbO2+], was about 1400 mg/litre, due to relatively low solubility of (SbO)2SO4 and (SbO2)2SO4.

Influence of Organic Solvents on Chalcopyrite Oxidation Ability of Thiobacillus ferrooxidans.

It has been shown that organic solvents used primarily for the extraction of metals from aqueous leach liquors decrease both the surface tension of the aqueous phase and the chalcopyrite oxidation ability of Thiobacillus ferrooxidans. For the reagents and modifiers investigated, the order of inhibition was found to be LIX 70 < LIX 73 < LIX 71 < LIX 64N < LIX 65N < TBP approximately isodecanol approximately nonylphenol < LIX 63 <<< D(2)EHPA approximately Kelex 100 < Kelex 120 <<< Alamine 336 approximately Alamine 308 approximately Alamine 310 < Alamine 304 < Adogen 381 approximately Aliquat 336 < Adogen 364. To avoid limitation in bacterial activity, organic matter should be removed from the recycling liquor prior to leaching.

Base competition of DNA isolated from Thiobacillus ferrooxidans grown on different substrates.

The present study indicates some anomalies with respect to the DNA base composition of Thiobacillus ferrooxidans when it is cultured on different substrates. The % GC of the DNA of this bacterium has been calculated by three different methods (melting temperature, CsCl density gradient centrifugation and ultra-violet absorbancy ratios) using Escherichia coli and Rhodospirillum rubrum as references. The main values for T. ferrooxidans grown on ferrous iron, chalcopyrite and lead sulfide concentrates were calculated to be 56.0, 60.1 and 54.4% GC respectively. Although these large differences are not completely understood, an attempt has been made to explain this phenomenon.

Microbiological oxidation of synthetic chalcocite and covellite by Thiobacillus ferrooxidans.

The microbiological oxidation of synthetic chalcocite and covellite has been investigated using an adapted strain of Thiobacillus ferrooxidans. Biodegradation of chalcocite was found to be 90 to 100% and that of covellite 45 to 60%. Optimum conditions for the oxidation of chalcocite were: pH, 1.7 to 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.01 M. For covellite, the optimum conditions were: pH 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.02 M. The energies of activation were determined to be 16.3 kcal (ca. 6.8 X 10(4) J) per mol and 11.7 kcal (ca. 4.8 X 10(4) J) per mol for chalcocite and covellite, respectively.

[Ferrous ion oxidation and uranium solubilization from a lowgrade ore by "Thiobacillus ferrooxidans" (author's transl)]. / Oxydation de l'ion ferreux et mise en solution de l'uranium d'un mineral par Thiobacillus ferrooxidans

The microbiological oxidation of ferrous ion and the extraction of uranium from a low-grade ore has been studied using an adapted strain of Thiobacillus ferrooxidans. The effect of temperature, pH, volumetric oxygen transfer coefficient, K1a, and aeration number, Ia, on the activity of the microorganism has been determined. The activation energy for ferrous iron oxidation was calculated to be - 13.9 +/- 0.1 kcal/mole and inactivation (thermal death of bacteria) 53.3 +/- 0.2 kcal/mole. Temperature coefficient, Q10, was estimated to be 1.8. Uranium extraction varied between 80 and 100%.