Arpad E. Torma

The role of Thiobacillus ferrooxidans in hydrometallurgical processes

The present article illustrates the increased interest which is manifested in the microorganisms, Thiobacillus ferrooxidans, involved in the biohydrometallurgical extraction processes. The wide varieties of problems currently studied are very important in order to gain a better understanding about the factors which are governing the growth of microorganisms, and as a consequence, the metal dissolution phenomena. In several mining sites, the microbiological leaching techniques are currently practiced at industrial-scale, especially for recovery of copper and uranium from low-grade materials. However, an accurate assessment of further potential possibilities for the application of microorganisms in leaching metal sulfides requires a more fundamental knowledge about the interactions of the physical and chemical factors with the growth of T. ferrooxidans in pure and mixed cultures including heterotrophic and thermophilic cohabitants. Altogether, the future industrial exploitation of these microbiological leaching techniques are very attractive in many countries of the world.

Impact of biotechnology on metal extractions

The present article provides information on the application of biotechnology in the valorization of mineral resources. Biohydrometallurgy is relatively a recent development but already employed in the copper, uranium and in a limited extent in precious metal processing industries. The basic principles of bioleaching and the mechanisms of bacterial action are discussed and specific examples are given for the biohydrometallurgy of the elements. An extended treatment of microbial activity is given with regard to gold and silver recoveries from ores and leach solutions, as well as for the desulfurization of coal, to represent tendencies of most active research areas. The article discusses also the biosorption processes and gives a short review of efforts devoted to biogenetic engineering of leaching organisms.

Microstructural and mechanical property evaluation of black-chrome coated solar collectors — II

Abstract Concentrating solar collector assemblies of the substrate steel surface electroplated with a nickel coating followed by a thin black chrome solar absorber overlayer have been studied for the role and optimization of plating parameters such as; plating time, current density, plating bath temperature, chromic acid concentration, role of chromonyx addition agent, anode-to-cathode ratio of the plating arrangement, current efficiency of electroplating, and role of substrate finish; and over-growths were evaluated in each case for solar absorptance values. Within the range studied (3–36 min), 18 min of plating time is seen to give the highest absorptance value (96%). Current density variation, within the limits of this study (21.6–54 A/dm2) shows that an optimum absorptance (93.2%) is attained with a current density of 43.2 A/dm2. Variations in bath temperature of plating (0–30°C) yields a maximum in absorptance (93.2%) in coatings done at 10°C. The optimum value in solar absorptance (97.9%) is obtained at 375.95 g chromic acid/l (50 oz/gal) addition to the plating bath, within the range, 225.57–413.54 g/l (30–55 oz/gal), studied. Chromonyx addition agent, suggested for the plating bath, is seen to optimize at 30% of the bath volume in the range (21–33% of the volume) studied. Anode-to-cathode proportions of the plating arrangement are seen to yield a maximum absorptance (98.4%) at a ratio of 2 within the ratios evaluated (1–6 anode/cathode ratios). Current efficiencies of plating show a much higher value (92%) for nickel electroplating than for black-chrome coating (0.20%) for platings done at 10°C, 43.2 A/dm2, and an electrode spacing of 1.27 cm. Finally, the role of substrate-surface finish, evaluated through coating black-chrome onto steel and nickel or nickel sheets show absorptance values to be quite similar in both cases, (93.0%) for black-chrome on steel plus nickel arrangement and (93.1%) for black chrome plated onto nickel sheets, at 10°C for a period of 3 min, and were extremely close in value for all bath temperatures (0–30°C) evaluated. Scanning electron microscopy and replication electron transmission microscopy done on plated and plated and ion-milled surfaces of solar collector growths did not yield conclusive data, but high magnification studies of the surfaces with the scanning electron microscope indicate an alteration of growth characteristics with variations in deposition temperatures. Finally, the strength of adhesion of the plated layers onto substrate surfaces was measured through tensile testing at ambient temperature. Values attained for adhesion strength (in excess of 100 kg/cm2 in each case) indicate that the electroplated nickel and black-chrome layers are well attached to their respective substrates and possible failure of these coatings is unlikely to be due to insufficient adhesion.

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.

Extraction Processes for Gallium and Germanium

The present article provides information on uses, mineral resources and production methods of gallium and germanium. Both of these metals are used in advanced technology. Gallium is mainly used in the production of high-speed computer chips (integrated circuits) and optoelectronic devices. Germanium is employed as semiconductor in electronics and infrared optic industries. They occur in nature in widely dispersed forms and are associated principally with aluminum and zinc minerals. Gallium is present in bauxite in isomorphous substitution with aluminum, and germanium is contained in significant amounts in sphalerite. In southwestern Utah, at the Apex Mine, gallium and germanium were found to be concentrated in jarosite and geothite, respectively. Gallium is conventionally obtained as a byproduct of aluminum, and germanium as byproduct of zinc processing. An exception to this rule is the Apex Mine ore which has served as the only primary source in the world for direct production of gallium and germanium. I...

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.

The microbiological extraction of less common metals

A developing technology, the microbiological leaching of the less-common and rare metals has yet to reach commercial maturity. Still, although the data are preliminary in nature, the ultimate application of biotechnological principles may provide a potential solution for the valorization of many low-grade mineral resources. The development of these processes for large-scale commercial applications will create new opportunities and challenges for the research community and minerals processing industry.

Desulfurization of Coal by Thiobacillus Ferrooxidans

Literature on the possibility of desulfurizing coal by microbiological leaching is limited. The earliest report was that of Zarubina et al. (1959) who indicated that 23 to 27% of sulfur was removed from their coal samples in 30 days. Other investigators (Silverman et al. 1961, 1963; Lorenz and Tarpley 1963; Clark 1966) commented on the beneficial effect of decreasing the particle size of coal samples and of adding small amounts of ferric sulfate to the leach solution. Recently, Dugan and Apel (1978) achieved an almost complete removal of pyrite from coal by using a mixed culture of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Capes et al . (1973) reported that the surface properties of pyrite and coal were changed during the microbiological leaching to such an extent that the separation of pyrite from coal by the conventional flotation technique was considerably increased.

Reduction of stibnite by hydrogen

Abstract The reduction of stibnite by hydrogen in the absence and in the presence of sulfur acceptors has been investigated at atmospheric pressure and at temperatures of 200 – 600 °C. The activation energy of these processes has been found to be 17.4 kcal mol −1 (−7.2 × 10 4 J), 20.4 kcal mol −1 (−8.5 × 10 4 J), and 27.7 kcal mol −1 (−11.6 × 10 4 J), in the absence of sulfur acceptors, with calcium oxide and with magnesium oxide, respectively. The calcium and magnesium sulfides can be removed from the reaction residues by leaching with dilute hydrochloric acid solution. The purity of the antimony metal produced in these processes varied between 98.0 and 99.5%. The hydrogen sulfide liberated can be converted into elemental sulfur or sulfuric acid; consequently, this method will not pollute the environment. On the basis of the experimental data of this investigation a flow sheet has been developed for the production of metallic antimony from high grade sulfide-bearing concentrates.

Microbiological leaching of a chalcopyrite concentrate and the influence of hydrostatic pressure on the activity of Thiobacillus ferrooxidans

SummaryThe effect of hydrostatic pressure on the activity of Thiobacillus ferrooxidans grown on chalcopyrite concentrate has been investigated. It was found that bacterial activity, measured by conventional respirometry, was little affected by subjecting these microorganisms to a pressure of 100 lbs/in2 (690 kPa). The total cooper concentration was as high as 18 g/l in 28 days of leaching at atmospheric pressure.