Leaching bacterial

2 Applications of Iron-Oxidizing Bacteria 5.2.1 Bacterial Leaching 

Copper is easily extracted with 5% sulfuric acid from the ores containing cupric hydroxide, cupric carbonate, and cupric oxide such as azurite, malachite, and teno-rite. However, copper is seldom extracted with sulfuric acid from copper ores containing cupric sulfides the presence of ferric ion is mandatory to extract copper with sulfuric acid from the ores, e.g., chalcopyrite [FeCuS2]. 

When the laboratory processes are applied to a strip copper mine, a long plastic pipe with many small holes is spread over the mine and the solution of ferric sulfate is sprayed on the ores. The solution containing cupric sulfate flows down the mine hill, collects in a pool made of acid-resistant concrete, and crude metal copper is obtained from the solution by substitution with metal iron. Besides copper, molybdenum, bismuth, zinc, etc. are leached from the respective ores using the bacterium. However, at present bacterial leaching is not carried out in Japan. 

At this point the author would like to refer to the collection of uranium using bacteria. In Japan, bacterial leaching of uranium has been tried experimentally 

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Bacterial cellulose Bacterial leaching Bacterial removal Bacteria, luminous Bactericide... 

Bacterial leaching is another example of oxidizing dissolution whereby specific bacteria either directiy attack the sulfide mineral or indirectiy enhance the regeneration of the oxidant. 

The bacterial leaching of uranium minerals is complex. This is because of the fact that uranium minerals are not sulfides and are not, therefore, directly attacked by the bacteria. However, the uranium sources usually have a substantial pyrite content which can be bac-terially oxidized to give an acidic ferric sulfate solution which is an effective leaching medium for uranium minerals. The reactions involved in the system can be shown in a simplified form as ... 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Bacterial leaching, minerals, 36 115-121 laboratory reactors, 36 116-117 monitoring organism growth, 36 117-119 nutrient effects, 36 119 pH control, 36 121 toxicity effects, 36 119 Bacterioferritin, see also Bacfer cluster, 43 362-363... 

Couillard, D. Zhu, S. (1992). Bacterial leaching of heavy metals from sewage sludge for agricultural application. Water, Air, and Soil Pollution, 63, 67-80. 

Dugan, P.R. and Apel, W.A. 1978. f,Microbial Desulfurization of Coal." In Metallurgical Application of Bacterial Leaching and Related Microbial Phenomenon." Editors, L.E. Murr Torma, A.E. Brieley, J.A. Academic Press, N.Y.pp. 223-250. 

Norris, P.R. Kelly D.P. 1978. Toxic Metals in Leaching Systems, pp. 83-209. In L.E. Murr, Torma, A.E. and Brierly J.A., Metallurgical Applications of Bacterial Leaching and Related Phenomena. Academic New York, 1978. 

Bacterial leaching of copper by Thiobacillus ferrooxidans has been practiced for years. Yearly, 250000 tons of copper are recovered by microbial leaching techniques in the USA. This process can be represented by the following simplified equations ... 

Uranium is also leached commercially by the same bacteria. Recently, bacterial leaching of gold in Africa has been patented by Pares and co-workers U3). Also, chemical and microbially assisted leaching has been studied and is applied to remove vanadium from by-products of coke and coke ash refinery 112). 

Schwartz, W. (ed.) Conference Bacterial Leaching 1977 GBF, Braunschweig-Stockheim, Weinheim-New York, Verlag Chemie 1977... 

Mehta, A. P. and L. E. Murr. 1983. Fundamental studies of the contribution of galvanic interaction to acid-bacterial leaching of mixed metal sulfides. Hydrometallurgy 9 235-256. 

BioNIC [Biological NICkel] A biological process for leaching nickel from its ores. It comprises bacterial leaching, solvent extraction, and electrowinning. Developed by BHP Billiton at Yabulu from 1999, but not commercialized by 2004 because no ore body of a suitable concentration and size had been identified. 

Ehrlich, H. L. (1980). Bacterial leaching of manganese ores. In Biogeochemistry of Ancient and Modern Environments, ed. P. A. Trudinger, M. R. Walter B. J. Ralph. Canberra Australian Academy of Science, pp. 609-14. 

Styriakova, I. Styriak, I. (2000). Iron removal from kaolins by bacterial leaching. Ceramics-Silikaty,44, 135 1. 

The only metals presently recovered on a commercial scale from their minerals using bacterial leaching as part of the process are copper (Z2) from mine waste dumps and uranium (M2) from old mine workings and mine waters. 

Sand W., Gehrke T., Jozsa P. G., and Schippers A. (2001) (Bio)chemistry of bacterial leaching-direct vs. indirect bioleaching. Hydrometallurgy 59, 159—175. 

Tributsch H. and Bennett J. C. (1981a) Semiconductor-electrochemical aspects of bacterial leaching II. Survey of rate controlling metal sulfide properties. J. Chem. Technol. 

The metal is extracted from the ore by the solubilizing action of the acid produced during bacterial growth. At the same time, insoluble metal sulfides are oxidized to soluble metal sulfates, either directly by the bacteria or indirectly by the action of the Fe(III) produced by bacterial oxidation of pyrite. Low-grade ores that cannot be economically extracted by conventional processes can be treated by this method, as described in Section IV. This process, which is usually described as bacterial leaching, has been carried out on an enormous scale for the extraction of copper. 

The existence of these chemical pathways for the oxidation of minerals during bacterial leaching does not exclude a direct role for bacteria. Both pathways may occur simultaneously, the relative importance of each depending upon the rate constants for the reactions and the concentration of Fe(III) present in solution. Experiments carried out on synthetic iron-free cobalt and nickel sulfides, using carefully washed cells of T. ferrooxidans to ensure the absence of Fe(III), showed consumption of oxygen and the solubilization of the metal as sulfate. Solubilization rates were appreciably increased on the addition of Fe(III). These results present support for the presence of both direct and indirect pathways (116). Recently, attempts have been made to compare the rates of these pathways for the oxidation of pyrite by T. ferrooxidans (74). 

There has also been some interest in heap leaching of low-quality refractory ores. This is a two-stage process, as bacterial leaching of the ore must be followed by leaching with alkaline cyanide to solubilize the gold. The heap must also be washed and neutralized before the cyanide leach can be applied (103). 

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