Vol. 11 No. 4 J. CENT. SOUTH UNIV. TECHNOL. Dec. 2004 Article ID: 1005 - 9784(2004)04 - 0375 - 05 Bacterial oxidation activity in heap leaching ® LIU Jian-she(~pt~J.~), XIA Hai-bo(~), WANG Zhao-hui(2E~,,~.),HU Yue-hua(iN~-g4~) (School of Resources Processing and Bioengineering, Central South University, Changsha 410083, China) Abstract. Bioleaching of sulfide minerals by bacteria, mainly Thiobacillus ferrooxidans ( T. f. ) and Thiobacillus thiooxidans, plays an important role in hydrometallurgy because of its economic and environmental attractions. The surveys of production process and the bacterial oxidation activity in the heap bioleaching were investigated. The re- suits show that pH value is high, bacteria biomass and ferric concentration are low, generation time (above 7.13 h) is long in leachate, and less bacteria are adsorbed on the ores. The bacteria in the teachate exposing on the surface and connecting with mineral, have much faster oxidation rate of Fe( 1] ) and shorter generation time, compared with those which are in the reservoir for a long time. There is diversity for oxidation activity of Fe( I1 ), while there is no diversity for oxidation of sulfur. So it is advisable to add sulfuric acid to degrade pH value to 2.0, add nutrients and shorten recycling time of leachate, so as to enhance bacteria concentration of leaehate and the leaching efficiency. Key words: heap bioleaching; oxidation activity; bacteria CLC number: TF18 Document code: A 1 INTRODUCTION In Dexing Copper Mine, Jiangxi Province, China, the reserves of crude ore with grade of 0.1% - 0.25% copper, have reached 320 Mt, and the total metal capacity of copper amounts to 560 kt c17. To reclaim them economically and effective- ly, a heap bioleaching plant, which has a design capacity of 2 000 t of cathode copper per year, was set up and put into service [2n. It is indicated that this technology can recover copper from ore eco- nomically and little pollution to the environment. The yield of heap bioleaching plant increased year by year and was up to about 1 200 t cathode copper in 2002. At the same time, the height of heap field rose from 160 m to 240 m. However, the process of bioleaching is affected by a variety of factors, such as temperature, pH value, oxygen, carbon dioxide, nutriments and so on. Once some factor affects the growth of bacteria, the bioleaching process will be deteriorated. The heap bioleaching recovery decreased distinctly, and the copper ion concentration dropped between June and July in 2003. Therefore, it was very important to investi- gate the bacterial oxidation activity in the heap field at this period, so as to enhance the leaching efficiency. 2 EXPERIMENTAL 2.1 Material Samples and bacteria: Leachate samples and ore samples were obtained from the heap bioleach- ing plant in Dexing Copper Mine. The bacteria for activity assay were obtained from leachate through enrichment culture. Culture medium: The culture was maintained in 4. 5 K medium whose component differs from 9 K culture medium only in Fe 2+ concentration, namely, the former is half as much as the latter. Its composition is as follows: 3.0 g/L (NH4)zSO4, 1. 0 g/L KC1, 0.5g/L K2HPO4, 0.5g/L MgSO4 • 7HzO, 0. 01 g/L Ca(NOa)z, 22.5 g/L FeSO4 • 7H20, distilled water and HeSO4 (modulating pH value to 2.0). 2.2 Analysis methods The pH value and Zeta potential of leachate were measured by means of pHS-25 acidity meter, and elemental concentrations of Fe 3+ and Cu 2+ in the leachate were determined with a Hitachi Z-800 atom absorbing spectrophotometer. The population of bacteria in leachate was counted by phase contrast microscope using an oil immersion lens under Galen Ill optics micro- scope Ea~. For the bacteria adsorbed on ore, the measure of population is similar, but before coun- ted, the bacteria should be washed down by dis- tilled water and laid calmly for 3 h. The amount of ferrous iron was determined by a volumetric titration method with potassium di- chromate. (9 Foundation item: Project (50321402) supported by China Science Fund for Distinguished Grop; project (50374075) supported by the National Natural Science Foundation of China Received date: 2004 - 02 - 16 ; Accepted date: 2004 - 04 - 07 Correspondence: LIU Jian-she, Professor; Tel, +86 731-8877216 ; E mail=ljscsu@263, ne~