Effect of Substrates During the Adaptation of Indigenous Bacteria in Bioleaching of Sulphide Ores

(eng) It is well known that thermophile bacteria (40-60°C) are indicated for leaching chalcopyrite. However, it is a long bioleaching process and this kind of bacteria is not available in indigenous areas. On the other hand, mesophilic bacteria (20-40°C) are easily found in many acidic drainage mines, which could be an opportunity to decrease investment costs as well as operation cost during the treatment. However, to achieve that mesophilic bacteria are able to leach chalcopyrite, it is necessary to select the appropriate conditions such as the choice of an adequate substrate, the pulp density, the pH, and oxidation reduction potential. In addition, a decrease in the latency period during bacterial adaptation and bioleaching process is necessary. Accordingly, the objective of this research is to study the bacterial adaptation of stocks in three culture media containing various sources coming from local sites of acidic drainage mines (Kipushi, Kisenda, Kamoto)at Katanga copperbelt (Democratic Republic of Congo, D.R.C) in order to develop bacterial species that are able to leach a sulphide refractory ore such as chalcopyrite. The three media consisted of a media containing gray sulphur, another with yellow sulphur and a third one with pyrite. At the end of several tests, the pyrite media was retained as the best culture medium, with an optimum pulp density of 2 % w/v, since a more rapid oxidation was observed, and the pyrite removed the lag phase. In addition, it had positive influence on the growth of cells, mostly when the pulp density is low, allowing availability of oxygen for bacterial action. Furthermore, a sharp loading of solid or again the coarse particle size during bioleaching process would lead to acid consumption by the gangue, which inhibits the growth of cells by probably damaging the cells.For this reason, bioleaching tests were performed with particle size (-75µm).The operating conditions of pH 1.8, 150 rpm and 30°C with a density of pulp 2 % w/v showed an optimum of 4,45 g/l obtained. Thus, it is demonstrated that the bacteria can be cultivated in a medium having pyrite-like substrate and it is expected that these mesophile species can leach also refractory sulphide ores such as chalcopyrite.