CONTROLLED MICROBIOLOGICAL IN-SITU SLOPE LEACHING OF A SULPHIDIC ORE

A mixed culture of Thiobacillus ferrooxidans, T. thiooxidans, and Lept ospirillum ferrooxidans was used for inoculation of a sulphidic ore bo dy for a bacterial in-situ stope-leaching experiment in the Ilba mine in Romania. The ore body was inoculated with 10(7) cells/g ore. Measur ements at six main sites of the ore body indicated that microbial leac hing was started by the inoculation. After about 8 weeks, sufficient m icrobial activity was measurable only in the upper third of the ore bo dy. Due to the angle of incidence of the ore (75 degrees), the leach l iquor percolated only through the upper part leaving two-thirds humidi fied unsatisfactorily. The leach results, metal mobilization, indicate d that by inoculation with the indigenous microorganisms efficient lea ching was achieved. Metal output after 18 months of operation amounted to 10% of Cu and 78% of Zn. In the winter months energy for aeration and circulation was not available and this was reflected by reduced va lues for microbial activity, temperature, and daily metal output. The biological metal mobilisation after 18 months of operation was as acti ve as at the beginning. Cu was mobilised predominantly by microbial le aching whereas Zn was leached mainly by chemical reactions. Both mecha nisms contributed equally to iron output.