THE SOCIEDAD MINERA PUDAHUEL BACTERIAL THIN-LAYER LEACHING PROCESS ATLO AGUIRRE

The thin-layer leaching process originally conceived and developed for leaching oxide ores has been successfully adapted to bacterial leachi ng of mixed and secondary sulphide ores. The process is currently bein g applied at the Sociedad Minera Pudahuel Lo Aguirre Plant. About 3000 ton of ore per day are being processed to produce 14000 ton of high-g rade copper cathodes per year, in a closed circuit integrated with SX- EW. Changes in the soluble copper grade of the ore from about 1.8% to 0.6% have occurred during the last years, which have been compensated by an equivalent increase in the insoluble copper grade. In addition, ore from satellite ore bodies has resulted in acid consumption variati ons ranging from 60 to 120 kg H2SO4 per ton of ore. The main sulphide mineralogical species are chalcocite and bornite, with small amounts o f chalcopyrite and covellite. An intensive research program in columns and large-scale heaps has been carried out to define the operating co nditions which assure adequate bacterial growth and bacterial activity towards the sulphides. Agglomerated ores with 1.7-2.5% CUT and 0.3-0. 6% Cus, with the insoluble copper mainly present as chalcocite-bornite , were leached at a flow rate of 0.2 1 min-1 m-2 with a SX-Raffinate s olution containing (in g l-1) 5-10 H2SO4, 2-4 Fe(T), 1-3 Fe+3, 0.5 Cu, as well as impurities resulting from a closed circuit operation. Copp er recoveries of 75-85% CUT were obtained after 180-250 days of total leaching time, depending on the copper grade, the mineralogical compos ition, and the acid consumption of the ore. Important bacterial activi ty was detected, About 10(3)-10(5) bacteria ml-1 were measured in effl uent solutions. Iron oxidation rates of 7-100 mug Fe2+ h-1 g-1, measur ed from respirometric tests on agglomerated ore, suggest that an adsor bed biomass of about 10(7)-10(8) bacteria g-1 must also be present. Fu rther applications of the bacterial thin-layer leaching process to Cer ro Colorado and Quebrada Blanca ores in North Chile are being studied.