Abstract
In this work the leaching of black shale ore and froth flotation concentrates produced from the black shale was studied. The complex black shale contained various sulphide minerals (alabandite, sphalerite, pyrrhotite, pentlandite, violarite, chalcopyrite, pyrite). Concentrations of base metals in the ore were Fe 13.2%, Mn 0.97%, Ni 0.3%, Zn 0.57%, Cu 0.23% and Co 0.03%. The base metal content was two to three times higher in the flotation concentrate than in the ore. Ore and concentrate were leached in shake flasks and stirred tank reactors at pulp density of 10 to 20%, pH 1.2 to 2.0 and 60 to 77°C. A thermophilic enrichment culture related to Sulfolobus metallicus was applied. The pulp was aerated with ambient air and dinitrogen gas was used in a control test. Experimental duration was from 12 to 49 days. Leaching of Mn, Fe, Zn, Ni, Cu, and Co was up to 96, 52, 99, 99, 97 and 76%, respectively. Mn and Zn were rapidly leached within the first 2 to 3 days. In test with the ore, metal recovery was negatively affected by precipitate formation towards the end of leaching period. The H2SO4 consumption was in the range of 177 to 346 g/kg ore and 11 to 122 g NaOH/kg ore was consumed respectively. In bioleaching tests with flotation concentrates the H2SO4 consumption was from 205 to 415 g/kg concentrate and 73 to 183 g NaOH/kg concentrate was consumed, respectively. The final redox potential varied between 423 and 710 mV vs. Ag/AgCl. In experiments with fine ground ore, -50 8m, the ferric iron was at best 64% of dissolved total iron. Compared with coarser material (250-355, 710-1000 8m) leaching proceeded best with fine ground ore -50 8m). In tests with coarse ore (710-1000 8m). dissolved ferric iron was up to 97% of the total dissolved iron. Mechanical stirring and fine particles caused increase of dead cell numbers during leaching. The study demonstrates that the thermophilic enrichment culture can leach complex black shale ore at high pulp density and temperature.
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