Activation of bacteria in agglomerated ores by changing the composition of the leaching solution

Abstract

This work presents preliminary results of a study to determine the technical feasibility of heap bioleaching of copper sulfides in a mixed ore that had previously undergone a chemical leach to recover the copper from the copper oxides in the ore. The recovery of the copper sulfides is economically and environmentally important. The first step in this study was to determine the presence of bacteria in samples of both the agglomerated ores taken from the heaps and the samples from the irrigation solution used in the leaching process. No bacteria were detected in either sample, probably because of the very low pH, the high concentration of sulfate (200 g/l), and the presence of other ions in the irrigation solution. On the other hand, the cultivation of bacteria from recently crushed, fresh mixed ore (oxide- sulfide), and from cured, agglomerated ore, showed the presence of a small bacterial population, with ferrous iron-oxidizing activity. This indicates that the ore initially contained viable bacteria that were inhibited in the heap. Based on these results, a glass laboratory column containing 700 g of agglomerated ore from a partially, chemically leached heap was set up. The ore in the column was irrigated in a closed circuit with nutrient medium containing 2 g of ferrous sulfate per liter. Bacteria were detected, and the redox potential in the leaching solution began to increase on day 20 of the bioleaching experiment, indicating the beginning of the bioleaching stage of the sulfide mineral. The data indicate that the bacteria initially present on the ore can be recovered after acid curing, and also after prolonged contact with a solution containing a high concentration of sulfate. These results indicate that it is technically possible to induce a change from a chemical leaching process with high ionic strength to a bacterial leaching process, by dilution of the irrigation solution.