In previous studies it has been showed that bacterially produced sulphuric acid is a good leaching agent for laterite tailings. In this work we evaluated heavy metals leaching from low grade laterite ore for cobalt and nickel extraction using sulphuric acid produced in situ by Acidithiobacillus thiooxidans under different culture conditions. In studies where that material was initially added to the cultures, considerable percentages of metals were leached (100 % Mn, 70 % Co, 7.5 % Ni, less than 5 % of Cr and Fe) after 18 days of incubation at low pulp densities (1 % and 2.5 %) of overburden. The maximum percentages were reached when cultures pH was approximately or below than 1.5. At higher pulp densities material was added to the cultures after different pre-cultivating times; also higher sulphur amounts were assayed; in such way about 100 % Mn, 60 % Co, 9 % Ni and Fe and 2.5 % Cr were leached. Although toxic metals were not completely leached, sequential extractions results indicate that these metals are not readily available. All studies finally suggest that bioleaching is a suitable technology for recovery of valuable metals as Co and remediation of mining residues by extraction of heavy metals.

Lateritic deposits contain oxide ores and usually consist of three layers, namely the limonitic, the saprolite and the garnieritic layer. Limonite, which comprises the top lateritic layer, is a homogeneous ore consisting mainly of goethite with which nickel is associated. Microbe-mineral interactions are of interest for biogeochemical cycles. Microorganisms which are able to mediate redox transformation of Fe-oxide containing minerals are of particular interest when effective bioremediation strategies for insoluble hydroxide and oxide minerals are designed. Quantitive real-time polymerase chain reaction (qPCR) is a culture independent method which is used for the quantification of environmental microorganisms. The aim of this work was to enumerate the microorganisms in different lateritic deposits at Moa mine (Holguin, Cuba) by qPCR and also to obtain Fe (III)-reducing enrichment cultures. A higher microbial abundance was detected in the sampling sites 5124 and 5125 and a lower one in the site 5121. Both, Archaea and Bacteria occurred in all samples except for site 5121 where Bacteria were not detected by qPCR. The Geobacteraceae which comprise Fe-(III)-reducing bacteria were detected at all five lateritic ore sites. The results indicate that these bacteria play a role fundamental in the formation of sediments with a number of oxidized or partially oxidized iron compounds such as magnetite, hematite, goethite and various Fe (III)-oxyhydroxides.