Cobalt and Nickel Recoveries from Laterite Tailings by Organic and Inorganic Bioacids

Cuban serpentines are known as one of the richest deposits of Ni and Co in the world. These ores are usually treated by pyrometallurgy or by hydrometallurgy. These processes generate huge volumes of mining residues, which still contains high amounts of Ni (0.25 %) and Co (0.09 %). Since metals are partially oxidized, the chances to use sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) which are able to generate sulfuric acid to leach the residues from Caron process have been evaluated. Thus, in this work, inorganic and organic acids produced in cultures with A. niger or A. thiooxidans respectively were used to study the extraction of Co and Ni from laterite tailings. The results were compared with those obtained in leaching experiments with direct inoculation of those microorganisms. 7 and 16 % of Ni and Co were leached after 3 days using A. niger and sucrose as carbon source. In stage batch one using A. thiooxidans and elemental sulfur as energy source higher percentages of metal solubilization were reached after 15 days. In stage batch two experiments were carried out using inorganic and/or organic bioacids. Metal recoveries in stage batch two using sulfuric bioacid were higher (79 % Ni and 58 % Co) than those obtained with citric bioacid (2.4 % Ni, and 38% Co). However metal recoveries using chemical leaching with citric acid were much higher (80.4 % Ni and 50 % Co using 0.5 M citric acid). Since the mineralogy composition of raw material is a parameter very important to select the leaching agent of oxide ore, the leaching of residue nickel-ferrous of the Caron process with bio-sulfuric acid produced in A. thiooxidans cultures could be an attractive alternative in the development of a sustainable technology in Cuban mining-metallurgy industry.