Because of the depletion of high grade mineral resources with simple mineralogical composition, and the increasing demand for strategic base metals such as Cu, Ni and Co, the production of these metals from complex and low grade ores and mine tailings is increasingly risen. Hydrometallurgical processes including leaching, purification and precipitation have a high potential for the treatment of these resources . In addition to economic benefits, the extraction of metals from tailings reduces the environmental issues. The ionic precipitation method is one of the important and applicable methods in concentration and purification of complex solutions. Among various metal precipitation techniques sulfide and hydroxide precipitation are one of the most intrestiong methods to remove impurities. The main purpose of this study is the cumulative recovery of Cu, Ni and Co from sulfate-based dilute solutions similar to bioleaching conditions using ionic precipitation. In this research, sulfidic and hydroxidic precipitations were used to concentrate the solutions. In the first phase, the effect of three factors, pH, temperature and molar ratio of sulfide to metals using the central composite design to recovery of Cu, Ni and Co from solutions containing Fe, Mg and Ca was studied. To determine the optimal conditions for recovery of mentioned metals, 17 tests were performed. Analysis of variance (ANOVA) with the high level of confidence (95%) was used for the analysis of responses obtained for each metal in order to obtain the best model for each metal.. The parameters of pH, sulfide to metals molar ratio and interaction of these factors as well as interaction of increased values of pH with sulfide to metals molar ratio was significant in Cu recovery. Statistical optimization of results for Cu showed that maximum recovery of Cu is obtained when pH and sulfide to metal molar ratio is 8 and 0.97, respectively. For recovery of Ni and Co, however, just the effect of pH and interaction of increased values of pH and temperature were significant. Also, statistical optimization suggests maximum recovery of 82.4% at pH 8 and 60? for Ni and 73.7% at pH 8 and 30? for Co. In the case of simultaneous precipitation of Ni and Co from low grade solutions, due to relatively high concentration of Ni as well as simply operating conditions, hydroxide precipitation were used to recovery of Ni and Co. These solutions were obtained from leaching of a lateritic low grade ore which Ni, Co and Mg composition in this solutions were 2.9, 0.12 and 26 g/L, respectively. For selective recovery of Ni and Co, the Fe and Al content of leach liquor was precipitated at pH 3.5, 90? and 2 h initially. Thereafter, the Ni and Co contents of solution obtained from Fe and Al precipitation step was precipitated at pH 7-7.5, 50? and 1.5 h. Results of the first hydroxide precipitation stage indicate that the removal of Fe and Al was selective so that just 6.4% Ni and 2.6% Co were removed in this step. Analysis of precipitate produced from second hydroxide precipitation stage revealed presence of 36.77% Ni and 2.63% Co in it. Keywords: Low grade ores, sulfide precipitation, hydroxide precipitation, central composite design
