Nickel and Cobalt Extraction from Greek Laterites Using Nitrate Solutions

The extraction of nickel and cobalt from a limonitic laterite sample, derived from a mine area in the Greek island of Euboea, was studied via an acid agitation leach process with nitric acid as the leaching agent, to determine the optimal conditions at which the highest possible extractions of nickel and cobalt were obtained in the pregnant solution. Two series of experiments were carried out. In the first series, the extractability of metals was studied by varying the leaching temperature at values of 60 °C, 80 °C and 100 °C. For the second series of tests, the metals’ extraction at different values of initial nitric acid concentrations of 1M, 2M and 4M was examined. Based on the results, the effect of temperature is characterized as particularly significant, as with its increase, the final recoveries of nickel and cobalt were particularly high. The variation in acid concentration had a significant effect but not like that of temperature. For extraction conditions of an S/L ratio of 20%, a temperature of 100 °C and a 2M HNO3 concentration, the highest recoveries of nickel and cobalt were obtained, namely 94.4% and 83.6%, respectively. Iron in all tests did not exceed dissolutions of more than 7.2% in the pregnant solution.