Extraction of nickel from lateritic ores at atmospheric pressure with agitation leaching

Nontronitic and limonitic type laterites from “Gördes” nickel deposit located in Western Turkey were subjected to sulfuric acid leaching at atmospheric pressure. Experiments were conducted in order to determine the optimum conditions for agitation leaching by studying various parameters, including time, acid concentration, leaching temperature and particle size. Agitation leach experiments showed that nickel and cobalt could be extracted from both ores. Nickel and cobalt extractions were 96.0% and 63.4% for nontronite; 93.1% and 75.0% for limonite after 24 h of leaching at 95 °C, respectively. Overall acid consumptions of ores under the optimum conditions were 669 kg H2SO4/ton dry ore for nontronite and 714 kg H2SO4/ton dry ore for limonite.Multi-step leaching experiments which included initial limonite leaching with or without filtration followed by nontronite leaching in pregnant solution or pulp were conducted in order to reduce the residual sulfuric acid concentration of the final pregnant leach solution. Experiments showed that nontronite could be used in neutralization of pregnant leach solution of limonite in which residual acid concentration was reduced from 97 g/L to 27 g/L after nontronite addition in multi-step leaching. During neutralization, nickel and cobalt extractions from nontronite fraction were in the range of 75–88% and 15–39% depending on the amount of nontronite addition, respectively. In practice, nontronite addition in the second stage of leaching would be controlled to optimize operational economics.