Extraction of Copper and Nickel from Low-Grade Nickel Sulfide Ore by Low-Temperature Roasting, Selective Decomposition and Water-Leaching Process

Low-temperature roasting, selective decomposition and water-leaching were used to extract nickel and copper from low-grade nickel sulfide ore with highly alkaline gangue. The effects of variable factors, such as the dosage of roasting additives, the ore particle size, roasting time and roasting temperature, selective decomposition temperature and leaching temperature on the conversion of metals were investigated. The roasting process contained liquid–solid and gas–solid reactions, which were controlled by internal diffusion. X-ray diffraction analysis of the roasting clinkers presented that the metal sulfides were first converted into intermediate products of metallic ammonium sulfate salts or metal sulfate by reacting with ammonium sulfate, and finally formed stable metal-sodium double salts by the action of sodium sulfate. Proportions of 99.13% nickel and 96.74% copper can be effectively extracted, while 95.95% iron was removed by selectively decomposing iron-containing sulfates to form ferric oxide, or separating as natrojarosite in a water-leaching process.