The extraction of valuable metals and phase transformation and formation mechanism in roasting-water leaching process of laterite with ammonium sulfate

Ammonium sulfate roasting-water leaching technology is a potential cleaner production process with low energy consumption, minor equipment corrosion and high selectivity contrasted with the traditional metallurgy process. Thermodynamic analysis showed that the main mineral of serpentine and magnesium iron ore in raw ore could react with ammonium sulfate, and the analysis through XRD and EDS also proved that most mineral phases were (NH4)3Fe(SO4)3, (NH4)2Mg2(SO4)3, Fe2O3, and SiO2 as roasting products. With the decomposition of original mineral in roasting process, valuable metals of nickel, cobalt and manganese disseminated in other host minerals could be released to react with ammonium sulfate and produce metal sulfate which could be leached into the water. However, the iron mainly existed in iron oxide was water-insoluble and remained in residues. The conditions of the ammonium sulfate roasting-water leaching process, such as ammonium sulfate dosage, roasting temperature, roasting time, leaching temperature, and leaching time have been investigated here. The roasting temperature (only 400 °C) is lower than other pyrometallurgical process, which leads to less energy consumption and equipment corrosion. The leaching of Ni, Co, Mn and Fe could be 90.8%, 85.4%, 86.7% and 9.98% at the optimal condition, and the selectivity extraction can be achieved.