Study On Reductive Roasting And Sulfuric Acid Selective Leaching Of Limonitic Laterite Ore

As the world’s nickel sulfide ore getting depletion now, development and exploit laterite ore are becoming the center for getting nickel resources. The laterite ore mainly includes scapolite and limonite. Limonites are rich in iron, chiefly as goethite (FeOOH), but low in magnesia and silica, suitable to be processed by hydrometallurgical methods which include high-pressure acid leaching and reductive roasting-ammonia leaching. In order to extract the nickel effectively, the reductive roasting of limonitic laterite followed by sulfuric selective leaching was investigated in this paper.The process of high-temperature dehydration of limonitic laterite was studied by TG-DSC analysis and thermostatic TG experiments in this paper. Then, using CO and CO2mixed gas as reducing agent, the process of reductive roasting of dehydrated limonitic laterite pellets was studied. It was found that the reduction degree of calcine was mainly affected by process parameters, such as reducing atmosphere, temperature and time. The phase composition and morphology of the reduction calcine was analyzed by X-ray diffraction and scanning electron microscope (SEM). The experimental results showed that the iron oxide in dehydrated limonitic laterite pellets (Fe2O3) can be reduced to Fe3O4, FeO, and FeO-Fe (small amount) mixture by adjusting the volume ratio of CO and CO2under appropriate calcine temperature.The unreacted shrinking-core model was used for investigating the kinetic processes of reductive roasting in this paper. The reduction rate process of iron oxide is controlled by inner diffusion and the apparent activation energy is15.59kJ/mol, frequency factor is0.18between the temperature810℃and1105℃. Reaction rate constants is inversely proportional to pellets diameter.The leaching process of calcine was studied in this paper. In the leaching system of sulfuric acid and Low-acid-ferrous ion solution, it was found that the leaching efficiency of calcine was mainly affected by process parameters, such as leaching time, pressure of oxygen and concentration of H+. The results showed that in the atmospheric pressure system with oxygen flow, leaching for8h about80.0%of nickel can be extracted from the pre-reduced calcine and Fe2+concentration was about2g/L. In the oxygen pressure system, under0.3MPa leaching for4h by sulfuric acid with A/O ratio0.459, about84.1%of nickel can be extracted and Fe2+concentration was3.59g/L.Leaching residues mainly contained goethite and small quantitive magnetite, It can be concluded selective leaching method was achieved in this paper and extract nickle by the way of the reductive roasting of limonitic laterite followed by sulfuric selective leaching to was carried out.