Sulphuric Acid Pressure Leaching Of Laterite And Recovery Of Nickel From Leaching Solution Using Direct Solvent Extraction

Abstract:With the depletion of nickel sulfide resources, the exploration has been focused on nickel laterite ones which account for70%of the total nickel resources. Hydrometallurgical process was the predominant technology for low-grade laterites processing. However, current hydrometallurgical process needs to be improved for its plurality of steps, high production costs and low yields. Pressure acid leaching of nickel laterites has the advantages of high nickel and cobalt recoveries and effective separation of iron and alumium from nickel and cobalt. A novel extractant consists of the sulfonic acid type extractant HA and the lipid neutral type one B could be employed to selectively extract nickel from low concentration of nickel solution, and effectively purify nickel and cobalt by separating them from the main impurities such as Fe, Cr, Mn, Mg, Ca, Al, Si. In order to extract Ni from nickel laterites with low costs and low pollution, the sulfuric acid high pressure leaching of laterite and recovery of nickel from leaching solution using direct solvent extraction were tested basing on the current research status on hydrometallurgy processes for laterite.The comparison of the sulphuric acid leaching for laterite with and without pressure was carried out. The effect of experimental parameters such as acid-ore ratio, temperature, reaction time, liquid-solid ratio and particle size was investigated, and the results indicated that the leaching with high pressure presents high leaching rate and better selectivity when these factors keeps the same.In high pressure leaching process, results also showed that acid/ore ratio and temperature were the leading factors affecting the nickel extraction, as well as the iron and aluminium contents in the leaching solution. With the increasing of the leaching temperature, nickel extraction increased while the content of iron in the leaching solution decreases. The nickel extractions increased with the increasing of acid to ore ratio, however, high acidity lead to the increasing of acid consumption and inhibits the hydrolysis of iron. The optimum conditions for pressure leaching were as follows:acid-ore ratio of0.5:1, leaching temperature of260℃, leaching time of0.5h, solid-liquid ratio of1:4. Under the optimum conditions, the leaching of nickel was91%, the leaching rate of iron was7.21%.The effects of extractant concentration, equilibrium pH value, extraction time, extraction temperature and phase ratio on the extraction of nickel were investigated. The results showed that with0.5mol·L-1HA+1mol·L-1B in sulphonated kerosene as extractant and60%saponification rate of extractant, the extraction rate of nickel from the leaching solution with pH of2.6reached96%in single stage extraction with O:A ratio of1:1(volume ratio of oil phase to aqueous phase) at30℃for5min. Under this optimum conditions, the five-stage counter current extraction with O:A ratio of1:2was tested and the extraction rate of nickel reached99%.After washed by dilute sulphuric acid solution, the nickel in loaded organic was stripped using100g-L-1H2SO4solution and the stripping rate reached98.5%in four-stage counter current stripping with O:A ratio of4:1at30℃for10min. Nickel concentration reached40g-L"1in the purified stripping solution. The removal rate of the main impurities Fe, Al, Ca, Cr, Zn, Mg, Mn exceeded99%.The short process of extraction of nickel from high pressure leaching solution by direct solvent extraction reduce lots of costs and has bright prospect in industrial application.