| As the rapid development of economy in China, the Chinese nickel consumption ranks first in the world with an average annual growth rate of 25% in recent years. However, its self-sufficiency rate is lower than 30%, and the key method to solve this problem is to develop the oversea nickel resources. At the same time, with the depletion of nickel sulfide resources, the exploration has been focused on nikcle laterite ones which account for 70% of the total nickel resources. In this study, novel hydrometallurgical processes have been chosen to recover nickel, cobalt and iron from nickel laterite based on the research on the mineralogical characterization of different layers of nickel laterite in southeast Asia area. This study provides reliable basis of clean and effective ways for low-grade nickel laterite processing.The corresponding hydrometallurgical processes were chosen based on the analysis of chemical composition, mineral phase and modes of occurrence of nickel and cobalt of different layers of nickel laterite. The results show that the main mineral in nickel laterite with high iron content is goethite while nickel exists in the form of lattice substituted in goethite and cobalt exists in the oxide form associated with manganese oxides. This kind of ore is usually treated by pressure sulfuric acid leaching process. The main minerals in transition layer are serpentine and goethite while nickel exists in the form of non-crystallization or weak crystallization or isomorphism in silicate, and cobalt exists in the manganese oxides. This kind of ore is usually treated by atmosphere sulfuric acid leaching process. The main minerals in saprolitic are serpentine, chlorite and montmorillonite. In these minerals, nickel exists in the form of adsorption or isomorphism in magnesium or iron silicate, which is easily dissolved in acid solution at atmospheric condition. However, this kind of ore is of high magnesium content and usually used as neutralizer for acid leach instead of being processed with acid.The thermodynamic study on atmosphere leaching of transition layer of nickel laterite was conducted and the results show that this method is feasible. The dynamic results in leaching process show that nickel extraction rate is controlled by diffusion through water film and iron dissolution rate is controlled by intraparticle diffusion which follows the liquid/solid shrinking core model. The experimental results show that the leaching temperature, sulfuric acid addition, leaching time, S/L ratio and mineral particles have significant effects on leaching efficiency. Under optimum conditions, the nickel extraction is more than 86% and the iron dissolution is only about 28%, which indicates the process is selective with nickel against iron. The leaching solution was neutralized by saprolitic followed by high-temperature hydrolysis of iron. The removal of iron, chromium and aluminum from leaching solution are 96.19%, 93.32% and 93.99%, respectively. The hydrolysis residue is mainly Fe2O3.The thermodynamic study on pressure leaching of limonite was conducted and the results show that the?GT value of goethite to hematite decreases with the increase of temperature, which indicates that the increase of temperature is helpful to reduce the iron dissolution and improve the nickel and cobalt extraction. The leaching experimental results show that the sulfuric acid addition and leaching temperature are the most effective factors. The higher the temperature, the better extraction results could be obtained. Both the extractions of nickel and cobalt are more than 95% and the iron dissolution is less than 2% under optimum conditions. The neutralization of pressure leaching solution by saprolitic was investigated and the results show that the nickel extraction from saprolitic is more than 65% and more than 90% acid is neutralized in this process.A novel treatment process was studied including iron and aluminum removal by limestone neutralization, nickel separation from cobalt and manganese by C272 centrifugation extraction and recovery of nickel from low nickel concentration solution by direct cyclone electrowinning. The results show that this method has the advantages of short route, high metal recovery, low energy consumption and clean production. The iron, aluminum and chromium concentration in purified solution are all lower than 0.02g/L after limestone neutralization, and the recovery of both nickel and cobalt are more than 95%. Then, the cobalt and manganese were separated from nickel by C272 centrifugation extraction. Both cobalt and manganese concentration in raffinate are lower than 0.002g/L, and the nickel concentration in stripping solution is lower than 0.05g/L. Meanwhile, the calcium extraction by C272 is quite low which avoids the calcium carbonate precipitation in stripping process. Compared to traditional extraction device, the centrifugation extractor shows the advantages including big flux, high stage efficiency and quick extraction speed. Selective cyclone electrowinning is a novel separation technology, which can be used for direct electrowinning of metals from low concentration solution. The experimental results of cyclone electrowinning of nickel show that the cathode nickel meets the requirement of national standard GB/TNi9990. The current efficiency is 93.8%, and the direct recovery of nickel is 93.6%. It indicates the cyclone electrowinning method shows advantages of high selectivity and low energy consumption.The iron in leaching residue was recovered as concentrate by reduction-roasting magnetic separation method. The results show that the iron resources from hydrolysis and pressure leaching processes are comprehensively utilized by this method. The iron content in concentrate is above 64%, and the sulfur content is lower than 0.2%, which totally meet the chemical component requirements of iron concentrate to iron-making industry. The weight percentage of iron concentrate is 79.5% and the iron recovery is 87.6%.In this study, based on the mineral differences of different layers of nickel laterite, two novel hydrometallurgical processes were investigated: atmosphere sulfuric acid leaching-iron removal by hydrolysis-neutralization by limestone-nickel separation by C272 centrifugation extraction-nickel recovery by direct cyclone electrowinning, and pressure sulfuric acid leaching-acid neutralization by saprolitic-neutralization by limestone-nickel separation by C272 centrifugation extraction-nickel recovery by direct cyclone electrowinning. These processes are quite feasible to treat the low-grade nickel laterite with high recovery of nickel and cobalt, and comprehensive utilization of iron. This study obtained large amounts of valuable process parameters and theoretic data, which are of great significance for comprehensive explosion and utilization of low-grade nickel laterite. |
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