| Nickel, one kind of important nonferrous metal, is widely used in the fields of stainless steel, heat-resistant alloys, batteries and various chemical products. In recent years, with the continuous decrease of nickel consumption in the world, the nickel consumption in China increased by25%average every year, which makes China’s nickel consumption rank first in the world.72%of nickel land-based resources in the world are reserved in nickel laterite, which only produce42%of nickel total output. As the depletion of nickel sulfide, nickel laterite is becoming the significant nickel resource in the world. Hydrometallurgical processes have many advantages including high recovery of valuable metals, excellent selectivity, low energy consumption, variety of products and so on, which are the main treatments for nickel laterite. In the paper, based on the analysis of mineral properties and characteristics, fundamental and technological study on treatment of low-grade limonitic nickel laterite from three different mine areas at home and abroad by hydrometallurgical processes were studied, which provide the theoretical and technological basis for the industrial processing of nickel laterite.Hydrometallurgical processes were distributed to nickel laterite from three different mine areas at home and abroad, based on the analysis of chemical composition, phase and mode of occurrence of element. For the limonitic nickel laterite from Qinghai Yuanshi Moutain area in China, the main phase is goethite, and cobalt content is extremely low. Nickel and cobalt exist in goethite in the form of lattice replacement. This ore was treated by reduction roasting-ammoniacal leaching process. For the limonitic nickel laterite from Tubay area in Philippines, the main phase is goethite, and cobalt content is comparatively high. Cobalt exists in manganese oxide particles in the form of physical adsorption. This ore was treated by sulfation roasting-leaching process. For the limonitic nickel laterite from Mati area in Philippines, the phases are goethite, magnetite, lizardite and talc, and magnesium content is comparatively high. Nickel mainly exists in goethite in the form of lattice replacement, and cobalt mainly exists in manganese oxide particles in adsorption form, and magnesium mainly exists as noncrystallne and weak-crystalline. This ore was treated by atmosphere hydrochloric acid leaching process.The fundamental and technology on treatment of nickel laterite by reduction roasting-leaching processes were studied. The thermodynamics show that nickel and cobalt oxides in laterite can be reduced to metal forms, and iron oxide can be mostly reduced to Fe3O4. Under certain ammoniacal leaching conditions, nickel and cobalt exist as stable ammonia complex in leaching solution, and Fe enters into residue as Fe(OH)3form. The suitable conditions of reduction roasting-leaching process were determined as follows:less than20mesh of mineral particle size,20wt.%of reductant addition,850℃of roasting temperature,30min of roasting time,40℃of leaching temperature,10min leaching time,133:88of NH3/CO2,70g/L of pulp density and0.1L/(min·g) of oxygen flow rate. Under these conditions, the leaching efficiencies of nickel, cobalt and iron are83.1%,45.1%and0.12%, respectively, and the ratio of nickel to iron is45.9in leaching solution, which shows a selective leaching of nickel over iron. The experimental design for optimization of reduction roasting process was done, and the results show that the leaching behavior of cobalt was effectively simulated by Response Surface Methodology (RSM), and the optimum conditions were dertemined as20wt.%of reductant addition,930℃of roasting temperature and30min of roasting time. However, the data distortion phenomenon appeared in the simulation of nickel in leaching process. The kinetics of leaching of nickel and cobalt were investigated, and the results show that the leaching behavior of nickel and cobalt fit well with the kinetic models of multiphase liquid/solid regional reactions. The apparent activation energies for nickel and cobalt extraction are18.07kJ/mol and8.99kJ/mol, respectively, which indicates that the leaching rate of nickel and cobalt were controlled by solid film diffusion.The fundamental and technology on treatment of nickel laterite by sulfation roasting-leaching process were studied, in which sulfation roasting-water leaching and sulfation roasting-ammoniacal leaching were used to treat nickel laterite. The thermodynamics indicate that all metal oxides in nickel laterite can react with concentrated sulfuric acid. After roasting process in determined temperature, some sulfates like iron sulfate were transformed to corresponding oxides, but nickel, cobalt and other metals remained as sulfates, which achieved the primary separation of nickel and cobalt from iron and other impurities. In ammoniacal leaching process, the increase of total ammonia concentration is beneficial to the increase of nickel and cobalt concentration, and the existence of CO32-has little effect on nickel ion concentration, but effectively decreases the concentration of cobalt and manganese ions. The suitable conditions of reduction roasting-water leaching process were determined as follows:20wt.%of water addition,40wt.%of sulfuric acid addition,700℃of roasting temperature,120min of roasting time, less than80mesh of mineral particle size,4wt.%of sodium sulfate addition and1kg/L of pulp density. Under these conditions, the leaching efficiencies of nickel, cobalt, iron and manganese are83.3%,92.8%,0.8%and94.3%, respectively, which show selective separation of nickel and cobalt over iron. The leaching residue, whose main phase is Fe2O3, meets the requirement of grade and chemical composition of level H62hematite concentrate. The suitable conditions of reduction roasting-ammoniacal leaching process were determined as follows:20wt.%of water addition,40wt.%of sulfuric acid addition,700℃of roasting temperature,30min of roasting time, less than80mesh of mineral particle size,4wt.%of sodium sulfate addition,5mol/L of ammonia concentration, lmol/L of ammonia carbonate,300g/L of pulp density,25℃of leaching temperature,10min of leaching time. Under these conditions, the leaching efficiencies of nickel, cobalt, iron and manganese are82.5%,61.0%,0.007%and22.1%, respectively. The experimental design for optimization of sulfation roasting process was done, and the overlaid of contour plots of nickel and iron extraction was displayed. The optimum area of Ni%≥80%&Fe%≤5%was determined, and in this area the experimental results show excellent agreement with the predicted ones, which indicates that it is quite successful to simulate the sulfation roasting process by RSM. The kinetics of sulfation of nickel and cobalt were investigated, and the results show that the apparent activation energies for nickel and cobalt sulfation are21.45kJ/mol and34.81kJ/mol, and the reaction rate constants for nickel and cobalt sulfation are1.05and1.09, respectively, which indicates that the sulfation rate of nickel and cobalt were controlled by solid film diffusion.The fundamental and technology on treatment of nickel laterite by hydrochloric acid leaching process at room temperature were studied. The thermodynamics show that the increase of temperature is beneficial to the reactions in hydrochloric acid leaching, and FeOOH and Fe2O3are stable in hydrochloric acid at atmosphere. The suitable conditions of hydrochloric acid leaching process were determined as follows:3:1of acid to ore ratio,80℃of leaching temperature,1h of leaching time,400g/L of pulp density, less than80mesh of mineral particle size, no addition of chloride. Under these conditions, the leaching efficiencies of nickel, cobalt, magnesium, iron and manganese are82.5%,70.3%,63.8%,63.7%and80.0%, respectively. The leaching residue mainly consists of goethite, magnetite, lizardite and talc, but with lower content of lizardite and talc compared to laterite ore. The kinetics of hydrochloric acid leaching of nickel, cobalt and iron were investigated, and the results show that the apparent activation energies for nickel, cobalt and iron extraction are71.64kJ/mol,68.73kJ/mol and98.52kJ/mol, respectively, which indicates that the leaching rate of nickel, cobalt and iron were controlled by surface chemical reactions. |
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