| Due to the rising demand situation for nickel of the society and the depletion of nickel sulfide resources with the rapid development of Chinese economy, it is increasingly urgent how to economically recovery nickel from the low-grade nickel laterite resources, which also is in line with society development tendency of the conservation and comprehensive utilization of resources. In this dissertation, the raw material of low-grade nickellaterite with limonite structure produced in Mambare, the independent State of Papua New Guinea had been studied. The sample is conducted on the mineralogy and chemical component analysis. Base on the occurrence, chemical disseminated state and mineral phase embedded properties of nickellaterite ore, the dissertation systematically study and analyze the process technologies of nickellaterite ore after reviewing the reference at home and abroad and summarizing the experience in the production of nickel oxide ore.The process technologies includes the leaching of nickellaterite ore with pretreatment, calcination with sulfuric acid following with water leaching, reductive calcination following with acid leaching, direct acid leaching with microwave-assisted, atmospheric agitation leaching and column leaching. Through theoretical analysis and experiments, a new process technology for low-grade nickel laterite ore was designed to develop with alow cost, high utilization of resources and low environmental pollution. The study also provides some new ideas and reference for the development and utilizationof low-grade nickel laterite ore.The properties of this nickellaterite ore can be determined based on the results of chemical analysis, mineral composition analysis, nickel phase analysis and screening analysis.The raw ore with properties of high iron content, low silicon and magnesium content and belong to a kind of nickellaterite with limonite structure. The raw ore were mainly consisted of serpentine class minerals such as nepouite, chrysotile and serpophite, poor crystalline goethite, magnatige, hematite, quartz, pyroxene, olivine, picotite and the Mn-Fe oxide phase which is rich in cobalt. Most of nickel and cobalt is contained in the serpentine class minerals and limonite in the form of isomorphism, and there is no indie oxide and silicate which is rich in nickel. The raw ore is fine and serious argillization, the particle of the raw ore more fine the nickel content more high. The nickel of raw ore 70.0% contained in-0.037mm size fraction,11.0% contained in-0.074?+0.037mm size fraction,23.57% contained in-0.246?+0.074mm size fraction and 2.89% contained in+0.246mm size fraction.In calcination with sulfuric acid-water leaching process, the leaching performance of nickel and cobalt in the nickel laterite ore was studied. All kind of leaching effects were studied on the leaching behavior both of valuable metal (such as nickel, cobalt) and impurities (such as iron). The chemical reaction characteristics between nickel laterite and acid and the chemical component of the acid leaching residue were analyzed. The optimized process parameters have been found for the calcination with sulfuric acid-water leaching process, of which calcination temperature is 250?, calcination time is 2.5h, liquid-solid ratio is 0.5ml-g-1, water leacing temperature is 60?, water-leaching time is 1.0h and liquid-solid ratio of water leaching (ml·g-1) is 8:1. The leaching rates of nickel, cobalt, and iron were 75.65%,57.34%,67.85% respectively. The process of the water leaching after low temperature calcination with sulfuric acid for low-grade nickel laterite is feasible, but the iron leaching rate is relatively higher.Based on thermodynamic analysis, the reductive calcination-two stages acid leaching process was studied with lignite as reducing agent, and the optimized technology parameters have been found, of which calcination temperature is 700?, the dosage of reducing agent is 40wt%, calcination time is 1.Oh, liquid-solid ratio is 0.5ml·g-1, leaching time is 2.Oh and liquid-solid ratio of leaching (ml·g-1) is 5:1 in reductive calcination-the first leacing stage and calcination time is 1.0h, liquid-solid ratio is 0.3ml·g-1, leaching temperature is 60? and liquid-solid ratio (ml·g-1) is 4:1 in the second leacing stage. Under optimum process conditions, nickel, cobalt and iron leaching rates were 87.66%,90.88%,36.01% respectively in the first leaching and after second leaching, the leaching rate for nickel, cobalt and iron were 93.55%, 96.04%,67.50% respectively. Comparing with one stage leaching, two stage leaching increased leaching rate by 6.0% for nickel and 5.0% for cobalt. But, meantime it also increased iron leaching rate which made the enrichment of nickel and cobalt unfavorable in following process. In addition, the terminal acid concentration is high (high free acid) when two stage leaching was used, but the nickel and cobalt leaching rate has not increased significantly with high terminal acid concentration, which indicates that nickel and cobalt in leaching residue can not be dissolved in acid, and also two stage leaching is undesirable for the processing this type nickel laterites. The results with the high temperature reductive calcination show that the structure of serpentine and other silicate minerals in nickel laterite ore was changed and the soluble silicate minerals were formed. The nickel in the ore was reduced tonickel alloy. The iron in the ore wasmostly reduced to magnetite iron with a small portion of gangue minerals as Wustite. After the reductive calcination, the selectively leaching of nickel can achieve in dilute acid solution.In the research of direct sulfuric acid leaching of nickel laterites ore with microwave-assisted, the effects of the leaching time, sulfuric acid concentration, leaching temperature and microwave power on nickel, cobalt leaching rate were studied. Based on the results of single factor experiment, orthogonal test actors and level were determined, and the optimized technology parameters have been found, of which micro-wave power is 600W, sulfuric acid concentration is 25%(v/v), leaching time is 1.5h and leaching temperature is 90?. Under optimal process parameters conditions, the leaching of nickel laterites ore with sulfuric acidby microwave-assisted was conducted, the nickel and cobalt leaching rate were 88.2% and 74.3% respectively. The results of orthogonal tests shows that the effect sequence of affecting factors on nickel leaching is micro-wave power, temperature, acidity and leaching time, on cobalt is acidity, temperature, micro-wave power and leaching time. Leaching kinetics study results shows that the leaching process of nickel was controlled by external diffusion and the leaching of cobalt was controlled by internal diffusion. According to Arrhenius'empirical formula, the apparent actiation energy of nickel and cobalt leaching is 39.1kJ/mol and 87.7kJ/mol respectively. From the results of SEM and XRD on leaching residue, it is found that the mineral crystalline and morphology have been changed during the reaction. Thist indicates that microwave radiation breaks minerals crystalline, which thereby enhance the leaching of nickel and cobalt.In nickel laterite ore leaching process with sulfuric acid under the atmospheric agitation, the dissertation investigated the effect of sulfuric acid concentration, leaching temperature, leaching time, liquid-solid ratio, leaching aids and other factors on the leaching rate of nickel and cobalt, and the optimized technology parameters have been found, of which the dosage of sulfirc acid is 0.3ml·g-1, leaching temperature is 95?, leaching time is 3.0h and liquid-solid ratio (ml·g-1) is 5:1. With optimized conditions, the nickel and cobalt's leaching rate can reach 59.18% and 41.37% respectively. Although the conventional agitation leaching process has many advantages such as simple flowsheet, low capital, easy operation, but the short coming are difficultly liquid solid separation, high nickel leftover in leaching residue, lower nickel concentrations and high iron concentration in mother liquid, complex recover process flowsheet, high acid consumption and production cost.In order to solve poor permeability in column leach since thefine nickel lateriteore, the pellets processing was used. Column leaching test results shows that the pellets made by ore without crushing,1.5% sodium silicate was added as binder, the dosage of 54kg/t oil of vitriol was added and curing time is 48h, the pellets was leached for 110 days in column at the condition of the volume of sprinkling is 15?40 L·(m2-h)-1 ,initial acid concentration is 10.0%, the dosage of acid consumption is 0.7t/t and pH is 0.5?1.0, the nickel and cobalt leaching rate were 78.10% and 50.19% respectively. After leaching, it is found that the pellets do not show serious rupture and mud phenomenon. Although there is low nickel and cobalt leaching rate in column leaching, the column (heap) leaching process is simple, low investment and low production costs. This technology is especially good for processing low-grade nickellaterite ore with less than 1.0% Ni grade. But, pelleting will result in increased costs, and limit by the binder, which due to the increase of ore particle size, the leaching rate will be relevant slow. |
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