With the increasing demand of nickel and decreasing reserves of nickel sulpHides in the world, the research needed on the utilization of laterite is becoming more and more urgent. However, domestic research in this field is still at the starting stage. In this thesis, a new method using organic acid on leaching laterite that has a high content of iron and the leaching mechanism were studied. The laterite mineralogy, leaching reaction rationale and thermodynamics, optimization of leaching system and various technological parameters during the leaching process, dynamics of nickel and cobalt leaching, as well as the organic acid regenerative cycle were also analyzed and expatiated.Mineralogy analyses indicated that the main minerals in laterite are goethite and gibbsite. 69.92% nickel scatters into the goethite in isomorpHism and 13.53% nickel disperses among the manganese minerals. Nickel, iron and aluminum interweave together in the laterite. 43.08% cobalt exists in oxides, while 29.23% cobalt distributes in the high valent state manganese minerals.The organic acid leaching fundamental research results showed that the leaching effect of citric acid-ammonium bifluoride leaching system based on their coordinating leaching effectiveness. The acidic ammonium bifluoride solution can destroy the layered silicate skeleton of clay minerals. The citric acid has strong acidity and reducibility. It can dissolve the partial goethite and the carbonate, and reduce the high valent state manganese minerals, promoting the fettered nickel and cobalt to come out. In addition, the citric acid has the strong chelate ability. The acid radical will react rapidly with Ni2+ and Co2+, which were dissociated from the mineral crystal lattice, forming the stable nickel, cobalt citric acid complex compound. The Eh-pH chart of Metal-H2O system indicated that FeOOH under the alkalinity condition is quite stable. When pH≤6.51, Eh=-0.4402～0.7708V, it starts to dissolve into Fe2+; When pH≤6.233, NiO transforms to Ni2+ in water; when pH=7.51, CoO starts to transform to Co2+. Under the acidic condition, nickel and cobalt can exist stably in two valent stage metallic ion shapes, causing Ni2+ and Co2+ to enter into solution.It was indicated that the tranditional acid leaching by using inorganic acids, including hydrochloric acid and sulfuric acid, is unable to get satisfactory performance in nickel and cobalt leaching without a large amount of iron ions produced during leaching. The four organic acid systems being studied in this thesis exhibit higher nickel and cobalt leaching with less iron ions produced than the inorganic acid leaching system. The Citric acid-ammonium bifluoride leaching system is the most effective one in extracting nickel and cobalt from the laterite with little iron being leached.Through the optimization of leaching process’s various technological parameters, optimized conditions of the leaching process were obtained. For the citric acid-ammonium bifluoride leaching system, the nickel and cobalt leaching may reach 49.56% and 89.91% when the appropriate citric acid concentration is 30g/L, the ammonium hydrogen fluoride concentration is 10g/L, the extraction time is 2 hours, the leaching temperatures is 30℃, the rotational speed is 23 rpm and the liquid to solid ratio is 1/10.According to the research on the leaching dynamics, nickel leaching belongs to the internal diffusion reaction, while cobalt leaching belongs to the combined chemical diffusion and internal diffusion reaction.The analysis of metallic ion content in a leaching solution indicated that the enrichment ratios of nickel and cobalt in solution surpass the iron obviously and manifest good metallic ion-leaching selectivity of the organic acid, reducing the difficulty in the following purification of solution. Through research on the stability of complex compounds and experimental tests, the citric acid complex compound will have hydrolysis gradually along with the time extension. Then the citric acid obtains the regeneration while nickel and cobalt form precipitation in the form of Ni（OH）2 and Co（OH）2.
Post about "direct leaching"
As a non-ferrous metal,molybdenum and nickel,used in a wide range,were limited resources.So the development and utilization of its lean and mixed ore is very necessary.There is one kind of molybdenum and nickel complex multi-metal mineral resource which has not been fully utilized because of its unique composition and physical and chemical properties.Traditional beneficiations or pyrometallurgical processes can hardly separate and extract molybdenum and nickel from that ore.Studies on hydrometallurgical process for that ore are also finite.Based on that,this paper mostly researched on the leaching and extraction process by experiments and found that the hydrometallurgical treatments for such ores were technically feasible.By theoretical analysis and experimental exploration,a complete hydrometallurgical process flow sheet was determined ultimately:direct leaching by nitric acid–impurity removal from leaching solution–precipitation of nickel sulphide–precipitation of magnesium carbonates–alkaline leaching of acid-leach residue and purifying residue–precipitation of calcium molybdate.The practical process parameters were found in experiments.Direct leaching using nitric acid was adopted and investigated.Under optimum conditions:liquid-solid ratio of 3,35%HNO3 and 10%H2SO4,70℃and 1.5h reaction, the leaching efficiency of Mo、Ni and Mg was 50%、97%and 85%respectively.In the following process,the total leaching rate of Mo could reach up to 90%by alkaline leaching of acid-leach residue.As the main impurities in the leaching solution,93% ferric could be removed by jarosite process.Special grade nickel sulfide concentrates could be gained by adding Na2S to the purified solution and adjusting the pH value by NaOH.After that,dolomites could be obtained by adding Na2CO3.Then,confected by the remanent solution,the mixed lixivium containing 10%NaOH and 5%Na2CO3 was used to leach the acid-leach residue and purifying residue.It could make the molybdenum transferred from the residue to the solution.Then the secondary calcium molybdates could be obtained by adding CaCl2 and adjusting the pH value by hydrochloric acid.In conclusion,according to that process,the recovery rate of Mo、Ni and Mg from the leaching solution was 80%、90%and 89%respectively,and secondary calcium molybdates、special grade nickel sulfide concentrates and dolomites could be obtained.The tests proved that the process was technically reliable and economically reasonable.It could effectively recover the valuable metals from the high carbon Ni-Mo ore.So it had an important reference value in the development and utilization of those molybdenum and nickel resources.