碳酸镍沉淀过程的研究以及介孔氧化镍的制备

Study on the precipitation process of nickel carbonate and synthesis of mesoporous nickel oxide

碳酸镍和氧化镍是重要的无机精细化学品,在化学、冶金、电子和能源等领域有广泛的应用。首先从碳酸镍沉淀过程的热力学分析出发,研究阴离子(SO42-,Cl–)对碳酸镍沉淀过程的影响。活度系数反映了电解质溶液中阳、阴离子之间和离子与溶剂之间微观作用程度的大小。笔者采用Meissner半经验模型计算了碳酸镍在不同条件下水溶液中的活度系数,并进一步估算了碳酸镍在其中的溶解度大小。估算结果表明,与氯化钠溶液体系相比,碳酸镍在硫酸钠溶液体系中的活度系数较小,因而溶解度较大。为了提高计算置信度,还采用了Bromley模型和Pitzer模型对相应体系的活度系数进行估算,计算结果与Meissner半经验模型的结果非常接近。实验测量了各溶液的表面张力和溶液在碳酸镍表面的润湿角。结果表明,碳酸镍在硫酸钠溶液体系中的固–液界面张力较大,微小晶粒在硫酸钠溶液体系中的溶解度也较大。以上结果表明,碳酸镍在硫酸钠溶液体系中较难析出结晶,在氯化钠溶液体系中则相对容易些。

Nickel carbonate and nickel oxide are important inorganic fine chemicals, widely used in chemical, metallurgical, electronic and energy sources industries. The research was beginning with studying the effects of anions on precipitation process of nickel carbonate. Activity coefficient shows the effect size of the microcosmic effects between ions and solvent. Meissner＇s semi empirical model was applied to calculate the average activity coefficients of nickel carbonate in different electrolyte solutions at different conditions. And the conditional solubility of nickel carbonate was also calculated. The calculated results show that activity coefficients of NiCO3 in sodium sulphate solutions are less than that in sodium chloride solutions, and the solubilities in sodium sulphate solutions are larger. To improve the confidence of the calculations, Bromley＇s and Pitzer＇s models were also applied to calculate activity coefficients. The calculation results of Bromley＇s and Pitzer＇s models are very close to Meissner＇s results. And then experiments were carried out to measure the surface tensions, and contact angles of solutions on NiCO3 surface. According to the experiment results, the solid-liquid interface tension between NiCO3 and sodium sulphate solution is larger than that between NiCO3 and sodium chloride solution. And the tiny crystal NiCO3 has larger solubility in sodium sulphate solutions, which indicates that crystallization of NiCO3 in sodium sulphate solution is more difficult than in sodium chloride solution. The influence of SO4^2- and Cl^- on precipitation and crystallization process of NiCO3 was also studied based on crystal dynamics. The supersaturations at different initial concentration of reaction system were compared. Diffusion coefficients of ions were described by Glasstone＇s model. The diffusion coefficients of Ni^2＋ and CO3^2- in chloride solutions are larger than those in sulphate solutions. In sulphate solutions, the diffusion coefficients and supersaturation are both less, therefore nucleation and growth rates are more slowly. Furthermore, the experiments of crystallization dynamics show that the reaction of nickel carbonate precipitation is a first order reaction while the reaction rate constant is about 0.02 min^-1. Based on the theoretical analysis above, technology process of nickel carbonate precipitation was studied subsequently. The effects of nickel salt, feeding mode, controlling pH, reaction temperature and aging condition on purity, particle size, appearance of product and recovery ratio of nickel were investigated. Then using industrial nickel electrolyte solution and sodium carbonate as the raw materials, nickel carbonate product with nickel content of about 51%, average particle size of 17 μm was prepared at optimal conditions, and the recovery ratio of nickel is around 99.5%. Nickel carbonate with high purity was obtained via an innovative impurity removal process, called wash-dry-rewash-redry process. The sodium and chlorine qualitative contents of the nickel carbonate purified by the innovative method are both less than 0.01% and the sulphate content is no more than 0.1%. The mechanism of sodium and chlorine adsorption onto nickel carbonate＇s surface was discussed, using Stem＇s model of electric double layer. Moreover computational simulation technology was applied to investigate on how anions affect the crystallization of NiCO3 at atom scale. The lattice structure was relaxed before establishing crystal surfaces. The computational unit cell parameters are very close to the experimental data. Five main surfaces were studied, i.e. the （104）, （100）, （110）, （001） and （101） surfaces. SO4^2- substitutes the CO3^2- on the outmost layer. Cl^- adsorbs onto the surfaces and has relative weaker interaction with the surfaces. Compared with only hydrated surfaces, the growth rates of defected hydrated surfaces significantly decrease, especially for SO4^2- defected ones. The （104） surface is the most stable surface and is mainly expressed in the equilibrium morphology of the resulting crystal. Finally, based on the study of nickel carbonate synthesis, nickel oxide with mesoporous structure was prepared by adding template into the nickel source and calcination. The effects of types of surfactant, dosage of surfactant, calcination temperature and calcination time on pore structure and specific surface area of nickel oxide were investigated. The results show that the surface area of the nickel oxide prepared by sodium dodecyl sulphate （SDS, anion surfactant） is much larger than those of which prepared by CTAB and octadecylamine. It is suggested that the inorganic species, basic nickel carbonate, is interacted with the template, SDS, by electrostatic attraction force. The precursor hardly has any surfactant residue after calcination. Nickel oxide with high specific surface area （〉200 m^2· g^-1） is synthesized by adding low amount of template at the mole ratio of SDS：Ni less than 0.1：1.0. The nickel oxide has H3 type hysteresis and the pore size distribution mainly ranges from 2 nm to 10 nm. And it has good thermal stability.