Research On Leaching Kinetics Of Low Grade Nieckel Oxide Ore In Ammonia-Ammonium-Water Systems

Nickel play an extremely important role in national economic field. With the high grade nickel resource is exhausting, the comprehensive exploitation of low grade nickel ore is urgent. But because of the complicated mineral composition and occurrence of low grade nickel ore, the problem of low leaching rate is yet not to solve,which greatly limits exploitation of low grade nickel ore.Thereby, leaching kinetics of low grade nickel oxide ore is researched in the system of ammonia-ammonium-water. The influences of temperature, concentration of lixivium, NH3/(NH4)2SO4(molar ratio), liquid/solid ratio, particle size and agitating speed were experimently investigated. The optimum experimental conditions were given: temperature 45℃, concentration of lixivium 5mol/L, NH3/(NH4)2SO4(molar ratio) 1:1, agitating speed 250r/min, liquid/solid ratio 50:1, particle size is 325-400 mesh, and O2 flow 0.4L/min。Under the optimum condition, the leaching rates of nickel and copper were 60.6% and 94%, respectively. According to the relationships between Cu,Ni leaching rate and time, kinetics model corresponds with the internal diffusion. The activation energy of Ni, Cu calculated through the Arrhenius equation were respectively 60.91 kJ/mol and 43.51kJ/mol, and the corresponding reaction orde 0.9907 and 0.7834. The high activation energy indicates that the process is controlled by the internal diffusion of solid. The EDS results of ore and leaching reside show that some nickel are equally distributed in the structure of silicate minerals and its density has no significant change. It suggests that nickel oxide steps into silicate ismophorsly, and cannot be extracted in ammonia-ammonium-water. This is the reason of low leaching rate.To further find the reason of low leaching rate for low grade nickel ore, the leaching reaction of NiO and Ni2SiO4 with different structure and morphologies was studied in the system of ammonia-ammonium-water. The results show that the crystallinity, grain size, and strain of NiO have an great influence on the leaching effect of nickel. The higher crystallinity, the bigger grain size, and the lower strain result in the low leaching rate. The leaching effect of Ni2SiO4 is simillar to NiO, and more difficult to leach.