The Reducibility Research Of Sodium Sulphate On The Hydrogen And Methane Reduction Process Of Nickel Laterite Ore

With the rapid development of the world’s iron and steel industry has directly stimulus to the sharp rise in global nickel production. Utilizing the nickel laterite ore to produce the nickel-iron alloy as the raw materials of stainless steelis one of the effective ways to guarantee the stainless steel industry sustainable development.As for the pyrometallurgical process for nickel laterite ore, there have been several investigations performed to use the coal or coke as a reducing agent at home and abroad. The continuing increase in the market price of coal, as well as its importance as a primary energy source in other fields, disadvantages carbon thermal reduction processes with high costs and relatively low energy efficiency.To solve this problem, from a resource recycling point of considering, the reasonable utilizingof waste heat and reducing gas from a large amount of surplus coke oven gas which was generated from the carbonization of coal as the heating source and the reducing agent used in reduction process can not only greatly decrease the cost of smelting but also reduce the waste of resource, and making the smelting process of nickel laterite ore more economically and environmentally.The experiment were firstly performed using a TPR instrument to study the reactivity of hydrogen and methane which were the main component of coke oven gas and to learn about whether the sodium sulphate as an activator could promote the crystal phase transition during the temperature-programmed reduction process. Further in-depth research focus on the hydrogen selectively reduction process of nickel laterite ore with addition of sodium sulphate,and according to the catalytic behavior of sodium sulphate tentatively selects the raw nickel laterite ore as a carrier using the impregnation method to prepare the reaction samples and the experiment results were analysed and discussed. During the experiment, the mineralogical properties of the raw nickel laterite, reduced ore and magnetic concentrate were characterized using thermodynamical calculation, ICP, TG-DSC, XRD and optical microscopy. The experimental results were shown in the following:(1) The H2-TPR and CH4-TPR characterization results of the nickel laterite ore with or without addition of sodium sulphate show that under the same experimental conditions the reactivity of H2is obviously higher than CH4. In the hydrogen atmosphere, the presence of sodium sulphate could overcome the kenetic problems faced by the laterite ore and accelerate the crystal phase transition and the occurrence of sulfurization reaction. Conversely, the activity of CH4was provided by the hydrogen ions generating from the radical reaction under catalysis by transition metals such as nickel, cobalt in the laterite ore, and is not itself occur a reduction reaction. A CH4consumption peak was observed at900℃.(2) According to the thermodynamic analysis known that for the Na2SO4-MgO-SiO2system, the sodium sulphate was reduced to Na2S by H2occurs in any temperatures and H2partial pressure. When the temperature was fixedat651℃and697℃, the sodium sulphate could react with SiO2to form different sodium silicate salt and react with MgSiO3at around750℃, but react with Mg2SiO4only if the temperature exceed1100℃, at the same time the SO2which were generated from the above reaction could react with FeO and NiO to form FeS and NiS at any hydrogen concentration, but when the temperature exceed1000K, the reaction were occurred by consuming a large amount of H2.(3) The experimental results about the major impact factors of the reduction roasting and magnetic separation process show that the reduction temperature and the sodium sulphate dosage could affect the catalytic activity of sodium sulphate and the crystal phase transition of the ore. Meanwhile, the reducing time and H2partial pressure, to some extent, influence the degree of iron oxides reduce, the magnetic field intensity and MOG play a significient role on the nickel and iron final beneficiation. The optimal conditions of the process of the reduction were obtained by selective reduction of laterite ore at800℃for220min in the presence of20wt%Na2SO4with an inlet gas mixture of70%H2in N2at a total flow rate of200L/h, and the reduced ore were separated by magnetic separation, grinding time10min, magnetic field intensity0.156T. The maximum nickel content and recovery of magnetic product were5.63%and83.59%, respectively.(4) The experiment selects the calcined laterite ore as the carrier, and then immersed in different concentration of sodium sulphate solution to prepare the reaction samples (coded as IM ore). The nickel content and recovery of the IM ore is slightly superior to the PM ore which was prepared by physical blending. The nickel content and recovery of the magnetic concentrate of the IM ore were6.38%and91.07%, respectively.(5) The study of optical microstructure of the reduced products showed that FeS was formed by the vulcanization of SO2could promote the formation of a molten Fe-FeS solid solution which could not only accelerate the aggregation of metallic ferronickel particles but also keep an obvious boundary with the dark gray gangues mineral and facilitate the downstream magnetic separation.