The Study On Laterite Selective Reduction With Carbon Monoxide And Carbon Dioxide Mixture Gas

Nickel as an important strategic metal is widely used in many areas, such asspecial steel, electroplating, catalysts, petrochemical, etc. Sulphides and laterites aretwo essential land-based nickel sources, and with the sulphides resource exhaustion,abundant laterites play a more and more important role in nickel production. Thereexist two kinds of primary processes of dealing with the laterites: hydrometallurgyand pyrometallurgy.The Indonesia laterite nickel ore was taken as the research object，which wasselectively reduced with the CO/CO2mixed gas in this study. The behaviors andmineral phase variation regularities of laterite nickel ore during roasting and reductionprocesses were researched with comprehensive use of principle of thermodynamics,kinetics, structural chemistry, modern analysis equipments such as X-ray powderdiffraction, optical microscope, scanning electron microscope, and brunauer emmettteller, etc..In this paper, mineralogical phase transformations of Indonesia nickel lateriteores during roasting were studied, so as to explore the influence of pre-roasting on thegas (50%CO+50%CO2) reduction degree. The experimental results show thatduring roasting process, goethite is dehydrolyzed at about300℃, which thentransforms to hematite, and serpentine decomposes to form amorphous siliconmagnesium salts at600~700℃, leading to crystallize olivine if roasting at highertemperature (825℃). Nickel and iron metallization rate increased with the increasingpre-roasting temperature by using50%CO+50%CO2gas mixture. The highestreduction rate can be achieved at86.81%when the sample is roasting at700℃,meanwhile, nickel metallization rate declined if the calcination temperature exceedthe olivine formation temperature.The reduction temperature, gas composition on the possibility of selectivereduction was studied by adding a controlled amount of CO/CO2mix gas. The Ni and Fe metallization rate were also investigated. The results showed that with increasingreduction temperature, the Ni and Fe metallization firstly increased and then dropped.The reason of this phenomenon is that the laterite was sintered when the temperatureexceeds825℃, and the gas was more difficult react with the nickel. In order tooptimize the selective reduction, CO content should be controlled between30~50%,temperature controlled between700~800℃, under this condition the nickel-ironratio of reduction products of laterite were more than2, and the nickel metallizationrates were more than90%.The selective reduction kinetics of laterite was studied by isothermal experiments.Through calculating the20kinds of kinetic mechanism functions, the best mechanismfunctions were determined. When the CO content of less than50%theAvrami-Erofeev equation (n=4) was determined to be mechanism function, whichbelonged to random nucleation and growth, activation energy were than50kJ/mol,which gradually reduced with the CO content increased; While the CO content was70%the G-B equation was determined to be mechanism functions, which belonged tothe dimensional diffusion equation, activation energy was39.63kJ/mol, which meansthat the increasing of CO content could promote the reduction of laterite.