Basic Study On Drying Characteristics And Pre-Reduction Of Garnierite

Nickel laterite ore comprises72%of the world land-based nickel resources, however, only comprises48%of the world nickel production. With the continuous depletion of high-grade sulfide nickel ores, the development and utilisation of nickel laterite ore have been got extensive interest, and have became a important metallurgy problem in international. Basic study on drying characteristics and pre-reduction has been performed according to garnierite in this paper, and theoretical guidance of pyrometallurgy for garnierite has been proposed by research results, which has important reference value for industrial production of garnierite.In this paper, around pyrometallurgy process of garnierite, drying characteristics and pre-reduction of garnierite were investigated systematically. Drying characteristics of garnierite were studied on low and high temperature drying, the results showed that low temperature drying process was divided into two stages, which were rising rate stage and reducing rate stage, activation energy of drying process was1.7kJ-mol-1. In high temperature drying process, the higher the temperature, the faster the dehydration rate, and the optimum drying time was30min. Garnierite was transformed from indefinite form magnesium silicate to (Mg,Fe)SiO4and Fe2O3with increasing temperature. With increasing moisture contents for dry basis, dynamic repose angle and static repose angle increased, internal friction angle and wall friction angle decreased. In the pre-reduction process of garnierite, reduction behavior of nickel and iron were studied, the results showed that in gas-solid reduction process, the reduction rate of metallic nickel and FeO content increased with increasing reaction temperature, but decreased abruptly at a temperature of850℃, which can be attributed to the phase transformation. With increasing reduction time, the reduction rate of metallic nickel increased and FeO content first increased and then decreased. The reduction rate of metallic nickel and FeO content increased with increasing CO content. A larger CO content means a higher partial pressure of reducing gas, promoting reduction of garnierite by enlarging interface of chemical reaction. With decreasing particle size of garnierite, the reduction rate of metallic nickel and FeO content increased, and when particle size of garnierite was too large, the internal diffusion rate and the reduction rate were slow. In solid-solid reduction process, the reduction rate of metallic nickel and FeO content increased with increasing reaction temperature and carbon content, because the reduction reactions of NiO and Fe3O4were endothermic reactions. With increasing reaction temperature, chemical activity of reaction materials and reaction gas molecular motion increased. The reduction rate of metallic nickel and FeO content first increased and then decreased with increasing reduction time and CaO content. With increasing reduction time, the reductants were consumed, and the reduction reaction was suppressed by CO2content increased; the effective contact area of reduction reaction was reduced by excess CaO content, it was unfavorable for solid-state deoxidisation. The chemical composition of reduction product of garnierite contained forsterite, quartz and little ferronickel.The reduction kinetics of garnierite were studied by C and CO reduction using Coats-Redfern method, the results showed that the reduction process of garnierite by C can be divided into two stages for200℃～500℃and500℃～950℃, Avarmi-Erofeev equation (n=4) was determined to be mechanism function, which belonged to random nucleation and growth, activation energy was171.91kJ-mol-1for the first stage and activation energy was52.75kJ-mol-1for the second stage, and then the reaction process of garnierite was controlled by interfacial chemical reaction and the reaction rate was determined by Boudouard reaction. The reduction process of garnierite by CO was divided into three stages:initial stage, middle stage and decaying stage, G-B equation was determined to be mechanism function of the initial stage, which belonged to three dimensional diffusion equation, and the main reactions were that NiO-Fe2O3can be transformed to Ni and Fe3O4. Avarmi-Erofeev equation (n=4) was determined to be mechanism function of the middle stage, which belonged to random nucleation and growth, the kinetics parameters of the middle stage were obtained: E=60.78kJmol-1A=125599.044β/(3655-T), the main reactions were that Fe3O4can be transformed to FeO or Fe. There was clear relationship between calculated values and measured values by mathematic model verification. The effects on analysis results accuracy of metallic nickel have been investigated. The optimum conditions were obtained:sample size was lower than0.1mm; extraction time was90min; bromine concentration in extractant was50ml/L; bromine-methanol amount was100mL. The advantages of the new method were high sensitivity, good precision and wide measuring range. Same sample was measured continuously for five times, the results showed that a SD of measurement results was less than0.015%and the recovery rates were in the range of97.8%and103.8%.