Research On The Funcion And Mechanism Of Sodium Thiosulfate In The Process Of Laterite Nickel Reucted By Carbon Monoxide

Nickel is an important material applying for the national economic and social development. In recent years, the demand for nickel-metal mineral resources increased rapidly with developing of industrialization and urbanization in China. But the shortage of nickel resources in our country lead to the rapid expansion of dependence on foreign nickel resources. At the same time, the highly competitive international market demand, the increasing supply-side monopoly and the rising market prices lead to a large restriction in using and developing of the nickel resources. In addition, as the decreasing of nickel sulfide ore, it is more urgent to develop more efficiently.In this work, an Indonesian laterite nickel ore was choosed as the reaserch object. Firstly, the properties of raw ore were analyzed in detail by characterization techniques such as XRD?TG?ICP and so on. Then we describe a process by choosing a fixed bed reactor and using CO as a reducing gas. Secondly, The effect of the concentration and the optimal technological condition of nickel iron with the new additive Na2S2O3 nickel iron was investigated. Thirdly, the mechanism of the additive in reduction roasting process were discussed. Finally, the product for reduction roasting and magnetic concentrate were analyzed and the migration accumulation law of nickel iron were studied by characterization techniques such as SEM and EDS. The following conclusions can be drawn by the results:(1) By the analysis of chemical method and ICP we can know that the laterite nickel ore is a typical low iron, high magnesium Si-Mg type lateritic nickel ore. Nickel is mainly occupy the lattice of magnesium through the effect of isomorphic phase and exist in the form of the silicate. Therefore its structure is more compact and stable.(2) The effects of different additives and laterite nickel ore shows that under the same experimental conditions the new additive sodium thiosulfate (Na2S2O3) is more superiorer than sodium sulfate (Na2SO4), sodium sulfide (Na2S), sodium carbonate (Na2CO3) and biomass ash for the separation effect of iron enrichment of nickel laterite nickel ore. The optimum conditions of reduction roasting-magnetic separation were obtained by selective reduction of laterite ore at 1100? for 60 min in the presence of 20wt% additive with the ratio of reducing gas CO/CO2 of 8/2 at a total flow rate of 200 ml/min, and the reduced ore were separated by magnetic separation, grinding time 1min, magnetic field intensity 0.15 T. Under these conditions, the maximum nickel content and recovery of magnetic product were 7.62% and 64.8%. But the recovery of iron was only 17.73%. It was 47.07% difference between Nickel and iron recovery which lead to achieve the goal of selective reduction of nickel iron on recycling.(3) Additive sodium thiosulfate played compound additive effect in reducing roasting process, which combines the function of the alkali metal salt and sulfur-containing agent. In the process of roasting the Na+ provided by additives can destroy the crystal phase structure of silicate at high temperatures and occupy the position of Ni+ which enables the Ni+ to released in the form of oxides and sulfides, and the Ni+ can be reduced easily in the subsequent reduction process. The elemental sulfur and the alkali metal sulfide released and decomposd by additives reacts with the iron oxide can form the iron ferrous sulfide with no magnetic. Thus allowing to throw the mineral iron out in the form of gangue which is conducive to the improvement of quality of nickel and iron recovery lower.(4) According to the analysis of reductive roasting product by SEM and EDS showed that it can be form a large number of low-melting phase FeS due to the effect between additive and nickel laterite and the FeS can reduce the internal melting point of particle to occur liquid so that it could accelerate the mass transfer process and provide passage for the migration of metal ions so that the nickel-iron particles aggregate and precipitate to obtained melt layer formed on the surface.(5) The analysis about magnetic concentrate by physical and microstructure showed that the degree of aggregation of nickel-iron alloy phase gradually increased, the composition of nickel and iron phase by the initial phase more iron less nickel to more nickel less iron and the degree of enrichment of nickel is also enhanced with the increasing use of additives and their content.