Upgrade of nickel and iron from low-grade nickel laterite by improving direct reduction-magnetic separation process

Low-grade saprolite nickel laterite,characterized by complicated minerals composition and fine-grained and complex dissemination,was commonly treated with a low recovery efficiency of Ni and Fe by conventional methods.Hence,an improved direct reduction and magnetic separation process was proposed.Meanwhile,the mechanisms on the enhanced growth of the Ni-Fe particles and the phase transformation in the nickel laterite pellets were explored.The low-nickel concentrates as a nucleating agent can obviously decrease the activation energy for growth of Ni-Fe alloy particles during the improved direct reduction process from 197.10 to 154.81 kJ/mol when the low-nickel concentrates were added from 0 to 20%.Hence,it is able to decrease nucleation barrier,induce the growth of Fe-Ni alloy particles and increase their average size.As a result,the size of Ni-Fe particles in the pellets from less than 10 lm grew to more than 20 lm,which is beneficial for the full liberation and recovery of Ni and Fe in subsequent magnetic separation process.Therefore,the preferable Ni-Fe alloy concentrates with 6.44%Ni and 82.48%Fe can be prepared with corresponding recovery rates of 96.90%and 95.92%,respectively,when adding 20%low-nickel concentrates.

Achieving efficient utilization of limonitic nickel laterite and CO_(2) emission reduction through multi-force field sintering process

Strengthening limonitic nickel laterite sintering and reducing CO_(2) emission were performed by the application of multiforce fields including external thermodynamic and pressure fields.Sinter pot tests of limonitic nickel laterite were carried out,and the relevant industrial production was briefed.The chemistry and mineralogy of product sinter and the thermodynamic and kinetic conditions during sintering were analyzed to reveal the relevant mechanism.The results indicate that sintering performance of limonitic nickel laterite in the new sintering process with multi-force fields is significantly improved with tumble index and productivity increased by 24.11%and 18.56%,respectively,and solid fuel rate reduced by 23.21%,compared with those in traditional sintering process.In this case,greenhouse and pollutant gas emissions are greatly reduced,and metallurgical performances of product sinter are excellent.The industrial production has been successfully conducted,indicating a bright application prospect.Mechanism analysis shows that the great improvement of thermodynamic and kinetic conditions during sintering and the densification of loose sinter can be achieved via the application of multi-force fields.Sinter microstructure is transformed from large thin-wall pores to small thin-wall pores or medium thick-wall pores with the dramatic reduction of sinter porosity and more formation of silico-ferrite of calcium and alumina(SFCA).Meanwhile,the homogenization of mineral compositions is achieved,and much denser interlocking texture between hercynite and SFCA is formed.The application of multi-force fields contributes to the substantial improvement of sintering performance of limonitic nickel laterite and CO_(2) emission reduction.

Significant influence of self-possessed moisture of limonitic nickel laterite on sintering performance and its action mechanism

In consideration of the abundant moisture of limonitic nickel laterite mined,it is essential to determine whether the selfpossessed moisture of limonitic nickel laterite after pre-dried is appropriate for sintering.Thus,based on the characterization of limonitic nickel laterite,the influence of its self-possessed moisture on sintering performance was expounded by sinter pot tests and the relevant mechanism was revealed by the systematical analyses of the granulation properties of sinter mixture,thermodynamic conditions during sintering and mineralogy of product sinter.The results indicate that the selfpossessed moisture of limonitic nickel laterite indeed has significant infuence on its sintering performance.At the optimum self-possessed moisture of 21 mass%,sinter indices are relatively better with tumble index,productivity and solid fuel rate of 48.87%,1.04 t m^(-2) h^(-1)and 136.52 kg t^(-1),respectively,due to the superior granulation properties of sinter mixture and thermodynamic conditions during sintering,relatively large amount of silico-ferrite of calcium and alumina and tighter sinter microstructure.However,sintering performance of limonitic nickel laterite is still much poorer than that of ordinary iron ores.It is feasible to strengthen limonitic nickel laterite sintering by inhibiting the over-fast sintering speed and improving the thermodynamic conditions during sintering.