Pressure nitric acid leaching of alkali-pretreated low-grade limonitic laterite

The pressure nitric acid leaching of alkali-pre- treated low-grade limonitic laterite, as well as removing impurity AI（III） and preparing intermediate product of nickel/cobalt sulphide from leaching liquor were investi- gated. After pretreatment, iron exists in the form of amorphous iron oxides, while nickel is adsorbed on the surface of iron oxides in the form of nickel oxide. The preferable pressure leaching conditions are determined as follows： leaching temperature of 458 K, leaching duration of 60 min, initial acidity of nitric acid of 1.90 mol.L-~ and liquid to solid ratio of 3：1 （volume to mass ratio）. Under these conditions, the leaching efficiencies of Ni, Co and A1 are 95 %, 88 % and 55 %, respectively, and that of Fe is less than 1%. The loss rates of Ni and Co are 1.8 % and 1.5 %, respectively, during the step of removing impurity AI（III）. The sulphide precipitation process produces the interim production of nickel/cobalt sulphides, recovering greater than 99 % of Ni and Co in the purified solution. The iron-rich （〉60 %） pressure leaching residue with low Cr, S can be further reclaimed as the raw materials for iron making.

Difference of sintering performance of different types of limonitic nickel laterite

To achieve the more extensive utilization of limonitic nickel laterite,the difference of sintering performance of different types of limonitic nickel laterite including high-gangue and low-gangue nickel ores was investigated by sinter pot tests and relevant mechanism analyses such as thermodynamic analysis and the chemistry and mineralogy of product sinter.With the type of limonitic nickel laterite transformed from high-gangue to low-gangue nickel ore,tumble index and productivity are improved from 45.87%and 0.97 t m^(-2) h^(-1) to 50.16%and 1.05 t m^(-2) h^(-1),respectively,and solid fuel rate is reduced from 140.52 to 131.13 kg/t,indicating that the low-gangue nickel ore possesses relatively better sintering performance.This is mainly due to the fact that the much lower contents of MgO and Al2O3 improve the formation ability and fluidity of liquid phase,which eventually contributes to the formation of relatively tighter sinter microstructure with the lower sinter porosity,more silico-ferrite of calcium and alumina amount and better bonding of hercynite by liquid phases.In addition,the metallurgical performance and nickel content of product sinter would not be reduced as different types of limonitic nickel laterite are blended for sintering.On this basis,it is entirely feasible to more widely utilize limonitic nickel laterite and simultaneously obtain much better-quality Ni-containing product sinter via effective sintering strengthening technologies.

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.