Study On Settling Properties Of Iron And Aluminium Precipitation Sludge From Leaching Solution Of Laterite Nickel Ore

Processing technology of nickel laterite ore has been developed domestically,encouraged by the rise of global concern on the carbon footprint,resulting in the growth of efficient battery production where nickel acts as an essential component.High-temperature acid leaching technology is considered a favorable and domestically new method to process nickel laterite ore to produce intermediate products due to its higher rejection of iron and other impurities present in the feed laterite.However,a small number of impurities,mainly iron and aluminium,remain in the post-autoclave leaching solution,which requires other processes to remove these impurities.The process is primarily achieved by neutralization and subsequent solid-liquid separation.The effective operation of solid-liquid separation of iron and aluminium removal precipitation becomes essential for the optimum recovery of nickel and cobalt in the subsequent stage.Therefore,a study on the settling property of iron and aluminium precipitation sludge from the leaching solution of laterite nickel ore was conducted.The physicochemical characteristics of slurry are evaluated,including density,morphology,zeta potential,particle size distribution,and chemical and phase composition.Density measurement of solid suspension on leaching solution shows the value of 2.848 g/cm~3 while the liquid medium of 1.685 g/cm~3.SEM micrograph of solid phase in suspended solution showed a needle-like and sheet morphology with a relatively flat and regular surface.The Zeta potential of iron and aluminium precipitation sludge of-7.400 m V indicates that the solid particles remain unstable in the suspension system.The particle size distribution of iron and aluminium precipitation sludge showed that as much as 72.500 wt.%of solid particles are below 64μm.Based on its physicochemical properties,iron and aluminium precipitation sludge might settle under natural conditions;however,based on the batch settling test,colloidal particles remain in the supernatant solution,requiring the addition of flocculant to accumulate and settle down,thus resulting in high clarity supernatant.The single effect of flocculant type,solid fraction,flocculant dosage,mixing degree,and temperature on the settling performance of iron and aluminium precipitation sludge was studied by applying a batch settling test.Settling of iron and aluminium precipitation sludge was performed under the addition of different flocculant types,showing the apparent influence of flocculant type on settling performance.Among all the flocculants,it is found that SC900 possessed the best performance.Additionally,settling speed significantly decreases with increasing solid fraction up to 4.00%,while with further increasing solid content,the change of settling speed is insignificant.Under the addition of flocculant,settling speed significantly increases with increasing flocculant dosage,while the underflow concentration is significantly decreased from 10 g/ton to 40 g/ton solid.Settling speed decreases with increasing mixing degree,while the underflow concentration substantially increases with increasing mixing degree from 2 to 8 times of inverting measuring cylinder.Furthermore,settling performed at 70°C possesses the highest settling speed at any height with the average settling speed value at 10 cm of152.055 mm/min,followed by 60,50,40,and 30°C with the average settling speed value of 136.583,133.139,115.018,and 105.868 mm/min respectively.Statistical Response Surface Methodology(RSM)with Box-Behnken Design(BBD)was applied to optimize the settling performance by involving solid fraction,flocculant dosage,mixing degree,and temperature as the influencing factors.Optimization of settling speed,underflow concentration,and suspended solid of supernatant were performed simultaneously by applying the overall desirability function.From the overall desirability calculation,it could be concluded that the optimal factors were 3.318 wt.%of solid fraction,42.881 g/ton flocculant dosage,four times mixing degree,and 56.806°C of temperature,which are estimated to result in 106.343 mm/min settling speed,13.442 wt.%underflow concentration,and 6.759 mg/L suspended solid of supernatant with corresponding overall desirability of 0.853.Verification experiments were conducted with three replications resulting in a mean value of102.431 mm/min,12.707 wt.%,6.000 mg/L of settling speed,underflow concentration,and suspended solid of supernatant,respectively.According to the verification experiments,the relative errors between predicted and measured results do not exceed 5%,implying that the proposed models are reliable.