AbstractsEngineering

Selective Reduction of Laterite Ore

by Jun Yang




Institution: University of New South Wales
Department: Materials Science & Engineering
Year: 2014
Keywords: Laterite; Nickel; Cobalt; Selective reduction; Extraction; Reduction degree; Mineralogy
Record ID: 1040997
Full text PDF: http://handle.unsw.edu.au/1959.4/54087


Abstract

The project studied reduction of garnieritic laterite ore with the aim to establish extent and rate of reduction of nickel, cobalt and iron oxides under different conditions, reduction mechanisms, and optimum conditions for selective reduction of nickel and cobalt oxides. Ore reduction with the size 53-200 μm and size < 53 μm was studied at 700-1000 ℃ in the CO-CO2 gas mixture containing 20-70 vol% CO; the gas flow rate varied in the range 350- 1050 mL/min. Reduced ore was leached in the Br-CH3OH solution to extract metallic Ni, Co and Fe, which amount was determined using ICP-AES analysis. The project also studied changes in the ore upon heating to 600-1000 ℃, and effect of heat treatment on the ore reduction. Phase changes in the annealing and reduction processes were examined by XRD and SEM/EDS. The mineral phases detected by XRD in the original ore included chlorite, talc, hematite and quartz. Traces of iron silicate, Fe-Cr spinel and monoxide phase were observed by EDS. Nickel was detected in chlorite, talc, iron silicate and monoxide. At 600 °C, dehydroxylation of chlorite occurred. Chlorite was converted into olivine (forsterite) and enstatite at 600-800 °C. Olivine crystallised at temperatures above 810 °C. Ni-bearing phases after heat treatment at 800-850 °C were forsterite, enstatite, talc, iron silicate and monoxide. Upon heating to 1000 °C, talc was converted into pyroxene. Metal oxides were reduced to ferroalloy (ferronickel). Extent of reduction of Ni, Co and Fe oxides increased with increasing temperature to 740 °C and decreased with further increasing temperature. Increase in CO concentration also had a positive effect on reduction of metal oxides; when CO content was lower than 60 vol%, degree of reduction of iron oxides was below 20%. Increase in CO concentration to 70 vol% significantly increased iron metallisation (> 50%). Gas flow rate above 700 mL/min had a minor effect on the ore reduction. Effect of the ore size on reduction of metal oxides was also insignificant. Optimal conditions for selective reduction of laterite ore included temperature 740 °C; CO concentration in the CO-CO2 gas mixture 60 vol% CO; gas flow rate 700 mL/min.