Reduction studies on low iron lateritic nickel ore

Nickel laterite deposits can be divided into two zones: an upper limonite zone and a lower saprolite zone. Mineralogically, nickel is mainly associated with the mineral goethite (FeOOH) in the limonite zone and with the mineral serpentine $rm(Mg,Fe)sb3Sisb2Osb5(OH)sb4$ in the saprolite zone. The reduction characteristics of the two minerals differ markedly. While nickel reductions of greater than 95% are easily obtained for limonitic ore, reductions for saprolite ores are typically between 75-85%. The lower nickel reductions for saprolitic ore are thought to be due to the mineral serpentine in these ores.;The reduction characteristics of two low iron ($<$10% Fe) saprolite ores have been studied. Characterization of the ores using petrographic techniques (chemical analysis, optical microscopy, DTA/TGA & XRD) indicate both ore samples contain a large fraction of magnesium silicate minerals, serpentine and olivine. The amount of reduced nickel and iron was quantified using a Cl$sb2$-methanol leach. XRD analysis showed three different metallic phases: taenite (Fe,Ni), awaruite (FeNi$sb3$) and an iron phase that contained a few percent nickel. SEM analysis of leached residues showed nickel to be present as unleached submicron metallics or as unreduced nickel with both being associated with magnesium silicate particles.;From this study it was concluded that about 62% of the nickel from the serpentine ores can be obtained in a leachable form if the reduction is carried out at 700$spcirc$C which is above the serpentine dehydration temperature of 450-650$spcirc$C but below the serpentine recrystallization temperature of 825$spcirc$C. However, if reduction temperatures above the serpentine recrystallization temperature or below the serpentine dehydration temperature are used, the available nickel in leachable nickel is lower.