RECOVERY OF PRECIOUS METALS USING NICKEL SULFIDE FIRE ASSAY COLLECTION - PROBLEMS AT NANOGRAM PER GRAM CONCENTRATIONS

The NiS fire assay is widely used for the separation and concentration of PGE and Au from geological materials, The effect of collector mass on the recovery of PGE and Au in a Pt ore grade (mu g g(-1)) sample a nd a komatiite sample which contained <10 ng g(-1) of PGE are reported . The PGE and Au recoveries were not a function of collector mass for the ore grade sample, The recovery of Ir, Os and Au from the komatiite sample did not significantly depend on the mass of the collector used but Ru, Ph, Pd, and Pt recoveries were reproducible and dependent upo n the collector mass, From these recoveries, estimates of the partitio n coefficients (K-d) were calculated for the sulfide and silicate melt phases, The K-d values were also estimated from direct analysis of th e two phases, The recoveries of the precious metals were not always in dependent of the collector-to-flux-ratio. Also, the K-d values were fo und to depend upon the PGE concentrations, The K-d values obtained for an ore-grade sample were 4 to 103-fold higher than those obtained for a sample which contained < 10 ng g(-1) PGE concentrations, Thus, when determining PGE concentrations at tow levels using NiS fire assay col lection, significant biases may occur.