Determination of Trace Rhodium in Geological Samples by Fire Assay and Neutron Activation Analysis

Two pre-concentration methods for rhodium in geological samples, lead fire assay and nickel sulfide fire assay, were briefly described. Using fire assay combined with neutron activation analysis (NAA), rhodium in 5 certified reference materials were measured. The recoveries of rhodium by lead and nickel sulfide fire assay were 81.5%±1.2% and 75.1%±3.9%, respectively, and the latter was proved to be independent on matrices of chemical standards and geological standard materials. The analytical results of rhodium in 5 geological standard materials are well agreed with the certified values. Rhodium of 10^-9 level was accurately measured by NAA combined with lead fire assay, and 10^－10 level was accurately measured by NAA combined with nickel sulfide fire assay. Interference factors in the two pre-concentration methods were discussed, and correction for lead absorption was also carried out. Calculations of the detection limits show that a higher sensitivity is available with a planar germanium detector and a nickel sulfide fire assay.