Determination of the Platinum Group Elements in Black Shale by Inductively Coupled Plasma-Mass Spectrometry with Nickel Sulphide Fire-assay

According to the characteristics of black shale with high abundants in C, S, Ni, Fe and Mo, the conventional reagent formula does not provide an ideal nickel sulphide button, which affects the accuracy of PGEs values. The improved reagent formula and optimized procedure of nickel sulphide fire assay have been developed for the determination of PGEs in black shale samples by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The addition of Potassium nitrate as an oxidant of the fusion flux increases the recovery of PGEs by about 10%. After digestion by HCl, there was still a great amount of precipitations on the bottom of the beaker. This problem was resolved by adding a moderate amount of ferric chloride (about 2-3 mL) with a hot solution and stirring. The detection limits of the method for PGEs are 0.054 ng/g for Ru, 0.040 ng/g for Rh, 0.40 ng/g for Pd, 0.032 ng/g for Ir, 0.27 ng/g for Pt and 0.026 ng/g for Os. The research results of different black shale samples are in good agreement with the reference values, showing that the method is reliable for determining the PGEs in black shale samples.