Application of potassium tetrafluorobromate to the rapid decomposition and determination of noble metals in chromites and related materials

Described is an effective new procedure for the preparation of chromites and other geological materials for the determination of the noble metals (NM). The procedure is based on the use of a mixture of KBrF4 and KHF2 obtained in situ by adding liquid BrF3 to a mixture of KHF2 and sample powder. South African Geostandards SARM-7 platinum ore from the Merensky Reef and SARM-65, a platinum-bearing chromite ore, were used for method development. Following fluorinative decomposition of samples, a homogeneous product is obtained which is suitable for instrumental analysis using either atomic absorption or emission spectrometry techniques. Sulfatization of fusion product using H2SO4 produces a non-hygroscopic material, which can be easily powdered and sampled directly into the argon plasma. Solution-based analytical techniques can be applied directly after fluorinative decomposition and conversion of resulting fluorides into chlorides by HCl treatment. The proposed new method, combined with spectrometric emission analysis of powders using a double-jet plasmatron dc plasma atomic emission spectrometry (AES) instrument achieved the following limits of detection (LOD) for the noble metals: Ag, Au and Pd: 1–2×10−2 g/ton; Pt: 5×10−2 g/ton; Ru, Rh, Ir and Os: 1–3×10−3 g/ton. Graphic furnace atomic absorption spectrometry (GFAAS) with preliminary extraction, LODs for NMs were: Pt and Ru: 1×10−2; Pd and Rh: 1×10−3; Au and Ag: 1–2×10−4 g/ton. The relative standard deviation of NM determinations was dependent on concentration and sample type but commonly was in the range of 3–15% dc plasma AES and 5–30% for extraction GFAAS.