Procedure for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry

Abstract

A procedure is described for the determination of ²¹⁰Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry of the 46.5 keV gamma ray of ²¹⁰Pb. The procedure involves microwave dissolution, removal of interfering Fe by extraction with thiocyanate in isobutyl methyl ketone and extraction of Pb as the diethyldithiocarbamate (DDTC) complex into CHCl₃. After evaporation of the CHCl₃, the DDTC complex is decomposed and Pb is precipitated as PbCrO₄. The chemical yield is determined gravimetrically and the precipitate is counted on a low-energy gamma-ray detector. Experiments proved the linearity between the ²¹⁰Pb counting result for PbCrO₄ masses in the range 15–100 mg. For materials with levels of approximately 500 Bq kg^–1, 10 g of material are processed and the PbCrO₄ preparate is counted for 24 h. Materials with a ²¹⁰Pb content lower than 75 Bq kg^–1 demand larger sample masses and/or longer counting times. The limit of determination is 75 Bq kg^–1. A relative standard deviation of 2.5–5.0% at the 500 Bq kg^–1 level for replicate ²¹⁰Pb determinations in phosphate ore and gypsum was achieved. An inaccuracy of the method of less than 10% was derived from results for selected materials, that were also analysed by direct gamma-ray spectrometry.