PROCEDURE FOR THE DETERMINATION OF PB-210 IN PHOSPHATE ORE, GYPSUM AND PHOSPHORIC-ACID BY RADIOCHEMICAL SEPARATION AND GAMMA-RAY SPECTROMETRY

A procedure is described for the determination of Pb-210 in phosphate ore, gypsum and phosphoric acid;by radiochemical separation and gamma- ray spectrometry of the 46.5 keV gamma ray of Pb-210. The procedure in volves 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 o f the CHCl3, the DDTC complex is decomposed and Pb is precipitated as PbCrO4. The chemical yield is determined gravimetrically and the preci pitate is counted on a low-energy gamma-ray detector. Experiments prov ed the linearity between the Pb-210 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 Pb-210 content lower than 75 Bq kg (-1) demand larger sample masses and/or longer counting times. The lim it 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 Pb-210 determination s in phosphate ore and gypsum was achieved. An inaccuracy of the metho d of less than 10% was derived from results for selected materials, th at were also analysed by direct gamma-ray spectrometry.