Operational speciation of uranium in inter-tidal sediments from the vicinity of a phosphoric acid plant by means of the BCR sequential extraction procedure and ICP-MS

Abstract

A method has been developed for the determination of uranium in sediment digests and sequential extracts by ICP-MS. No interferences were found due to the presence of the extractant matrices (0.11 mol l ^–1 acetic acid, 0.1 mol l ^–1 hydroxylammonium chloride, 1.0 mol l ^–1 ammonium acetate and 30% v/v aqua regia) provided ²³⁶ U was used as internal standard and the samples were diluted 5-fold with 5% v/v nitric acid prior to analysis. Detection limits (8 ng g ^–1 for extracts and 20 ng g ^–1 for digests) were adequate for determination of uranium at environmental levels. Results obtained by ICP-MS for aqua regia digests were slightly lower than those obtained by alpha spectrometry, but overall recoveries of uranium by sequential extraction were generally within ±10% of pseudototal values. Application of the developed method to inter-tidal sediments collected from the vicinity of the Albright and Wilson phosphoric acid plant, Whitehaven, Cumbria, confirmed the presence of significant technological enhancement of uranium at Whitehaven Harbour but showed that concentrations had decreased since the plant discontinued phosphate ore processing in 1992. Results of the sequential extraction suggested that spillage of phosphate ore (containing up to 120 µg g ^–1 uranium) during shipping may have made a significant contribution to the environmental contamination observed.