Method development for the extraction of naturally occurring radionuclides in marine sediments

The ability of marine sediments to adsorb naturally occurring radionuclides is dependent upon the surface area to volume ratio of the particles and hence their grain size. Finer sediments have a greater surface area to volume ratio and so a greater adsorption capacity per unit volume of sediment. Some sediments contain naturally occurring radionuclides within their lattice structure, due to the mineralogy of the source rock, as well as those adsorbed onto particle surfaces. Four marine sediments, differing in grain size and mineralogy, were chosen to investigate the efficiency of different chemical extraction methods. Leaching with 6 M hydrochloric acid is the most widely adopted procedure for extracting the adsorbed activity. This work compares total dissolution with mineral acid leaching methods to investigate the extent to which each method invades the lattice structure. Naturally occurring radionuclides in the 238U-decay series were isolated and purified by co-precipitation and ion-exchange techniques. Radioactive tracers were used as internal standards to determine the chemical yield. Quantitative and qualitative determinations were performed using alpha spectrometry. This work has resulted in: (i) optimum methods for the extraction of radionuclides in each type of sediment; and (ii) a critical comparison of the techniques through consideration of the tracer yield.