A multi-method approach for the study of lanthanum speciation in coastal and estuarine sediments

Abstract

Two independent analytical methods (sequential extraction and kinetic extraction methods) were applied in order to understand the distribution and speciation of La in the coastal and estuarine sediments from the central east coast of India. Sequential extraction study revealed that La was primarily present as inert complexes (~ 50–60% of the total La) in all the sediments. Amounts of ~ 20–30% of the total La in all the sediments were found to associate with the total organic carbon (TOC) in the sediments. The dissociation rate constants of La–sediment complexes obtained from kinetic extraction studies revealed that the concentration of thermodynamically weak complexes of La gradually increased with the increasing La/TOC ratio in the sediments. The results of this investigation demonstrate that combination of two analytical methods having complementary analytical capabilities can provide a better physicochemical picture of La speciation than either one of the method can do alone. Combination of the data obtained from sequential extraction and kinetic extraction methods suggest that TOC is one of the key factors in controlling speciation and distribution of La in the sediments.