Sorption Values for Palladium and Lead

The most prevailing oxidation state of palladium (Pd) in water is +II. It hydrolyses strongly, but forms also important complexes with soft ligands, such as chloride. Palladium is one of the most important transition metals among the fission products in waste from nuclear fuel. No data on the sorption of Pd (or other platinum groups elements) on cementitious materials are available to date. A reasonable estimate of Pd behaviour can be obtained by considering appropriate chemical analogies. Based on valency, hydrolysis behaviour, and availability of sorption data, lead (Pb) is selected as best choice. The main factors influencing Pb sorption on cementitious materials are the initial Pb concentration (an increase leads to a decrease of sorption) and especially pH or C/S ratio, where a decrease leads to an increase of lead sorption. Kinetic data for Pb sorption indicate a fast initial (chemical) sorption step, followed by a much slower process, possibly involving diffusion into the solid matrix.