Aspects of uranium adsorption by microorganisms

The biosorption of uranium (VI) from process and synthetic solutions was investigated. Adsorption capacities in process solutions were substantially less than in synthetic solutions of similar uranium and sulphate content. Biosorption was particularly poor in solutions of low pH. The reduction of the biosorption capacity was attributed to the competition of the ferric ion for the adsorption sites. Only cationic species of iron competed successfully, while anionic species such as hexacyanoferrate (III) were poorly adsorbed. Capsular polysaccharides extracted from plasmid transformed bacteria and algal alginate were observed to possess higher uranium sorption capacity than whole cells. The uranyl ion was believed to bind to the carboxylic residues of these biopolymers. Neither the biomass nor the polysaccharides displayed significant selectivity for uranium.