THE EFFECT OF FULVIC-ACID ON THE SORPTION OF ACTINIDES AND FISSION-PRODUCTS ON GRANITE AND SELECTED MINERALS

Organic material is present at low concentrations, typically 1-2 mg/l in terms of dissolved organic carbon (DOG), in groundwaters deep in gr anitic rock. Hydrophobic and hydrophilic acids may complex inorganic c ontaminants and change their sorption behaviour on geological material s. This report describes a series of experiments performed under aerob ic conditions to investigate the effects of fulvic acid over a concent ration range of 0-5 mg/l DOC on the sorption of Sr-85, Cs-137, U-233, Pu-238 and Am-241 by crushed granite, biotite, goethite, montmorilloni te and quartz. In addition, similar solutions were used to study the e ffects of dissolved fulvic acid on the sorption of Tc-99 and I-125 On each of the above solids except quartz. The fulvic acid was extracted from groundwater collected at a depth of 240 m in the granitic rock of the Underground Research Laboratory near Lac du Bonnet, Manitoba. In all experiments, the sorption of the fulvic acid by the geological mat erials was in the order goethite > montmorillonite > biotite > granite > quartz. No sorption of Tc was observed from any of the solutions on any of the solids. Low sorption of I on montmorillonite occurred in t he presence of the dissolved organic material. No sorption of I was ob served with the other solids used. Only montmorillonite sorbed any app reciable amount of Sr in this study with the fulvic acid having no eff ect on this sorption. All the solids except quartz sorbed substantial amounts of Cs, but sorption was not affected by the organic material i n solution. Each of the solids sorbed U with no difference in sorption observed due to the dissolved organic. In general,Pu sorption decreas ed as the concentration of dissolved fulvic acid increased. However, s orption of Pu on quartz remained at approximately the same levels rega rdless of the concentration of organic in solution. Generally high sor ption of Am was found. Lowest sorption of Am on all solids occurred fr om the solution with the highest concentration of fulvic acid. Sorptio n of Am on granite decreased as the concentration of the organic in so lution increased. This study indicated that, under aerobic conditions, the effect of dissolved organic material on sorption of radioisotopes depends on the radioisotope in question and the concentration of the organic in solution. Crown Copyright (C) 1996 Published by Elsevier Sc ience Ltd