Removal of radioactive strontium from water by coagulation–flocculation with ferric hydroxide

Abstract

AbstractA systematic study of the removal of the radioactive fission product strontium from aqueous solution by ferric hydroxide flocs has shown that strontium can be removed effectively, in contrast to caesium which is poorly removed (⩽5%) under all conditions examined. Removal of strontium was enhanced by raising pH to a maximum of 10.5, increasing the iron/strontium ratio, or by adding phosphate ion, provided the phosphate/iron mole ratio did not exceed 0.33. In the absence of phosphate the optimum conditions for strontium removal, over the range of iron and strontium concentrations examined, were pH 10 and strontium/iron mole ratio 0.08. Addition of phosphate reduced the pH at which significant removal was obtained to about 8. The mechanism of removal has been identified as an ion‐exchange reaction at the surface of the ferric hydroxide particles; consequently, when considering the process for the removal of stron‐tium‐90 from hard natural or process waters competitive effects from the larger concentrations of calcium and magnesium present in the water would become important.