Two processes for decontamination of radioactive aqueous wastes by precipitation and coagulation.

In an investigation of the efficiency of the calcium/ferric phosphate process for removal of various radio-isotopes from solution using a sludge blanket clarifier 70 per cent, removal of uranyl and strontium ions and mixed fission products was achieved but cesium removal was poor, in agreement with other workers. Dosing ion concentrations were 80 p.p.m. PO4---, 50 p.p.m. Ca++ and 40 p.p.m. Fe+++, used at an initial pH of 11.5. Use of a lower concentration and lower pH values did not materially affect removals. In batch experiments to find the optimum concentration of ions for precipitation at a pH of 9.5 it was found that concentrationsof 90 p.p.m. PO4---, 50 p.p.m. Ca++ and 40 p.p.m. Fe+++ leave very small residual concentrations in the supernate. Removals of radio-isotopes from solution by precipitation using the aluminium hydroxide process are comparable with those in the calcium/ferric phosphate process, except for that of strontium. It is recommended that 8.0 be used as the maximum pH for the precipitation of aluminium hydroxide in the sludge blanket clarifier. Thickening experiments with a sludge blanket clarifier using both processes show that the degree of thickening is governed by the size and relative proportions of the clarifier