Novel procedure for removal of the radioactive metals from aqueous wastes by the magnetic calcium alginate

Abstract

Upon incorporation of iron oxide particles into calcium alginate gels, composite magnetic materials called ferrogels can be obtained. It has already been found that the alginic ferrogel sorbent can be applied for purification of aqueous solutions containing ions of various heavy metals. In present paper, batch sorption experiments were carried out to remove radionuclides of caesium(I), strontium(II), europium(III) and americium(III) from aqueous solutions. The recovery of the radioactive metals was achieved by direct dosing of sodium alginate/iron carbonyl, followed by stirring the system for 2 h. The process was investigated as a function of the following parameters: pH, initial concentration of calcium ions and the amount of the dispersed iron in the 2% (w/w) aqueous solution of sodium alginate. The optimum conditions were: 15 g/L of iron carbonyl suspended in 1 L of aqueous solution of sodium alginate and about 20 g CaCl2 added to 1 L of the solution containing the radiometals. The results revealed that trivalent Am-241 was totally eliminated. Also trivalent Eu-152/154, divalent Sr-85 and monovalent caesium-137 were removed with the efficiency of about 80, 50 and 30%, respectively. It was found that exchange of calcium chloride with other metal salts does not influence significantly the removal efficiency. Laboratory-scale pilot experiments have shown that with aim to purify water, excess of the gelling agent can be removed with the method of nanofiltration. A one-step procedure for decontamination of liquid radioactive waste has been proposed. Calcium alginate with the inner magnetic core formed from iron carbonyl was found to be effective for aqueous solutions containing Am(III), Eu(III) and Sr(II) radionuclides, while only 30% of Cs(I) was removed in this process. It was demonstrated that there is no need to prepare the sorbent beads prior to the batch sorption.