Kinetics of radiocesium released from contaminated soil by fertilizer solutions

Abstract

137Cs is one of the major artificial radionuclides found in environments; but the mechanisms behind fertilizer-induced 137Cs desorption from soil remain unknown. This study aimed to investigate the kinetics and mechanisms underlying the various cations and anions that cause Cs release from soil under acidic conditions. NH 4H 2PO 4 (1 M), 0.5 M (NH 4) 2SO 4, 1 M NH 4Cl, 1 M KCl or 1 M NaCl solutions were added to 137Cs-contaminated soil. The power function model well described the short term 137Cs desorption with the solutions. The rate coefficients for 137Cs release from soil in NH 4H 2PO 4, (NH 4) 2SO 4, NH 4Cl, and KCl solutions were 7.7, 7.3, 6.8, and 6.1 times higher than the rate observed in a NaCl solution, respectively. The NH 4H 2PO 4 and (NH 4) 2SO 4 solutions induced significantly greater 137Cs release from the contaminated soil than the NH 4Cl, KCl and NaCl solutions. After four times repeated extractions with the fertilizer solutions, the total amount of 137Cs extracted by (NH 4) 2SO 4 and NH 4Cl solutions reached equilibrium, while that extracted using an NH 4H 2PO 4 solution continued to increase. The combined effect of phosphate and protons was the major mechanism behind 137Cs release from contaminated soils, when an NH 4H 2PO 4 solution was used.