Hydrothermal treatment of bottom ash from the incineration of municipal solid waste: Retention of Cs(I), Cd(II), Pb(II) and Cr(III)

The retention of Cs+, Cd2+, Pb2+ and Cr3+ by the compounds formed as a result of the hydrothermal treatment of the bottom ash from the fluidized-bed incineration of municipal solid wastes is examined in this work. The amount of Cs+ retained and the distribution coefficient, Kd, were considerably lower than those for Cd2+, Pb2+ and Cr3+, independently of the type of compounds formed by the different bottom ash treatments. The high percentage of Cs+ retained (31%), with a Kd of 222 ml/g, occurred after treatment of the bottom ash in NaOH at 200 °C, where zeolite-type A (Na6[AlSiO4]6·4H2O) was the major compound, together with aluminum tobermorite (Ca5Si5Al(OH)O17·5H2O). In the case of Cd2+, Pb2+ and Cr3+, the amount retained was ∼99% under all of the conditions studied.