INTERACTION OF MUNICIPAL SOLID-WASTE ASH WITH WATER

Municipal solid waste (MSW) incineration ash is composed mainly of glasses and common minerals. We examine the dominant chemical reactions occurring between water and MSW ash using batch reactors. The ash-water solutions are dominated by ions released by soluble salts. X-ray diffraction documents the dissolution of soluble salts and the precipitation of at least one secondary alteration mineral. Three types of reactions are identified. (1) After rapid exhaustion of soluble salts, sodium and potassium exhibit nearly steady-state behavior due to the slow release of ions from less soluble minerals and glasses. Approximately 10 kg of anhydrous salts could be precipitated from a solution contacting each metric ton of ash. (2) Calcium and sulfate concentrations are controlled by either gypsum or anhydrite equilibrium after a few hours. Iron, aluminum, and manganese concentrations rapidly equilibrate with respect to hydroxide or oxide solid phases. (3) Silicon clearly shows temperature-dependent kinetic behavior, but its rate of release into solution is slowed by back-reaction of a secondary silicate phase.