Influence of mixture ratio and pH to solidification/stabilization process of hospital solid waste incineration ash in Portland cement

Solidification/stabilization (S/S) is an established utilization technology to treat hazardous wastes. This research explored the influence of pH (3-12) on the immobilization of heavy metals present in five mixtures of hospital solid waste incinerator ash and Portland cement, following two different processes of waste solidification/stabilization (cement hydration and granulation). In general, cement hydration process resulted in more stable products than granulation process. A high ash content in the mixture with Portland cement (60 wt%) resulted in the highest immobilization of Pb2+ and Cu2+, while a low ash content in the mixture (10 wt%) resulted in the lowest leachability of Zn2+. When ash and Portland cement was mixed in equal proportions (50 wt%) the highest encapsulation was observed for Ni2+, Cd2+ and Cr3+. Neutral and weak alkaline pH values within the range pH = 7-8 resulted in the lowest leachability of the monitored heavy metals.