Development of a Heavy Metal Immobilization Process Using Geopolymers

Abstract

Geopolymers using coal fly ash, an industrial byproduct from coal-fired power plants, have the ability to immobilize heavy metals during the curing process, and are expected to be used in the field of environmental remediation. The low reactivity of coal fly ash and the long curing time required for curing are practical issues. In this study, geopolymers were prepared by the mechanical treatment of coal fly ash particles under relaxed curing conditions, and the effect of the mechanical treatment on the Pb²⁺ immobilization ability of coal fly ash was investigated. The mechanically treated coal fly ashes were subjected to the mechanical treatment, and the increase in specific surface area and the decrease in crystallinity promoted the leachability of Al³⁺ and Si⁴⁺ ions, which are necessary for hardening of the geopolymer. As a result, the geopolymer could be cured at room temperature and in a short time, and the room temperature curing showed the same high Pb²⁺ immobilization capacity as that of the heat curing. It is suggested that the mechanical treatment of coal fly ash particles contributes not only to the curing reactivity of the geopolymer but also to its heavy metal immobilization ability.

Graphical Abstract

SEM images and specific surface area of coal fly ash milled by various comminution time.