Pre-treatment and utilisation of municipal solid waste incineration bottom ashes towards a circular economy

Abstract

Two billion tonnes of municipal solid wastes are generated globally, and incineration of non-recyclable wastes is done extensively in developed countries. A large part of the resulting ashes remains unutilized due to various obstacles and ends up in landfills. Use in concrete as aggregate or supplementary cementitious material is a potential high value application, which is deterred mainly by presence of metallic aluminium that causes cracks from aluminium hydroxide formation and high porosity from hydrogen release on reaction with water. Various researchers have used treatment with alkalis prior to utilization as a mitigation strategy. This paper studied an alternative technique, pre-treatment by immersing ash in water allowing the aluminium to react in presence of inherent alkalis in the ash and accelerating the reaction by increasing temperature. The effect of this treatment on mitigating expansion and hydration and strength development of mortar with 25% replacement of cement by ash has been studied and is reported in this article. The treatment was found to be effective and the strength of mortar with 25% pre-treated ash replacement exceeded 85% of that of the control mortar at 90 days of age. A possible beneficiation scheme for the industrial treatment of ashes to maximise the resource utilisation is also proposed.