Fly Ash Pollutants, Treatment and Recycling

Abstract

This chapter reviews fly ash typology, composition, treatment, deposition, recycling, functional re-use, and metals and organic pollutants abatement. Fly ash is a by-product of power and incineration plants operated either on coal and biomass, or municipal solid waste. The growing of environmental awareness and increasing energy and material demand will foster recycling. Recycling will help to reuse valuable materials which would otherwise be wasted, and reduce energy consumption and greenhouse gas emissions from extract ion and processing. Fly ash is world’s fifth largest material resource because of the large amount of ash produced in the world. Fly ash can be classified into several categories: coal fly ash obtained from power plant burning coal; flue gas desulphurisation fly ash, that is the byproduct generated by the air pollution control equipment in coal-fired power plants to prevent (reduce) the release of SO2; biomass fly ash produced in the thermal conversion of biomass; and municipal solid waste incineration (MSWI) fly ash, that is the finest residue obtained from the scrubber system in a municipal solid waste incineration plant. Fly ash often contains pollutants such as heavy metals and organic compounds. The composition of fly ash is very variable, depending on their origins, then also the pollutants can be very different. For example, MSWI fly ash are the most problematic ash in terms of contaminant content. We review existing techniques for fly ash inertization, separately considering heavy metals entrapment or organic abatement. We show that fly ash is a valuable resource with potential use in several applications like agriculture, synthesis of zeolite and geopolymer, adsorbent and building materials. Finally all advantages in fly ash recovery and re-use are discussed. It is shown that fly ash recycling will reduce landfilling disposal, raw materials employ, greenhouse gas emission and water consumption.