(Bourtsalas, 2015)

In the UK, a growing proportion of household waste is disposed of via Energy from Waste (EfW) plants, overtaking landfill in 2020 as the main disposal method for the UK’s residual municipal waste (52% in 2020) (Tolvik, 2021). Energy from Waste plants normally use combustion and essentially serve two purposes: they burn waste to generate energy (mainly electricity, but also heat) and in the process, they reduce the volume of waste to be disposed.

The contents of one bin bag to the next might vary considerably, but when the material is viewed in aggregate at the scale of material required for incineration, these differences tend to even out (DEFRA, 2014) to longer term trends. A 2017 survey by WRAP indicates that at a national scale, the material predominantly comprises of paper & card (30.4%), food waste (24.5%), plastic (19.4%), and a range of other materials in lower amounts of less than 5% (Scholes, 2020).

The bottom ash generated in the UK’s energy from waste plants contains a mixture of ‘parent’ waste materials that survived incineration, including metals, glass, ceramics, rock and unburned organic residues, alongside secondary products that were generated from the incineration process such as slag and ash.

IBA material ranges in size from 0.01mm to 100mm, and there is typically a fractionation of elements depending on particle size (Loginova et al., 2019), with metals most concentrated in the size fraction >50mm, batteries, coins in the fraction 16-50mm, glass, ceramics and aluminium in the fraction between 8-16mm and mineral materials in the finer fractions (Huber et al., 2020) (del Valle-Zermeño et al., 2017). An overall compositional range has been estimated by (Šyc et al., 2020) ranging between 5-15% ferrous metals, 1-5% non-ferrous metals, 10-30% glass and ceramics, 1-5% unburned organics and 50-70% minerals.

IBA typically goes through a metal recovery stage, which accounts for around 1.9% of the total fuel input (Tolvik, 2021) and it is weathered, before being recycled as construction aggregate or disposed of to landfill. The weathering process exposes the IBA to water and CO2 in the air, resulting in the carbonation and hydration of mineral phases, the binding of dissolved elements and leaching of highly dissovable salts, resulting in greater chemical stability and reduced reactivity (Bourtsalas, 2015).

The predominant application for IBA is as a construction aggregate for road construction and it is therefore in the UK is typically processed and graded in size ranges corresponding to the Specification for Highway Works 600 and 800 series. Previous research has identified the fine fraction of IBA as the most problematic for secondary uses (Bourtsalas, 2015),

(Bourtsalas, 2015)
(Tolvik, 2021)
(DEFRA, 2014)
(Šyc et al., 2020)
(Loginova et al., 2019)