Accelerated carbonation of different size fractions of MSW IBA and the effect on leaching

• Degree of carbonation of IBA decreased as size increased.
• This decrease is due to decreasing total Ca content and portlandite phase.
• Percentage reduction in leaching did not correspond to degree of carbonation.
• This reduction was attributed to decrease in pH and formation of secondary mineral.

Accelerated carbonation has been studied as a treatment method for MSW IBA, and the main advantage is that it can shorten the treatment duration from months to days, compared to natural weathering. This study investigated the effect of accelerated carbonation on different size fractions of IBA collected from two incineration plants in Singapore. The different size fractions were ground to <425 μm to minimise the influence of morphological difference on carbonation efficiency from that of chemical and mineralogical differences. Total element content was carried out for IBA collected from both incineration plants and the different size fractions. XRD was also used to analyse the mineralogical composition of IBA. Results showed that the degree of carbonation decreased as the size increased, which in turn corresponded to decreasing total Ca content and portlandite phase. The leaching behaviour of Pb, Zn, Cu, Cr and soluble constituents like DOC, Cl−, and SO42− were evaluated. It was found that carbonation resulted in the reduction of leaching of most constituents, except Cl− and SO42−. The reduction in leaching after carbonation can be attributed to the decrease in pH and formation of secondary minerals, rather than the precipitation of calcite. The research also suggested that since the leaching of soluble constituents from untreated IBA is mainly from the fine fractions and the fine fractions are more reactive to accelerated carbonation, size separation is beneficial in improving the carbonation efficiency and reducing the volume of IBA that needs to be treated, which can potentially reduce the treatment cost of IBA.