Enhanced solidification/stabilization of lead in MSWI fly ash treatment and disposal by gelatinized sticky rice

Recently, innocent treatment of heavy metals in hazardous waste has become a hot topic in China. In particular, lead (Pb) as a typical heavy metal, is one of the easiest leaching heavy metal elements for municipal solid waste incineration (MSWI) fly ash. In this paper, different dosages of gelatinized sticky rice (SR) as green additives were added into the mixture of MSWI fly ash (FA) and ordinary Portland cement (OPC) to solidify/stabilize Pb in an attempt to optimize cement solidification. The leaching behaviour of Pb, hydration phases and hydration microstructure were determined by Toxicity Characteristic Leaching Procedures (TCLP) leaching test, Tessier sequential extraction method, XRD, BET and SEM. The results showed that Pb leaching concentration significantly decreased when adding 10% OPC and 30% gelatinized SR solution compared to only OPC treatment, and increasing dosage of SR also reduced Pb leaching concentration and met the criteria of landfill after curing 28 days. Additionally, increase of gelatinized SR dosage made Pb in fraction of Fe-Mn oxides more easily transformed into the stable crystal and organic matter structure of FA solidified products, and the growth of hydration products were restricted and particle size became finer. The addition of gelatinized SR also reduced initial/final setting times and increased compressive strength. The data suggest that the addition of gelatinized SR provides a new and clean approach to enhance the FA/OPC solidification/stabilization and reduce the leaching concentration of heavy metals in MSWI fly ash.