Sludge gasification: Mineral behaviours and the high-value utilisation of gasification ash

Gasification technology is one of the advantageous methods to dispose sewage sludge, and the sludge gasification ash has the potential to be reused as an auxiliary material for rock wool production. In this study, the mineral behaviour of two sludge samples (dyeing sludge and municipal sludge) in gasification process, as well as the impacts of sludge gasification ash on the properties and mineral behaviours of raw material of rock wool, were investigated through qualitative and quantitative analyses. Results show that the minerals in dyeing sludge are mainly Fe-oxides and Fe-silicates because of high Fe content, while that in municipal sludge are primarily silicates and phosphates containing Ca, Mg, Fe, and Al. The municipal sludge gasification ash presents superior performance than dyeing sludge gasification ash on decreasing ash fusion temperatures, mineral behaviours, and liquid-phase content of raw material of rock wool at high temperatures. With the addition of dyeing sludge gasification ash, iron spinel comes into existence and Fe-compounds contents increases significantly. Moreover, the heavy metals in sludge gasification ash samples are successfully solidified, presenting an extremely low risk of leaching toxicity. It is favorable to provide a theoretical foundation for the ash chemistry of sludge gasification and the value-added utilisation of sludge gasification ash.