Removal of soluble chlorides and valorization of incineration bottom ash through alkali fusion and hydrothermal techniques

Abstract

Improving the removal of chloride as well as the quality and application value of products is crucial for the practical treatment and utilization of waste incineration bottom ash. This research innovatively employed alkali fusion and hydrothermal techniques to achieve these objectives simultaneously and compared with traditional methods. Additionally, the effects of different parameters and the optimal operating conditions were identified and the characteristics of synthetic zeolite were examined. Experimental results demonstrated that waste incineration bottom ash is highly alkaline and contains 0.97% of soluble chlorides. Traditional leaching and washing methods achieved chloride removal efficiencies ranging from 82% to 91%; however, residual chloride levels in the bottom ash still exceeded acceptable limits for reusing as alternative construction materials. Using alkali fusion and hydrothermal technologies can significantly reduce soluble chlorides to below 0.02% and achieving nearly 100% removal efficiency while also producing high-quality zeolites from incineration bottom ash. The optimal operational conditions were identified as a silica-to-aluminium ratio of 20, an alkali/ash ratio of 2.0, a liquid-to-solid ratio of 150 and a hydrothermal time of 24 hours. The resulting synthetic zeolite was identified as ZSM-23 and exhibited favourable properties suitable for various applications, featuring a specific surface area of up to 853.19 m² g⁻¹. The findings demonstrate that alkali fusion and hydrothermal techniques is a superior alternative method for the treatment and utilization of waste incineration bottom ash, which has multiple functions, benefits and development potential.