Utilization of contaminated air pollution control residues generated from sewage sludge incinerator for the preparation of alkali-activated materials

The air pollution control (APC) residues from the sewage sludge incinerators are harmful to the environment due to their relatively rich soluble salts and heavy metal content. In this paper, the APC residues were pre-treated by water washing at the different liquid to solid ratios (L/S), and a ternary contour diagram was introduced to optimize the composition of slag, waste glass powders and APC residues in alkali-activated materials (AAMs). The result showed that the washing method could remove sulfate of APC residues, while the heavy metals and chloride required a higher L/S ratio to achieve a higher removal rate. Incorporation of the APC residues reduced the compressive strength of AAMs mortar, but the AAMs prepared with the washed APC residues showed a higher compressive strength than the unwashed APC residues. The sulfate from the unwashed APC residues can be used as an activator to improve the drying shrinkage of the AAMs due to the formation of ettringite, while the washed APC residues can be used as a precursor of the AAMs due to the rich aluminosilicate content. The leaching test results indicated that up to 30% washed APC residues incorporated into AAMs showed little leaching of heavy metals. On the contrary, when more than 10% unwashed APC residues are used, the pre-treatment is necessary before they can be utilized for preparing AAMs due to the leaching of heavy metals.

Automated summary

This paper investigates the potential application of water washing pre-treatment to improve the utilization of air pollution control (APC) residues in alkali-activated materials (AAMs). The results show that water washing can effectively remove sulfates from the residues, while higher liquid to solid ratios are required for the removal of heavy metals and chlorides. The AAMs prepared with washed residues exhibit higher compressive strength and lower leaching of heavy metals.