Stabilization of Heavy Metals in Municipal Sludge Using a Slag-Based Modifying Agent

Abstract

Taking urban domestic sludge as the research object, a slag-based modifying agent was used to modify sludge under different dosages and curing times, and the solidification effect of six heavy metals in the sludge, namely Zn, Cr, Cu, Pb, As, and Cd, were evaluated by analyzing stability efficiency and morphological changes. The results showed that the stability efficiency improved as curing time and dosage increased, reaching the maximum when the curing time was 14 d and the dosage was 50%. Under these conditions, Cu reached the maximum of 69.62%, and the most rapid growth was observed when dosages were 5%-20%. Through the regression analysis of adding amount, maintenance time and stability efficiency, it was found that the fitting correlation coefficient Cu was the highest 0.97, with a strong degree of fitting and a strong interaction between adding amount and maintenance time, which had a significant influence on the stability efficiency. In addition, Pb and As were the residual state, Cu and Cr were oxidizable state and residue state, Zn and Cd were reducible and extractable state as the main forms in the sludge after modifying, respectively. With the increase of curing time or dosage, the residual state of each heavy metal increased by 7%-86%. The results showed that the slag-based modifying agent could effectively solidify heavy metals in sludge and reused solid wastes such as sludge.