Exploration of novel high-temperature heavy metals adsorbent for sludge incineration process: Experiments and theoretical calculations

Adsorption is an effective and environment-friendly method to control the pollution of volatile and semi-volatile heavy metals (HMs) produced during municipal sludge incineration. In this study, the effect of a novel high-temperature adsorbent (attapulgite) on the migration and transformation mechanisms of HMs (Cr, Cu, Zn, Ni, and Pb) was investigated and compared with the conventional adsorbent (kaolin). The results of experiments and characterization showed attapulgite possessed improved adsorption effects than kaolin due to the smaller crystal distortion and more active sites reserved at 850 ℃. Furthermore, it was found that volatile HMs (Pb, and Zn) tend to be retained in the fly ash, while low-volatile HMs were adsorbed in the bottom slag by Si-Al-based absorbents. Meanwhile, the analytical results of BCR and TCLP tests showed that the proportion of unstable fraction of HMs in the adsorption products of attapulgite was much lower than that of raw dry sludge, and exhibited better leaching stability than kaolin. Theoretical calculations revealed that the adsorption of typical heavy metal forms at high temperatures by attapulgite exhibited a tight chemical adsorption, furthermore, the heavy metal oxides were more susceptible to removal by attapulgite (1 1 0) surface than the corresponding heavy metal chlorides. This work demonstrated the effectiveness of attapulgite in controlling heavy metals in furnaces and provided a new perspective on the development of this field. • Attapulgite was applied to adsorb volatile heavy metals in sludge incineration. • The leaching toxicity of bottom slag after adding adsorbent was evaluated. • Dehydroxylation played an important role in the adsorption process. • The adsorption of heavy metals on attapulgite surface was investigated by the DFT method. • The adsorption energy of metal oxides was higher than that of its chlorides.