Reduction of heavy metal emissions by adding modified attapulgite to sludge in bubbling fluidized bed incineration process

Abstract

The utilization of natural mineral adsorbents to adsorb heavy metals generated from sludge incineration was currently a research hotspot. To enhance the adsorption capacity of the adsorbent, a combination of thermal activation and acid-washing modification methods was designed to modify natural attapulgite. The effects of adding the adsorbent on the distribution of heavy metals (Cr, Cu, Ni, Zn, Pb, and Cd) were tested in a laboratory-scale bubbling fluidized bed reactor. The results indicated that increasing the incineration temperature could promote the transformation of heavy metals into the stable state in the incineration ash (bottom slag and fly ash), while facilitating the volatilization and enrichment of semi-volatile heavy metals (Zn, Pb, and Cd) in the fly ash. The addition of modified attapulgite during the sludge incineration process was superior to raw attapulgite, as it enhanced the capacity of unit adsorbents to adsorb and immobilize heavy metals in flue gaseous, thus reducing the emission of heavy metals. BCR and TCLP experiments indicated that a greater proportion of heavy metals in the incineration ash were transformed into the residual fraction, thereby reducing environmental risks. Characterization revealed that the composite modification approach promoted the adsorbent to expose more active sites and increase the active amorphous components, which improved the adsorption and immobilization of heavy metals.