The effects of chloride additives on adsorption of heavy metals during incineration

The dynamic adsorption behaviors and characteristics of heavy metals on a sorbent at different temperatures have been investigated, in a previous study by the same authors. The present work focuses on the dynamic adsorption behaviors of Cr, Cu, Pb, and Cd on a sorbent (silica sand with limestone) under various chloride additive conditions (no chloride; an organic chloride, polyvinyl chloride [PVC]; and an inorganic chloride, sodium chloride [NaCl]), and estimates the adsorption saturation point of the sorbent during fluidized-bed incineration. The results will enable us to evaluate the effects of various chloride additives on the adsorption efficiency of heavy metals and to determine when the sorbents should be renewed. From the perspective of controlling heavy metal emissions, the results indicated that (1) using the NaCl additive generally led to a higher adsorption capacity than did a PVC additive or no additive at all; and (2) cadmium was extremely difficult to remove in any situation. Most adsorption curves of chloride additives did not reach the adsorption saturation point because of their relatively high volatility. Under the same chloride additives condition, the adsorption capacities of the sorbent for the four metals followed the sequence Pb>Cu>Cr>Cd with no chloride additive; Cr>Pb>Cu>Cd with PVC additives; and Cu>Cr>Pb>Cd with NaCl additives.