Effects of chlorides on Cd transformation in a simulated grate incinerator during sludge incineration process

The effects of organic chloride-PVC and inorganic chloride-NaCl on Cd partitioning during sludge incineration with adding Cd( CH3COO)2·2H2O to the real sludge were investigated using a simulated tubular incineration furnace. And transformation and distribution of Cd were studied in different sludge incineration operation conditions. The results indicated that the partitioning of Cd tended to be enhanced in the fly ash and fule gas as the chloride content increasing. The migration and transformation of Cd-added sludge affected by different chloride were not obvious with the increasing of chloride content. With increasing temperature,organic chloride( PVC) and inorganic chloride( NaCl) can reduce the Cd distribution in the bottom ash. However,the effect of chlorides,the initial concentration and incineration time on Cd emissions had no significant differences. Using SEM-EDS and XRD technique,different Cd compounds including CdCl2,Na2CdCl4,K2CdCl6,K2CdSiO4 and NaCdO2were formed in the bottom ash and fly ash after adding NaCl to the sludge. In contrast,after adding PVC to the sludge,the Na2CdCl4 and CdCl2were the main forms of Cd compounds,at the same time,K4CdCl6 and K6CdO4were also formed. The two different mechanisms of chlorides effects on Cd partitioning were affected by the products of Cd compound types and forms.