Recovery of heavy metals in electrostatic precipitator ash by carbon dioxide as a pre-extraction reagent

This study investigated the efficiency of heavy metal separation and recove ry in electrostatic precipitator (ESP) ash from a municipal solid waste inc inerator (MSWI) when carbon dioxide is used as the pre-extraction agent. Th e experiments were conducted at 120 degreesC with pH values of 3-6 and liqu id-to-solid (L/S) ratios varying from 10:1 to 40:1. The results indicate th at an increase in the L/S ratio enhances the separation and recovery effici ency of heavy metals in the MSWI ash. The separation efficiency of Cd, Cr, and Zn increased significantly with the increased L/S ratio. The pH level w as the prominent factor affecting the extraction of heavy metals from ESP a sh: at pH 3-4, maximum amounts of Cd and Cr were extracted. However, due to the increased release of ions with increased CO32- Zn was relatively solub le at high pH values. In cases with an L/S ratio of 40:1 and pH 3, the Cd, Cr, and Cu extraction amounts were 86.4%, 71.2%, and 34.9%, respectively. P b and its compounds remained in a stable state under experimental condition s. The above results point toward the feasibility of heavy metal recovery a nd fly ash reutilization when carbon dioxide is used as the pre-extraction agent. Both greenhouse gas (CO2) emissions and acid extraction operating co sts are reduced with this process.