Selective extraction of heavy metals from sewage sludge via combined process of acid leaching and ion exchange resins adsorption: Optimization and performance evaluation

Heavy metals (HMs) in sewage sludge (SS) are major obstacles that limit the land application of SS. Although the removal of HMs with acid leaching and cation exchange resins (CER) adsorption has been investigated, neither process alone could meet the simultaneous demand for efficient HMs removal and good preservation of nutrients. In this report, sulfuric acid (H2SO4) and acetic acid (AC) were used to dissolve HMs from the SS, and subsequent CER adsorption was conducted to selectively extract the HMs from acid leachate. With the addition of 5 mmol/L H2SO4, the maximum leaching efficiency of Ni, Cu, Zn and Fe were 64.0%±2.7%, 29.0%±3.7%, 98.4%±4.1% and 16.4%±0.3%, respectively. No significant inhibition effect of Fe in the leachate on the HMs adsorption with CER has been observed. The CER with sulfonate groups (R-SO3H) showed higher Ni, Cu and Zn adsorption efficiency than the CER with thioureido groups (R-SH) and carboxylic groups (R-COOH) in the acid leachate. The optimal operation condition with a combined usage of H2SO4 and R-SO3H is characterized by the advantages of high HM removal efficiency, affordable cost, and low energy consumption through the evaluation with the triangulation model.