Immobilization of cadmium onto activated carbon by microwave irradiation assisted with humic acid

Adsorption is an effective method for the removal of heavy metal ions from wastewater. However, technologies are needed to regenerate the saturated adsorbents for reuse and to immobilize the adsorbed heavy metal ions for the final disposal of the disused adsorbents. The presence of humic acid in water may influence adsorption and the subsequent immobilization of heavy metal ions. In this study, microwave irradiation was adopted to regenerate granular activated carbon (GAC) saturated with Cd2+ and to also immobilize Cd2+ onto GAC. The effects of humic acid on adsorption of Cd2+ onto GAC and the immobilization of Cd2+ by microwave irradiation were investigated. The results showed that specific concentrations of humic acid promoted the adsorption of Cd2+ onto GAC as well as the immobilization of Cd2+ by microwave irradiation, which may be attributed to the complexation of humic acid with Cd2+, as indicated by the three-dimensional fluorescence spectra. Several important parameters including microwave power, irradiation time and water content of GAC were found to have significant effects on the immobilization of Cd2+ onto GAC by microwave irradiation. Evaluation based on the toxicity characteristic leaching procedure (TCLP) showed that for the dried GAC, approximately 89% immobilization of Cd2+ was achieved with 750 W of microwave irradiation for 10 min. This technology may also be effective for the immobilization of other metal ions, including Cu2+, Zn2+ and Pb2+.