Removal of thallium from wastewater by a combination of persulfate oxidation and iron coagulation

Thallium (Tl) removal from wastewater using a ferrous iron-persulfate (Fe2+-S2O82−) Fenton-like system was investigated. Factors influencing Tl removal, namely S2O82− dosage, Fe2+/S2O82 molar ratio, reaction pH, coagulation pH, co-existing metal ions, co-existing organic matter, and initial Tl concentration, were examined. The results show that Tl removal efficiency increased with increasing S2O82− dosage. Effective Tl removal (>96%) was achieved when the Fe2+/S2O82− molar ratio was higher than 1:1. The reaction pH had little effect on Tl removal, while the coagulation pH significantly affected it. Coagulation pH exceeded 10 was favorable to Tl removal (>96%). Tl removal efficiency was reduced by about 30% when the concentration of co-existing organic matter was higher than 100 mmol/L. More than 90% of Tl was removed when the initial Tl concentration increased from 20 μM to 150 μM. Based on the SEM-EDS, XPS and FT-IR spectroscopic analyses, it is concluded that the absorption of colloidal ferric hydroxide and the oxidative precipitation of the Fe2+-S2O82− system are the main mechanisms for the removal of Tl. Given the excellent Tl removal and stable performance, the Fe2+-S2O82− system could be an effective and promising alternative for Tl removal from wastewater.