Removal of thallium in water/wastewater: A review

The frequent occurrence of thallium (Tl) in surface water has led to the imposition of strict environmental regulations. The need for an overview of effective and feasible technology to remove Tl from water/wastewater has therefore become urgently. This review introduced the current available methods for Tl removal, including adsorption, oxidation-reduction precipitation, solvent extraction and ion exchange processes, and summarized their advantages and disadvantages. The results showed that a single treatment technology was difficult to remove Tl to a trace level of "μg L^-1", which required combined multi-technology to enhance the removal efficiency. In addition, the potential emergency and feasible technologies for Tl removal were recommended. However, several fundamental issues, such as the comparative toxicity of Tl(I) and Tl(III), the confliction of hydrolysis constants, the interference of complexant ligands as well as the influence of redox potential, were still needed to be addressed, since they would profoundly affect the selection of adopted treatment methods and the behavior of Tl removal. Future research efforts concerning the improvement of existing Tl removal technologies should be devoted to (a) developing multi-functional chemicals and adsorbents, non-toxic extractants, easy-recovery ion exchange resin and high-efficient coupling technology for advanced treatment, (b) carrying out large-scale experiments and economic assessment for real wastewater, and (c) providing safe-disposal treatment for the exhausted adsorption materials or sludge.