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.

Performance of poly(styrene-co-divinylbenzene) functionalized with different aminophosphonate pendant groups, in the removal of phenolic compounds from aqueous solutions

In the present work, we describe the synthesis and characterization of styrene-6.7%-divinylbenzene copolymers functionalized with aminophosphonate groups by “one-pot” reactions. Different aminophosphonate groups were grafted on the copolymer with the aim of obtaining adsorbents for removal of phenolic compounds from aqueous solutions. Adsorption experiments were carried out in batch system. The phenolic compounds studied were phenol and 2,4,6-trimethyl-phenol. The best adsorption capacity was observed in the case of polymeric adsorbents functionalized with aminophosphonate groups in para- position of the aromatic nucleus for both phenol and 2,4,6-trimethyl-phenol. In comparison, the copolymers with the functional groups in ortho- position and respectively in meta- position were slightly less efficient. The differences in adsorption efficiency may be explained taking into account the structure of the adsorption active centers. The possible explanation is that the active functional groups responsible for the adsorption process, grafted in ortho- or meta- position could be affected by possible steric hindrance effects. The difference between the adsorption capacities of the polymers of the same series, are rather small and depending on the nature of the radical found in the structure of the aminophosphonate: isopropylamine or isobuthylamine.

Thallium Transfer from Hydrochloric Acid Media into Pure Ionic Liquids

Pure hydrophobic ionic liquids are known to extract metallic species from aqueous solutions. In this work we have systematically investigated thallium (Tl) extraction from aqueous hydrochloric acid (HCl) solutions into six pure fluorinated ionic liquids, namely imidazolium- and pyrrolidinium-based ionic liquids with bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)-imide anions. The dependence of the Tl extraction efficiency on the structure and composition of the ionic liquid ions, metal oxidation state, and initial metal and aqueous acid concentrations have been studied. Tl concentrations were on the order of picomolar (analyzed using radioactive tracers) and millimolar (analyzed using inductively coupled plasma mass spectrometry). The extraction of the cationic thallium species Tl(+) is higher for ionic liquids with more hydrophilic cations, while for the TlX(z)(3-z) anionic species (where X = Cl(-) and/or Br(-)), the extraction efficiency is greater for ionic liquids with more hydrophobic cations. The highest distribution value of Tl(III) was approximately 2000. An improved mathematical model based on ion exchange and ion pair formation mechanisms has been developed to describe the coextraction of two different anionic species, and the relative contributions of each mechanism have been determined.