Removal of low concentration Hg 2+ from natural waters by microporous and layered titanosilicates

Abstract

Mercury is one of the most toxic heavy metals present in aquatic systems, exhibiting a complex behaviour in the environment, where it may persist for decades after the source of pollution is stopped. Hence, it is important to, both, study the complex phenomena that control the transference of mercury to the environment, and develop new techniques for its removal from the aquatic systems. In this context, a particularly promising line of research is the synthesis of materials capable of uptaking mercury from aqueous systems. Microporous and layered titanosilicates have unique physical and chemical properties due to their structure. Here, the microporous materials ETS-10, ETS-4, AM-2 and layered AM-4 have been prepared and their capacity to uptake Hg 2+ from aqueous media found to be ETS-4 > ETS-10 > AM-2 and AM-4. For these four materials, the kinetics of the Hg 2+ removal from water is better described by a pseudo second-order model. The presence of the competitive Ca 2+, Na + and Mg 2+, which are the dominant cations in freshwater, does not reduce the ETS-4 mercury uptake capacity, even when their concentrations are much larger than the concentration of Hg 2+. Although the presence of these ions slows down slightly the kinetics of Hg 2+ sorption by ETS-4, this process is still second-order. High Cl − concentrations greatly reduce the Hg 2+ sorption capacity of ETS-4 and slow down the uptake kinetics, due to the formation of neutral or negatively charged mercury chloro-complexes. Thus, ETS-4 may not be efficient in the remediation of salty or sea waters.