Removal of mercury (II) from aqueous solutions by multiwalled carbon nanotubes coated with manganese oxide

Background and aims: Water pollution by heavy metals is one of the most important environmental problems. Among the heavy metals,mercury (Hg) is a very toxic metal and its high concentration can lead to impaired pulmonary and renal dysfunction. The aim of this studywas to determine the amount of Hg removal by carbon nanotubes coated with manganese (Mn) oxide from aqueous solutions.Methods: In this study, multi-walled carbon nanotubes coated with Mn oxide were prepared and used to remove Hg from aqueousenvironments. In addition, the physical and structural characteristics of the nanotubes were determined by the X-ray diffraction (XRD). Theimpact of diverse variables was further investigated, including the initial concentration of Hg, the initial pH of the solution, contact time,mixing rate, as well as the amount of nano-composite and the impacts of confounders (nitrate and chloride). Finally, optimum conditionsfor each of these parameters were obtained by the Taguchi statistical method.Results: The XRD analysis showed that the nanotubes were properly coated with Mn oxide. Furthermore, the results demonstrated thatunder pH ۷, the rate of mixing of ۱۵۰ rpm, the contact time of ۶۰ minutes, the amount of nano-composite of ۶۰ mg, and the initial densityof Hg ۸۰ mg/L can be achieved by removing ۹۵% Hg. Moreover, the confounder factors of nitrate and chloride reduced the amount of Hgremoval by ۴ and ۵%, respectively.Conclusion: Based on the results, the nanotubes coated with Mn oxide can be used as easy and strong absorbents for the rapid absorptionof Hg from drinking water and industrial wastewater.

Keywords:

Mercury , Multi-walled carbon nanotubes , Nano-manganese , Taguchi method