Performance and mechanism of copper removal from wastewater by sodium tetraethylenepentamine-N,Nʹ,Nʹʹ,Nʹʹʹ,Nʹʹʹʹ-pentadithiocarboxylic acid

Abstract Dithiocarboxylic(DTC)-type heavy metal chelating agents have received increasing attention since they can be used to treat wastewater for heavy metal removal efficiently. In this article, we used some of them, such as a conventional single-DTC chelating agent-sodium dimethyl dithiocarbamate (SDD), a new multi-DTC chelating agent-sodium tetraethylenepentamine-N, Nʹ, Nʹʹ, Nʹʹʹ, Nʹʹʹʹ-pentadithiocarboxylic acid (TEPA-5DTC). We observed that the residual concentration of Cu2+ treated by TEPA-5DTC can be low than the limitation(0.3 mg⋅L-1) at pH 5~10 while the wastewater treated by SDD cannot meet the limitation at overall pH, which means TEPA-5DTC has better efficiency of heavy metal removal and pH-resistance. According to the binding force by UV, XPS and FTIR methods and the microscopic shape of the chelating products by TEM and AFM observation, we found that the advantage of TEPA-5DTC strongly depended on the number of functional groups and the structure of molecules. The mechanistic studies suggested that TEPA-5DTC and Cu2+ can form a two-dimensional flat-type super molecule complex that increased the chelating efficiency and improved the settleability of the dregs compared to SDD. Furthermore, depending on the result of XRD analysis on the product of low temperature incineration of dregs formed by chelating agents and Cu2+, it showed a great potential of recycling copper through smelting. Given that TEPA-5DTC have much greater ability of copper removal and stability in different pH condition than SDD, this work urges the development of TEPA-5DTC for efficient elimination of copper.