Synthesis of heavy metal chelating agent with four chelating groups of N1,N2,N4,N5-tetrakis(2-mercaptoethyl)benzene-1,2,4,5-tetracarboxamide (TMBTCA) and its application for Cu-containing wastewater

Highlights: ► A new heavy metal chelating agent of TMBTCA with four chelating groups was prepared and characterized. ► The effects of mole ratio of reactants, reaction temperature, reaction time on the yield of TMBTCA were illustrated. ► The effects of mole ratio of TMBTCA/Cu2+, reaction time and pH on its application properties were researched. ► This new chelating agent could effectively remove Cu2+ and CuEDTA to much lower than 0.5 mg/L. - Abstract: A novel heavy metal chelating agent, N1,N2,N4,N5-tetrakis(2-mercaptoethyl) benzene-1,2,4,5-tetracarboxamide (TMBTCA), was designed with four chelating groups, and a facile one-step synthetic procedure was developed with pyromellitic dianhydride (PMDA) and cysteamine hydrochloride (CHC) as raw materials by aqueous acylation. The effects of mole ratio of reactants (CHC/PMDA), reaction temperature, and reaction time on the yield of TMBTCA were studied. Its application for Cu-containing wastewater was investigated. The experimental results showed that the maximum yield of TMBTCA was 75.92%, as the mole ratio of CHC/PMDA reached 4.8, reaction temperature was 5 °C, and reaction time was 6 h. It was observed that TMBTCA could effectively remove Cu2+ and CuEDTA to much lower than 0.5 mg/L (the discharge limit of copper ions in China). Furthermore, TMBTCA showed more affinity for cadmium and copper than some traditional commercial precipitants, such as DTC, TBA and TMT, via comparison of their ability for heavy metal removal, and the precipitates of Cu-TMBTCA and Cd-TMBTCA presented good stability in leaching tests. The results can provide a reference for design and further research on new kind of heavy metal chelating agent with more bonding sites, especially for heavy metal precipitation in PCB wastewater treatment.