Selective extraction of cadmium(II) and Zinc(II) from hydrochloric acid with an alkylated piperazine derivative

Abstract

1,4-Di[[di(2-ethylhexyl)carbanoyl]methyl]piperazine (DDCMP) has been newly synthesized in a project to develop extractants with high selectivity and extraction abilities for cadmium(II) over zinc(II) and nickel(II) from the viewpoints of environmental protection and metal recycle from such wastes as Ni/Cd batteries and home electronics. The extraction selectivity for metals from hydrochloric acid was investigated using DDCMP in toluene at 303 K. DDCMP exhibited a high selectivity for cadmium(II) over zinc(II). In order to determine the reason for the high selectivity for cadmium(II), the extraction equilibria of cadmium(II) and zinc(II) were quantitatively studied by examining the concentration dependence of chloride and hydrogen ions on the extraction equilibria. Cadmium(II) was extracted as a 1:2 complex through ion pair formation and coordination bonding with the two nitrogen atoms of the piperazine moiety, respectively, while zinc(II) was extracted as a 1:1 complex through coordination bonding with the two nitgrogen atoms. We found that the selective extraction of cadmium(II) over zinc(II) is due to the difference in the extracted species with DDCMP. Stripping of cadmium(II) and zinc(II) was quantitatively performed by a single contact batch method using distilled water and dilute acids such as nitric acid hydrochloric acid sulfuric acid.