Cd-ion removal using 1,1,1-tris(methyl N-carbodithioic acid)-9-decene extractant: synthesis, extraction behaviors, and mechanism

Industrialization has increased the demand for hazardous metal ion removal. One of the critical steps in the metal removal process is extraction, and the most important component is the extraction reagent. Herein, 1,1,1-Tris(methyl N-carbodithioic acid)-9-decene (TriDTC) was synthesized together with the corresponding monopodal compound (MonoDTC) and its heavy-metal-ion extraction behavior was studied. Compared with MonoDTC, TriDTC exhibited higher extractability and selectivity for Cu(ii), Pb(ii), and Cd(ii). MonoDTC exhibited selectivity for Cu(ii) based on the dithiocarbamate functionality, whereas TriDTC exhibited selectivity not only for Cu(ii) but also for Pb(ii) and Cd(ii) owing to size-discriminating and converging effects based on the tripodal framework. The slope analysis results showed that the Cd extraction mechanism using TriDTC is an ion-exchange mechanism, in which one Cd ion is extracted by releasing two protons from two TriDTC molecules to form six Cd-S bonds, producing a Cd complex with a coordination number of 6. Meanwhile, the extraction of Cu(ii) with MonoDTC follows an ion exchange mechanism, which undergoes coordination changes as a function of shaking time in acidic media.