Batch extraction studies of cationic and anionic heavy metallic species by a mixed solvent extraction system

Removal of toxic heavy metals from wastewaters and their recovery is a challenging problem. Simultaneous and synergistic batch extraction from water of copper present as a cation (Cu2+) and Cr6+ present as an anion (HCr2O7-) into a mixed solvent extraction system have been studied. The mixed solvent extraction system consists of the diluent kerosene, the cation exchanger LIX 84, and trioctyl amine (TOA) which extracts anions via ion-pair formation with a proton. Highly efficient extraction has been achieved for both copper and chromium. Simultaneous extraction of two cations, Cu2+ and Zn2+, as well as the anionic form of Cr6+, (HCr2O7-), has also been studied using mixtures of LIX 84, di-2-ethylhexyl phosphoric acid (D2EHPA), and TOA in the diluent kerosene. For an appropriate mixture composition, all three metallic ionic species can be simultaneously extracted with high efficiency. The extent of complexation between the basic extractant, TOA, and the acidic extractant/s is important in determining the extraction efficiency. A model developed for the extraction of Cu2+ using a mixed solvent extraction system provides a reasonable description of the observed extraction behavior and provides a first step for modeling.