Extraction of Co²⁺ and Cd²⁺ from wastewater using hydrophobic ionic liquids as solvents

Extraction of Co²⁺ and Cd²⁺ into hydrophobic ionic liquids of [Bmim]PF₆, [Hmim]PF₆ and [Omim]PF₆ is investigated for examining their removal from wastewater. The results indicate that the extraction rates of both Co²⁺ and Cd²⁺ are very low without chelator. However, the extraction rates are greatly enhanced from 2.06% to 96.37% for Co²⁺ and 1.82% to 93.68% for Cd²⁺ after the addition of chelator. The addition of different chelators also has a certain impact on the removal rates of heavy metal ions. The longer carbon bond the ionic liquids have, the better the extraction is. Similar to traditional solvent n-butanol, pH has a great impact on the removal rates of Co²⁺ and Cd²⁺. When pH<2, the extraction rates of Co²⁺ and Cd²⁺ are close to zero. While for pH>6, the extraction rates are above 90%. The pH swing effect is used to strip the heavy metal ions from ionic liquids, and the reuse of ionic liquids is realized.