Solid-Phase Extraction of Cobalt(II) from Lithium Chloride Solutions Using a Poly(vinyl chloride)-based Polymer Inclusion Membrane with Aliquat 336 as the Carrier

Abstract

The extraction of cobalt(II) from solutions containing various concentrations of lithium chloride, hydrochloric acid, and mixtures of lithium chloride plus hydrochloric acid is reported using a poly(vinyl chloride) (PVC)-based polymer inclusion membrane (PIM) containing 40% (w/w) Aliquat 336 as a carrier. The extraction from lithium chloride solutions and mixtures with hydrochloric acid is shown to be more effective than extraction from hydrochloric acid solutions alone. The solution concentrations giving the highest amounts of extraction are 7 mol L⁻¹ for lithium chloride and 8 mol L⁻¹ lithium chloride plus 1 mol L⁻¹ hydrochloric acid for mixed solutions. Cobalt(II) is easily stripped from the membrane using deionized water. The cobalt(II) species extracted into the membrane are CoCl₄²⁻ for lithium chloride solutions and HCoCl₄⁻ for mixed solutions; these form ion-pairs with Aliquat 336. It is also shown that both lithium chloride and hydrochloric acid are extracted by the PIM and suppress the extraction of cobalt(II) by forming ion-pairs in the membrane (i.e. R₃MeN⁺·HCl₂⁻ for hydrochloric acid and R₃MeN⁺·LiCl₂⁻ for lithium chloride).