Recovery of the Co(II) ions from thiocyanate aqueous solutions using cellulose triacetate/tri-n-octylamine/tributyl phosphate polymer inclusion membranes

A polymer inclusion membrane (PIM) bearing desired physical, mechanical, and extraction properties towards cobalt(II) ions as their anionic thiocyanate complexes, composed of 40 wt% of cellulose triacetate (CTA), 25 wt% of the extractant tri-n-octylamine (TOA), and 35 wt% of tributyl phosphate (TBP) as the plasticizer, is introduced. A 3.5 cm dimeter segment of this PIM extracts quantitatively cobalt ions (initial concentration 26 mg L⁻¹) from 50 mL solution adjusted to 0.1 mol L⁻¹ sodium thiocyanate and pH 4 (acetate buffer), after 2 h shaking (200 rpm) on an orbital shaker, and at room temperature. The back-extraction process is performed by 16 h by contacting the loaded PIM with 50 mL solution of ethylenediaminetetraacetic acid (EDTA) (0.25 mol L⁻¹) regulated to pH 8 (phosphate buffer). The investigated PIM presents selective attitude towards Co(II) with respect to Cd(II), Ni(II), Pb(II), Mn(II), Cr(III), Al(III), and Cr(VI) ions. Analysis of the extraction data confirms the formation of the [(TOAH⁺)₂(Co(SCN)₄²⁻)] complex as the extracted species. The maximum PIM’s capacity is appraised to be 19.75 mg per g of the PIM. Pseudo-second order and Langmuir models describe well respectively the kinetics and the isotherm of the process.