extraction of co(ii) from thiocyanate solutions using polymer inclusion membranes composed of cellulose triacetate as the base polymer and trioctylamine as extractant

Polymer inclusion membranes (pims) has oppened a new horizon for introducing new strategies for developing the environmentally friendly membrane based techniques for the separation-recovery of many environmentally and economically important metals [1]. they are known as alternatives for the solvent extraction techniques, in which the consumption of great amount of toxic, expensive, and flammable organic dilunets is indispensable. the characteristics of pims can be tuned by varying its consituents i.e. the base polymer (homopolymers, copolymers, polymers blends, and cross-linked polymers [2] and the extractant. in some cases, the type and the amount of the plasticizer used affects also the pims chracteristics [3]. first, in the present project, the optimal polymer inclusion membrane with suitable physical, mechanical and extraction properties including a combination of 40% w/w cellulose triacetate (cta) polymer, 25% w/w trioctylamine (toa) extractant and 35% w/w tributyl phosphate (tbp) plasticizer was selected. the membrane was capable to extract completely co(ii) from 50 ml of solution containing 26 mg l-1 co(ii) in 0.1 m ammonium thiocyanate solution and 0.2 m buffer acetic acid/acetate at ph=4 over time 2 hours and back extraction of co(ii) from 50 ml of solution containing 0.2 m buffer phosphoric acid/phosphate at ph=8 with 0.25 m edta for 16 hours. the selectivity of the investigated membrane toward co(ii) was evaluated by performing competitive extraction experiments of co(ii) in the presence of various cations and anions. the application of real aqueous samples and nickel-cadmium battery sample leached were investigated. the study to determine the extracted species confirmed the mechanism of ion pair formation (toah+)2(co(scn)4). the maximum capacity of the membrane made in cobalt extraction is 19.75 mg of cobalt ions per gram of membrane.the kinetic and isotherm studies revealed that the sorption of co(ii) by the optimized membrane is a adsorption and chemisorption process.