Adsorption performance of activated carbon pellets immobilized with organophosphorus extractants and an amine: A case study for the separation of Pt(IV), Pd(II), and Rh(III) ions in chloride media

We attempted to anchor polymeric functional molecules on the activated carbon surface such that precious metal ions bind selectively in a mixed chloride solution. We immobilized Cyanex 301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid), MSP-8 (bis(3-ethyl methyl)monothiophosphoric acid) and a primary amine (tris(hydroxymethyl)aminomethane) on the surface of activated carbon (SUPRA Norit, 0.8), which served as a polymeric support. X-ray photoelectron spectroscopy results showed that ketones, esters, and carboxylic acids on the carbon surface interacted covalently with the amino group or sulfur groups from the organophosphorus extractants. The characteristic binding energies of N 1s, S 2s, and P 2s were recorded qualitatively at 399, 167.4, and 164 eV, respectively. The optimum sorption of amine, MSP-8, and Cyanex 301 acid by activated carbon averaged 15, 75, and 150 mg/g, respectively. Amine-treated activated carbon exhibited an affinity for platinum ions while thiophosphate-treated activated carbons showed an affinity for palladium ions in chloride media. Rhodium complex ions were not adsorbed by the chemically treated carbons. Excess sorption of organophosphorus extractants or the amine significantly increased the hydrophobicity of activated carbon pellets and consequently affected adsorption of metal ions.