Ion exchange/adsorption of rhodium(III) from chloride media on some anion exchangers

Abstract

Ion exchange/adsorption of rhodium(III) from chloride media was investigated with some commercial anion exchange resins like Sumichelate MC-10 resin, and Diaion WA10, WA21, SA20A and SA21A resins as well as crosslinked Cu(II)-templated chitosan and compared with Fe(III)-templated oxine type of chemically modified chitosan (Fe-oxine-chitosan) studied in previous work. A significant amount of rhodium is adsorbed from low acidic solution and better distribution ratios of rhodium adsorption on these commercial resins were found in all cases when tin is present in the solution. However, some amount of Rh(III) is also adsorbed in all cases except for Diaion WA10 even in the absence of tin. Rhodium is hardly adsorbed on crosslinked Cu(II)-templated chitosan (Cu-chitosan) when tin is absent in the feed solution. However, in the presence of tin, an appreciable amount of rhodium is adsorbed at low acidity while the distribution ratio decreases with the increase in hydrochloric acid concentration. When tin is present in the solution, the order of adsorption ability of the resins was found to be: WA21>SA21A>MC-10>Fe-oxine-chitosan>WA10>SA20A≈Cu-chitosan at low acidity (about 3 mol/dm 3 HCl), and MC-10>WA21>SA21A>SA20A>Fe-oxine-chitosan>WA10>Cu-chitosan at high acidity (about 9 mol/dm 3 HCl). On the other hand, when tin is absent, the order of adsorption ability was found to be: MC-10>WA21>SA20A>SA21A>WA10>Fe-oxine-chitosan>Cu-chitosan. It is obvious that MC-10 resin possesses the highest adsorption ability where 66.0% rhodium was adsorbed at 3 mol/dm 3 HCl even when tin is absent in the feed solution. The maximum rhodium adsorption capacity of Diaion WA21 was evaluated to be 0.59 and 0.9 mol/kg dry adsorbent when tin is absent and present in the solution, respectively, while the maximum rhodium adsorption capacity of MC-10 resin was evaluated to be 1.4 mol/kg dry adsorbent in both cases whether tin is absent or present in the solution. The adsorption mechanism, in which resin is first protonated on contact with hydrochloric acid and subsequently adsorbs rhodium as an ion-pair complex is proposed. Stripping of rhodium from loaded adsorbents was carried out using some mineral acids accompanied by some oxidizing agents like H 2O 2, HNO 3, NaClO 3 and NaClO. A significant amount of rhodium was stripped by a single contact with these stripping agents. However, the best stripping was accomplished with hydrochloric acid containing sodium chlorate.