Adsorptive separation of rhodium(III) using Fe(III)-templated oxine type of chemically modified chitosan

The oxine type of chemically modified chitosan was prepared by the template crosslinking method using Fe(III) as a template ion. Batchwise adsorption of rhodium(II) on this chemically modified chitosan was examined from chloride media in the absence and presence of a large amount of tin(II). It was observed that the Fe(III)templated oxine type of chemically modified chitosan shows better performance for rhodium adsorption than that of the original chitosan. When Sn(II) is absent from the solution, Rh(III) is hardly adsorbed on the modified chitosan and the order of selectivity of the adsorption of Rh(III), Pt(IV), and Cu(II) was found to be Pt(IV) > Cu(II) approximate to Rh(III). On the other hand, adsorption of rhodium is significantly increased in the presence of Sn(II) and the selectivity order of the adsorption was drastically changed to Rh(LII) > Pt(IV) >> Cu(II), which ensures selective separation of Rh(III) from their mixture. Adsorption of Rh(III) increases with an increase in the concentration of Sn(II) in the aqueous solution, and maximum adsorption is achieved at a molar ratio, [Sn]/[Rh], of >6. The adsorption of Rh(III) decreases at a high concentration of hydrochloric acid. The maximum adsorption capacity was evaluated to be 0.92 mol/kg-dry adsorbent. Stripping tests of rhodium from the loaded chemically modified chitosan were carried out using different kinds of stripping agents containing some oxidizing agent. The maximum stripping of rhodium under these experimental conditions was found to be 72.5% by a single contact with 0.5 M HCl + 8 M HNO3.