Thermal-Swing Extraction of Cd(II) by Thermosensitive Gel Crosslinked with Nitrogen-donor Ligands

摘要

A thermal swing extraction system using a thremosensitive gel,poly-N-isopropylacrylamide (NIPA) crosslinked with 2,6-di(3-vinylbenzyl-1,2,4-triazol-5-yl)pyridine (BTP) was proposed.Extraction of Cd(II) in an aqueous nitrate solution and elution with acidic solutions (Ph=1 to 5) were tested by two thermosensitive gels prepared by the ultrasonic polymerization and the ordinary radical polymerization,called US-gel and FR-gel,respectively.Cd(II) was extracted in the gel shrunken at higher than LCST (lower critical solution temperature,31 deg C) and released from the gel swollen at less than LCST.Such temperature-change of extractability for the US-gel was larger than that for the FR-gel.The US-gel,in which aggregates of BTP molecules are not formed,in suitable to the thermal-swing extraction system.The elution of Cd(II) into a weakly acidic solution (pH >2) was promoted by the volume phase transition of gel from the shrinking state to the swelling one.Even in a very weakly acidic solution of pH 5,more than 50% of Cd(II) extracted was eluted by the volume phase transition of gel.These results suggest that the elution operation with volume phase transition of gel is very effective for reducing a quantity of eluting agent.