In the present study, in order to examine the N,N-dimethylaminopropylacrylamide/acrylamide {DMAPAA/AAm} hydrogels' capabilities of repetitive heavy-metal-anion recovery from waste fluid, the authors performed successive Cr(VI) adsorption and the adsorbed-Cr(VI) desorption experiments. It has been proved that the DMAPAA/AAm gels show both of the high Cr(VI)-capturing functionality and Cr(VI)-desorption efficiencies. The results in the present study have demonstrated a possibility of a heavy-metal-anion recycling system in which the hydrogels are reused a number of times.

The successive Ni(II) adsorption and adsorbed-Ni(II) desorption experiments have been performed in order to clarify the repetitive heavy-metal-cation recovering functionality of p-Styrenesulfonicacidsodiumsalt/Acrylamide (p-SSAS/AAm) and Sodium acrylate/Acrylamide (SA/AAm) gels, and also to examine the effect of the terminal group in the side chain. It has been revealed that the SA/AAm gels show high recovering functionality usable in the actual applications while that the p-SSAS/AAm gels can be used in limited conditions.

pH-dependences of Ni(II)-adsorbing and -desorbing properties of p-styrenesulfonicacidsodiumsalt/acrylamide (p-SSAS/AAm) and sodium acrylate/acrylamide (SA/AAm) gels have been investigated. Though the p-SSAS/AAm gel can capture more amount of Ni(II) even at a low pH region, its desorption ratio is below ~92 wt% even in 3 M of HCℓ concentration. On the other hand, though Ni(II)-capturing efficiencies of the SA/AAm gel is lower; its Ni(II)-desorption ratio is ~100 wt% in all the measured HCℓ concentrations.

The authors have investigated heavy-metal-anion (hexavalent chromium, Cr(VI)) adsorption and desorption properties of N,N-dimethylaminoethylacrylamide/acrylamide (DMAEAAm/ AAm) gels successively. Though the DMAEAAm/AAm gels show relatively low Cr(VI)-capturing efficiencies, the hydrogels have a possibility of actual use as a heavy-metal-anion recovering material because the DMAEAAm/AAm gels with some compositions show high desorption efficiency of the captured-Cr(VI), which is advantageous to a heavy-metal-anion recycling system with repetitive use of the hydrogel.

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