Selective Recovery of Metal Ion by Using Hydrogel With Different Inner pH

Abstract

New metal ion recovery method with hydrogels as a reaction and separation media has been investigated. Hydrogels based on copolymers of 2‐(Dimethylamino)ethyl methacrylate, N‐3‐(Dimethylamino)propyl acrylamide, and N,N‐dimethylacrylamide are prepared. Diethyleneglycol dimethacrylate is used as a crosslinker. The hydrogel with tertiary amino group exhibited high pH value inside of them when they swelled in water because the tertiary amino group was protonated by water and produced hydroxide ion was retained in the hydrogel. When the hydrogel is immersed in the metal ion aqueous solution, the metal ion diffused into the hydrogels to produce metal hydroxide in the hydrogel. The metal hydroxide within hydrogel is easily separated from the solution. The recovery amount of the metal in the hydrogel is increased with the concentration of the metal ions in the solution. The pH value of the hydrogel could be controlled by the concentration monomers at the preparation. The selective recovery of a certain metal ion from the mixed metal ion solution is attained by controlling the pH value of the hydrogel. The results obtained here suggest the possibilities of the novel metal ion recovery method replacing the coagulation and/or adsorption methods.