Reactions of calcium ion with polyacrylate and its copolymers

Abstract

Calcium hypochlorite is one of the most commonly used chlorine compounds in water treatment. It contains at least 70 percent available chlorine. However, it presents an encountered problem since calcium ions tend to precipitate with various anions such as carbonate, sulfate or phosphate and therefore clog the valves or pumping systems. This research attempts to correct this problem. Polyacrylate including its co- and terpolymer were chosen to be the trapping agents by chelating with the calcium ions and dispersing agents in some calcium carbonate residue since it possesses desirable qualities, i.e., high water solubility and low toxicity. The comparison of the chelation of 3 types of polyacrylates (homopolymer, copolymer and terpolymer) with the calcium ion from calcium oxide or calcium hypochlorite were performed. Various effects have been investigated in order to determine the optimum conditions for the chelation between calcium (II) ions and each polyacrylate. The chelation was confirmed by IR spectroscopy. The optimum conditions that allow the least precipitation of calcium ions are 1:4 weight ratio of calcium salt to polyacrylate (homopolymer and copolymer) or 1:1.5 weight ratio of calcium salt to polyacrylate (terpolymer) and water as the solvent medium. It is shown that the precipitation of polyacrylate (homopolymer and copolymer) with calcium hypochlorite is minimized at pH 7 while pH 11 is required for calcium oxide. In the case of terpolymer the precipitation with calcium hypochlorite is minimized at pH 3 while pH 7 is required for calcium oxide. The chelation prefers at low reaction temperature. The complex formed from the reaction of homopolymer of polyacrylate and calcium (II) ions is found to be thermally stable and its stability is the highest compared with the co-or terpolymer.