Influence of ionic and nonionic dextrans on the formation of calcium hydroxide and calcium carbonate particles

The effects of nonionic, cationic, and anionic dextrans on the precipitation of calcium hydroxide and calcium carbonate particles in aqueous solutions were investigated by varying different experimental parameters. Nonionic dextrans had no observable effect on the resulting dispersions. The addition of ionic dextrans in basic solutions altered the morphology of calcium hydroxide. Precipitation of calcium carbonate particles, in the presence of urea, was influenced significantly only by the anionic dextran, which affected both the morphology and the crystal structure of the precipitated particles. In neutral or slightly acidic solutions, Ca2+ ions reacted with anionic dextrans to form a coacervate, which was the result of neutralization of the sulfate groups of the polymer by this cation. The so formed ion pairs could be eliminated by the addition of an excess of nonbinding Nat ions, resulting in the dissolution of the separated phase. (C) 2001 Elsevier Science B.V. All rights reserved.