THE EFFECT OF ANIONIC POLYELECTROLYTES ON THE CRYSTALLIZATION OF CALCIUM-OXALATE HYDRATES

Calcium oxalate was precipitated from supersaturated calcium oxalate solutions in the presence of different water soluble polymers: poly(acrylic acid), poly(methacrylic acid), poly(styrene sulfonate-alt-maleic anhydride), poly(maleic anhydride), and poly(vinyl sulfonate). The supersaturated solutions were made with initial calcium and oxalate concentrations of 4×10-3M and 1.5×10-3M respectively. In the presence of anionic polyelectrolytes there was a change in the hydrate from of calcium oxalate which precipitated. With low concentrations of polyelectrolyte (up to 1 ppm) only the monohydrate was formed, at intermediate concentration (1-50 ppm) trihydrate was the predominant product, and at high concentrations (above 50 ppm) the dihydrate form was the dominant product. Nonpolyelectrolytes had no effect on the crystallization and thus only calcium oxalate monohydrate was formed. This effect was found to occur with all polyelectrolytes used regardless of molecular weight or charge. The change from one hydrate from to another occured at a lower polymer concentration with the low molecular weight polymers. © 1990.