Effects of Carboxylic Acids on the Crystallization of Calcium Carbonate

✍ Scribed by Norio Wada; Kiyoshi Kanamura; Takao Umegaki

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 174 KB
• Volume: 233
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.2000.7215

✦ Synopsis

The effects of seven carboxylic acids, i.e., acrylic acid, maleic acid, tartaric acid, malic acid, succinic acid, and citric acid, on CaCO 3 crystallization were studied using the unseeded pH-drift method along with a light-scattering technique. Experiments were started by mixing solutions of CaCl 2 and NaHCO 3 in the presence or absence of additives. The crystallization was studied by recording the decrease in pH resulting from the reaction Ca 2+ + HCO - 3 → CaCO 3 + H + . A given amount of carboxylic acid was added to the solution of CaCl 2 or NaHCO 3 before mixing the reactants. The pH profiles obtained in the case of the CaCl 2 solution containing an additive were similar to those for the NaHCO 3 solution containing one, and when an additive was added after the onset of crystallization, the growth of CaCO 3 immediately stopped. The light-scattering observations, in all cases, indicated that CaCO 3 nucleation occurred at 10-20 s after mixing of the reactants. The results indicated that the nucleation of CaCO 3 was not influenced by the presence of carboxylic acids, but CaCO 3 crystal growth was reduced by their adsorption to the surface of the CaCO 3 crystals. These phenomena were explained by assuming a stronger affinity of the carboxylic acids for CaCO 3 particles than for the free Ca 2+ ions in solution. The crystallization of CaCO 3 in the presence of additives was divided into three stages: nucleation, growth incubation, and growth periods.