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The stability of calcium carbonate supersaturated solutions was studied for temperatures between 25 C-80 C and pH 8.0-9.0. The stability diagrams showed narrow supersaturation ranges for which very reproducible induction times could be obtained. Investigation of the precipitation process by a plethostatic experimental approach enabled the identification of vaterite as the initially forming crystalline phase, throughout the pH and temperature ranges investigated. The precipitation took place via a polynuclear mechanism. EHDP caused not only retardation in the rates of precipitation, but resulted in stabilisation of the vaterite. An apparent activation energy of 46 kJ/mol was obtained for the precipitation reaction. Seeded growth experiments on calcite seed crystals over the temperature range of 10-37 C gave second order kinetics suggesting a spiral growth mechanism. In all cases calcite was the only phase forming. The presence of additives such as orthophosphate and oxalate reversed the surface charge of the calcite particles while metal ions such as Cd(2+) or Zn(2+) resulted in reduction of the rates of precipitation by adsorption on the surface of the calcite particles.

Additional information

Authors: KOUTSOUKOS P G, University of Patras (GR)
Bibliographic Reference: EUR 12187 EN (1990) 44 pp., MF, ECU 4
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