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Precipitation and dissolution mechanisms of calcium carbonate are important processes for the regulation of pH in natural waters and for the transport of pollutants to and from the sediments. In the present work the precipitation of calcium carbonate in supersaturated solutions made from synthetic seawater was investigated by the introduction of calcite seed crystals at conditions of sustained solution supersaturations. Aragonite was found to form on the calcite seed crystals when the magnesium concentration was 53.3mM, while below this concentration calcite was the only phase forming. The kinetics of formation of both calcite and aragonite showed strong dependence on the solution supersaturation and the apparent order was found to be 7, suggesting a polynuclear mechanism. Throughout the crystal growth process the number of seed crystals remained constant, while their size increased.

The stability of calcium carbonate supersaturated solutions was studied between 25−80°C and pH 8.00–9.00. The stability diagrams showed narrow supersaturation ranges, for which very reproducible induction times could be obtained. Investigation of the precipitation process by a plethostatic (i.e., in which a constant number of moles is maintained) experimental approach, enabled us to identify vaterite as the initially forming crystalline phase, throughout the pH and temperature range investigated. The precipitation took place via a polynuclear mechanism. Ethane-1-hydroxyethylideno-1,2-diphosphonic acid (EHDP) caused not only retardation in the rates of spontaneous precipitation but resulted also in stabilization of the initially forming vaterite. An apparent activation energy of 46 kJ mol −1 was obtained for the precipitation reaction of vaterite. Seeded growth experiments on calcite seed crystals over the temperature range 10–37°C, gave second order kinetics suggesting a spiral growth mechanism. In all cases, calcite was found to be 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 a marked reduction of the rates of precipitation by adsorption on the active growth sites on the surface of the calcite crystals.