Calcite growth and the inhibiting effect of iron(III)

Abstract

Calcite growth and the inhibiting effect of ferric ions on this growth was investigated over a range of solution conditions: the pH's, 7.0, 7.5 and 8.0; the temperatures, 15, 25 and 35°C; the initial supersaturation range, 2 to 13; all at an alkalinity of 0.15M, an ionic strength of 0.15M, and in contact with a gas phase of constant CO 2 partial pressure. A free drift, seeded growth technique was used. In the absence of iron, the growth rate was found to depend linearly on the calcium concentration, with an activation energy of 11 kcal/mol. The inhibiting effect of iron was quantified by comparing the growth rate constants measured in the presence and absence of iron. Comparison at the different pH's, temperatures, and supersaturations showed that the concentration of iron needed for almost complete calcite growth inhibition depends primarily on supersaturation. Ferric ions are very effective calcite growth inhibitors. A 1μM total ferric ion concentration was sufficient to completely inhibit calcite growth in solutions at supersaturations smaller than 4.