Kinetics of calcite nucleation: Magnesium ion inhibition and ionic strength catalysis

Kinetics of calcite crystallization from dilute MgCl2 solutions equilibrated with aragonite and atmospheric CO2 were studied. Patterns of per cent calcite against time and Mg++ concentration against time indicate Mg++ inhibits calcite nucleation and in the process is incorporated into the calcite lattice. Uptake of Mg++ by calcite nuclei was then used to monitor calcite nucleation rates under conditions of constant supersaturation and varying ionic strength. Nucleation rates were found to be proportional to the square root of the ionic strength. An analogy between nucleation catalysis by ionic strength and colloid flocculation by salts in aqueous solution is suggested.