Temperature effects on spontaneous supersaturation of calcium citrate in presence of lactate

Supersaturation of calcium salts of low solubility is important for biomineralisation. The dynamics of solutions supersaturated in calcium citrate prepared by dissolving calcium lactate and sodium citrate in water, serving as a mineralisation model, were characterised electrochemically and by small-angle X-ray scattering. The process was divided into: (i) citrate assisted dissolution of calcium lactate with an enthalpy of activation of 115 kJ mol⁻¹; (ii) a metastable homogeneous supersaturation phase, where calcium ion activity continues to increase despite constant calcium concentration; (iii) calcium ion activity decreasing with an enthalpy of activation of 30 kJ mol⁻¹ together with 3-dimensional crystallisation with an enthalpy of activation of 177 kJ mol⁻¹. The differences in activation enthalpies lead to a higher degree of supersaturation at higher temperatures but longer lasting supersaturation at low temperature as was seen for critical supersaturation of up to a factor of 20 resulting in non-linear temperature effects for calcium mobility.