Formation of Calcium and Magnesium Molybdate Complexes in Dilute Aqueous Solutions
- M. E. Essington
In order to increase our understanding of the chemistry of Mo in soil, waste-affected soil, and waste-disposal environments, it is imperative to understand the processes controlling the aqueous and solid-phase distribution of Mo. Recent research shows the importance of alkaline earth metal ion pairs with molybdate in aqueous solutions. However, ion association constants for these species have not been rigorously determined. The objectives of this study were to measure conditional ion association constants (log cQ) for the formation of Ca and Mg molybdate ion pairs. Potentiometric titrations were performed at pH 7 and 25 °C in NaNO3 ionic media. The logcQ values were converted to the zero-ionic-strength molar reference state (log Q) using the Davies equation. The mean log Q and standard free energy of formation (ΔGof) values for the formation of CaMoO04 are 2.57 ± 0.08 and −1405.19 ± 1.60 kJ mol−1, respectively. The mean log Q and ΔGof values for the formation of MgMoO04 are 3.03 ± 0.13 and −1309.08 ± 2.06 kJ mol−1, respectively.
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