Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils

The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption dissolution–precipitation reactions. Ca binding calcareous soils depends on the degree solution saturation with respect to CaCO3. Mg may be bound precipitating calcite. Here, we investigated incorporation into calcite via recrystallization vaterite, which simulates a very low supersaturation wide range ratios pH conditions. Increasing (0.2 10) decreased partition coefficient from 0.03 0.005. An approximate thermodynamic mixing parameter (Guggenheim a0 = 3.3 ± 0.2), that is valid for dilute systems was derived experiments at lowest initial ratio (i.e., 0.2). At elevated ratios, aragonite preferentially formed, indicating kinetic controls partitioning Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated not incorporated aragonite. model suggests ?1) Mg-calcite becomes unstable relative pure Finally, our results suggest abiotic only effective removal like soil solution, if already low.