Table 1.
Metal | Phosphate salt | Ksp | [PO43−] (M) | Carbonate salt | Ksp | [CO32−] (M) | Selectivity |
---|---|---|---|---|---|---|---|
Calcium | Ca3(PO4)2 | 2 × 10−33 | 5 × 10−17 | CaCO3 | 3 × 10−9 | 3 × 10−9 | 8 × 107 |
Iron (III) | FePO4•2H2O | 10 × 10−16 | 10 × 10−15 | FeCO3* | 3 × 10−11* | 3 × 10−11* | 3 × 104* |
Gallium (III) | GaPO4 | 1 × 10−21 | 1 × 10−21 | Ga2(CO3)3 | N/A | - | - |
Barium | Ba3(PO4)2 | 3 × 10−23 | 6 × 10−12 | BaCO3 | 2 × 10−9 | 2 × 10−9 | 8 × 1013 |
The calculated phosphate and carbonate concentrations listed are those required for precipitation with the corresponding metal if the metals are assumed to be at a normalized unit molarity of 1 M. Selectivity was calculated by dividing the minimum carbonate concentration for precipitation by the minimum phosphate concentration required for precipitation. All calculations are shown in the Supporting Material.
Since the Ksp for Fe2(CO3)3 was not available we used the Ksp of FeCO3 as an estimate.