With high solid loadings (6 or 9 grock mL -1 ), calcite dissolution triggered precipitation of Ca-P and Mg-P minerals, as indicated by compositional changes in both solution and rock and further supported by XRD analyses that exposed new Ca-P (brushite, CaHPO₄.2H₂O) and Mg-P (newberyite, Mg(PO3OH).3H2O) phases after neutralization (Figure ). Amorphous precipitates and phase transformations may also have occurred but had no significant effect on the practical outcome. A positive-feedback loop may explain the progression of the reaction over 48 h, with precipitation of phosphate minerals causing decreases in pH and Ca concentration, driving further calcite dissolution that again increased pH and Ca and promoted phosphate precipitation. The relative stability of the solution composition over time with low solid loadings (0.5-2 grock mL -1 ) suggests that the lower amount of dissolved calcite was insufficient to trigger significant precipitation of phosphate minerals.