Remineralisation of Reverse Osmosis (RO) Water Using Synthetic Aragonite

Reverse osmosis (RO) treated water often requires remineralisation to restore Ca 2+ ions, hardness and alkalinity, particularly for potable water. This study compares the dissolution characteristics of two forms of calcium carbonate, aragonite and calcite. Aragonite, with a specific surface area of 3.2 m 2 /g versus 1.7 m 2 /g for calcite, has an interlocking crystal structure that enhances its physical robustness. Dissolution experiments in laboratory deionised water show that aragonite produces ~9 times more Ca 2+ ions than calcite during the first 5 min, primarily due to its greater surface area rather than increased solubility. Both minerals increased the pH of treated water from ~6.5 to ~8.4. Synthetic aragonite allows rapid Ca 2+ release due to greater surface area and equivalent pH buffering. Aragonite offers potential advantages for industrial scale RO water remineralisation, and the potential sustainability benefits from using synthetic aragonite granules compared to aragonite extracted from the environment are discussed.