Potential applications of quarry dolomite for post treatment of desalinated water

Recent WHO publications recommend a minimum concentration of 10 mg Mg/L in desalinated water. Dolomite dissolution was investigated as means of adding magnesium ions to desalinated water at the post treatment stage, in addition to Ca2+ ions and carbonate alkalinity. The results show that dolomite dissolution per se is not feasible for post treatment purposes, because dolomite stops dissolving at a relatively low pH, rendering the alkalinity and Calcium Carbonate Precipitation Potential values very low and negative, respectively. To overcome this problem three combined dolomite-calcite dissolution alternatives were investigated. The results show that the most promising method is to dissolve dolomite and then use the CO2(aq)-rich effluent to further dissolve calcite. Applying such in-series dissolution, it is possible to produce water with the following quality criteria: alkalinity = 75 mg/L as CaCO3, [Mg2+] = 12.4 mg/L, [Ca2+] = 120 mg/L as CaCO3, pH 8.17. However, the resultant total hardness value is high (170 mg/L as CaCO3). The operational costs of this alternative were approximated at 0.042 $ m(-3) product water.