A different approach for seawater decalcification pretreatment using carbon dioxide as precipitator

• The CO2 dissolution performance in seawater with different T, S and pH was measured.
• A function was proposed to fit the solubility of CO2 in seawater with high salinity.
• The controllable seawater decalcification was realized by ventilating carbon dioxide.
• This approach not only removes calcium in seawater but also realizes carbon sequestration.

Fouling, mainly caused by insoluble calcium salts, deteriorates the performance of process equipments, such as membranes and heat exchangers, during the desalination process. In this study, a new strategy of seawater decalcification pretreatment using carbon dioxide as precipitator was proposed. Firstly, the solubility data of carbon dioxide in seawater was extended to higher temperatures and salinities, and the pH effects on the dissolution performance of carbon dioxide were studied, since the dissolution rate of CO2 in the seawater was assumed to be the decisive rate of the calcite precipitation rate. A new modified Bunsen function was proposed to fit the solubility data of CO2 in seawater when salinity was higher than 70‰. Then the controllable decalcification of seawater was realized by ventilation with carbon dioxide using a recycling tower. Furthermore, the decalcification rates with time were studied under various conditions, such as flow ratio of carbon dioxide in gas (F), liquid–gas ratio (R) and different pH values. It was found that about 86.9% calcium ions were removed in 70 min under the best experimental conditions: F was 10.6%, Qair = 134.2 m3/h and QCO2 = 16.0 m3/h; R was 21.3; and pH was 7.9.