'High-pH softening pretreatment' for boron removal in inland desalination systems

Boron removal from water remains a challenge. In fact, it is largely unclear whether softening pretreatments enhance boron removal in groundwater desalination systems. We therefore investigated the feasibility of a high-pH softening pretreatment for boron removal from magnesium dominated groundwater samples obtained from an existing desalination facility. Different alkaline reagents were trialled with brackish groundwater initially containing 5 mg/L of boron. The results indicated that the lime and soda ash softening treatment was a better option than the caustic soda alternative, achieving 33% boron removal by sorption of hydroxyborate ions onto precipitated magnesium silicates. The process could be further optimized by the addition of MgCl2·6H2O before the softening process. In addition, a secondary polishing treatment by means of adsorption with MgO was investigated. A total of 9% extra boron removal was achieved in both cases. This 'high-pH softening pretreatment' could enhance compliance with strict boron standards in inland facilities using reverse osmosis or electrodialysis technology.