'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 center dot 6H(2)O 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.