Pretreatment and the effect of cations and anions on prevention of silica fouling

Silica is one of the major foulants in desalination of brackish water. Its presence limits the water recovery and in addition once foulant is formed, the removal and cleaning is almost impossible. Therefore, the aim is to prevent silica fouling from the inception. One of the many complicating factors is the effect of various cations and anions present in the water on silica polymerization. Usually, there is a pretreatment stage for removing as much silica as possible prior to the actual desalination step. It is of great importance to know the effect of most predominant cations and anions on the polymerization and hence tailoring the pretreatment stage to emphasize the removal of most troublesome components. This study is tailored towards pretreatment stage and addresses the chemistry of silica removal and polymerization of silica in presence of Ca and Mg and at various pH and concentrations in batch tests constant volume reactors. Also the effectiveness of silica removal by increase in pH and addition of lime, soda ash, and sodium aluminate in field tests have been investigated.