Silica Removal by a Novel Electrochemical System

The presence of silica in brackish water greatly complicates desalination processes. Mitigation of silica scale by dosage of anti-scalants has proved to be an elusive task. The common method of silica removal is by its precipitation at high pH with polyvalent metal hydroxides. A convenient way for achieving a high pH is by applying an electric current in an electrochemical cell. Silica removal was investigated using a novel electrochemical technique, based on a cation exchange membrane (ECM). The ECM system overcomes a major drawback of current electrochemical technology, enabling reduction of the cathode area by a factor of 10 to 20. The effects of current density and pH on the silica precipitation were studied. Results support the hypothesis that silica removal is an adsorption process rather than a chemical precipitation reaction. The highest silica removal was achieved at the optimal Mg to SiO₂ molar ratio of 4:1. Silica depletion increased with current density reaching an asymptotic limit of 92% at a solution pH of 10.8, and a current density of 200 A/m². Results of this study indicate that silica removal by the ECM system can be a viable process.