Dissolved silica, a ubiquitous sparingly soluble species in natural waters and industrial wastewaters, is a major concern for membrane desalination processes due to its tendency to form silica scale which significantly limits attainable water recoveries. In this work, we propose an electrosorption pretreatment technology to selectively remove silica from saline waters, effectively mitigating silica scaling in subsequent membrane processes. Specifically, we utilize a flow-through electrode configuration to enhance the electro-generation of hydroxide at the cathode. As the feedwater flows through the cathode, monosilicic acid reacts with the hydroxide to form negatively charged silicate ions, which are then electrosorbed at the downstream anode. A silica-selective anode is fabricated by functionalizing the macropores of a commercial activated carbon cloth with aluminum-based nanoparticles. The aluminum-based nanoparticle modification enables the selective removal of silica by facilitating preferential transport of silica species into the electrode’s micropores due to the high affinity of silica for aluminum hydroxides. Dissolved silica is rapidly and selectively removed by the flow-through electrode technology, with the silica-electrosorption kinetics and removal rates are readily controlled through tuning the applied voltage and flow rate. Moreover, the functionalized electrodes are stable over multiple cycles and can be effectively regenerated by reversing the applied voltage. Overall, the silica-electrosorption technology demonstrated in this study offers a facile, chemical-free method for treating silica-rich feedwaters.

Flow-through electrosorption process for selective removal of silica

ACS Fall 2021

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