Mitigating silica fouling in electro-electrodialysis: Anode compartment modification and process intensification approaches

Abstract

Electro-electrodialysis (EED) based causticization of industrial (agro-based paper mills) green liquor experiences severe silicate fouling issues (especially in anode compartment) resulting frequent shutdown, dismantling, cleaning and reassembling challenges. Therefore, continuous causticization through EED process becomes difficult. Appropriate design modification of the anode compartment along with periodic silica removal could overcome frequent shutdown issues, and execution of EED process for longer duration. The novel mechanism of silicon removal using EED process by the precipitant is also presented. Their treatment performances in removing silicon were statistically evaluated and confirmed by instrumental techniques. Using modified design and 200 cm2 of membrane area, 500 mL of 2.56 mol·L−1 of NaOH (92% Na+ ion recovery) could be produced in 4 h by electrolyzing 500 mL of industrial green liquor under constant current density, 60 mA·cm−2. Proposed modification could result ∼21% improvement in caustic recovery/energy consumption compared to unmodified anode compartment. With improve the performance which is the average current efficiency 74.5% and energy consumption 4.42 kWh·kg−1, was recorded.