Electrocoagulation of Silica Nanoparticles in Wafer Polishing Wastewater by a Multichannel Flow Reactor: A Kinetic Study

A simplistic and systematic procedure has been developed for the design and upscaling of a multichannel, continuous-flow electrocoagulation reactor of monopolar configuration for the removal of submicron particles from wastewater. Using wastewater generated from the chemical-mechanical planarization process as the target wastewater, a series of laboratory-scale studies were conducted to determine the required operating conditions for the efficient removal of the ultrafine silica particles. These operating criteria included charge loading $(⩾8\mathrm{F}∕{\mathrm{m}}^3)$ , current density $(⩾5.7\mathrm{A}∕{\mathrm{m}}^2)$ , hydraulic retention time $(⩾60\min )$ , as well as the initial pH (7–10). Furthermore, a steady-state transport equation with second-order reaction kinetics was employed to describe the rate of coagulation as the rate-limiting factor. The actual kinetic constant determined from the laboratory-scale experiments was approximately $1.2\times {10}^{-21}{\mathrm{m}}^3∕\mathrm{s}$ , which was three orders of magnitude smaller than that calculated based on Brownian coagulation. The model was subsequently validated with a series of experiments using a pilot-scale electrocoagulation reactor geometrically similar to the laboratory-scale reactor with nearly 20 times volumetric scaleup.