The removal mechanisms involved in the continuous-flow electrocoagulation for the treatment of a polishing wastewater containing negatively charged silica particles are described in the report. The mechanisms are derived from the experimental measurement of pH, zeta-potential and turbidity as a function of reaction time, as well as from the sludge characterization. Two types of distinct mechanisms are proposed, one involving particle destabilization by oppositely charged ferrous ions, the other involving a complexation or physical bridging by iron hydroxides/hydroxyl complexes. The former mechanism is apparently responsible for the formation of “surface sludge”, whereas the latter mechanism is responsible for the sediment sludge. Both mechanisms are important to the silica removal based on the measurement of sludge quantity.

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