Simultaneous removal of chromium(VI) and fluoride by electrocoagulation–electroflotation: Application of a hybrid Fe-Al anode

• A combined EC–EF process is used for simultaneous removal of Cr(VI) and fluoride.
• The EC step involves integrated reduction of Cr(VI) and coagulation of fluoride.
• In EF step, the separation solid/liquid was improved.
• The interest of hybrid anode is to avoid supplementary EC step.

A combined two-step EC–EF process was designed to simultaneously remove Cr(VI) and fluoride from pretreated acidic semiconductor effluents. The EC step comprises integrated reduction of chromium(VI) with coagulation of fluoride, while in the EF step, clarification takes place. In EC step a hybrid Fe–Al was used as sacrificial anode and stainless steel as cathode. Initially, the effect of anodic material on EC–EF efficiency was investigated and it was found that the combination 2Fe–2Al gives the optimum results. Most of Cr(VI) removal was ascribed to iron plates, while fluoride removal was mainly ascribed to aluminum plates. Presence of coagulants enabled the removal of suspended solids which are present in initial solution. Effects of initial pH, current intensity, anions nature, chloride concentration and initial concentration on EC–EF process efficiency using hybrid anode were studied. The behavior of the hybrid anode depends on both iron and aluminum individual properties toward pollutants. Under optimum conditions, residual concentrations of Cr(VI) and fluoride and turbidity after EC–EF were found under national discharge standards.