Coupling extraction–flotation with surfactant and electrochemical degradation for the treatment of PAH contaminated hazardous wastes

The performance of a two-stage process combining extraction of polycyclic aromatic hydrocarbons (PAHs) with an amphoteric surfactant (CAS) followed by electro-oxidation of PAH-foam concentrate was studied for the decontamination of aluminum industry wastes (AIW) and polluted soils. The PAH suspensions extracted from AIW and soils were treated in a 2 L-parallelepipedic electrolytic cell containing Ti/RuO₂ anodes and stainless steel cathodes. Current densities varying from 4.6 to 18.5 mA cm⁻² have been tested with and without addition of a supporting electrolyte (6.25 to 50 kg Na₂SO₄ t⁻¹ of dry waste). The best performance for PAH degradation was obtained while the electrolytic cell was operated during 90 min at a current density of 9.2 mA cm⁻², with a total solids concentration of 2.0%, and in presence 12.5 kg Na₂SO₄ t⁻¹. The application of the process on AIW (initial PAH content: 3424 mg kg⁻¹) allowed extracting 42% of PAH, whereas 50% of PAH was electrochemically degraded in the resulting foam suspensions. By comparison, 44% to 60% of PAH was extracted from polluted soils (initial PAH content: 1758 to 4160 mg kg⁻¹) and 21% to 55% of PAH was oxidized in the foam suspensions. The electrochemical treatment cost (including only electrolyte and energy consumption) recorded in the best experimental conditions varied from 99 to 188 USD $ t⁻¹ of soils or AIW treated.