Improvement of a three-step process for the treatment of aluminium hazardous wastes containing PAHs (benzo[b,j,k]fluoranthene and chrysene) and fluoride

Abstract

Hazardous wastes from a primary aluminium production plant could be decontaminated by a three-step process. First, the PAHs contained in these wastes were extracted with an amphoteric surfactant (0.25% or 0.50% w/w of cocamidopropylhydroxysultaine [CAS]) by cell or column flotation, depending on the particle size fraction (under or above 500 μm). Then, the fluorides were stabilized with lime (8% w/w) or a mixture of lime (4% w/w) and phosphoric acid (0.95% w/w). The decontaminated wastes satisfied the Quebec PAH norm, fixed at 1000 mg kg−1, with values of 900±352 mg kg−1 and 624±179 mg kg−1 for benzo(b,j,k)fluoranthene (BJK) at laboratory and pilot scales, respectively. The fluoride stabilization in the treated wastes was characterized by TCLP values of 138±67 mg F− L−1 and 29.5±7.6 mg F− L−1 for laboratory and pilot experiments, which were under the Quebec norm (<150 mg F− L−1). Finally, the metals in the process effluent were recovered by precipitation with sulphuric acid (10% v/v), and the final effluent and metallic residue obtained were recirculated without liquid fraction enrichment impact. The whole process was successfully tested at pilot scale. The preliminary economic study showed the potential of the process for the treatment of aluminium hazardous wastes.