Traitement et stabilisation chimique de déchets d’aluminerie contaminés en ions fluorures.

Aluminium plant production wastes are contaminated by fluoride according to TCLP (toxicity characteristics leaching procedure) and Quebec legislation (>150 mg F-/L). Those wastes contain 2-323 g F-/kg. The extraction of fluoride by acid leaching (H2SO4, pH 1.5) at total solids content between 1% and 16% allows the removal of approximately 33% of F- but does not respect the TCLP regulation. However, the chemical stabilization of aluminium wastes by use of calcium hydroxide (Ca(OH)2) at a concentration varying from 10 to 12 g/L in the suspension of EC (100 g/L) allowed us to record lower concentrations of fluoride ions (110-115 mg F-/L) in the leachate from the TCLP test. The subsequent treatment of the dehydration filtrate of stabilized residues by decreasing the pH from the initial value (pH 11.9 or 12.0) to pH values between 7.0 and 8.5 by addition of an inorganic acid (H2SO4, 10 mol/L) removed up to 98% of fluoride ions by precipitation. [ABSTRACT FROM AUTHOR]