from first principles PP-I-1

PP-III-19Hydrotalcite-Like Catalytic Materials Obtained from Industrial Wastes forOxidation of Sulfur CompoundsCruceanu A. 1 , Zavoianu R. 1 , Pavel O.D. 1 , Bradu C. 1 , Duţu L. 1 , Mara L. 21 University of Bucharest, Faculty of Chemistry, Department of Organic Chemistry,Biochemistry and Catalysis, Bd. Regina Elisabeta, No. 4-12, S3, Bucharest 030018, Romania2 National Institute for Research and Development for Nonferrous and Rare Metals,Bucharest, Romaniaancacruceanu@gmail.comThis contribution concerns the preparation, characterization and the catalytic activity ofhydrotalcite-like (HT) materials obtained from red mud (RM) industrial waste in the oxidationof sulfide ions from wastewaters with air. Several hydrotalcite-like compounds with thegeneral formula Mg x Al 0.75 Fe 0.25(RM) (where x = Mg/(Al+Fe) = 2-5) have been prepared by coprecipitationat constant pH = 10 using red mud as the main source for Fe cations. Taking intoaccount the chemical composition of the red mud, the amounts of Al and Mg were adjusted inorder to obtain the desired molar ratio Mg/(Al+Fe) using aqueous solutions ofMg(NO 3 ) 2 x6H 2 O and Al(NO 3 ) 3 x9H 2 O. NaOH and Na 2 CO 3 aqueous solutions were added inorder to adjust the pH and favour the precipitation of the hydrotalcite-phase. For comparisonpurposes, hydrotalcite-like materials Mg x Al 0.75 Fe 0.25(HT) with the same Mg/(Al+Fe) ratio wereprepared according to the standard co-precipitation method at low supersaturation usingaqueous solutions of Fe, Al and Mg nitrates, NaOH and Na 2 CO 3 [1]. The solids have beencharacterized by XRD, DRIFTS, DR-UVVis-NIR, BET and their surface base sites weredetermined using a method consisting in the irreversible adsorption of organic acids withdifferent pK a [2]. The catalytic tests were performed during 2 h under continuous stirring atroom temperature using different air flows in the range 1.8 – 5.4 L/h and sulfideconcentrations in the wastewater varying from 50 to 200 mg/L. XRD results showed thatMg x Al 0.75 Fe 0.25(RM) materials have a slightly modified HT-structure compared to thecorresponding Mg x Al 0.75 Fe 0.25(HT) materials. The catalytic tests results could be well correlatedto the variation of the number of weak and medium strength base sites of the catalystsconfirming the important role played by the basicity in the reaction mechanism.References:[1] D. Tichit, M.H. Lhouty, A. Guida, B.H. Chiche, F. Figueras, A. Auroux, D. Bartalini, E. GarroneJ. Catal., 151 (1995) 50.[2] R. Ionescu, R. Birjega, E. Angelescu, O.D. Pavel, R. Zavoianu, Catal. Lett. 34 (2010) 309.170