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Characterization of bayer hydrotalcites formed from bauxite refinery residue liquor / Sara J. Palmer in Industrial & engineering chemistry research, Vol. 50 N° 9 (Mai 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 9 (Mai 2011) . - pp. 5346-5351 Titre : Characterization of bayer hydrotalcites formed from bauxite refinery residue liquor Type de document : texte imprimé Auteurs : Sara J. Palmer, Auteur ; Ray L. Frost, Auteur Année de publication : 2011 Article en page(s) : pp. 5346-5351 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Refinery Résumé : The precipitate formed during the seawater neutralization (SWN) of Bayer liquors has been characterized by a variety of techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma―optical emission spectroscopy (ICP-OES), infrared and Raman spectroscopy, and thermal analysis. Three mineralogical phases are detected: (I) hydrotalcite, (2) calcite (CaCO3), and (3) aragonite (CaCO3). It is proposed that two hydrotalcite structures form and have the formulas Mg8Al2(OH)12(CO32―,SO42―)·xH2O and Mg6Al2(OH)16(CO32―,SO42―)·xH2O. The Mg, Al molar ratio of the Bayer hydrotalcite is dependent on both the pH and the composition of the initial Bayer liquor. It is proposed that carbonate and sulfate ions are intercalated predominantly into the hydrotalcite interlayer; however, small amounts of arsenate, vanadate, and molybdate have been shown to be removed from solution. The formation of Bayer hydrotalcite assists in the removal of oxy-anions of transition metals from bauxite refinery residues, through a combination of intercalation and adsorption reactions involving the newly formed hydrotalcite. Infrared and Raman spectroscopy also confirmed the presence of hydrotalcite, calcite, and aragonite, showing characteristic wavenumbers of hydroxyl stretching modes for hydrotalcite, and antisymmetric stretching modes of carbonate for the calcium carbonate minerals. ICP-OES also confirmed the removal of oxy-anions from Bayer liquors. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24128656 [article] Characterization of bayer hydrotalcites formed from bauxite refinery residue liquor [texte imprimé] / Sara J. Palmer, Auteur ; Ray L. Frost, Auteur . - 2011 . - pp. 5346-5351. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 9 (Mai 2011) . - pp. 5346-5351 Mots-clés : Refinery Résumé : The precipitate formed during the seawater neutralization (SWN) of Bayer liquors has been characterized by a variety of techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma―optical emission spectroscopy (ICP-OES), infrared and Raman spectroscopy, and thermal analysis. Three mineralogical phases are detected: (I) hydrotalcite, (2) calcite (CaCO3), and (3) aragonite (CaCO3). It is proposed that two hydrotalcite structures form and have the formulas Mg8Al2(OH)12(CO32―,SO42―)·xH2O and Mg6Al2(OH)16(CO32―,SO42―)·xH2O. The Mg, Al molar ratio of the Bayer hydrotalcite is dependent on both the pH and the composition of the initial Bayer liquor. It is proposed that carbonate and sulfate ions are intercalated predominantly into the hydrotalcite interlayer; however, small amounts of arsenate, vanadate, and molybdate have been shown to be removed from solution. The formation of Bayer hydrotalcite assists in the removal of oxy-anions of transition metals from bauxite refinery residues, through a combination of intercalation and adsorption reactions involving the newly formed hydrotalcite. Infrared and Raman spectroscopy also confirmed the presence of hydrotalcite, calcite, and aragonite, showing characteristic wavenumbers of hydroxyl stretching modes for hydrotalcite, and antisymmetric stretching modes of carbonate for the calcium carbonate minerals. ICP-OES also confirmed the removal of oxy-anions from Bayer liquors. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24128656

Use of hydrotalcites for the removal of toxic anions from aqueous solutions / Sara J. Palmer in Industrial & engineering chemistry research, Vol. 49 N° 19 (Octobre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 8969–8976 Titre : Use of hydrotalcites for the removal of toxic anions from aqueous solutions Type de document : texte imprimé Auteurs : Sara J. Palmer, Auteur ; Ray L. Frost, Auteur Année de publication : 2010 Article en page(s) : pp. 8969–8976 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Hydrotalcites  Aqueous  solutions Résumé : The removal of toxic anions has been achieved using hydrotalcite via two methods: (1) coprecipitation and (2) thermal activation. Hydrotalcite formed via the coprecipitation method, using solutions containing arsenate and vanadate up to pH 10, are able to remove more than 95% of the toxic anions (0.2 M) from solution. The removal of toxic anions in solutions with a pH of >10 reduces the removal uptake percentage to 75%. Raman spectroscopy observed multiple A1 stretching modes of V−O and As−O at 930 and 810 cm−1, assigned to vanadate and arsenate, respectively. Analysis of the intensity and position of the A1 stretching modes helped to identify the vanadate and arsenate specie intercalated into the hydrotalcite structure. It has been determined that 3:1 hydrotalcite structure predominantly intercalate anions into the interlayer region, while the 2:1 and 4:1 hydrotalcite structures shows a large portion of anions being removed from solution by adsorption processes. Treatment of carbonate solutions (0.2 M) containing arsenate and vanadate (0.2 M) three times with thermally activated hydrotalcite has been shown to remove 76% and 81% of the toxic anions, respectively. Thermally activated hydrotalcite with a Mg:Al ratio of 2:1, 3:1, and 4:1 have all been shown to remove 95% of arsenate and vanadate (25 ppm). At increased concentrations of arsenate and vanadate, the removal uptake percentage decreased significantly, except for the 4:1 thermally activated hydrotalcite. Thermally activated Bayer hydrotalcite has also been shown to be highly effective in the removal of arsenate and vanadate. The thermal activation of the solid residue component (red mud) removes 30% of anions from solution (100 ppm of both anions), while seawater-neutralized red mud removes 70%. The formation of hydrotalcite during the seawater neutralization process removes anions via two mechanisms, rather than one observed for thermally activated red mud. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101104r [article] Use of hydrotalcites for the removal of toxic anions from aqueous solutions [texte imprimé] / Sara J. Palmer, Auteur ; Ray L. Frost, Auteur . - 2010 . - pp. 8969–8976. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 8969–8976 Mots-clés : Hydrotalcites  Aqueous  solutions Résumé : The removal of toxic anions has been achieved using hydrotalcite via two methods: (1) coprecipitation and (2) thermal activation. Hydrotalcite formed via the coprecipitation method, using solutions containing arsenate and vanadate up to pH 10, are able to remove more than 95% of the toxic anions (0.2 M) from solution. The removal of toxic anions in solutions with a pH of >10 reduces the removal uptake percentage to 75%. Raman spectroscopy observed multiple A1 stretching modes of V−O and As−O at 930 and 810 cm−1, assigned to vanadate and arsenate, respectively. Analysis of the intensity and position of the A1 stretching modes helped to identify the vanadate and arsenate specie intercalated into the hydrotalcite structure. It has been determined that 3:1 hydrotalcite structure predominantly intercalate anions into the interlayer region, while the 2:1 and 4:1 hydrotalcite structures shows a large portion of anions being removed from solution by adsorption processes. Treatment of carbonate solutions (0.2 M) containing arsenate and vanadate (0.2 M) three times with thermally activated hydrotalcite has been shown to remove 76% and 81% of the toxic anions, respectively. Thermally activated hydrotalcite with a Mg:Al ratio of 2:1, 3:1, and 4:1 have all been shown to remove 95% of arsenate and vanadate (25 ppm). At increased concentrations of arsenate and vanadate, the removal uptake percentage decreased significantly, except for the 4:1 thermally activated hydrotalcite. Thermally activated Bayer hydrotalcite has also been shown to be highly effective in the removal of arsenate and vanadate. The thermal activation of the solid residue component (red mud) removes 30% of anions from solution (100 ppm of both anions), while seawater-neutralized red mud removes 70%. The formation of hydrotalcite during the seawater neutralization process removes anions via two mechanisms, rather than one observed for thermally activated red mud. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101104r