The hydrothermal treatment of exhausted FCC catalysts with zeolite was optimized by varying the chemical composition of the synthesis mixture. The zeolitic products obtained were used to evaluate their ability for the capture of Cr(III) cations from aqueous solutions. It was shown that the zeolitic product materials were capable of reducing the Cr(III) ion concentration to values lower than 1.2 ppm. The chromium ion-containing solids were afterwards solidified in cement mortars on which leaching studies of this cation were made. The results obtained showed that the synthesized solids acted as effective Cr(III) ion immobilizers and that their inclusion as additives in cement formulations could provide an environmental friendly disposal procedure.Fil: González, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pereyra, Andrea Marisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina. Universidad Tecnológica Nacional. Facultad Regional La Plata; ArgentinaFil: Basaldella, Elena Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina. Universidad Tecnologica Nacional. Facultad Regional La Plata; Argentin

Basaldella, Elena Isabel

González, Maximiliano

Pereyra, Andrea Marisa

Adsorption Science & Technology

Maximiliano R. González

Andrea M. Pereyra

Elena I. Basaldella

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Trivalent Chromium Ion Removal from Aqueous Solutions Using Low-Cost Zeolitic Materials Obtained from Exhausted FCC Catalysts

CONICET Digital

Reprinted fromAdsorption Science & Technology2011  Volume 29  Number 7Multi-Science Publishing Co. Ltd.5 Wates Way, Brentwood, Essex CM15 9TB, United KingdomTrivalent Chromium Ion Removal fromAqueous Solutions Using Low-costZeolitic Materials Obtained from ExhaustedFCC CatalystsMaximiliano R. González, Andrea M. Pereyra andElena I. Basaldella629Trivalent Chromium Ion Removal from Aqueous Solutions Using Low-costZeolitic Materials Obtained from Exhausted FCC Catalysts†Maximiliano R. González1, Andrea M. Pereyra1,2 and Elena I. Basaldella1,2* (1) CINDECA,CCT- La Plata–CONICET, Universidad Nacional de La Plata, 47 N 257 (B1900AJK), La Plata, Argentina. (2)Universidad Tecnológica Nacional, Facultad Regional La Plata, 124 y 60, 1900- La Plata, Argentina.(Received 30 April 2011; accepted 2 July 2011)ABSTRACT: The hydrothermal treatment of exhausted FCC catalysts withzeolite was optimized by varying the chemical composition of the synthesismixture. The zeolitic products obtained were used to evaluate their ability for thecapture of Cr(III) cations from aqueous solutions. It was shown that the zeoliticproduct materials were capable of reducing the Cr(III) ion concentration tovalues lower than 1.2 ppm. The chromium ion-containing solids were afterwardssolidified in cement mortars on which leaching studies of this cation were made.The results obtained showed that the synthesized solids acted as effective Cr(III)ion immobilizers and that their inclusion as additives in cement formulationscould provide an environmental friendly disposal procedure.INTRODUCTIONWater pollution caused by the presence of heavy metal ions represents one of the most frequentenvironmental problems widely known at present. Such heavy metal cations accumulate in livingorganisms and are considered harmful for human health because of their cytotoxic andcarcinogenic effects (Bagchi et al. 2002). The cation-exchange properties of zeolitic materials are one of their fundamental characteristics,allowing their application as selective ion sorbents in purification processes. To date, the ion-exchangeprocesses of zeolites with uni- and di-valent cations have been widely studied. As far as trivalentcations are concerned, it is known that faujasite (FAU) zeolites are suitable materials for the removalof aquo-stabilized Cr(III) ion species generally present in the aqueous phase (Gazola et al. 2006).In addition, spent solid FCC catalysts are considered as being incapable of regeneration.Large volumes of refinery catalysts are purchased to replace non-regenerable refinery catalysts,with the volume of the spent amount approaching that of the newly bought material. Such spentcatalysts have been attracting the attention of environmental authorities in many countries for thepast few years. There are some indications that all exhausted refinery catalysts might be classifiedas hazardous materials in the future (Furimsky 1996). Hence, special precautions should be takenduring their storage, transportation and disposal to avoid future liabilities. Perhaps, the bestsolution would be the reclamation of all components of spent catalysts, but nowadays mostexhausted catalysts are solidified with cement and buried in landfill sites. Exhausted FCCcatalysts are also used as raw materials for manufacturing cement, ceramics, bricks or tiles (Hsu1996; Su et al. 2001; Tseng et al. 2005; Zornoza et al. 2009). † Published in the Festschrift of the journal dedicated to Prof essor Giorgio Zgrablich on the occasion of his 70th birthdayand to celebrate his 50 years as a faculty member at the National University of San Luis in Argentina.* Author to whom all correspondence should be addressed. E-mail: eib@quimica.unlp.edu.ar.We have previously analyzed the use of exhausted FCC catalysts as raw materials for zeolitesynthesis (Basaldella et al. 1995, 2006, 2009). The fusion pre-treatment method proposed byAbdemeizien-Hamoudi and Siffert (1989) was used to improve the reactivity of the catalysttowards zeolitic conversion. These authors described a method by which the quartz present inclays could be eliminated by thermal treatment with Na2CO3 at 800 °C. It was found that suchalkaline fusion increases the zeolitic nature of the solid phases (Basaldella et al. 2009). Inaddition, there are also reports regarding the incorporation of natural or artificial zeolites incementitious materials (Caputo et al. 1999; Perraki et al. 2010).The aim of the present work was the optimization of the conversion of exhausted FCC catalystsinto zeolitic products. Additionally, the ability of these products to remove Cr(III) cations presentin aqueous solution was tested, and the polluted solids obtained after chromium ion removalincorporated into cementitious matrices. The retention of Cr(III) cations inside these matrices wasevaluated by performing normalized washing tests, while their matrix engineering properties wereinvestigated to study the feasibility of using the mortar formulation as a chromium ion immobilizer,thereby providing a potentially safe construction material.EXPERIMENTALHydrothermal synthesis of zeolitic productsAn equilibrium catalyst (CAT) was used as the source of silica and alumina for the hydrothermalsynthesis. This catalyst was a waste material arising from a commercial unit employed forfluidized bed catalytic cracking (FCC). Synthesis of the zeolites was undertaken from mixtures ofthe catalyst and Na2CO3 (Baker, A.R. standard) as described by Basaldella et al. (2009). Thus, the mixtures were calcined at 800 °C for 2 h under static conditions. Three Na2CO3/CATratios were used employing different weight proportions of Na2CO3 (0, 25 and 50 wt%). Synthesisleading to hydrothermal crystallization was undertaken in a closed vessel at 90–95 °C withoutstirring. Reaction mixtures were prepared by adding NaOH solution to the calcined mixture atroom temperature, followed by stirring to achieve homogeneity. Separately, commercial sodium aluminate (36.5% Al2O3, 29.6% Na2O, 33.9% H2O) was addedto an aluminate/starting mixture at a 0.02 w/w ratio, again with stirring to achieve homogeneity.This mixture was allowed to rest for 48 h at room temperature without stirring. The weight ofNa2O added to the reaction mixture was calculated so as to attain a selected H2O/Na2O ratio. The mixed gels were heated at 95 °C in closed propylene containers with samples being taken atdifferent reaction times, the solid being separated from the liquid by centrifugation. The solidfractions were washed until the pH value of the wash water reached 10 and then dried at 110 °C. Thecompositions of the reaction mixtures and the synthesis conditions employed are detailed in Table 1.In the data listed, the elapsed reaction time is indicated by adding the number of correspondinghours at the end of the sample. Thus, for example, 1279–2 h indicates that the sample consistedof mixture 1279 after remaining for 2 h at the reaction temperature.CharacterizationThe composition of the starting catalyst was determinded via an electron microprobe (EDX)coupled to a scanning electron microscope. Such EDX chemical analysis gave the composition50.6 wt% SiO2, 47.8 wt% Al2O3, 1.4 wt% Na2O and 0.2 wt% other metallic oxides.630 M.R. González et al./Adsorption Science & Technology Vol. 29 No. 7 2011Characterization of the initial solids used for the synthesis and of the reaction products wascarried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. TheX-ray diffraction measurements were obtained using a Philips 3020 diffractometer (40 kV, 20 mA,Cu Kα radiation via a Ni filter, step width 0.04° and counting time 2.0 s/step). The types of zeolitesand other crystalline phases obtained were determined by comparing their diffraction profiles withpublished data (Breck 1974). The Rietveld method (Rietveld 1969) was used for quantitativedetermination of the crystalline phases. This consists of refining a crystal structure by minimizingthe weighted squared difference between the observed and calculated diffraction patterns.The “FullProf” program (Rodriguez-Carvajal 1990) was used to perform the Rietveld analysis.The crystallographic data used for each phase were extracted from the literature. The size andmorphology of the particles obtained were determined by scanning electron microscopy (Philips505 instrument) using samples coated with a gold film.Ion-exchange studiesIon-exchange experiments were conducted under stirring by contacting 1–3 g of each zeolitic samplewith 1  of chromium ion solution containing ~42 ppm of Cr(III) ions. The chromium ion solutionwas prepared by dissolving the appropriate amount of Cr(NO3)3 • 9H2O (Anedra, p.a.) in distilledwater. The pH value of the final solution was noted as 3.53. Samples of the suspension werecollected at pre-determined times, with the liquid being separated from the solid by filtration. Thesolid phases were oven-dried at 110 °C and stabilized at room temperature at 35% relative humidity.Chromium Ion Removal by Zeolitic FCC Catalysts 631TABLE 1. Initial Compositions, Products and Conversions Achieved in Different TestsTest Na2CO3 NaAlO2 H2O/Na2O Zeolite Conversion(w/w%)a (w/w%)b (w/w%)b type (% XRD)c1272–2 h − 2 27 − −1272–3 h − 2 27 − −1272–21 h − 2 27 X > A 681272–2 h 50 2 27 A + trX 601272–3 h 50 2 27 A + trX 901272–21 h 50 2 27 trA + HS 101279–1 h − − 27 X > A 351279–2 h − − 27 X > A 401279–3 h − − 27 X > A 451280–1 h 25 − 27 X > A 401280–2 h 25 − 27 X > A 661280–3 h 25 − 27 X > A 681281–1 h 25 2 27 A ≥ X 601281–2 h 25 2 27 A ≥ X 701281–3 h 25 2 27 A ≥ X 704012–1 h 50 2 33 A > X 604012–2 h 50 2 33 A > X 704012–3 h 50 2 33 A > X 854016–1 h 50 2 45 − −4016–2 h 50 2 45 A + trX 704016–3 h 50 2 45 A + trX 85To determine the chromium(III) ion concentration, the liquid phases were analyzed by atomicabsorption spectrometry (AAS) employing an IL 457 model double-beam spectrophotometer.Solid phases were analyzed by X-ray diffraction (XRD) methods.Stabilization testsThe product obtained after cation exchange of the 1273–3 h test sample (1273–3 h/Cr) wasstabilized in a cementitious matrix obtained from natural siliceous sand and normal Portlandcement CPC 40. A series of cement mortars (prisms of size 40 × 40 × 160 mm) were prepared.The series included four mortars, a reference mortar (Z0, without the zeolitic product) and threemortars in which 8 wt%, 20 wt% and 30 wt% cement was replaced by 1273–3 h/Cr. The samplesare referred to below as Z8, Z20 and Z30, respectively. The mix proportions used were awater/cement w/w ratio of 0.45 and a sand/cement w/w ratio of 2.6. These matrices were curedfor 28 d at 25 °C and 100% relative humidity. The hardened mortars were subjected tocompressive and flexural strength measurements. A leaching test was also performed with the aimof analyzing the environmental impact of incorporating the chromium-bearing zeolite incementitious materials. The release of Cr(III) ions from the cured mortars Z10, Z20 and Z30 wasestimated by performing the leaching test with the crushed mortar in acidic media employingstandard methods (US EPA, Method 1311, 1992). The solid compact was first ground (grain size< 125 µm) and the powdered sample then placed in contact with an acetic acid solution at pH = 5.0(liquid/solid ratio = 20). The Cr(III) ion concentration was determined in the liquid phase byatomic absorption spectroscopy (AAS) after 18 h contact time.RESULTS AND DISCUSSIONFigures 1 and 2 overleaf show the X-ray diffraction patterns for solid samples taken during selectedexperiments of zeolite synthesis. These characterizations were carried out in order to analyze theinfluence of sodium aluminate addition and alkaline fusion. At short reaction times (< 1 h), thediffractograms obtained indícate that all the samples examined exhibited sharp peaks in the 20 < 2θ< 25 region, being typical of silica glasses. At longer times, the conversion of the zeolitic phases wasappreciable, with many of the reaction products exhibiting high percentages of NaA (LTA) and NaX(FAU) (see data listed in Table 1). Another general feature was that allowing the reaction to proceedfurther led to the conversion of NaA to hydroxysodalite (HS), as can be seen from the X-raydiffraction pattern depicted in Figure 2. In addition, some samples also exhibited traces of natrite,nepheline, low carnagieite, mullite and anatase. Comparing the results for samples obtained with orwithout alkaline fusion pre-treatment (Figures 1 and 2, respectively) shows that the production ofzeolitic products was faster when such pre-treatment was applied. Furthermore, the crystallization ofNaA zeolite was favoured when higher percentages of sodium carbonate were employed andadditional aluminium was added (Table 1, samples 1273–3 h, 4012–3 h, 4016–4 h). Test 1279, whichwas carried out in the absence of both fusion and extra aluminium addition, led to a very lowconversion percentage. The mixture which presented a high conversion to zeolitic materialscontaining a higher content of zeolite X was obtained using 25 wt% sodium carbonate and addingsodium aluminate (Table 1, sample 1281–3 h). Comparison of the results for series 1273, 4012 and4016 indicates that a higher water/silica ratio had little effect on the synthesis process. Selected products of such hydrothermal syntheses were tested in the Cr(III) ion-exchangereaction, employing an initial Cr(III) ion concentration in the liquid phase of 40.3 ppm. In all632 M.R. González et al./Adsorption Science & Technology Vol. 29 No. 7 2011cases, excellent cation retentions were observed after 10 min contact time, with the Cr(III) ionconcentration in solution being reduced to < 1.2 ppm. Figure 3 overleaf shows the developmentof the amounts of Cr(III) ions retained with time. The best results were achieved with the NaAsample containing the greatest amount of zeolite (1273–3 h), whose use led to Cr(III) ionChromium Ion Removal by Zeolitic FCC Catalysts 6337060504030201000 5 10 15 202θ (degrees)Intensity (a.u.)25 30 35 403 h2 h1 h0 h45Figure 1. X-Ray diffraction patterns for the products of test 1272.7060504030201000 5 10 15 202θ (degrees)Intensity (a.u.)25 30 35 403 h2 h1 h0 h45Figure 2. X-Ray diffraction patterns for the products of test 1273.concentration values in the aqueous phase of < 0.3 ppm. The Rietveld compositional analysisresults obtained for this sample are detailed in Table 2.The morphology and particle size of the reaction products were estimated via scanning electronmicroscopy. The product obtained without alkaline fusion retained the morphology of the startingcatalyst, since spherical particles of ca. 60–100 µm in diameter were observed even after reaction[Figure 4(a)]. These spheres were composed of zeolitic crystals whose morphology is depicted inFigure 4(c). When the fusion treatment was used for activation, the integrity of the starting catalystwas partially lost [Figure 4(b)]. The corresponding analysis for the solid obtained in one of thetests with a high LTA percentage (1273–3 h) indicated that the product was mainly composed ofcubic crystals whose sizes were smaller than 1 µm [Figure 4(d)].The results of lixiviation studies undertaken on the Z10, Z20 and Z30 mortars are shown inTable 3. The Cr(III) ion concentration values in the supernatant liquid at the end of such tests werealways less than 0.5 ppm. Such results enable these materials to be classified as non-hazardouswastes suitable for landfill or construction (Zornoza et al. 2009).634 M.R. González et al./Adsorption Science & Technology Vol. 29 No. 7 2011TABLE 2. Rietveld Analysis of Sample1273–3 hZeolite Content (wt%)LTA zeolite 5Sodium nepheline 13Low carnagieite 4Mullite 1Hydroxysodalite 6Anatase < 1201510500 5 10 15 20 25 30Time (min)Cr(III) ion retention [mg Cr(III)/g sold sample]abcdFigure 3. Evolution of Cr(III) ion concentration in the solid phase employing different products obtained in thehydrothermal synthesis during the exchange reaction: (a) sample 1272–21 h; (b) sample 1273–3 h; (c) sample 1280–3 h;(d) sample 1281–3 h. Experimental conditions: Cr(III) ion conc. in solution at zero time = 40.3 ppm; weight of solidphase = 2 g.CONCLUSIONSThe conversion of exhausted FCC catalysts to zeolitic products of commercial interest provides avalid alternative for their disposal. Activation by alkaline fusion has been shown as an appropriatemethod for improving such transformation to provide a solid with a high content of zeoliticphases. The results obtained in cation-exchange experiments indicate that such products could beused for the removal of Cr(III) ions from aqueous media.Additionally, the feasibility of including such Cr(III) ion-bearing zeolitic materials incementitious blocks was studied. It was found that ca. 20 wt% of the zeolitic product could beused to replace the Portland cement without altering the engineering properties of the resultingChromium Ion Removal by Zeolitic FCC Catalysts 635(a) (b)(c) (d)Figure 4. SEM micrographs of test products with and without alkaline fusion: (a) and (c), sample 1271–21 h,magnification ×200 and ×5000, respectively; (b) and (d), sample 1273–3 h, magnification ×200 and ×5000, respectively.TABLE 3. Results of Leaching Tests forDifferent MortarsaSample % Zeolite Conc. (mg/)Z8 8 0.061Z8 8 0.064Z20 20 0.077Z20 20 0.072Z30 30 0.105Z30 30 0.135a Leaching time for all samples = 18 h.matrices. In this case, mortars with acceptable mechanical strength levels were obtained whichgave appropriate performances in the leaching test. ACKNOWLEDGEMENTSThe authors wish to thank A. Ermili for performing the various experiments. E.I.B. is a memberof the Commission of Scientific Research, CIC-PBA. REFERENCESAbdemeizien-Hamoudi, K. and Siffert, B. (1989) Appl. Clay Sci. 4, 1.Bagchi, D., Stohs, S.J., Downs, B.W., Bagchi, M. and Preuss, H.G. (2002) Toxicology 180, 5.Basaldella, E.I., Kikot, A. and Tara, J.C. (1995) Lat. Am. Appl. Res. 25, 55.Basaldella, E.I., Paladino, J.C., Solari, M. and Valle, G.M. (2006) Appl. Catal. B 66, 186.Basaldella, E.I., Torres Sánchez, R.M. and Conconi, M.S. (2009) Appl. Clay Sci. 42, 611.Breck, D.W. (1974) Zeolite Molecular Sieves, Wiley, New York.Caputo, D., De Gennaro, B., Pansini, M. and Colella, C. (1999) Stud. Surf. Sci. Catal. 125, 723Furimsky, E. (1996) Catal. Today 30, 223.Gazola, F.C., Pereira, M.R., Barros, M.A.S.D., Silva, E.A. and Arroyo, P.A. (2006) Chem. Eng. J. 117, 253.Hsu, W.C. (1996) Ceram. Trans. 15, 20.Perraki, T., Kontori, E., Tsivilis, S. and Kakali, G. (2010) Cem. Concr. Compos. 32, 128.Rietveld, H.M. (1969) J. Appl. Crystallogr. 2, 65.Rodriguez-Carvajal, J. (1990) “FullProf: A Program for Rietveld Refinement and Pattern MatchingAnalysis”, Satellite Meeting on Powder Diffraction of the XVth Congress of the IUCr, Toulouse, France,p. 127.Su, N., Chen, Z. and Fang, H. (2001) Cem. Concr. Compos. 23, 111.Tseng, Y., Huang, C. and Hsu, K. (2005) Cem. Concr. Res. 35, 782.US EPA (1992) Method 1311. Toxicity Characteristic Leaching Procedure, US Environmental ProtectionAgency, Washington, DC, U.S.A.Zornoza, E., Payá, J., Monzó, J., Borrachero, M.V. and Garcés, P. (2009) Constr. Build. Mater. 23, 1323.636 M.R. González et al./Adsorption Science & Technology Vol. 29 No. 7 2011

Trivalent chromium ion removal from aqueous solutions using low-cost zeolitic materials obtained from exhausted FCC catalysts

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The hydrothermal treatment of exhausted FCC catalysts with zeolite was optimized by varying the chemical composition of the synthesis mixture. The zeolitic products obtained were used to evaluate their ability for the capture of Cr(III) cations from aqueous solutions. It was shown that the zeolitic product materials were capable of reducing the Cr(III) ion concentration to values lower than 1.2 ppm. The chromium ion-containing solids were afterwards solidified in cement mortars on which leaching studies of this cation were made. The results obtained showed that the synthesized solids acted as effective Cr(III) ion immobilizers and that their inclusion as additives in cement formulations could provide an environmental friendly disposal procedure

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Trivalent chromium ion removal from aqueous solutions using low-cost zeolitic materials obtained from exhausted FCC catalysts

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