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Zeolite formation by hydrothermal treatment of waste solution from selectively leached kaolinite
January 2002
Materials Letters 52 Ž2002. 91–95 www.elsevier.comrlocatermatlet
Zeolite formation by hydrothermal treatment of waste solution from selectively leached kaolinite Jadambaa Temuujin a,) , Kiyoshi Okada a , Kenneth J.D. MacKenzie b a
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan b New Zealand Institute for Industrial Research and DeÕelopment, P.O. Box 31-310, Lower Hutt, New Zealand Received 7 December 2000; accepted 2 May 2001
Abstract Zeolite formation has been achieved by hydrothermal treatment of the waste solution from selective leaching by 2 M NaOH solution of kaolinite calcined at 10008C for the preparation of mesoporous g-Al 2 O 3. The spent leaching solution was hydrothermally treated at 1008C and at 1508C for 12–72 h. The initial product Žhydroxysodalite. is converted to zeolite P after longer reaction times. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Kaolinite; g-Alumina; Leaching; Zeolite
1. Introduction A new preparation method of g-Al 2 O 3 from clay minerals such as kaolinite, Al 2 ŽOH.4 Si 2 O5 , by a selective leaching method has been reported w1,2x. Before being leached, the kaolinite was calcined at 10008C, which converted it into a mixture of g-Al 2 O 3 and amorphous silica. After leaching with KOH solution, the solid product Ž g-Al 2 O 3 . has a microtexture consisting of fine alumina grains inter-connected by residual amorphous SiO 2 with mesopores formed in the pseudomorphic particles. This material shows good gas and water vapour adsorption properties w2,3x. The leaching solution Ž4 M KOH. can be recovered as a waste by-product. If NaOH solution is used as the leaching agent, it can act as a precursor ) Corresponding author. Permanent address: Institute of Chemistry and Chemical Technology, Mongolian Academy of Sciences, Ulaanbaatar 51, Mongolia. E-mail address: [email protected] ŽJ. Temuujin..
solution for zeolite synthesis because it contains Si, Al and Na. The objective of this work is to study the porous properties of the g-Al 2 O 3 formed by leaching with sodium hydroxide, and to synthesize zeolite from the resulting waste solution.
2. Experimental Georgia kaolinite ŽAl 2 Si 2 O5 ŽOH.4 . calcined at 10008C for 24 h was used as the starting material. Three-gram aliquots were leached with 250 ml of NaOH solution Ž2 M. at 908C for 2 h with stirring. The suspension was centrifuged from the solution, which was stored in a teflon beaker. The solid precipitate was washed three times with distilled water and dried at 1008C overnight. The chemical composition of the leachate was determined by ICP to be Na s 42.5, Si s 2.56 and
00167-577Xr02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 3 7 2 - X
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
92
Al s 0.65 grl. This solution was placed in a teflon beaker inside a hydrothermal bomb Ž50 ml. and reacted at 1008C and 1508C for 12, 24, 48 and 72 h. After hydrothermal treatment, the bomb was rapidly cooled by immersing in flowing cold water. The resulting precipitates were collected by centrifuging, washed three times with distilled water, and dried at 1008C for 12 h. The samples reacted at 1008C for 24, 48 and 72 h are denoted Z-100a, Z-100b and Z-100c, and those reacted at 1508C for 12, 24, 48 and 72 h are denoted Z-150a, Z-150b, Z-150c and Z-150d, respectively. No crystalline phases were formed in the solution reacted at 1008C for 12 h. The phases formed in the other samples were characterized by powder X-ray diffraction using a Rigaku Geigerflex diffractometer with monocromated Cu–K a radiation, and FTIR ŽShimadzu FTIR PC8000 . by suspending the samples in KBr disks. The specific surface area was measured by the BET method using nitrogen gas as adsorbate at y1968C with a Quanta Chrome Autosorb-1 instrument. The textures of the samples were observed by scanning electron microscopy ŽHitachi S-8000..
3. Results and discussion 3.1. Porous g-alumina The chemical composition and porous properties of the original calcined kaolinite and the NaOHleached materials are shown in Table 1, which also lists the chemical composition and porous properties of a KOH-leached sample w2x for comparison. The porous properties and chemical composition of gAl 2 O 3 obtained using NaOH solution are very simi-
lar to those of g-alumina obtained using KOH w2x. These results show that NaOH is as suitable as a leaching agent as KOH is for the preparation of mesoporous g-Al 2 O 3 . Since the NaOH leached sample has mesopores of uniform pore size Žabout 3 nm radius. and a pore size distribution quite similar to that of the KOH leached sample w1,2x, we conclude that changing the hydroxide solution does not affect the chemical composition or porous properties of the resulting galumina. 3.2. Zeolite formation from waste solution of NaOHleached calcined kaolinite Fig. 1a shows the XRD patterns of the Z-100 series zeolites. Formation of a zeolite-type compound was observed after 24-h reaction at this temperature. Although it was difficult to identify all the observed peaks, the diffractogram could best be matched with the patterns of hydroxysodalite, 4Na 2 O P 3Al 2 O 3 P 6SiO 2 P H 2 O ŽJCPDS card 11-401. and zeolite P, Na 5.7 Al 5.7 Si 10.3 O 32 P 12H 2 O ŽJCPDS card 34-524.. With increasing reaction time, the peak intensity of hydroxysodalite increased at the expense of the unidentified peaks, and the peaks assigned to zeolite P also became gradually more intense at the expense of the hydroxysodalite peaks. After 72 h reaction only the peaks of zeolite P and hydroxysodalite were present in the XRD pattern of the sample. These results suggest that hydroxysodalite transforms to more stable zeolite P w4x under these conditions. Zeolite P exists in high and low silica forms w5x, the latter has both cubic and tetragonal structures. The present samples contained residual hydroxysodalite, together with either tetragonal zeolite P or a mixture of the tetragonal and cubic forms.
Table 1 Chemical composition and porous properties of samples Sample Original kaolinite KOH leached g-Al 2 O 3 NaOH leached g-Al 2 O 3
Chemical compositionrmass Ž%. Al 2 O 3 SiO 2 TiO 2 K 2O
Fe 2 O 3
Na 2 O
Surface area Žm2 gy1 .
Pore volume Žml gy1 .
47.4 84 85
0.6 1 1.3
0 0 1.9
9.9 244 242
0.09 0.72 0.68
50.2 6.8 8.1
1.4 5.5 3.3
0.14 1.4 0
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
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change. Therefore, to synthesize another type of zeolite, it is necessary to modify the waste solution by adding another component. Fig. 2 shows the FTIR spectra of these samples. Differences in the spectra within each series were not marked, suggesting that FTIR spectroscopy is relatively insensitive to differences between the zeolite products. The initial SirAl ratio in the solution Žabout four. should favor the crystallization of faujasite-type zeolites such as X and Y, but the large
Fig. 1. Ža. XRD patterns of Z-100 series samples. Žb. XRD patterns of Z-150 series samples.
The same crystallization behavior was also observed in the Z-150 series samples ŽFig. 1b., in which the formation of zeolite-related compounds began at shorter times than for the Z-100 series. The product from Z-150a was a mixture of hydroxysodalite and zeolite P, becoming solely zeolite P after 72 h reaction. The amount of zeolite increased at a higher reaction temperature, but the crystalline products were the same at both temperatures. The raw material for the zeolite synthesis was the leachate from selectively leached calcined kaolinite, the chemical composition of which, clearly, will not
Fig. 2. Ža. FTIR spectra of Z-100 series samples. Žb. FTIR spectra of Z-150 series samples.
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J. Temuujin et al.r Materials Letters 52 (2002) 91–95
excess of sodium ions in the solution possibly facilitated the initial formation of hydroxysodalite. The FTIR spectrum of the sample obtained after 1008C for 72 h is similar to those of samples produced at 1508C, suggesting that zeolite P, which crystallizes well at 1008C after 72 h, is also formed at 1508C at shorter reaction times. These samples show broad absorption bands in the range 3050–3740 cmy1 , allowing differently bonded types of water to be resolved. The Z-150d sample showed bands at 1650, 1089, 989, 742, 669, 597 and 450 cmy1 , in agreement with the infrared spectral data for zeolite P w5x. The vibrations common to all zeolites are the asymmetric stretching modes, which appear in the region 950–1250 cmy1 . The shape of this band is reported to be sensitive to the framework SirAl ratio, and its position shifts to lower wave numbers with increasing Al content w6x. The absorption bands of the Z-150 series samples in this region shift slightly to lower wave numbers, consistent with this suggestion. The SirAl ratios in hydroxysodalite and zeolite P are 1.0 and 1.8, respectively. The SirAl ratios in these phases are in agreement with our observations. The spectra of the Z-100a and Z-100b samples resembles that of hydroxysodalite reported elsewhere w7x. Fig. 3 shows the S.E.M. photographs of the Z-100 and Z-150 series samples. The particles of Z-100a have the appearance of sheet-like aggregated structures. The particle morphologies in the Z-100b and Z-100c samples change to ball-like aggregates, the size of which increases with longer leaching time. These aggregated particles probably correspond to hydroxysodalite. On the other hand, prismatic particles observed in the Z-100b sample may correspond to zeolite P. The morphology of Z-150a and Z-150b consists of mixtures of oval and prismatic particles, while Z-150d contains prismatic particles only. In this series of samples, the size of the particles increases with longer holding time, possibly growing by the Ostwald ripening process.
material are very similar to those of the g-alumina obtained by using KOH. Hydrothermal treatment at 1008C and 1508C of the spent NaOH leaching solution results in the formation of zeolite-related phases.
4. Conclusion It is possible to prepare porous g-alumina from calcined kaolinite by using NaOH as the leaching agent rather than KOH. The porous properties of this
Fig. 3. Ža. S.E.M. pictures of Z-100 series samples. Žb. S.E.M. pictures of Z-150 series samples.
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
95
Fig. 3 Ž continued ..
Hydroxysodalite is formed initially, transforming to zeolite P after prolonged reaction times.
Acknowledgements J.T. thanks Japan Society for the Promotion of Science ŽJSPS. for the award of research fellowship under which present work was carried out. A part of this work is financially supported by Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
References w1x K. Okada, H. Kawashima, Y. Saito, S. Hayashi, A. Yasumori, J. Mater. Chem. 5 Ž1995. 1241. w2x K. Okada, T. Tomita, A. Yasumori, J. Mater. Chem. 8 Ž1998. 2863. w3x K. Okada, Y. Saito, M. Hiroki, T. Tomita, S. Tomura, J. Porous Mater. 4 Ž1997. 253. w4x L.V.C. Rees, S. Chandrasekhar, Zeolites 13 Ž1993. 524. w5x B.R. Albert, A.K. Cheetham, J.A. Stuart, C.J. Adams, Microporous Mesoporous Mater. 21 Ž1998. 132. w6x A. Miecznikowski, J. Hanuza, Zeolities 5 Ž1985. 188. w7x V.C. Farmer ŽEd.., The Infrared Spectra of Minerals, Mineralogical Society, London, 1974, p. 372.
Materials Letters 52 Ž2002. 91–95 www.elsevier.comrlocatermatlet
Zeolite formation by hydrothermal treatment of waste solution from selectively leached kaolinite Jadambaa Temuujin a,) , Kiyoshi Okada a , Kenneth J.D. MacKenzie b a
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan b New Zealand Institute for Industrial Research and DeÕelopment, P.O. Box 31-310, Lower Hutt, New Zealand Received 7 December 2000; accepted 2 May 2001
Abstract Zeolite formation has been achieved by hydrothermal treatment of the waste solution from selective leaching by 2 M NaOH solution of kaolinite calcined at 10008C for the preparation of mesoporous g-Al 2 O 3. The spent leaching solution was hydrothermally treated at 1008C and at 1508C for 12–72 h. The initial product Žhydroxysodalite. is converted to zeolite P after longer reaction times. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Kaolinite; g-Alumina; Leaching; Zeolite
1. Introduction A new preparation method of g-Al 2 O 3 from clay minerals such as kaolinite, Al 2 ŽOH.4 Si 2 O5 , by a selective leaching method has been reported w1,2x. Before being leached, the kaolinite was calcined at 10008C, which converted it into a mixture of g-Al 2 O 3 and amorphous silica. After leaching with KOH solution, the solid product Ž g-Al 2 O 3 . has a microtexture consisting of fine alumina grains inter-connected by residual amorphous SiO 2 with mesopores formed in the pseudomorphic particles. This material shows good gas and water vapour adsorption properties w2,3x. The leaching solution Ž4 M KOH. can be recovered as a waste by-product. If NaOH solution is used as the leaching agent, it can act as a precursor ) Corresponding author. Permanent address: Institute of Chemistry and Chemical Technology, Mongolian Academy of Sciences, Ulaanbaatar 51, Mongolia. E-mail address: [email protected] ŽJ. Temuujin..
solution for zeolite synthesis because it contains Si, Al and Na. The objective of this work is to study the porous properties of the g-Al 2 O 3 formed by leaching with sodium hydroxide, and to synthesize zeolite from the resulting waste solution.
2. Experimental Georgia kaolinite ŽAl 2 Si 2 O5 ŽOH.4 . calcined at 10008C for 24 h was used as the starting material. Three-gram aliquots were leached with 250 ml of NaOH solution Ž2 M. at 908C for 2 h with stirring. The suspension was centrifuged from the solution, which was stored in a teflon beaker. The solid precipitate was washed three times with distilled water and dried at 1008C overnight. The chemical composition of the leachate was determined by ICP to be Na s 42.5, Si s 2.56 and
00167-577Xr02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 3 7 2 - X
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
92
Al s 0.65 grl. This solution was placed in a teflon beaker inside a hydrothermal bomb Ž50 ml. and reacted at 1008C and 1508C for 12, 24, 48 and 72 h. After hydrothermal treatment, the bomb was rapidly cooled by immersing in flowing cold water. The resulting precipitates were collected by centrifuging, washed three times with distilled water, and dried at 1008C for 12 h. The samples reacted at 1008C for 24, 48 and 72 h are denoted Z-100a, Z-100b and Z-100c, and those reacted at 1508C for 12, 24, 48 and 72 h are denoted Z-150a, Z-150b, Z-150c and Z-150d, respectively. No crystalline phases were formed in the solution reacted at 1008C for 12 h. The phases formed in the other samples were characterized by powder X-ray diffraction using a Rigaku Geigerflex diffractometer with monocromated Cu–K a radiation, and FTIR ŽShimadzu FTIR PC8000 . by suspending the samples in KBr disks. The specific surface area was measured by the BET method using nitrogen gas as adsorbate at y1968C with a Quanta Chrome Autosorb-1 instrument. The textures of the samples were observed by scanning electron microscopy ŽHitachi S-8000..
3. Results and discussion 3.1. Porous g-alumina The chemical composition and porous properties of the original calcined kaolinite and the NaOHleached materials are shown in Table 1, which also lists the chemical composition and porous properties of a KOH-leached sample w2x for comparison. The porous properties and chemical composition of gAl 2 O 3 obtained using NaOH solution are very simi-
lar to those of g-alumina obtained using KOH w2x. These results show that NaOH is as suitable as a leaching agent as KOH is for the preparation of mesoporous g-Al 2 O 3 . Since the NaOH leached sample has mesopores of uniform pore size Žabout 3 nm radius. and a pore size distribution quite similar to that of the KOH leached sample w1,2x, we conclude that changing the hydroxide solution does not affect the chemical composition or porous properties of the resulting galumina. 3.2. Zeolite formation from waste solution of NaOHleached calcined kaolinite Fig. 1a shows the XRD patterns of the Z-100 series zeolites. Formation of a zeolite-type compound was observed after 24-h reaction at this temperature. Although it was difficult to identify all the observed peaks, the diffractogram could best be matched with the patterns of hydroxysodalite, 4Na 2 O P 3Al 2 O 3 P 6SiO 2 P H 2 O ŽJCPDS card 11-401. and zeolite P, Na 5.7 Al 5.7 Si 10.3 O 32 P 12H 2 O ŽJCPDS card 34-524.. With increasing reaction time, the peak intensity of hydroxysodalite increased at the expense of the unidentified peaks, and the peaks assigned to zeolite P also became gradually more intense at the expense of the hydroxysodalite peaks. After 72 h reaction only the peaks of zeolite P and hydroxysodalite were present in the XRD pattern of the sample. These results suggest that hydroxysodalite transforms to more stable zeolite P w4x under these conditions. Zeolite P exists in high and low silica forms w5x, the latter has both cubic and tetragonal structures. The present samples contained residual hydroxysodalite, together with either tetragonal zeolite P or a mixture of the tetragonal and cubic forms.
Table 1 Chemical composition and porous properties of samples Sample Original kaolinite KOH leached g-Al 2 O 3 NaOH leached g-Al 2 O 3
Chemical compositionrmass Ž%. Al 2 O 3 SiO 2 TiO 2 K 2O
Fe 2 O 3
Na 2 O
Surface area Žm2 gy1 .
Pore volume Žml gy1 .
47.4 84 85
0.6 1 1.3
0 0 1.9
9.9 244 242
0.09 0.72 0.68
50.2 6.8 8.1
1.4 5.5 3.3
0.14 1.4 0
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
93
change. Therefore, to synthesize another type of zeolite, it is necessary to modify the waste solution by adding another component. Fig. 2 shows the FTIR spectra of these samples. Differences in the spectra within each series were not marked, suggesting that FTIR spectroscopy is relatively insensitive to differences between the zeolite products. The initial SirAl ratio in the solution Žabout four. should favor the crystallization of faujasite-type zeolites such as X and Y, but the large
Fig. 1. Ža. XRD patterns of Z-100 series samples. Žb. XRD patterns of Z-150 series samples.
The same crystallization behavior was also observed in the Z-150 series samples ŽFig. 1b., in which the formation of zeolite-related compounds began at shorter times than for the Z-100 series. The product from Z-150a was a mixture of hydroxysodalite and zeolite P, becoming solely zeolite P after 72 h reaction. The amount of zeolite increased at a higher reaction temperature, but the crystalline products were the same at both temperatures. The raw material for the zeolite synthesis was the leachate from selectively leached calcined kaolinite, the chemical composition of which, clearly, will not
Fig. 2. Ža. FTIR spectra of Z-100 series samples. Žb. FTIR spectra of Z-150 series samples.
94
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
excess of sodium ions in the solution possibly facilitated the initial formation of hydroxysodalite. The FTIR spectrum of the sample obtained after 1008C for 72 h is similar to those of samples produced at 1508C, suggesting that zeolite P, which crystallizes well at 1008C after 72 h, is also formed at 1508C at shorter reaction times. These samples show broad absorption bands in the range 3050–3740 cmy1 , allowing differently bonded types of water to be resolved. The Z-150d sample showed bands at 1650, 1089, 989, 742, 669, 597 and 450 cmy1 , in agreement with the infrared spectral data for zeolite P w5x. The vibrations common to all zeolites are the asymmetric stretching modes, which appear in the region 950–1250 cmy1 . The shape of this band is reported to be sensitive to the framework SirAl ratio, and its position shifts to lower wave numbers with increasing Al content w6x. The absorption bands of the Z-150 series samples in this region shift slightly to lower wave numbers, consistent with this suggestion. The SirAl ratios in hydroxysodalite and zeolite P are 1.0 and 1.8, respectively. The SirAl ratios in these phases are in agreement with our observations. The spectra of the Z-100a and Z-100b samples resembles that of hydroxysodalite reported elsewhere w7x. Fig. 3 shows the S.E.M. photographs of the Z-100 and Z-150 series samples. The particles of Z-100a have the appearance of sheet-like aggregated structures. The particle morphologies in the Z-100b and Z-100c samples change to ball-like aggregates, the size of which increases with longer leaching time. These aggregated particles probably correspond to hydroxysodalite. On the other hand, prismatic particles observed in the Z-100b sample may correspond to zeolite P. The morphology of Z-150a and Z-150b consists of mixtures of oval and prismatic particles, while Z-150d contains prismatic particles only. In this series of samples, the size of the particles increases with longer holding time, possibly growing by the Ostwald ripening process.
material are very similar to those of the g-alumina obtained by using KOH. Hydrothermal treatment at 1008C and 1508C of the spent NaOH leaching solution results in the formation of zeolite-related phases.
4. Conclusion It is possible to prepare porous g-alumina from calcined kaolinite by using NaOH as the leaching agent rather than KOH. The porous properties of this
Fig. 3. Ža. S.E.M. pictures of Z-100 series samples. Žb. S.E.M. pictures of Z-150 series samples.
J. Temuujin et al.r Materials Letters 52 (2002) 91–95
95
Fig. 3 Ž continued ..
Hydroxysodalite is formed initially, transforming to zeolite P after prolonged reaction times.
Acknowledgements J.T. thanks Japan Society for the Promotion of Science ŽJSPS. for the award of research fellowship under which present work was carried out. A part of this work is financially supported by Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
References w1x K. Okada, H. Kawashima, Y. Saito, S. Hayashi, A. Yasumori, J. Mater. Chem. 5 Ž1995. 1241. w2x K. Okada, T. Tomita, A. Yasumori, J. Mater. Chem. 8 Ž1998. 2863. w3x K. Okada, Y. Saito, M. Hiroki, T. Tomita, S. Tomura, J. Porous Mater. 4 Ž1997. 253. w4x L.V.C. Rees, S. Chandrasekhar, Zeolites 13 Ž1993. 524. w5x B.R. Albert, A.K. Cheetham, J.A. Stuart, C.J. Adams, Microporous Mesoporous Mater. 21 Ž1998. 132. w6x A. Miecznikowski, J. Hanuza, Zeolities 5 Ž1985. 188. w7x V.C. Farmer ŽEd.., The Infrared Spectra of Minerals, Mineralogical Society, London, 1974, p. 372.