- Email: [email protected]
Utilization of calcite and waste glass for preparing construction materials with a low environmental load
Journal of Environmental Management 92 (2011) 2881e2885
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Utilization of calcite and waste glass for preparing construction materials with a low environmental load Hirotaka Maeda a, *, Haruki Imaizumi b, Emile Hideki Ishida b a b
Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Graduate School of Environmental Studies, Tohoku University, 6-6-20 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 September 2010 Received in revised form 25 May 2011 Accepted 10 June 2011 Available online 26 July 2011
In this study, porous calcite materials are hydrothermally treated at 200 C using powder compacts consisting of calcite and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of calcite and glass in the hydrothermal treatment plays an important role in the solidification of calcite without thermal decomposition. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Calcite Glass Hydrothermal treatment Porous materials
1. Introduction The amount of CO2 discharged into the atmosphere has increased during the past decade, leading to global warming. Thus, the importance of decreasing the amount of CO2 discharged as a countermeasure to environmental problems has increased. The main cause of CO2 emissions in the cement industry is the synthesis of lime by sintering limestone at a high temperature. To reduce the amount of CO2 discharged in the cement industry, an alternative method is to solidify calcium carbonate powders, used as starting materials, at a low temperature. The solidification process of metastable calcium carbonate powders has been reported to utilize a transformation from aragonite to calcite by hydrothermal hot pressing (Hosoi et al., 1997). Recycling and reuse of waste glass have attracted the attention of many researchers as a means to protect the environment. However, the practice of adding waste soda-lime-silica glass to concrete, which is a general method of recycling glass, leads to a decline in strength and causes excessive expansion of cement owing to the sodium in waste glass (Chen et al., 2002; Shao et al., 2000; Dyer and Dhir, 2001; Xie et al., 2003; Sobolev et al., 2007). Soda-lime-silica glasses have been reported to be converted into a tobermorite-like layered calcium silicate by hydrothermal
* Corresponding author. Tel./fax: þ81 52 735 5198. E-mail address: [email protected] (H. Maeda). 0301-4797/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2011.06.021
treatment under subcritical conditions (Miyake et al., 2004). Mori (2003) reported the extraction of pure silica from waste colored glass by alkali fusion with potassium hydroxide. The extraction of heavy metal ions from waste colored glass was also proposed for utilizing a glass phase separation (Chen et al., 2006). Currently, novel methods of recycling wastes such as these are being sought. Research has been conducted into the hydrothermal treatment at a temperature below 200 C (1.56 MPa) and the solidification behavior in a CaOeSiO2eH2O system (Isu et al., 1995; Watanabe et al., 2001). The formation of deposits, such as tobermorite and calcium silicate hydrate gel (CeSeH gel), among the particles of starting materials enhances the strength of the hydrothermally solidified material during treatment in a CaOeSiO2eH2O system (Maeda et al., 2007, 2009a). The hydrothermal treatment is performed at relatively low temperatures and is an effective method of solidifying the calcite powder, because the powder dose not decompose at these temperatures. It is well known that calcite exhibits extremely low solubility in a stable phase in polymorphs. Our strategy for the solidification of calcite involves increasing strength through the formation of new deposits, which originated from waste glass, on the calcite surface as a matrix phase for the purpose of producing a novel construction material with a low environmental load. In this paper, we prepare hydrothermally solidified materials by using calcite and waste glass as the starting materials, and we examine hydrothermal solidification using ordinary soda-lime-silica glass for clarifying the influence of its chemical composition on solidification.
2882
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
2. Materials and methods
3. Results and discussion Fig. 1 shows the bending strength of samples A and B after treatment. The bending strength of both types of powder compacts was 0.08 MPa prior to treatment. Samples A and B show a similar trend in strength development as a function of the treatment. However, sample A had a bending strength almost three times that of sample B during treatment. Fig. 2 shows the porosity of samples A and B as a function of the treatment. The porosity of both types of powder compacts was z40%. The porosities of sample A decreased within 2 h of treatment to z31% and subsequently increased after 2 h. In contrast, the porosity of sample B increased to z48% during treatment. The difference in the strength of samples A and B is presumed to have an influence on porosity. However, it is evident that the strength of the samples develops independent of porosity. Fig. 3 shows the XRD patterns of samples A and B before and after treatment. The XRD pattern prior to treatment showed that the powder compacts consist of a crystalline calcite phase. Almost no significant change was observed after 2 h of treatment in either of the two samples. New peaks corresponding to mordenite (ICDD card No. 29-1257), stratlingite (ICDD card No. 80-1579), and an unnamed zeolite (ICDD card No. 21-133) were clearly observed in the XRD patterns of both samples after 10 h of treatment. It is proposed that the chemical composition of the glasses has little Table 1 Chemical compositions of Ryukyu glass and slide glass determined by X-ray fluorescence and thermogravimetric analysis (mass %). Glass
SiO2
CaO
Na2O
K2O
Al2O3
Others
Ig loss
Ryukyu glass Slide glass
80.9 78.1
5.8 11.4
7.7 5.0
1.5 1.8
0.7 0.2
3.4 3.5
0 0
10
5
0 0
2
4
6
8
10
Time / hour Fig. 1. Bending strength of samples A (,) and B (B) as a function of treatment time.
effect on the crystalline phases formed after treatment under our experimental conditions. Zeolite with micropores has a higher capacity to adsorb ammonia gas than alumina and silica gel (Helminen et al., 2000). The existence of zeolite phases is expected to lead to the adsorption of harmful matter. Fig. 4 shows the pore-size distribution curves of samples A and B before and after treatment. The pore-size distribution curve of both samples prior to treatment had a peak at a diameter of around 2 mm. This peak is attributed to the pores among the starting material particles in the powder compacts. Almost no significant change was observed after 2 h of treatment in the pore-size distribution curve of sample A. On the other hand, the peak at a diameter of around 2 mm of sample B shifted toward a larger
50
45 Porosity (%)
Calcite (Wako Pure Chemical Industries, Ltd., Osaka, Japan) and two types of glass, which were sieved through a mesh of 25e75 mm, were used as starting materials. Table 1 shows the chemical compositions of the two types of glass: colored Ryukyu glass, which is a traditional craft material in Okinawa, Japan (average particle size: d50 ¼ 58.5 mm), and ordinary soda-lime-silica glass (slide glass, average particle size: d50 ¼ 48.2 mm), as determined by X-ray fluorescence and thermogravimetric analyses. The mass ratio of glass to calcite was 1:1. This ratio was determined by an optimization process based upon a trial-and-error approach for achieving a satisfactory strength of the hydrothermally solidified materials in our preliminary experiments (Imaizumi et al., 2010). A mixture of the starting materials was added at 10 mass% to distilled water. The mixture was then uniaxially pressed at 10 MPa in a stainless-steel die (15 40 mm). The powder compacts (4 15 40 mm) were set in a Teflon-lined stainless-steel apparatus (volume: 90 cm3) and subjected to hydrothermal treatment under saturated steam pressure at 200 C for various time periods. The hydrothermally solidified materials prepared using Ryukyu glass and soda-lime-silica glass are denoted as sample A and B, respectively. The flexural strength of the samples was estimated by a threepoint bending test at a loading rate of 0.5 mm/min. At least four samples were used for the flexural strength test. The porosity of the samples was calculated using density as measured by the Archimedes’ method. The crystalline phases in the samples were identified by X-ray diffraction (XRD) analysis. The fracture surface morphology was observed using a scanning electron microscope (SEM). The pore-size distribution of the samples was determined by mercury intrusion porosimetry. At least two samples were used for all tests, with the exception of the strength test.
Bending Strength / MPa
15
40
35
30 0
2
4
6
8
10
Time / hour Fig. 2. Porosity of samples A (,) and B (B) as a function of treatment time.
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
2883
Fig. 3. XRD patterns of samples A (a) and B (b) before and after treatment. (C) calcite, (B) mordenite, (,) unnamed zeolite, and (7) stratlingite.
diameter after 2 h of treatment. After 10 h of treatment, both samples had a bimodal peak at diameters of around 0.02 and 2 mm, respectively. The reactivity of the glasses in samples A and B in the initial stage (at 2 h) of treatment was observed using an SEM, as shown in Fig. 5. The SEM micrograph of sample A shows round glass particles. Conversely, square glass particles similar to the pulverized starting material are observed in the SEM micrograph of sample B. The spaces among the particles in sample B were greater those than in sample A. Sample A is expected to show a higher durability for water than sample B because of a higher silica and alumina content and a lower alkali content. During the initial stage of treatment, the glasses in sample A dissolved only around the surface, leading to
a
the formation of a hydrated layer on the surface. As a result, adjacent particles connected with each other. That is, the aggregation of glass particles caused a decrease in the porosity of sample A after 2 h of treatment. SEM observation indicated that glass with a smaller particle size was removed from sample B after 2 h of treatment owing to the higher solubility caused by the higher alkali content. This loss of glass particles resulted in the formation of relatively large pores with a diameter of 4 mm. As a consequence, the porosity of sample B increased in the initial stage. Fig. 6 shows the fracture surface of samples A and B after 10 h of treatment. Numerous fine plate-like and network-like deposits, which filled the spaces among the calcite particles, were observed in the SEM micrographs of samples A and B, respectively. It appears
b
Fig. 4. Pore-size distribution curves of samples A (a) and B (b) before and after treatment.
2884
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
Fig. 5. SEM micrographs of cross-sectional polished face of samples A (a) and B (b) after 2 h of treatment. Bar scale shows 40 mm.
Fig. 6. SEM micrographs of fracture face of samples A (a) and B (b) after 10 h of treatment. Bar scale shows 2 mm.
that the chemical compositions of the glasses influenced the morphology of the deposits. The filling of the macropores in the spaces among the particles in the powder compacts by forming calcium aluminosilicate hydrates such as hydrogarnet has been reported to play an important role in enhancing the strength of the samples after the hydrothermal treatment in a CaOeSiO2eAl2O3eH2O system (Maeda et al., 2009b, 2009c). In this work, numerous deposits such as mordenite are proposed to fill in the spaces in the powder compact, resulting in an increase in strength. As shown in the SEM micrographs (Fig. 6), the structure intertwining with each deposit formed among the particles of the starting materials leads to the formation of mesopores. The porous calcite-solidified materials discussed here are potential candidates as construction materials having a low environmental load.
of spaces among the particles in the powder compacts by new deposits. The morphology of the deposits was influenced by the chemical composition. Using silica-rich soda-lime glasses and calcite in the hydrothermal treatment is an alternative method for the solidification of calcite without CO2 gas emissions. This method could potentially be used as a novel recycling method for waste glasses. Appendix. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jenvman.2011.06.021. References
4. Conclusions Novel calcite-solidified materials were prepared by the hydrothermal treatment of the powder compacts consisting of calcite and two types of glass. After treatment, zeolite phases and stratlingite were formed as a result of the transformation of the glasses. The bending strength after treatment increased as a result of the filling
Chen, D., Masui, H., Miyoshi, H., Akai, T., Yazawa, T., 2006. Extraction of heavy metal ions from waste colored glass through phase separation. Waste Manag. 26, 1017e1023. Chen, G., Lee, H., Young, K.L., Yue, P.L., Wong, A., Tao, T., Choi, K.K., 2002. Glass recycling in cement production-an innovative approach. Waste Manage. 22, 747e753. Dyer, T.D., Dhir, R.K., 2001. Chemical reactions of the glass cullet used as cement component. J. Mater. Civil Eng. 13, 412e417.
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885 Helminen, J., Helenius, J., Paatero, E., Turunen, I., 2000. Comparison of sorbents and isotherm models for NH3-gas separation by adsorption. AIChE J. 46, 1541e1555. Hosoi, K., Hashida, T., Takahashi, H., Yamasaki, N., Korenaga, T., 1997. Solidification behavior of calcium carbonate via aragonite-calcite wet transformation with hydrothermal hot pressing. J. Mater. Sci. Lett. 16, 382e385. Imaizumi, H., Maeda, H., Nakamatsu, R., Jing, Z., Ishida, E.H., 2010. Hydrothermal solidification of waste glass and calcium carbonate. J. Soc. Inorg. Mater. Jpn. 17, 30e35 (in Japanese). Isu, N., Teramura, S., Ishida, H., Mitsuda, T., 1995. Influence of quartz particle size on the chemical and mechanical properties of autoclaved aerated concrete (II) fracture toughness, strength and micropore. Cem. Concr. Res. 25, 249e254. Maeda, H., Ymazaki, T., Ishida, E.H., 2007. Hydrothermal preparation of solidification materials from metakaolinite, quartz and slaked lime. J. Ceram. Soc. Jpn. 115, 447e449. Maeda, H., Kato, S., Ishida, E.H., 2009a. Preparation of hydorthermally solidified mesoporous materials from diatomaceous earth for moisture control application. Int. J. Appl. Ceram. Technol. 6, 431e436.
2885
Maeda, H., Okada, T., Ishida, E.H., 2009b. Hydrothermal solidification of zeolite/ tobermorite composites. J. Ceram. Soc. Jpn. 117, 147e151. Maeda, H., Hashimoto, Y., Ishida, E.H., 2009c. Solidification mechanism of allophane by hydrothermal reaction. Appl. Clay Sci. 44, 71e74. Miyake, H., Chen, D., Akai, T., 2004. A novel process utilizing subcritical waste to recycle soda-lime-silicate glass. J. Non-cryst. Solids 337, 280e282. Mori, H., 2003. Extraction of silicon dioxide from waste colored glasses by alkali fusion using potassium hydroxide. J. Mater. Sci. 38, 3461e3468. Shao, Y., Lefort, T., Moras, S., Rodriguez, D., 2000. Studies on concrete containing ground waste glass. Cem. Concr. Res. 30, 91e100. Sobolev, K., Trüker, P., Soboleva, S., Iscioglu, G., 2007. Utilization of waste glass in ECO-cement: strength properties and microstructural observations. Waste Manag. 27, 971e976. Watanabe, O., Kitamura, K., Maenami, H., Ishida, H., 2001. Hydrothermal treatment of silica sand complex with lime. J. Am. Ceram. Soc. 84, 2318e2322. Xie, Z., Xiang, W., Xi, Y., 2003. ASR potentials of glass aggregates in water-glass activated fly ash and portland cement mortars. J. Mater. Civil Eng. 15, 67e74.
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Utilization of calcite and waste glass for preparing construction materials with a low environmental load Hirotaka Maeda a, *, Haruki Imaizumi b, Emile Hideki Ishida b a b
Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Graduate School of Environmental Studies, Tohoku University, 6-6-20 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 September 2010 Received in revised form 25 May 2011 Accepted 10 June 2011 Available online 26 July 2011
In this study, porous calcite materials are hydrothermally treated at 200 C using powder compacts consisting of calcite and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of calcite and glass in the hydrothermal treatment plays an important role in the solidification of calcite without thermal decomposition. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Calcite Glass Hydrothermal treatment Porous materials
1. Introduction The amount of CO2 discharged into the atmosphere has increased during the past decade, leading to global warming. Thus, the importance of decreasing the amount of CO2 discharged as a countermeasure to environmental problems has increased. The main cause of CO2 emissions in the cement industry is the synthesis of lime by sintering limestone at a high temperature. To reduce the amount of CO2 discharged in the cement industry, an alternative method is to solidify calcium carbonate powders, used as starting materials, at a low temperature. The solidification process of metastable calcium carbonate powders has been reported to utilize a transformation from aragonite to calcite by hydrothermal hot pressing (Hosoi et al., 1997). Recycling and reuse of waste glass have attracted the attention of many researchers as a means to protect the environment. However, the practice of adding waste soda-lime-silica glass to concrete, which is a general method of recycling glass, leads to a decline in strength and causes excessive expansion of cement owing to the sodium in waste glass (Chen et al., 2002; Shao et al., 2000; Dyer and Dhir, 2001; Xie et al., 2003; Sobolev et al., 2007). Soda-lime-silica glasses have been reported to be converted into a tobermorite-like layered calcium silicate by hydrothermal
* Corresponding author. Tel./fax: þ81 52 735 5198. E-mail address: [email protected] (H. Maeda). 0301-4797/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2011.06.021
treatment under subcritical conditions (Miyake et al., 2004). Mori (2003) reported the extraction of pure silica from waste colored glass by alkali fusion with potassium hydroxide. The extraction of heavy metal ions from waste colored glass was also proposed for utilizing a glass phase separation (Chen et al., 2006). Currently, novel methods of recycling wastes such as these are being sought. Research has been conducted into the hydrothermal treatment at a temperature below 200 C (1.56 MPa) and the solidification behavior in a CaOeSiO2eH2O system (Isu et al., 1995; Watanabe et al., 2001). The formation of deposits, such as tobermorite and calcium silicate hydrate gel (CeSeH gel), among the particles of starting materials enhances the strength of the hydrothermally solidified material during treatment in a CaOeSiO2eH2O system (Maeda et al., 2007, 2009a). The hydrothermal treatment is performed at relatively low temperatures and is an effective method of solidifying the calcite powder, because the powder dose not decompose at these temperatures. It is well known that calcite exhibits extremely low solubility in a stable phase in polymorphs. Our strategy for the solidification of calcite involves increasing strength through the formation of new deposits, which originated from waste glass, on the calcite surface as a matrix phase for the purpose of producing a novel construction material with a low environmental load. In this paper, we prepare hydrothermally solidified materials by using calcite and waste glass as the starting materials, and we examine hydrothermal solidification using ordinary soda-lime-silica glass for clarifying the influence of its chemical composition on solidification.
2882
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
2. Materials and methods
3. Results and discussion Fig. 1 shows the bending strength of samples A and B after treatment. The bending strength of both types of powder compacts was 0.08 MPa prior to treatment. Samples A and B show a similar trend in strength development as a function of the treatment. However, sample A had a bending strength almost three times that of sample B during treatment. Fig. 2 shows the porosity of samples A and B as a function of the treatment. The porosity of both types of powder compacts was z40%. The porosities of sample A decreased within 2 h of treatment to z31% and subsequently increased after 2 h. In contrast, the porosity of sample B increased to z48% during treatment. The difference in the strength of samples A and B is presumed to have an influence on porosity. However, it is evident that the strength of the samples develops independent of porosity. Fig. 3 shows the XRD patterns of samples A and B before and after treatment. The XRD pattern prior to treatment showed that the powder compacts consist of a crystalline calcite phase. Almost no significant change was observed after 2 h of treatment in either of the two samples. New peaks corresponding to mordenite (ICDD card No. 29-1257), stratlingite (ICDD card No. 80-1579), and an unnamed zeolite (ICDD card No. 21-133) were clearly observed in the XRD patterns of both samples after 10 h of treatment. It is proposed that the chemical composition of the glasses has little Table 1 Chemical compositions of Ryukyu glass and slide glass determined by X-ray fluorescence and thermogravimetric analysis (mass %). Glass
SiO2
CaO
Na2O
K2O
Al2O3
Others
Ig loss
Ryukyu glass Slide glass
80.9 78.1
5.8 11.4
7.7 5.0
1.5 1.8
0.7 0.2
3.4 3.5
0 0
10
5
0 0
2
4
6
8
10
Time / hour Fig. 1. Bending strength of samples A (,) and B (B) as a function of treatment time.
effect on the crystalline phases formed after treatment under our experimental conditions. Zeolite with micropores has a higher capacity to adsorb ammonia gas than alumina and silica gel (Helminen et al., 2000). The existence of zeolite phases is expected to lead to the adsorption of harmful matter. Fig. 4 shows the pore-size distribution curves of samples A and B before and after treatment. The pore-size distribution curve of both samples prior to treatment had a peak at a diameter of around 2 mm. This peak is attributed to the pores among the starting material particles in the powder compacts. Almost no significant change was observed after 2 h of treatment in the pore-size distribution curve of sample A. On the other hand, the peak at a diameter of around 2 mm of sample B shifted toward a larger
50
45 Porosity (%)
Calcite (Wako Pure Chemical Industries, Ltd., Osaka, Japan) and two types of glass, which were sieved through a mesh of 25e75 mm, were used as starting materials. Table 1 shows the chemical compositions of the two types of glass: colored Ryukyu glass, which is a traditional craft material in Okinawa, Japan (average particle size: d50 ¼ 58.5 mm), and ordinary soda-lime-silica glass (slide glass, average particle size: d50 ¼ 48.2 mm), as determined by X-ray fluorescence and thermogravimetric analyses. The mass ratio of glass to calcite was 1:1. This ratio was determined by an optimization process based upon a trial-and-error approach for achieving a satisfactory strength of the hydrothermally solidified materials in our preliminary experiments (Imaizumi et al., 2010). A mixture of the starting materials was added at 10 mass% to distilled water. The mixture was then uniaxially pressed at 10 MPa in a stainless-steel die (15 40 mm). The powder compacts (4 15 40 mm) were set in a Teflon-lined stainless-steel apparatus (volume: 90 cm3) and subjected to hydrothermal treatment under saturated steam pressure at 200 C for various time periods. The hydrothermally solidified materials prepared using Ryukyu glass and soda-lime-silica glass are denoted as sample A and B, respectively. The flexural strength of the samples was estimated by a threepoint bending test at a loading rate of 0.5 mm/min. At least four samples were used for the flexural strength test. The porosity of the samples was calculated using density as measured by the Archimedes’ method. The crystalline phases in the samples were identified by X-ray diffraction (XRD) analysis. The fracture surface morphology was observed using a scanning electron microscope (SEM). The pore-size distribution of the samples was determined by mercury intrusion porosimetry. At least two samples were used for all tests, with the exception of the strength test.
Bending Strength / MPa
15
40
35
30 0
2
4
6
8
10
Time / hour Fig. 2. Porosity of samples A (,) and B (B) as a function of treatment time.
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
2883
Fig. 3. XRD patterns of samples A (a) and B (b) before and after treatment. (C) calcite, (B) mordenite, (,) unnamed zeolite, and (7) stratlingite.
diameter after 2 h of treatment. After 10 h of treatment, both samples had a bimodal peak at diameters of around 0.02 and 2 mm, respectively. The reactivity of the glasses in samples A and B in the initial stage (at 2 h) of treatment was observed using an SEM, as shown in Fig. 5. The SEM micrograph of sample A shows round glass particles. Conversely, square glass particles similar to the pulverized starting material are observed in the SEM micrograph of sample B. The spaces among the particles in sample B were greater those than in sample A. Sample A is expected to show a higher durability for water than sample B because of a higher silica and alumina content and a lower alkali content. During the initial stage of treatment, the glasses in sample A dissolved only around the surface, leading to
a
the formation of a hydrated layer on the surface. As a result, adjacent particles connected with each other. That is, the aggregation of glass particles caused a decrease in the porosity of sample A after 2 h of treatment. SEM observation indicated that glass with a smaller particle size was removed from sample B after 2 h of treatment owing to the higher solubility caused by the higher alkali content. This loss of glass particles resulted in the formation of relatively large pores with a diameter of 4 mm. As a consequence, the porosity of sample B increased in the initial stage. Fig. 6 shows the fracture surface of samples A and B after 10 h of treatment. Numerous fine plate-like and network-like deposits, which filled the spaces among the calcite particles, were observed in the SEM micrographs of samples A and B, respectively. It appears
b
Fig. 4. Pore-size distribution curves of samples A (a) and B (b) before and after treatment.
2884
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885
Fig. 5. SEM micrographs of cross-sectional polished face of samples A (a) and B (b) after 2 h of treatment. Bar scale shows 40 mm.
Fig. 6. SEM micrographs of fracture face of samples A (a) and B (b) after 10 h of treatment. Bar scale shows 2 mm.
that the chemical compositions of the glasses influenced the morphology of the deposits. The filling of the macropores in the spaces among the particles in the powder compacts by forming calcium aluminosilicate hydrates such as hydrogarnet has been reported to play an important role in enhancing the strength of the samples after the hydrothermal treatment in a CaOeSiO2eAl2O3eH2O system (Maeda et al., 2009b, 2009c). In this work, numerous deposits such as mordenite are proposed to fill in the spaces in the powder compact, resulting in an increase in strength. As shown in the SEM micrographs (Fig. 6), the structure intertwining with each deposit formed among the particles of the starting materials leads to the formation of mesopores. The porous calcite-solidified materials discussed here are potential candidates as construction materials having a low environmental load.
of spaces among the particles in the powder compacts by new deposits. The morphology of the deposits was influenced by the chemical composition. Using silica-rich soda-lime glasses and calcite in the hydrothermal treatment is an alternative method for the solidification of calcite without CO2 gas emissions. This method could potentially be used as a novel recycling method for waste glasses. Appendix. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jenvman.2011.06.021. References
4. Conclusions Novel calcite-solidified materials were prepared by the hydrothermal treatment of the powder compacts consisting of calcite and two types of glass. After treatment, zeolite phases and stratlingite were formed as a result of the transformation of the glasses. The bending strength after treatment increased as a result of the filling
Chen, D., Masui, H., Miyoshi, H., Akai, T., Yazawa, T., 2006. Extraction of heavy metal ions from waste colored glass through phase separation. Waste Manag. 26, 1017e1023. Chen, G., Lee, H., Young, K.L., Yue, P.L., Wong, A., Tao, T., Choi, K.K., 2002. Glass recycling in cement production-an innovative approach. Waste Manage. 22, 747e753. Dyer, T.D., Dhir, R.K., 2001. Chemical reactions of the glass cullet used as cement component. J. Mater. Civil Eng. 13, 412e417.
H. Maeda et al. / Journal of Environmental Management 92 (2011) 2881e2885 Helminen, J., Helenius, J., Paatero, E., Turunen, I., 2000. Comparison of sorbents and isotherm models for NH3-gas separation by adsorption. AIChE J. 46, 1541e1555. Hosoi, K., Hashida, T., Takahashi, H., Yamasaki, N., Korenaga, T., 1997. Solidification behavior of calcium carbonate via aragonite-calcite wet transformation with hydrothermal hot pressing. J. Mater. Sci. Lett. 16, 382e385. Imaizumi, H., Maeda, H., Nakamatsu, R., Jing, Z., Ishida, E.H., 2010. Hydrothermal solidification of waste glass and calcium carbonate. J. Soc. Inorg. Mater. Jpn. 17, 30e35 (in Japanese). Isu, N., Teramura, S., Ishida, H., Mitsuda, T., 1995. Influence of quartz particle size on the chemical and mechanical properties of autoclaved aerated concrete (II) fracture toughness, strength and micropore. Cem. Concr. Res. 25, 249e254. Maeda, H., Ymazaki, T., Ishida, E.H., 2007. Hydrothermal preparation of solidification materials from metakaolinite, quartz and slaked lime. J. Ceram. Soc. Jpn. 115, 447e449. Maeda, H., Kato, S., Ishida, E.H., 2009a. Preparation of hydorthermally solidified mesoporous materials from diatomaceous earth for moisture control application. Int. J. Appl. Ceram. Technol. 6, 431e436.
2885
Maeda, H., Okada, T., Ishida, E.H., 2009b. Hydrothermal solidification of zeolite/ tobermorite composites. J. Ceram. Soc. Jpn. 117, 147e151. Maeda, H., Hashimoto, Y., Ishida, E.H., 2009c. Solidification mechanism of allophane by hydrothermal reaction. Appl. Clay Sci. 44, 71e74. Miyake, H., Chen, D., Akai, T., 2004. A novel process utilizing subcritical waste to recycle soda-lime-silicate glass. J. Non-cryst. Solids 337, 280e282. Mori, H., 2003. Extraction of silicon dioxide from waste colored glasses by alkali fusion using potassium hydroxide. J. Mater. Sci. 38, 3461e3468. Shao, Y., Lefort, T., Moras, S., Rodriguez, D., 2000. Studies on concrete containing ground waste glass. Cem. Concr. Res. 30, 91e100. Sobolev, K., Trüker, P., Soboleva, S., Iscioglu, G., 2007. Utilization of waste glass in ECO-cement: strength properties and microstructural observations. Waste Manag. 27, 971e976. Watanabe, O., Kitamura, K., Maenami, H., Ishida, H., 2001. Hydrothermal treatment of silica sand complex with lime. J. Am. Ceram. Soc. 84, 2318e2322. Xie, Z., Xiang, W., Xi, Y., 2003. ASR potentials of glass aggregates in water-glass activated fly ash and portland cement mortars. J. Mater. Civil Eng. 15, 67e74.