- Email: [email protected]
The synthesis of zeolites from fly ash and the properties of the zeolite products
Journal of Geochemical Exploration 62 Ž1998. 305–309
The synthesis of zeolites from fly ash and the properties of the zeolite products G. Steenbruggen ) , G.G. Hollman UniÕersity of Utrecht, Faculty of Earth Sciences, Department of Geochemistry, P.O. Box 80021, 3508 TA Utrecht, The Netherlands Accepted 6 November 1997
Abstract Fly ash produced during the combustion of powdered coal could be converted up to 45% into zeolite. By varying the experimental conditions different types of zeolite were produced, e.g. zeolite Na-P1, zeolite K-G and zeolite ZK19. By this zeolitization process the cation exchange capacity ŽCEC. was raised from 0.02 to circa 2.4 meqrg. Anionic heavy metals were largely extracted by the process water. Sorption experiments indicated that the selectivity series for zeolite Na-P1 is Ba ) Cu ) Cd f Zn ) Co ) Ni. Besides cation exchange reactions, precipitation of hydroxides also played a role in the immobilization of heavy metals in the column experiments carried out. Column leaching experiments showed that relative to the original fly ash, the zeolitized fly ash has a better environmental quality. The results of the sorption experiments suggest that the zeolite product can be applied in environmental technology as an immobilizer of pollutants. q 1998 Elsevier Science B.V. All rights reserved. Keywords: zeolite; fly ash; synthesis; adsorption; application
1. Introduction At present, almost all fly ash produced by coal combustion in The Netherlands Žabout 900,000 tonryear. is used in the production of building materials. This application is mainly based on the pozzolanic properties of the coal fly ash ŽCFA., by which calcium oxides, silica and water react to form calcium silicate hydrates ŽCSH.. Formation of these CSH phases improves the strength of concrete and makes it possible to convert fly ash into many other products Že.g. lytag granules..
)
Corresponding author. E-mail: [email protected]
However, present possibilities for the use of combustion residues, such as CFA, may decrease in the near future because of stricter environmental regulations and changes in CFA quality. The latter is a result of the co-combustion of organic waste material and changes in combustion techniques. To avoid a waste problem, new applications for this kind of combustion residues are needed. One possible new application for CFA is the synthesis of zeolite products: a process analogous to the formation of natural zeolites from volcanic deposits. Both volcanic ash and CFA are fine-grained and contain a large amount of aluminosilicate glass. In natural conditions, this glass fraction may be converted into zeolites by the influence of percolat-
0375-6742r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 5 - 6 7 4 2 Ž 9 7 . 0 0 0 6 6 - 6
306
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
ing hot groundwater ŽBarrer, 1982., while the zeolites may subsequently be converted into analcime and feldspar, i.e. glass ™ zeolite™ analcime™ feldspar This process may take tens to thousands of years in natural conditions. In laboratory conditions, this conversion can be speeded up to merely days or even hours, both in the case of volcanic ash and that of CFA. Research on this subject has been published by e.g. Aiello et al. Ž1971., De’Gennaro et al. Ž1988., Barth-Wirsching et al. Ž1993. on the zeolitization of volcanic ash, and by e.g. Kato et al. Ž1984, 1987., Holler and Wirsching Ž1985., Henmi Ž1987., Singer ¨ and Berkgaut Ž1995., Lin and Hsi Ž1995., Querol et al. Ž1995., Park and Choi Ž1995. and Amrhein et al. Ž1996. on the zeolitization of CFA and the characteristics of the product. To examine the possibilities of zeolite formation from Dutch coal fly ash, this research project was started in 1994. The aims of this project are: Ž1. To establish the optimal conditions for the formation of zeolite products from CFA and the economic viability of the process. Ž2. To examine the applicability of the synthesized zeolite products for the immobilization of environmental pollutants. Presented in this article is an introduction to the research project being carried out in order to achieve the aims mentioned above.
2. Materials and methods The zeolitization process in its simplest form is a relatively straightforward process. CFA was mixed with a hydroxide solution in a Teflon reaction vessel and incubated at a temperature of 90 to 1508C and autogenous pressure. Incubation below 1008C was carried out by putting the closed reaction vessels in a thermostatic bath, while for reactions at temperatures above 1008C reaction vessels were put inside steel bombs and heated in an oven. At the end of the experiment, mixtures were quenched and the reaction products recovered by filtration. Important experimental parameters include temperature, reaction time, liquidrsolid ratio ŽLrS., hydroxide concentration,
type of hydroxide solution and intensity of mixing. Examination of the influence of these parameters on the zeolitization process is part of the ongoing research project. For this purpose a range of analytical techniques is being used, namely X-ray diffraction ŽXRD., including standard addition methods for quantitative analysis, scanning electron microscopy with energy-dispersive X-ray analyser ŽSEMrEDS., ICP–AES and AAS. In addition, the cation exchange capacity ŽCEC. of the zeolite products was measured by means of the ammonium acetate method ŽISRIC, 1992.. Research on the applicability of the synthesized zeolite products focuses on two objects: Ž1. their adsorption properties; and Ž2. the leaching behaviour of the heavy metals present in the products Žimportant in the light of regulatory norms.. Research on the adsorption properties was carried out by batch and column experiments. Firstly, batch experiments with a zeolite product consisting of 40% zeolite Na-P1 Žgismondine-type zeolite. were carried out in order to determine the adsorption isotherms 2q 2q , Co 2q, Cu2q, Ni 2q, Pb 2q and for NHq 4 , Ba , Cd 2q Zn . Secondly, the selectivity series for the adsorption of these elements, except Pb and NHq 4 , was established by the equilibration of the zeolite product with a solution containing three of the elements. Every possible combination of three elements out of the six elements ŽBa, Cd, Co, Cu, Ni, and Zn. was tested. All the batch experiments were carried out in duplicate to check the reproducibility of their results. Thirdly, column experiments were carried out to examine the adsorption properties of the zeolite product in a more practical situation. In these experiments, samples of the zeolite products were percolated with a solution artificially polluted with heavy metals and with the effluent of a waste water treatment plant, with a high concentration of ammonium Ž600 mgrl.. According to Dutch environmental regulations, the leaching of some elements out of fly ash is too high for some purposes. To determine the leaching behaviour of the zeolite products, they were subjected to a standard column test ŽNEN 7343., developed by the Dutch Normalization Institute ŽNederlands Normalisatie Instituut, 1995. to determine the leaching of inorganic components from granular materials.
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
307
3. Results and discussion Treatment of CFA with a 2 M NaOH at temperatures of 90 to 1508C resulted in the synthesis of zeolite Na-P1. Figs. 1 and 2 depict CFA particles before and after alkaline treatment at 908C and show that zeolite crystals have formed on the surface of residual fly ash particles. Analysis by XRD in combination with standard addition methods showed that the zeolite products obtained at different temperatures, contain 40 to 45% by weight of zeolite Na-P1. Table 1 presents the mineralogical composition of the untreated and treated CFA. Fig. 3 presents X-ray diffraction patterns for the untreated CFA and CFA zeolitized at 1508C. More detailed analysis of X-ray diffraction patterns by the Rietveld method is in progress. See Van der Laan en Van Vliet Ž1997. for information on the advantages of this method. As a result of zeolite synthesis, CEC increased from 0.02 meqrg for the original CFA to circa 2.4 meqrg for the zeolite product. Experiments carried out with KOH and mixtures of NaOH and KOH solutions Ž1 : 1 and 2 : 1. and under otherwise similar conditions as the experiments carried out with NaOH discussed above, resulted in the synthesis of zeolite K-G Žchabazite-type zeolite. and zeolite ZK19 Žphillipsite-type zeolite.. The fate of the heavy metals in CFA during the zeolitization process is of major importance. Analysis of CFA, zeolite products and processing and washing water showed that during the zeolitization process, cation-forming heavy metals Že.g. Cu, Pb,
Fig. 2. Coal fly ash particle, after 12 h zeolitization at 908C with a 2 M NaOH solution ŽLrS 2.5..
Zn. stayed behind in the zeolite product, either because they were absorbed into the zeolite framework or because they precipitated as hydroxides. Most anion-forming elements on the other hand Že.g. As, Mo, Se., proved to be quite mobile and were to a large extent extracted during the process. The release of exchangeable Naq from the zeolite product to the solution in the batch experiments, carried out to establish the adsorption isotherms of zeolite Na-P1, suggested that its complete CEC is available for exchange with heavy metals and ammonium. The additional batch experiments indicated that the selectivity series for this zeolite product with 40% Na-P1 is: Ba ) Cu ) Cd f Zn ) Co ) Ni The duplicate batch experiments indicated these results to be reproducible. The laboratory column Table 1 Mineralogical composition of coal fly ash before and after zeolitization with a 2 M NaOH solution
Fig. 1. Coal fly ash particle, prior to zeolitization.
Mineral phase
Raw CFA Ž%.
Zeolitized CFA Ž%.
Glass Quartz Mullite Iron oxides Žhematite, magnetite. Calcium and magnesium hydroxides Zeolite Na-P1
70 4 15 8
20 2 13 7
0
10
0
40–45
308
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
experiments confirmed the above-mentioned selectivity series. At the moment of breakthrough of elements Žat which moment the adsorption capacity is completely used by the heavy metals., Ni was the first element to appear in the percolate. The next element detected was Co, and so on in the reverse order of the selectivity series shown above as is shown in Fig. 4. This process also indicates the possibility of regeneration of the zeolite product, after the adsorption of contaminants, because of the reversibility of the adsorption Žin case all sites are occupied, Ni is released before Co, etc... In the column experiments, more metals were taken out of the solution per gram of zeolite product than could be accounted for by the CEC. The reason for this is that due to the high pH Ž10 at the beginning, 8 at the end., not only cation exchange, but precipitation of hydroxides as well, removed the metals from the solution. The laboratory column
Fig. 4. Breakthrough in successive order of Ni, Co, Zn, Cd, Cu, Pb and Ba in colum experiment with zeolite Na-P.
experiment with the effluent of a waste water treatment plant showed that about 90% of the CEC is used for the adsorption of ammonium, and that the exchanged zeolite can be easily regenerated by the use of a NaCl-solution. The results of the standard leaching column tests showed that the environmental quality has improved after the zeolitization process. Only the leaching of the elements Se and V still poses a problem regarding the regulatory norms. Preliminary results suggest that this may be solved by washing the fly ash prior to zeolitization.
4. Conclusions
Fig. 3. X-ray diffraction patterns of coal fly ash and coal fly ash converted to zeolite Na-P1. Qs quartz, M s mullite, H s iron oxides, P s zeolite Na-P1.
Alkaline treatment of Dutch coal fly ash leads to the synthesis of zeolites, resulting in a product with up to 45% zeolite and a cation exchange capacity of about 2.4 meqrg. During the process, cationic heavy metals are mostly immobilized while anionic heavy metals are largely extracted. As demonstrated by the standard leaching column tests ŽNEN 7343., this results in a better environmental quality of the zeolite product relative to the untreated coal fly ash. Zeolitized fly ash has very promising capacities for immobilizing environmental pollutants like heavy metals and ammonium. It appears that the complete cation exchange capacity can be used for the re-
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
moval of heavy metals from solution and that the zeolite can easily be regenerated.
Acknowledgements This research has been financed by the Electric Power Companies of The Netherlands and by a grant from the Dutch Ministry of Economic Affairs ŽSenter..
References Aiello, R., Colella, C., Sersale, 1971. Zeolite formation from synthetic and natural glasses. In: Flanigan, E.M., Sand, L.B. ŽEds.., Molecular Sieve Zeolites, I. 2nd International Conference, Advances in Chemistry Series 101, American Chemical Society, Washington D.C., pp. 51–62. Amrhein, C., Haghnia, G.H., Kim, T.S., Mosher, P.A., Gagajena, R.C., Amanios, T., De La Torre, L., 1996. Synthesis and properties of zeolites from coal fly ash. Environ. Sci. Technol. 30, 735–742. Barrer, R.M., 1982. Hydrothermal chemistry of zeolites. Academic Press, London, 360 p. Barth-Wirsching, U., Holler, H., Klammer, D., Konrad, B., 1993. ¨ Synthetic zeolites formed from expanded perlite: type, formation conditions and properties. Mineral. Petrol. 48, 275–294. De’Gennaro, M., Colella, C., Franco, E., Stanzione, D., 1988. Hydrothermal conversion of trachytic glass into zeolite. 1. Reactions with deionized water. Neues Jahrb. Mineral. Monatsh. 4, 149–158.
309
Henmi, T., 1987. Increase in cation exchange capacity of coal fly ash by alkali treatment. Clay Sci. 6, 277–282. Holler, H., Wirsching, U., 1985. Zeolite formation from fly ash. ¨ Fortschr. Mineral. 63, 21–43. ISRIC, 1992. Cation exchange capacity ŽCEC. and exchangeable bases. In: van Reeuwijk, L.P. ŽEd.., Procedures for Soil Analysis. International Soil Reference and Information Centre, Wageningen, 3rd ed., pp. 9.1–9.4. Kato, Y., Kakimoto, K., Tomari, M., 1984. Analysis and utilization of coal ash. Report of Special Project Research on Energy, SPEY-12, pp. 399–404. Kato, Y., Asahara, T., Kakimoto, K., Tomari, M., 1987. Studies on the utilization of coal ash. Studies of special project research on energy under grant in aid of scientific research of the Ministry of Education, Science and Culture, Japan, pp. 311–316. Lin, C.-F., Hsi, H.-C., 1995. Resource recovery of waste fly ash: synthesis of zeolite-like materials. Environ. Sci. Technol. 29, 1109–1117. Nederlands Normalisatie Instituut, 1995. Leaching characteristics of solid earthy and stony building and waste materials. Leaching tests. Determination of the leaching of inorganic components from granular materials with the column test. NEN 7343. Park, M., Choi, J., 1995. Synthesis of phillipsite from fly ash. Clay Sci. 9, 219–229. Querol, X., Plana, F., Alastuey, A., Fernandez-Turiel, J.L., Lopez-Soler, A., 1995. Synthesis of industrial minerals from fly ash. In: Pajares, J.A., Tascon, ´ J.M.D. ŽEds.., Coal Science. Elsevier, Amsterdam, pp. 1979–1982. Singer, A., Berkgaut, V., 1995. Cation exchange properties of hydrothermally treated coal fly ash. Environ. Sci. Technol. 29, 1748–1753. Van der Laan, S.R., Van Vliet, A., 1997. A concise analytical strategy applied to waste treatment technology. J. Geochem. Explor. 61 Žthis issue..
The synthesis of zeolites from fly ash and the properties of the zeolite products G. Steenbruggen ) , G.G. Hollman UniÕersity of Utrecht, Faculty of Earth Sciences, Department of Geochemistry, P.O. Box 80021, 3508 TA Utrecht, The Netherlands Accepted 6 November 1997
Abstract Fly ash produced during the combustion of powdered coal could be converted up to 45% into zeolite. By varying the experimental conditions different types of zeolite were produced, e.g. zeolite Na-P1, zeolite K-G and zeolite ZK19. By this zeolitization process the cation exchange capacity ŽCEC. was raised from 0.02 to circa 2.4 meqrg. Anionic heavy metals were largely extracted by the process water. Sorption experiments indicated that the selectivity series for zeolite Na-P1 is Ba ) Cu ) Cd f Zn ) Co ) Ni. Besides cation exchange reactions, precipitation of hydroxides also played a role in the immobilization of heavy metals in the column experiments carried out. Column leaching experiments showed that relative to the original fly ash, the zeolitized fly ash has a better environmental quality. The results of the sorption experiments suggest that the zeolite product can be applied in environmental technology as an immobilizer of pollutants. q 1998 Elsevier Science B.V. All rights reserved. Keywords: zeolite; fly ash; synthesis; adsorption; application
1. Introduction At present, almost all fly ash produced by coal combustion in The Netherlands Žabout 900,000 tonryear. is used in the production of building materials. This application is mainly based on the pozzolanic properties of the coal fly ash ŽCFA., by which calcium oxides, silica and water react to form calcium silicate hydrates ŽCSH.. Formation of these CSH phases improves the strength of concrete and makes it possible to convert fly ash into many other products Že.g. lytag granules..
)
Corresponding author. E-mail: [email protected]
However, present possibilities for the use of combustion residues, such as CFA, may decrease in the near future because of stricter environmental regulations and changes in CFA quality. The latter is a result of the co-combustion of organic waste material and changes in combustion techniques. To avoid a waste problem, new applications for this kind of combustion residues are needed. One possible new application for CFA is the synthesis of zeolite products: a process analogous to the formation of natural zeolites from volcanic deposits. Both volcanic ash and CFA are fine-grained and contain a large amount of aluminosilicate glass. In natural conditions, this glass fraction may be converted into zeolites by the influence of percolat-
0375-6742r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 5 - 6 7 4 2 Ž 9 7 . 0 0 0 6 6 - 6
306
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
ing hot groundwater ŽBarrer, 1982., while the zeolites may subsequently be converted into analcime and feldspar, i.e. glass ™ zeolite™ analcime™ feldspar This process may take tens to thousands of years in natural conditions. In laboratory conditions, this conversion can be speeded up to merely days or even hours, both in the case of volcanic ash and that of CFA. Research on this subject has been published by e.g. Aiello et al. Ž1971., De’Gennaro et al. Ž1988., Barth-Wirsching et al. Ž1993. on the zeolitization of volcanic ash, and by e.g. Kato et al. Ž1984, 1987., Holler and Wirsching Ž1985., Henmi Ž1987., Singer ¨ and Berkgaut Ž1995., Lin and Hsi Ž1995., Querol et al. Ž1995., Park and Choi Ž1995. and Amrhein et al. Ž1996. on the zeolitization of CFA and the characteristics of the product. To examine the possibilities of zeolite formation from Dutch coal fly ash, this research project was started in 1994. The aims of this project are: Ž1. To establish the optimal conditions for the formation of zeolite products from CFA and the economic viability of the process. Ž2. To examine the applicability of the synthesized zeolite products for the immobilization of environmental pollutants. Presented in this article is an introduction to the research project being carried out in order to achieve the aims mentioned above.
2. Materials and methods The zeolitization process in its simplest form is a relatively straightforward process. CFA was mixed with a hydroxide solution in a Teflon reaction vessel and incubated at a temperature of 90 to 1508C and autogenous pressure. Incubation below 1008C was carried out by putting the closed reaction vessels in a thermostatic bath, while for reactions at temperatures above 1008C reaction vessels were put inside steel bombs and heated in an oven. At the end of the experiment, mixtures were quenched and the reaction products recovered by filtration. Important experimental parameters include temperature, reaction time, liquidrsolid ratio ŽLrS., hydroxide concentration,
type of hydroxide solution and intensity of mixing. Examination of the influence of these parameters on the zeolitization process is part of the ongoing research project. For this purpose a range of analytical techniques is being used, namely X-ray diffraction ŽXRD., including standard addition methods for quantitative analysis, scanning electron microscopy with energy-dispersive X-ray analyser ŽSEMrEDS., ICP–AES and AAS. In addition, the cation exchange capacity ŽCEC. of the zeolite products was measured by means of the ammonium acetate method ŽISRIC, 1992.. Research on the applicability of the synthesized zeolite products focuses on two objects: Ž1. their adsorption properties; and Ž2. the leaching behaviour of the heavy metals present in the products Žimportant in the light of regulatory norms.. Research on the adsorption properties was carried out by batch and column experiments. Firstly, batch experiments with a zeolite product consisting of 40% zeolite Na-P1 Žgismondine-type zeolite. were carried out in order to determine the adsorption isotherms 2q 2q , Co 2q, Cu2q, Ni 2q, Pb 2q and for NHq 4 , Ba , Cd 2q Zn . Secondly, the selectivity series for the adsorption of these elements, except Pb and NHq 4 , was established by the equilibration of the zeolite product with a solution containing three of the elements. Every possible combination of three elements out of the six elements ŽBa, Cd, Co, Cu, Ni, and Zn. was tested. All the batch experiments were carried out in duplicate to check the reproducibility of their results. Thirdly, column experiments were carried out to examine the adsorption properties of the zeolite product in a more practical situation. In these experiments, samples of the zeolite products were percolated with a solution artificially polluted with heavy metals and with the effluent of a waste water treatment plant, with a high concentration of ammonium Ž600 mgrl.. According to Dutch environmental regulations, the leaching of some elements out of fly ash is too high for some purposes. To determine the leaching behaviour of the zeolite products, they were subjected to a standard column test ŽNEN 7343., developed by the Dutch Normalization Institute ŽNederlands Normalisatie Instituut, 1995. to determine the leaching of inorganic components from granular materials.
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
307
3. Results and discussion Treatment of CFA with a 2 M NaOH at temperatures of 90 to 1508C resulted in the synthesis of zeolite Na-P1. Figs. 1 and 2 depict CFA particles before and after alkaline treatment at 908C and show that zeolite crystals have formed on the surface of residual fly ash particles. Analysis by XRD in combination with standard addition methods showed that the zeolite products obtained at different temperatures, contain 40 to 45% by weight of zeolite Na-P1. Table 1 presents the mineralogical composition of the untreated and treated CFA. Fig. 3 presents X-ray diffraction patterns for the untreated CFA and CFA zeolitized at 1508C. More detailed analysis of X-ray diffraction patterns by the Rietveld method is in progress. See Van der Laan en Van Vliet Ž1997. for information on the advantages of this method. As a result of zeolite synthesis, CEC increased from 0.02 meqrg for the original CFA to circa 2.4 meqrg for the zeolite product. Experiments carried out with KOH and mixtures of NaOH and KOH solutions Ž1 : 1 and 2 : 1. and under otherwise similar conditions as the experiments carried out with NaOH discussed above, resulted in the synthesis of zeolite K-G Žchabazite-type zeolite. and zeolite ZK19 Žphillipsite-type zeolite.. The fate of the heavy metals in CFA during the zeolitization process is of major importance. Analysis of CFA, zeolite products and processing and washing water showed that during the zeolitization process, cation-forming heavy metals Že.g. Cu, Pb,
Fig. 2. Coal fly ash particle, after 12 h zeolitization at 908C with a 2 M NaOH solution ŽLrS 2.5..
Zn. stayed behind in the zeolite product, either because they were absorbed into the zeolite framework or because they precipitated as hydroxides. Most anion-forming elements on the other hand Že.g. As, Mo, Se., proved to be quite mobile and were to a large extent extracted during the process. The release of exchangeable Naq from the zeolite product to the solution in the batch experiments, carried out to establish the adsorption isotherms of zeolite Na-P1, suggested that its complete CEC is available for exchange with heavy metals and ammonium. The additional batch experiments indicated that the selectivity series for this zeolite product with 40% Na-P1 is: Ba ) Cu ) Cd f Zn ) Co ) Ni The duplicate batch experiments indicated these results to be reproducible. The laboratory column Table 1 Mineralogical composition of coal fly ash before and after zeolitization with a 2 M NaOH solution
Fig. 1. Coal fly ash particle, prior to zeolitization.
Mineral phase
Raw CFA Ž%.
Zeolitized CFA Ž%.
Glass Quartz Mullite Iron oxides Žhematite, magnetite. Calcium and magnesium hydroxides Zeolite Na-P1
70 4 15 8
20 2 13 7
0
10
0
40–45
308
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
experiments confirmed the above-mentioned selectivity series. At the moment of breakthrough of elements Žat which moment the adsorption capacity is completely used by the heavy metals., Ni was the first element to appear in the percolate. The next element detected was Co, and so on in the reverse order of the selectivity series shown above as is shown in Fig. 4. This process also indicates the possibility of regeneration of the zeolite product, after the adsorption of contaminants, because of the reversibility of the adsorption Žin case all sites are occupied, Ni is released before Co, etc... In the column experiments, more metals were taken out of the solution per gram of zeolite product than could be accounted for by the CEC. The reason for this is that due to the high pH Ž10 at the beginning, 8 at the end., not only cation exchange, but precipitation of hydroxides as well, removed the metals from the solution. The laboratory column
Fig. 4. Breakthrough in successive order of Ni, Co, Zn, Cd, Cu, Pb and Ba in colum experiment with zeolite Na-P.
experiment with the effluent of a waste water treatment plant showed that about 90% of the CEC is used for the adsorption of ammonium, and that the exchanged zeolite can be easily regenerated by the use of a NaCl-solution. The results of the standard leaching column tests showed that the environmental quality has improved after the zeolitization process. Only the leaching of the elements Se and V still poses a problem regarding the regulatory norms. Preliminary results suggest that this may be solved by washing the fly ash prior to zeolitization.
4. Conclusions
Fig. 3. X-ray diffraction patterns of coal fly ash and coal fly ash converted to zeolite Na-P1. Qs quartz, M s mullite, H s iron oxides, P s zeolite Na-P1.
Alkaline treatment of Dutch coal fly ash leads to the synthesis of zeolites, resulting in a product with up to 45% zeolite and a cation exchange capacity of about 2.4 meqrg. During the process, cationic heavy metals are mostly immobilized while anionic heavy metals are largely extracted. As demonstrated by the standard leaching column tests ŽNEN 7343., this results in a better environmental quality of the zeolite product relative to the untreated coal fly ash. Zeolitized fly ash has very promising capacities for immobilizing environmental pollutants like heavy metals and ammonium. It appears that the complete cation exchange capacity can be used for the re-
G. Steenbruggen, G.G. Hollmanr Journal of Geochemical Exploration 62 (1998) 305–309
moval of heavy metals from solution and that the zeolite can easily be regenerated.
Acknowledgements This research has been financed by the Electric Power Companies of The Netherlands and by a grant from the Dutch Ministry of Economic Affairs ŽSenter..
References Aiello, R., Colella, C., Sersale, 1971. Zeolite formation from synthetic and natural glasses. In: Flanigan, E.M., Sand, L.B. ŽEds.., Molecular Sieve Zeolites, I. 2nd International Conference, Advances in Chemistry Series 101, American Chemical Society, Washington D.C., pp. 51–62. Amrhein, C., Haghnia, G.H., Kim, T.S., Mosher, P.A., Gagajena, R.C., Amanios, T., De La Torre, L., 1996. Synthesis and properties of zeolites from coal fly ash. Environ. Sci. Technol. 30, 735–742. Barrer, R.M., 1982. Hydrothermal chemistry of zeolites. Academic Press, London, 360 p. Barth-Wirsching, U., Holler, H., Klammer, D., Konrad, B., 1993. ¨ Synthetic zeolites formed from expanded perlite: type, formation conditions and properties. Mineral. Petrol. 48, 275–294. De’Gennaro, M., Colella, C., Franco, E., Stanzione, D., 1988. Hydrothermal conversion of trachytic glass into zeolite. 1. Reactions with deionized water. Neues Jahrb. Mineral. Monatsh. 4, 149–158.
309
Henmi, T., 1987. Increase in cation exchange capacity of coal fly ash by alkali treatment. Clay Sci. 6, 277–282. Holler, H., Wirsching, U., 1985. Zeolite formation from fly ash. ¨ Fortschr. Mineral. 63, 21–43. ISRIC, 1992. Cation exchange capacity ŽCEC. and exchangeable bases. In: van Reeuwijk, L.P. ŽEd.., Procedures for Soil Analysis. International Soil Reference and Information Centre, Wageningen, 3rd ed., pp. 9.1–9.4. Kato, Y., Kakimoto, K., Tomari, M., 1984. Analysis and utilization of coal ash. Report of Special Project Research on Energy, SPEY-12, pp. 399–404. Kato, Y., Asahara, T., Kakimoto, K., Tomari, M., 1987. Studies on the utilization of coal ash. Studies of special project research on energy under grant in aid of scientific research of the Ministry of Education, Science and Culture, Japan, pp. 311–316. Lin, C.-F., Hsi, H.-C., 1995. Resource recovery of waste fly ash: synthesis of zeolite-like materials. Environ. Sci. Technol. 29, 1109–1117. Nederlands Normalisatie Instituut, 1995. Leaching characteristics of solid earthy and stony building and waste materials. Leaching tests. Determination of the leaching of inorganic components from granular materials with the column test. NEN 7343. Park, M., Choi, J., 1995. Synthesis of phillipsite from fly ash. Clay Sci. 9, 219–229. Querol, X., Plana, F., Alastuey, A., Fernandez-Turiel, J.L., Lopez-Soler, A., 1995. Synthesis of industrial minerals from fly ash. In: Pajares, J.A., Tascon, ´ J.M.D. ŽEds.., Coal Science. Elsevier, Amsterdam, pp. 1979–1982. Singer, A., Berkgaut, V., 1995. Cation exchange properties of hydrothermally treated coal fly ash. Environ. Sci. Technol. 29, 1748–1753. Van der Laan, S.R., Van Vliet, A., 1997. A concise analytical strategy applied to waste treatment technology. J. Geochem. Explor. 61 Žthis issue..