Characterization and cation exchange properties of zeolite synthesized from fly ashes
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Characterization and cation exchange properties of zeolite synthesized from fly ashes Weiping Ma,a) Paul W. Brown, and Sridhar Komarneni Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 6 January 1997; accepted 3 June 1997)
Zeolite P was formed from class F fly ash under hydrothermal conditions. The fly ash was reacted with 2.8 or 5 M NaOH at 100 ±C. Zeolite of the above type was produced regardless of the NaOH concentration or the addition of quartz, thus indicating its formation over a wide range of conditions. The zeolite produced was of the NaP-type with a fibrous morphology. Analysis of the pore structure of this zeolite by the BET method indicates a type II isotherm. The specific surface areas of synthesized zeolites increased from 28.5 to 41.1 m2yg when the NaOH concentration was increased from 2.8 to 5.0 M. This zeolite showed a significant selectivity for the uptake of Cs and Sr. Cs uptake ranged from 7.67 to 8.61 meqy100 g while that of Sr ranged from 9.8 to 10.54 meqy100 g. The value obtained depended on the specific synthesis conditions. These values are higher than those observed for tobermorite prepared from the same fly ash even though the tobermorite exhibited a higher specific surface area.
I. INTRODUCTION
Because of the large amount of fly ash generated annually, there is continuing interest in establishing ways in which it may be used. Therefore, identification of further means to facilitate the use of fly ash and avoid the need to dispose of it is desirable. To achieve this goal, it is essential to establish the nature of the phases that form in the presence of selective additives and assess whether these phases are capable of sequestering hazardous species. We previously reported that tobermorite (Ca5 Si6 H2 O18 ? 4H2 O) with partial substitution of Si by Al could be synthesized from fly ash under hydrothermal conditions1 and could be used for selective exchange of Cs or Sr.2 It was the objective of the present study to build on these results by producing zeolite from fly ash. Further, it was the objective to compare the abilities of tobermorite and zeolite produced from the same ashes to sequester Cs and Sr. The technology leads to the probability of a new application of fly ash in environmental waste disposal. Fly ashes and natural volcanic glasses treated with NaOH have been reported to produce several types of zeolites.3–6 This is a potentially attractive process because it may offer the benefits of facilitating waste separation and possibly immobilization. Zeolites constitute a framework based on an infinitely extending three-dimensional network of SiO4 and fAlO4 g21 tetrahedra linked through common oxygen atoms. The framework structure encloses cavities occupied by large ions a)
Present address: Holnam, Inc., Dundee, Michigan 48131. J. Mater. Res., Vol. 13, No. 1, Jan 1998
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