Na-Pl zeolite

Kim et al. [19] have synthesized Na-Pl zeolite from coal fly ash by using aqueous solution of 2-3 M NaOH at 100 to 150 °C. It has been reported that Faujasite and Hydroxy-sodaUte are formed when NaOH solution concentrations are maintained at 4 and 5 M, respectively. It has been observed that all MulUte, Quartz and Hematite disappeared after hydrothermal treatment at 160 °C. The final synthesis product containing zeolites, Analcime, with Na-Pl, and Cancrinite with Na-Pl, can be found corresponding to alkali concentration of 2 and 4 M, respectively. It has also been reported that Cancrinite increases if the NaOH concentration is 5 M or more. The authors have opined that Na-Pl zeolite having CEC value of 215 meq./lOO g would exhibit strong afftnity towards Pb and Sr. 

Adamczyk and Bialecka [5] have established the process of hydrothermal synthesis of zeolites and optimized the conditions of synthesis to get as much quantity of zeolite as possible in the shortest activation time. The process of preliminary activation has been carried out at room temperature with NaOH solution. In addition, further activation has been carried out at variable temperatures (viz., 80, 120, 140, 150, 170, 180, 200 and 320 °C), and at 6 h reaction time, in a 1 1 PROLABO autoclave fitted with a stirring electromagnetic system at activation pressure equal to the pressure of the steam generated in the course of heating the suspension. It has been reported that there has been an increase in the content of Na-Pl zeolite as compared to Analcime from 120 to 170 °C of activation temperature, thereafter its content gets reduced at 180 °C and again increased beyond this temperature up to 320 °C along with formation of more Analcime. Diffraction patterns of the material synthesized at 120 °C demonstrate the presence of MuUite and Hematite reflections. 

Figure 5. A further stage in the nu- Figure 6. Final stage showing crys-cleation of zeolite tals of Na-Pl and basic sodalite...

The B zeolites have been called, at various times, phillipsite-like, harmotome-like, Na-P-like, and gismondine-like phases. This nomenclature has arisen by comparison with the x-ray diffraction patterns of mineral zeolite specimens. Since the B zeolites first were identified, however, the structures of phillipsite, harmotome, and gismondine have been determined, and a structure was proposed by Barrer (2), based on x-ray powder diffraction data, for Na-Pl, the equivalent of cubic Linde Bi. 

X-ray diffraction patterns of Linde B zeolites are shown in Figure 2 and Table II. The similarity of the main diffraction peaks is obvious. The synthetic phases produced by various workers have been arranged in Table III to show their relationship to each other. Zeolite Bx is correlated with the cubic body-centered phases of Barrer (2) (Na-Pl) and Taylor and Roy s Na-Pc (13). The Linde B2, B3, Br and B6 phases are similar to the tetragonal body-centered phases of Barrer (2) (Na-P2) and... 

The crystal structure of the synthetic zeolite Na-Pl, represented by the formula NaeAleSiio,12H20, has been solved by X-ray methods. It is closely related to the gismondine-type framework. 

Fig. 8. a Isothermal DTA trace showing the endotherm connected with the Na-Pl Na-P2 transformation b DTA curve of Ba-exchanged Linde A zeolite, showing the sharp endotherm connected with lattice collapse (reproduced by permission from [35])... 

Si/Al molar ratio in the activated fly ash, zeolites can be classified/graded as low silica zeolites , intermediate silica zeolites and high silica zeolites , as listed in Table 2.2. In general, for zeolites, an increase in this parameter (i.e., Si/Al from 0.5 to infinity) [5] can significantly result in the increase in various other parameters (viz., acid resistivity, thermal stability and hydrophobicity) except few parameters (viz., hydrophilicity, acid site density and cation concentration) which get decreased [5, 8, 10,40, 41]. In general, synthetic zeolites hold some key advantages over their counterparts i.e. natural zeolites. Zeolites type A, X, Y, P and Na-Pl are well known synthetic zeolites synthesized from fly ash which have a wider range of industrial applications than the natural zeolites [1, 8, 20, 22, 36, 42, 43]. 

The most common physical properly of the ash zeolites is its specific surface area, which is dependent on the extent of dissolution of fly ash particles in alkaline solvents [19, 22, 31]. In line with this, another important physical property of zeolites is their void volume which can directly be correlated with the CEC of the synthesized product (e.g., fly ash zeolites, Na-Pl) and which in turn depends upon the specific area as depicted in Fig. 2.3a, b [1, 22]. Moreover, both CEC and the surface area of the ash zeolites are found to undergo significant variations with increase in molarity and the reaction time, as depicted in Fig. 2.3c, d [22, 29]. From the trends depicted in Fig. 2.3c, it can be observed that the CEC increases, marginally, with an increase in concentration, however, the same is noticed to be fluctuating, randomly, with an increase in reaction time. This can be attributed to the variations in the pore size and volume, as depicted in Fig. 2.3a. On the contrary, the surface area maintains an increasing trend with increase in concentration and the reaction time, as depicted in Fig. 2.3d, which can be attributed to increase in dissolution of fly ash ingredients (viz., glass. Quartz and Mullite). 

Fig. 2.6 SEM micrographs of the a Fly ash (spherical morphology), b Na-A (cubic morphology), c Sodalite (ball shaped morphology), d Cancrinite (Hexagonal, prismatic, needle like morphology), e Zeolite Y (cubic morphology), f Zeolite Na-X (octahedral morphology) [8]. g Mordenite (acicular or prismatic crystals) and Analcime (spherical crystals), h Clinoptilolite (hexagonal) and NaPl (ball shaped), i Fibrous Na-Pl, j Na-Pl (polycrystalline), k Na-A with emerging agglomerates and I Na-X (Cubic) [8]...

Conventional hydrothermal 8 NaOH, KOH, Na2C03 90-150 24-96 Chabazite, Na-Pl, Phillipsite, Sodalite, zeolite KH, 4A, A, P, Zeolite X, Y Low yield, low purity, structural-heterogeneity [1-5]... 

Fernandez et al. [31] have synthesized zeolites by reflux heating of stirred mixture of fly ash and 2.5 M NaOH and/or KOH solution, on an electrically heated plate at 100 °C for 24 or 48 h by maintaining solution to fly ash ratio (L/S) as 0.005 L/g. The potential reuse of waste alkaline solution has been evaluated for activation of a fresh fly ash sample. It has been observed that there is no change in the CEC value of zeolitic product obtained, which is an anomaly and should be researched further. It has also been reported that the zeolitic yield has been up to 38 % (viz., Na-Pl and Analcime) and 34 % (viz., Chabazite) for NaOH and KOH activations, respectively. The mineral phase transition has been attributed to the activation of majority of amorphous glass with NaOH, whereas MuUite and Quartz can get dissolved under strong alkaline conditions. It has been demonstrated that the products obtained after NaOH activation can get contaminated with more leachates and trace elements like Cd and As, as compared to KOH activation from fly ash. 

Inada et al. [6] have synthesized zeolites employing different coal fly ash sources, bearing different silica-alumina compositions by hydrothermal alkaline treatment. It has been observed that zeolites Na-Pl and/or Hydroxy-sodalite appear after the treatment at 100 °C in aqueous NaOH solution for 24 h. It has been demonstrated that zeolite Na-Pl can be synthesized predominantly from silica-rich fly ash at a low NaOH concentration with maximum yield at 2 M NaOH. They have opined that the presence of Hydroxy-sodalite can be found by employing 4 M NaOH concentration, whereas zeolite Na-Pl can fuUy disappear at 5 M NaOH. The cation exchange capacity of the product with a large content of zeolite Na-Pl has been found to reach a value of 300 meq./100 g. It has been concluded that silica addition effectively enhances the formation of zeolite Na-Pl, even at a high NaOH... 

Wu et al. [34] have studied the effect of additives on synthesis of zeolite from coal fly ash due to hydrothermal conversion. The authors have demonstrated the effect of addition of sodium halide, Na2Si04 and Al(OH)3, prior to synthesis process for the adjustment of the Si/Al ratio of the reaction matrix, on waste solution and the CEC of final products produced, after zeoUtization of the fly ash. The addition of NaCl and NaF has been found to ameliorate the crystallinity and CEC of the synthesized zeolite. However, NaF has been reported to be a better option for the improved effects. It has been concluded that Na enhances the crystallization of zeolites, while F favors the dissolution of the fly ash. It has been observed that the waste solutions contain large amount of Si and little Al, due to the formation of a zeolite, Na-Pl (as per the Joint Committee of Powder Diffraction Standard, JCPDS,... 

Shigemoto et al. [9] have reported about selective formation of Na-X zeolite from a mixture of coal fly ash procured from two different sources. It has been reported that most of the fly ash particles got converted into silicates and aluminates of sodium during 1 h of fusion at 773 K, whereas the hydrothermal activation for 6 h of the fused product, crystallized into Na-X, Na-A, Na-Pl and Hydroxy-sodalite zeolites in different proportions based on Na/Fly ash ratio (i.e., 1.2-1.8) employed and Al content of fly ash. It has been opined that fly ash enriched with aluminium, can be crystallized to zeolite Na-A in place of Na-X. 

Gmtzeckand Siemer [45] have investigated the synthesis of zeolites from a mixture of class-F fly ash and slurry of sodium aluminate prepared in proportion of 3 1 (i.e., Na Al). They have reported that a class-F fly ash reacts with the slurry to synthesize zeolites from a highly alkaline waste stream. The reaction has been studied as a function of mixture (i.e., fly ash slurry) composition (3 2, 1 1, and 1 2), time (1, 3, and 7 days), and temperature (80, 130, and 180 °C). The X-ray diffraction analysis of the products has indicated that the reaction between fly ash and sodium aluminate can result final yield as zeolite A, Na-Pl, and Hydroxy-sodalite at 80, 130 and 180 °C, respectively. It has been clarified that the bulk of the sodium has been incorporated into the zeolitic phases. 

Based on the X-ray diflEractograms of both these ashes (OLA and OHA) and their activated residues, as depicted in Fig. 5.21a, b, results obtained after peak matching with the help of JCPDS data files [35] have been listed in Table 5.38. It can be deciphered from these results that the ALA samples contain fewer crystals of zeolite Na-Pl (refer Fig. 5.6). Most specifically, the residue ALA6 exhibits the presence of the zeolite Na-Pl for M < and Hydroxy-sodalite for M > [23]. On the other hand. Fig. 5.4b exhibits the peaks corresponding to the zeolites Na-Pl and Hydroxy-sodalite in the residue, AHA2. However, as listed in Tables 5.4 and 5.5, the zeolites, Cancrinite and Analcime, were also found in the residue AHA6. This... 

F. 5.21 a XRD patterns of the OLA and the superior ALA samples, where Q, ML, P and S represent Quartz, Mullite, zeolite Na-Pl and Hydroxy-sodalite, respectively, and 0 is the angle of scattering of X-ray. b XRD patterns of the OHA and the superior AHA samples (where Q, ML, P, C, S and A represent Quartz, Mullite, zeolite Na-Pl, Cancrinite, Hydroxy-sodalite and Analcime, respectively)... 

Fig. 5.22 Micrographs of the samples, a OLA and b OHA, where Q, ML, GL and P designate Quartz, Mullite, glass and zeolite Na-Pl, respectively...

Further, from the data presented in Table 6.2 it can also be derived that C5, and planar alignment, h k I, corresponding to a specific mineral phase (say zeolite Na-Pl in the residues 1.5-R2-24 and 3.0-R2 8, refer Fig. 6.8) vary and hence crystal anisotropy and structural disorder of the residues, obtained at the end of the TSA, could be verified. In addition, residues 1.5-R2-24 are found to have higher value of the CS (=95 nm) as compared to their counterpart 3.0-R2-48, for which CS is 60 nm. This can be attributed to better nucleation and crystal growth in residues 1.5-R2-24. Hence, the superiority of residues 1.5-R2-24 gets reconfirmed. 

The residues 1.5-R2-24 have been found to exhibit majority of newly formed spherules of diameter ranging from 30 to 50 nm, which commensurate with the zeolite, Na-Pl (designated by P the fibrous lumps in Fig. 6.9c), which is an improvement over the residues formed by resorting to conventional methods [2,6,7]. In addition, fewer ball shaped crystals viz. Hydroxysodalite [7], Faujasite [8],... 

On the other hand, from Fig. 6.9e it can be observed that the residues 3.0-R2-48 also contain the haU shaped crystals viz. Hydroxy-sodalite, larger in size ranging from 900 to 1000 nm. Apart from this, fewer ctystal shapes and sizes of Faujasite (prismatically shaped, 1 pm long) and zeohte Na-Pl (spherules of 100 nm size) are also found to he present in these residues. Accordingly, the higher CEC of the residues 1.5-R2-24, being die most superior residues, can be attributed to its polyciystalline zeoUtic phase (viz., Na-Pl, Cancrinite and Na-A) as compared to the residues 3.0-R2-48, which comprises of different types of zeolites (viz., Hydroxy-sodalite and Faujasite) and hence exhibits a lesser CEC. 

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