Hydroxy-sodalite

Two zeolite species, Z-21 and Na-V, have been synthesized in the Na system. Collela and Aiello (29) report the crystallization of zeolite Na-V from the reaction of a rhyolitic glass in strong caustic solution. It is formed in the crystallization fields of X and I (hydroxy sodalite), the phase crystallizing being a function of agitation conditions and temperature. Collela and Aiella suggest that Na-V is structurally related to zeolite N... 

An alternative route to the occlusion of salts in zeolite systems is by means of high temperature reactions involving previously imbibed salts. This procedure has been successfully employed to fill the zeolite cages of X, Y and A zeolites with anions such as chloride, bromide, iodide, nitrate and chlorate (refs. 4,7). It offered a possible means of occluding the oxyanions of transition metals such as Cr, Mo and W in the sodalite cages of hydroxy-sodalite and zeolites. 

Hydroxy-sodalite was prepared from metakaolin in 4 mol l-1 NaOH at 80°C. 

Salt loaded noseans were prepared by a high temperature reaction between excess salt and hydroxy-sodalite (ref. 8) ... 

Studies of high temperature, dry salt reactions with hydroxy-sodalite have provided useful insights into the behaviour of zeolites when loaded with high melting point salts and reacted at elevated temperatures. Such reactions at temperatures above the effective melting point of the salt are likely to lead to the formation of both amorphous aluminosilicate phases and crystalline product phases such as nephilene and nosean. 

Khajavi, Jansen, and Kapteijn (2010) used an R2-type ESU-PVMR for the esterification of acetic acid with ethanol and acetic acid with 1-butanol. In these two cases, a mbular hydroxy sodalite (SOD) membrane was used. The reactions were performed using equimolar mixtures of acetic acid and organic alcohol at 363 K. Amberlyst 15 was chosen as solid acid catalyst. The special feamre of the SOD membrane was the absolute selectivity toward water and the relative high stability under the reaction conditions. In fact, the water selectivity in these experiments was above 1,000,000 and... 

Fukui et al. [33] have investigated the effects of NaOH concentration on the crystal stracture and the rate of reaction of the synthesized zeolite from fly ash with a hydrothermal treatment method. They have reported that fly ash or the mixture of fly ash and silica powder results in an increase in the reaction rates with the increase of NaOH concentration due to increase of the dissolution rate of silicate ion and aluminate ion. It has been clarified that the NaOH concentration also affects the crystal structure of synthesized zeolites. It has been concluded that the proportion of Phillipsite continues to be lower than the increasing proportion of Hydroxy-sodalite in the product with the increase in the concentration of NaOH. 

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... 

Fukui et al. [8] have utilized NaCl for synthesis of Phillipsite from fly ash by hydrothermal treatment with microwave heating. It has been reported that the crystallinity of Philhpsite can be increased by addition of NaCl in the hydrothermal reaction matrix with low concentration of NaOH, whereas no effects have been reported in case of high concentration of NaOH. However, microwave heating has been a favorable tool for the generation of Hydroxy-sodalite. It has been demonstrated that the substitution of NaCl by NaOH can reduce the rate of dissolution of aluminate and silicate ions from fly ash. As such, the rate of generation of aluminosilicate gel can be enhanced by employing microwave heating of the solution. 

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. 

Park et al. [15, 16] have established the molten-salt method for the synthesis of zeolitic materials without any addition of water. The zeohtization of fly ash has been demonstrated by employing various mixtures of NaOH, KOH, or NH4F as mineralizers and NaNOs, KNO3, or NH4NO3 as solvent instead of demineralized water in hydrothermal method. It has been reported that zeolites like Hydroxy-sodalite and Cancrinite can get crystallized from mixture of NaOH and... 

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)... 

Legends Q-Quartz, ML-Mullite, H-Haematite, P-Na-PI zeolite, S-Hydroxy-sodalite, C-Canainite, A-zeolite Na-A, F-Faujasite,... 

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. 

Fig. 6.10 Various sizes of surface pores in the residues a 1.5-R2-24 and b 3.0-R2-48, where A, C, F, S and P are designations for fly ash zeolites Na-A, Cancrinite, Faujasite, Hydroxy-sodalite and Na-Pl, respectively...

Hydroxy-sodalite, Sodalite, Na-X and Philipsite are also established for uptake of Ni, Cd, Cu, Cs, Pb, Hg and Sr cations from contaminated water, soil and gas as adsorbent. In short, zeolites can act as detoxing agent to decontaminate the environment and hence facilitate its conservation. 

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