Use of drinking water sludge in the production process of zeolites

This study reports the synthesis of zeolites A, X, and P, cancrinite, and sodalite using sludge generated in a drinking water plant. Two experimental steps were carried out: (1) fusion and (2) hydrothermal treatment. Crystallization was achieved by means of a 2³ experimental design with central point with the following factors: temperature, time, and solid/liquid ratio. The sludge presented Si and Al contents (SiO₂/Al₂O₃ = 1.7) which allow the synthesis of zeolites with high cation exchange capacity. The content of organic matter was considerable (loss on ignition 26.1 %), but is eliminated in the fusion step at 550 °C. This process also permits the conversion of the initial aluminosilicates into zeolite precursors (sludge–NaOH mix of 1:0.785 g/g). Hydrothermal treatment then permits the crystallization of the aforementioned zeolites. These materials showed high cation exchange capacities as compared to other commercial and experimentally synthesized zeolites, and can be used in the removal of heavy metals such Cd²⁺, Pb²⁺, Cu²⁺, Fe²⁺, and ammonium present in water, providing an interesting new option in wastewater treatment and remediation of soils.     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

Reconstructive and displacive transformations of tectosilicates

By using the thermally induced phase transformation initial zeolites were converted into pure carnegieite, stuffed derivative of cristobalite. The polymorphs obtained from Na-LTA are stoichiometric (NaAlSiO₄), since those obtained from Na-FAU zeolite are non-stoichiometric (Na_1-xAl_1-xSi_1+xO₄). Stoichiometric carnegieite have cubic structure, while non-stoichiometric carnegieite crystallized in cubic and orthorhombic forms. ²⁹Si MAS NMR spectra show a very large but expecting difference between stoichiometric and non-stoichiometric carnegieite. The spectrum of stoichiometric carnegieite has only one peak Si(4Al), while the spectrum of non-stoichiometric carnegieite consist few superimposed peaks assigned to Si(4Al), Si(3Al), Si(2Al), Si(1Al) and Si(0Al). DTA study indicates the occurrence of displacive phase transition of all synthesized carnegieite. The transition temperature is depending on silicon aluminum order: T _m=690°C for stoichiometric, T _m=565 and 660°C for non-stoichiometric, low-temperature and high-temperature carnegieite, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crystallization of ZSM-12 Zeolite with Different Si/Al Ratio

In this work the acid properties of a series of HZSM-12 zeolites with different Si/Al ratio were studied. The ZSM-12 crystals were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na₂O:x Al₂O₃:100SiO₂:2000H₂O, with x = 0.50, 0.67, 1, 1.25 and 2, respectively. The gels were crystallized at 140^∘C for 6 days, then washed, dried and calcined to remove the MTEA template. The samples were ion-exchanged with an ammonium chloride solution and calcined again to obtain the zeolites in the acid form. The materials thus obtained were characterized by XRD, SEM, BET, TG and n-butylamine adsorption. The Si/Al ratio in the reaction mixture affects the amount of zeolite produced and the size of the particles. The XRD analysis indicated that the ZSM-12 zeolite crystallizes in a pure form only with Si/Al ratio above 33. The SEM analysis showed the presence of crystallites with very well defined prismatic shapes. The removal of the MTEA of the pores of the ZSM-12 by TG indicated that there are two kinds of internal sites occupied by MTEA inside the structure. The BET area of the ZSM-12 decreases proportionally with the crystallinity of materials. The desorption of n-butylamine showed that the acid site density is proportional to aluminum content, but the Si/Al ratio shows little influence on the relative strengths of these sites.     

Study of the stability of zeolites Na-A and Na-X in mother liquors

It was shown that Na zeolites of A and X types are unstable under the conditions of hydrothermal synthesis and are easily recrystallized to form other zeolites with more compact crystal structures and higher Si/Al ratios. Zeolite X is recrystallized to phillipsite (zeolite P), and zeolite A is recrystallized to phillipsite from gels with the SiO₂/Al₂O₃ ratio equal to 2 and to socialite from gels with SiO₂/Al₂O₃ < 2 (zeolite J). The nucleation of secondary zeolite phases occurs as the result of rearrangement and decomposition of the lattice of primary crystals.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2415–2418, October, 1996.     

Formation and Properties of Losod,a New Sodium Zeolite

Losod, a new type of crystalline hydrated sodium aluminosilicate, Na₁₂Al₁₂Si₁₂O₄₈ · q H₂O, has been prepared from reaction mixtures containing bulky quaternary alkylammonium ions, particularly azonia-spiro[4.4]nonane, besides sodium ions. Losod crystallizes from batches with a low sodium content (Na/Al ≤ 1 and Si/Al ≈? 1). The quaternary ammonium hydroxide primarily serves as a source of hydroxide ions and is not incorporated into the zeolite crystals. These bulky bases provide a useful means for controlling the alkalinity of the system independently of the concentration of the necessary cations built into the zeolite. The crystals of Losod are hexagonal (a = 12.91 and c = 10.54 Å) and the proposed framework structure shows a polytypic relationship to sodalite and cancrinite. Losod has reversible sorption and ion exchange properties typical of a small-pore zeolite and in essential agreement with the proposed structure.     

Der Chromat‐Nosean Na8[Al6Si6O24](CrO4) — ein zeolithisches Gelbpigment?

A Chromate(VI) Oxide Ceramics Na₈[Al₆Si₆O₂₄](CrO₄) with Zeolitic Nosean Structure and Pigment Properties The cages of the zeolitic sodalite lattice can be occupied by half by the tetrahedral CrO₄^2— group, yielding a thermally stable, intense lemon‐yellow pigment, in which the colour centres are shielded completely from the atmosphere. The analyses yielded compositions Na₈[Al_6+2δSi_6—2δO₂₄](CrO₄)_1—δ with a small surplus of Al³⁺ and a CrO₄^2— deficiency (δ ≅ 0.15).     

Synthesis of aluminosilicates under high pressure and using sulfur as directing agent

Two aluminosilicates were prepared under hydrothermal conditions. Silica, sodium aluminate, sodium sulfide and sulfur were used as raw materials. Starting with similar reacting mixtures, analcime (zeolite, Na(Si₂Al)O₆·H₂O) and beidellite (clay, Na_0.3Al₂(Si, Al)₄O₁₀(OH)₂·2H₂O) were synthesized by varying pressures, 2 kbar and 1 kbar, respectively. Sulfur was present in both aluminosilicate surfaces, which confer to them particular adsorption properties. Additionally, water adsorption isotherms, under dynamical conditions, were obtained. Fractal dimension values and SEM micrographs reveal very different textural and morphological properties of the two prepared aluminosilicates     

The use of X-ray fluorescence (XRF) analysis in predicting the alkaline hydrothermal conversion of fly ash precipitates into zeolites

The use and application of synthetic zeolites for ion exchange, adsorption and catalysis has shown enormous potential in industry. In this study, X-ray fluorescence (XRF) analysis was used to determine Si and Al in fly ash (FA) precipitates. The Si and Al contents of the fly ash precipitates were used as indices for the alkaline hydrothermal conversion of the fly ash compounds into zeolites. Precipitates were collected by using a co-disposal reaction wherein fly ash is reacted with acid mine drainage (AMD). These co-disposal precipitates were then analysed by XRF spectrometry for quantitative determination of SiO₂ and Al₂O₃. The [SiO₂]/[Al₂O₃] ratio obtained in the precipitates range from 1.4 to 2.5. The [SiO₂]/[Al₂O₃] ratio was used to predict whether the fly ash precipitates could successfully be converted to faujasite zeolitic material by the synthetic method of [J. Haz. Mat. B 77 (2000) 123]. If the [SiO₂]/[Al₂O₃] ratio is higher than 1.5 in the fly ash precipitates, it favours the formation of faujasite. The zeolite synthesis included an alkaline hydrothermal conversion of the co-disposal precipitates, followed by aging for 8 h and crystallization at 100 °C. Different factors were investigated during the synthesis of zeolite to ascertain their influence on the end product. The factors included the amount of water in the starting material, composition of fly ash related starting material and the FA:NaOH ratio used for fusing the starting material. The mineralogical and physical analysis of the zeolitic material produced was performed by X-ray diffraction (XRD) and nitrogen Brunauer-Emmett-Teller (N₂ BET) surface analysis. Scanning electron microscopy (SEM) was used to determine the morphology of the zeolites, while inductively coupled mass spectrometry (ICP-MS), Fourier transformed infrared spectrometry (FT-IR) and Cation exchange capacity (CEC) [Report to Water Research Commission, RSA (2003) 15] techniques were used for chemical characterisation. The heavy and trace metal concentrations of the zeolite products were compared to that of the post-synthesis filtrate and of the precipitate materials used as Si and Al feed stock for zeolite formation, in order to determine the trends (increase or decrease) and ultimate fate of any toxic metals incorporated in the co-disposed precipitated residues.     

Distribution of Europium Ions in Ion-Exchanged NaX and NaY Zeolites

The chemical environments of europium-exchanged NaX (Si/Al =1.16) and NaY (Si/Al = 2.29) zeolites have been investigated by means of ¹²⁹Xe NMR and isotherm measurements of adsorbed xenon. EuNaX and EuNaY samples with varied concentrations of Eu cations were subjected to diverse chemical and thermal treatments, namely dehydration, reduction, oxidation, and re-reduction. Thermal analyses of hydrated EuNaX and EuNaY samples indicate that both the structural stability and the saturation concentration of water increase with increasing Eu content. For dehydrated EuNaY zeolites, the Eu³⁺ cations tend to replace Na⁺ ions at S2 sites and tend to be located in framework supercages; similar behavior is found for Eu²⁺ ions after reduction. After subsequent oxidation, Eu³⁺ ions migrate from supercages into small sodalite and/or D6R cages; similar results were deduced for samples after re-reduction. In contrast to the behavior observed in EuNaY, Eu³⁺ ions tend to exchange for Na⁺ ions in the sodalite and/or D6R cages in dehydrated EuNaX zeolites, regardless of the thermal treatment; this behavior is ascribed to the existence of unlocalized S3 Na⁺ in EuNaX samples.     

Die Kristallstruktur des Natriumoxohydroxoaluminathydrates Na2[Al2O3(OH)2] · 1,5 H2O

The Crystal Structure of the Sodium Oxohydroxoaluminate Hydrate Na₂[Al₂O₃(OH)₂] · 1.5 H₂O The crystal structure of the sodium oxohydroxoaluminate hydrate Na₂[Al₂O₃(OH)₂] ·s 1.5 H₂O (up to now described as Na₂O · Al₂O₃ · 2.5 H₂O and Na₂O · Al₂O₃ · 3 H₂O, respectively) was solved. The X-ray single crystal diffraction analysis (tetragonal, space group P-42₁m, a = 10.522(1) Å, c = 5.330(1) Å, Z = 4) results in a polymeric layered structure, consisting of AlO_3/2(OH) tetrahedral groups. Between these layers the Na⁺ ions are situated, which form tetrameric groups of face-linked NaO₆ octahedra. The involved O^2? ions are due to Al? O? Al bridges, Al? OH groups and water of crystallization. ²⁷Al and ²³Na MAS NMR investigations confirm the crystal structure analysis. The relations between the crystallization behaviour of the compound and the constitution of the aluminate anions in the corresponding sodium aluminate solution and in the solid, respectively, are discussed.     

Preparation of ZSM‐5 Coated on Monolithic Interconnected Macroporous Al2O3 Using Cheap n‐Butylamine as Template

Using cheap n‐butylamine as template, ZSM‐5 zeolites have been successfully synthesized and coated on monolithic interconnected macroporous Al₂O₃ by the secondary growth method. The use of cheap n‐butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM‐5 zeolites were prepared from synthetic mixtures with different H₂O/Na₂O or SiO₂/Al₂O₃ ratio. The synthesized samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR) and N₂ adsorption‐desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n‐butylamine template as template. During the hydrothermal reaction process, the morphology of the micrometer‐sized support was well maintained. The irregular crystals were formed in a wide range of the H₂O/Na₂O or SiO₂/Al₂O₃ ratio of synthetic mixtures and coated on monolithic Al₂O₃. The relative crystallinity of the zeolites was highest at H₂O/Na₂O=250 or SiO₂/Al₂O₃=160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.     

Isoconversional Kinetics of Thermal Processes in Mixtures Based on Metakaolin and Sodium Hydroxide

This study investigated the thermal behavior of the mixtures 6Al₂Si₂O₇: 12NaOH and 6Al₂Si₂O₇: 12NaOH: 2Al₂O₃ which are designed for synthesis of LTA (Linde type A) zeolite. XRD, SEM, and Synchronous thermal analysis (STA) have been used. It was found that after evaporating suspensions, molding pellets, and drying, small amounts of LTA and sodium hydroaluminates have been formed in the sample. The removal of crystallization water occurs on heating up to 400°C. In the temperature range from 400 to 850°C, Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈ are synthesized by interaction of metakaolin with sodium hydroxide. The formation of mullite and nepheline is also observed. It was shown that preactivation of powders in the vibratory mill allows reducing the starting temperature of synthesis at 50–100°C. For the range 400–850°C using Ozawa–Flynn–Wall analysis, the values of apparent activation energy and preexponential factor have been calculated. It was established that the apparent activation energy for mixtures without preactivation made 200–290 kJ mol⁻¹. After preactivation, E values decreased to 130–170 kJ mol⁻¹. Also it was shown that alumina excess inhibits nepheline and mullite formation.     

Breaking the Passivation: Sodium Borohydride Synthesis by Reacting Hydrated Borax with Aluminum

A significant obstacle in the large-scale applications of sodium borohydride (NaBH₄) for hydrogen storage is its high cost. Herein, we report a new method to synthesize NaBH₄ by ball milling hydrated sodium tetraborate (Na₂B₄O₇ ⋅ 10H₂O) with low-cost Al or Al₈₈Si₁₂, instead of Na, Mg or Ca. An effective strategy is developed to facilitate mass transfer during the reaction by introducing NaH to enable the formation of NaAlO₂ instead of dense Al₂O₃ on Al surface, and by using Si as a milling additive to prevent agglomeration and also break up passivation layers. Another advantage of this process is that hydrogen in Na₂B₄O₇ ⋅ 10H₂O serves as a hydrogen source for NaBH₄ generation. Considering the low cost of the starting materials and simplicity in operation, our studies demonstrate the potential of producing NaBH₄ in a more economical way than the commercial process.     

Combinatorial Approach to the Hydrothermal Synthesis of Zeolites

One hundred or more solid-state syntheses can be conducted in parallel and employed for the combinatorial hydrothermal syntheses of zeolites by using a novel multiautoclave design. The operation of the multiautoclave was ascertained by the reinvestigation of the complete Na₂O-Al₂O₃-SiO₂ ternary system in a single experiment. In the picture on the right, the shaded areas on the left show the crystallization fields of the different phases obtained.     

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P₂O₅/SiO₂ and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al₂O₃:1.0 P₂O₅:1.2 DPA:0.3 SiO₂:120 H₂O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P₂O₅/SiO₂ molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m²/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.     

MAS-NMR investigations of the crystallization behaviour of lithium aluminum silicate (LAS) glasses containing P2O5 and TiO2 nucleants

Lithium aluminum silicate (LAS) glass of composition (mol%) 20.4Li₂O-4.0Al₂O₃-68.6SiO₂-3.0K₂O-2.6B₂O₃-0.5P₂O₅-0.9TiO₂ was prepared by melt quenching. The glass was then nucleated and crystallized based on differential thermal analysis (DTA) data and was characterized by ²⁹Si, ³¹P, ¹¹B and ²⁷Al MAS-NMR. XRD and ²⁹Si NMR showed that lithium metasilicate (Li₂SiO₃) is the first phase to c form followed by cristobalite (SiO₂) and lithium disilicate (Li₂Si₂O₅). ²⁹Si MAS-NMR revealed a change in the network structure already for the glasses nucleated at 550 °C. Since crystalline Li₃PO₄, as observed by ³¹P MAS-NMR, forms concurrently with the silicate phases, we conclude that crystalline Li₃PO₄ does not act as a nucleating agent for lithium silicate phases. Moreover, ³¹P NMR indicates the formation of M-PO₄ (M=B, Al or Ti) complexes. The presence of BO₃ and BO₄ structural units in all the glass/glass-ceramic samples is revealed through ¹¹B MAS-NMR. B remains in the residual glass and the crystallization of silicate phases causes a reduction in the number of alkali ions available for charge compensation. As a result, the number of trigonally coordinated B (BO₃) increases at the expense of tetrahedrally coordinated B (BO₄). The ²⁷Al MAS-NMR spectra indicate the presence of tetrahedrally coordinated Al species, which are only slightly perturbed by the crystallization.     

Synthesis and structural chemical examination of faujasite type zeolite and its new structural modification

On the basis of the aluminate solution of alumina production and sodium silicate a faujasite-type zeolite was synthesized as well as its new structural modification. Thermostability nature and temperature of dehydration of this zeolite were found. It is shown that the ratio of the starting components SiO₂/Al₂O₃ and Na₂O/Al₂O₃ greatly affects the direction of the crystallization of zeolites.     

MAS-NMR studies of lithium aluminum silicate (LAS) glasses and glass-ceramics having different Li2O/Al2O3 ratio

Emergence of phases in lithium aluminum silicate (LAS) glasses of composition (wt%) xLi₂O-71.7SiO₂-(17.7−x)Al₂O₃-4.9K₂O-3.2B₂O₃-2.5P₂O₅ (5.1≤x≤12.6) upon heat treatment were studied. ²⁹Si, ²⁷Al, ³¹P and ¹¹B MAS-NMR were employed for structural characterization of both LAS glasses and glass-ceramics. In glass samples, Al is found in tetrahedral coordination, while P exists mainly in the form of orthophosphate units. B exists as BO₃ and BO₄ units. ²⁷Al NMR spectra show no change with crystallization, ruling out the presence of any Al containing phase. Contrary to X-ray diffraction studies carried out, ¹¹B (high field 18.8 T) and ²⁹Si NMR spectra clearly indicate the unexpected crystallization of a borosilicate phase (Li,K)BSi₂O₆, whose structure is similar to the aluminosilicate virgilite. Also, lithium disilicate (Li₂Si₂O₅), lithium metasilicate (Li₂SiO₃) and quartz (SiO₂) were identified in the ²⁹Si NMR spectra of the glass-ceramics. ³¹P NMR spectra of the glass-ceramics revealed the presence of Li₃PO₄ and a mixed phase (Li,K)₃PO₄ at low alkali concentrations.     

Zur Kenntnis der kristallinen Phasen in den Systemen MO?Al2O3?H2O (MI = K,Na)

On the Crystalline Phases of the Systems M O? Al₂O₃? H₂O (M^I = K, Na) In the system K₂O? Al₂O₃? H₂O the compounds K₂O · Al₂O₃ · 3 H₂O, K₂O · Al₂O₃ · 2 H₂O and K₂O · Al₂O₃ · 1 H₂O exist. The results of ²⁷Al and ¹H NMR and IR spectroscopic investigations as well as thermoanalytical measurements confirm the existence of dimeric anions with tetrahedrally coordinated Al for the 3-hydrate. In the case of the two other hydrates higher molecular anions occur, also formed by AlO₄ tetrahedra. In the system Na₂O? Al₂O₃? H₂O a compound with a composition Na₂O · Al₂O₃ · 2,5 H₂O and two alkali oxide rich phases (Na/Al > 3) are observed. In monosodium aluminate hydrate there are highly polymerized anions with tetrahedrally coordinated Al, whereas the alkali oxide rich phases are probably built up by monomeric [Al(OH)₆]^3? anions.