Search

The increasing production of sewage sludge at global level has addressed the search for technical solutions to take advantage from it, reducing the environmental burden originating from its disposal. Anaerobic digestion is a suitable option to handle sewage sludge in accordance with circular economy principles, as it generates a methane-rich biogas and a digestate with potential fertilizing properties. Several techniques have been proposed to enhance anaerobic digestion performances and, among these, the application of static magnetic field (SMF) has recently gained attention. Nonetheless, the effects of high-intensity SMF on the sewage sludge destined to anaerobic digestion and its impact on the anaerobic digestion process have not been evaluated yet. This study aims to determine the effects of a 1.5 T SMF on the chemical composition of sewage sludge as well as on methane generation during anaerobic digestion. The main parameters influencing the SMF (i.e., flow rate, mixing ratio of magnetized to non-magnetized sludge, number of pumping cycles, and total solid content) were varied to evaluate the impact of different exposure conditions on the chemical characteristics and methane potential of sewage sludge. An extensive exposure to the high-intensity SMF applied resulted in a 24% decrease of methane production, reduced the concentration of the monitored ionic species (i.e., NH4+, NO3−, PO43−, SO42− and Mg2+) in the liquid phase of sewage sludge, and promoted the precipitation of compounds with valuable fertilizing properties, e.g., struvite. These outcomes suggest that high-intensity SMF, although negatively influencing methane generation, can promote the precipitation, and possibly the recovery/recycle of valuable compounds from sewage sludge, enhancing its proper management in a circular economy perspective. Graphical abstract

The photo-catalytic degradation of a textile azo-dye as Methyl Orange was studied in an innovative unit constituted by a channel over which a layer of titanium dioxide (TiO2) catalyst in anatase form was deposited and activated by UVB irradiation. The degradation kinetics were followed after variation of the chemical, physical, and hydraulic/hydrodynamic parameters of the system. For this purpose, the influence of the TiO2 dosage (g/cm3), dye concentration (mg/L), pH of the solution, flow-rate (L/s), hydraulic load (cm), and irradiation power (W) were evaluated on the degradation rates. It was observed that the maximum dosage of TiO2 was 0.79 g/cm3 while for higher dosage a reduction of homogeneity of the cement conglomerate occurred. The Langmuir&ndash, Hinshelwood (LH) kinetic model was followed up to a dye concentration around 1 mg/L. It was observed that with the increase of the flow rate, an increase of the degradation kinetics was obtained, while the further increase of the flow-rate associated with the modification of the hydraulic load determined a decrease of the kinetic rates. The results also evidenced an increase of the kinetic rates with the increase of the UVB intensity. A final comparison with other dyes such as Methyl Red and Methylene Blue was carried out in consideration of the pH of the solution, which sensibly affected the removal efficiencies.

The low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purpo...

The recovery of iron and other heavy metals by the formation of Fe(III) (hydr)oxides is an important application of microbially-driven processes. The mineral characterization of the precipitates formed during Fe(II)-mediated autotrophic denitrification with and without the addition of Cu, Ni, and Zn by four different microbial cultures was investigated by X-ray fluorescence (XRF), Raman spectroscopy, scanning electron microscopy equipped with energy dispersive X-Ray analyzer (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray Powder Diffraction (XRD) analyses. Fe(II)-mediated autotrophic denitrification resulted in the formation of a mixture of Fe(III) (hydr)oxides composed of amorphous phase, poorly crystalline (ferrihydrite) and crystalline phases (hematite, akaganeite and maghemite). The use of a Thiobacillus-dominated mixed culture enhanced the formation of akaganeite, while activated sludge enrichment and the two pure cultures of T. denitrificans and Pseudogulbenkiania strain 2002 mainly resulted in the formation of maghemite. The addition of Cu, Ni and Zn led to similar Fe(III) (hydr)oxides precipitates, probably due to the low metal concentrations. However, supplementing Ni and Zn slightly stimulated the formation of maghemite. A thermal post-treatment performed at 650 °C enhanced the crystallinity of the precipitates and favored the formation of hematite and some other crystalline forms of Fe associated with P, Na and Ca.

The simultaneous removal of nitrate (15 mg N-NO3- L−1) and phosphate (12 mg P-PO43- L−1) from nutrient-polluted synthetic water was investigated in a recirculated pyrite-packed biofilter (RPPB) under hydraulic retention time (HRT) ranging from 2 to 11 h. HRT values ≥ 8 h resulted in nitrate and phosphate average removal efficiency (RE) higher than 90% and 70%, respectively. Decrease of HRT to 2 h significantly reduced the RE of both nitrogen and phosphorus. The RPPB showed high resiliency as reactor performance recovered immediately after HRT increase to 5 h. Solid-phase characterization of pyrite granules and backwashing material collected from the RPPB at the end of the study revealed that iron-phosphate, -hydroxide and -sulfate precipitated in the bioreactor. Thermodynamic modeling predicted the formation of S0 during the study. Residence time distribution tests showed semi-complete mixing hydrodynamic flow conditions in the RPPB. The RPPB can be considered an elegant and low-cost technology coupling biological nitrogen removal to the recovery of phosphorus, iron and sulfur via chemical precipitation.

The paper reports an experimental laboratory study aimed at investigating the effectiveness of low pressure grouting with nano-silica compounds as a remedial against liquefaction of sandy soils and to optimize the technique rendering it more attractive from the technical and economical viewpoint. The grout herein adopted is a three-component mix of an aqueous suspension of sub-micrometric silica particles, water and an aqueous solution of sodium chloride. The latter, raising the pH of the suspension triggers the formation of the silica gel that clogging the soil pores reduces the mobility of the grains and, hopefully, produces a stiffer response and a reduced contractive tendency of the material. A preliminary set of laboratory vane tests is performed to observe the gelling time of the material and fix the curing time of the samples by measuring the increase of shear resistance. Thus, reconstituted samples of a silica sand, manufactured at two different initial levels of density are treated with nano-silica grout prepared with a silica concentration ranging from 1.2% to 5.0% in weight. The samples are transferred into a fully servo-controlled triaxial cell and subjected to monotonic drained and cyclic undrained tests at variable stress amplitudes. The comparison among the monotonic tests on treated and untreated samples reveals an increase of peak strength and a more dilative tendency, increasing with the amount of injected silica. The comparison of cyclic undrained tests shows a lower tendency of the treated material to accumulate excess pore pressures with cycles and a retarded liquefaction proving that the grouting of sands with nano-silica can be profitably adopted to mitigate the effects of liquefaction of loose sandy deposits., http://papers.16ecee.org/files/16ECEE-Salvatore%20et%20al-2018.pdf

Recyclable aggregates of mesoporous titania with different anatase–rutile ratios have been prepared by thermal treatments of either amorphous or peptized precursors. These last two have been obtained by hydrolysis of either Ti(OC2H5)4 or of Ti(OC2H5)4 in mixture with 5 mol % Zr(OC3H7)4 at room temperature in the presence of NH4OH as a catalyzing agent. The anatase–rutile ratio, the recyclable aggregates of the nano-sized particles, the mesoporosity, the surface area and the crystallinity of the resulting crystallized products of titania can be controlled by the synthesis parameters including: concentration of ammonia catalyst, stirring time and concentration of the peptizing HNO3, drying method of peptized precursors, calcination temperature, and finally the ramp rate up to the titania crystallization temperature. A broad range of synthesis parameters control the crystal sizes of titania particles produced. This allows catalyst preparation with very different crystal size, surface area, anatase to rutile crystal ratio and various mesoporous structures. Drying by lyophilization of precursors reduce the aggregation of the primary particles giving micro-/macroporous structures.

The paper represents the “state of the art” on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditional and innovative Portland-free lime-based mortars in the conservation of cultural heritage, and the recycling and management of wastes to reduce consumption of natural resources in the production of construction materials. The latter is one of the main concerns in terms of sustainability since nowadays more than 75% of wastes are disposed of in landfills.

This work reports on the fundamental properties of nanostructured catalysts active in the main carbon oxides’ conversion processes for sustainable energy supply: methanation and co-methanation of CO2. Transition metals (e.g. Ni, Pd, Pt, Co, Ru, Rh) are active species in both reactions. Ni has been the most studied because of its cheapness. Monometallic and bi-metallic Ni and Ni3Fe catalysts supported on Gadolinia-doped ceria (GDC) have been synthesized, characterized and tested in the temperature range 200–600[Formula: see text]C. In the methanation reaction, the monometallic catalyst showed higher performance with respect to the bi-metallic catalyst. At 400[Formula: see text]C, the CO2 conversion overcomes 90% with CH4 selectivity of 100%. In co-methanation, the highest CO2, CO and H2 conversion values over monometallic Ni/GDC catalyst were obtained at 300[Formula: see text]C; at higher temperatures, conversion decreases. The GDC support plays a pivotal role in both reactions, enhancing the basicity of the catalyst and improving the dissociation of carbon oxide species adsorbed on Ni sites.

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Photocatalytic degradation of atenolol in aqueous suspensions using specifically synthetized mesoporous based TiO2 materials as photocatalysts under UVC (254 nm) irradiation was investigated. A batch reactor and a UV lamp 16 W power were used to test the ATL removal with several initial concentrations of ATL (4.5 - 30 mg/L) and four synthetized TiO2 photocatalysts, characterized by different BET surface areas and average pore sizes. Moreover, the effect of solution pH (4.8 - 9.0) and of the oxygen presence were investigated. The performances of the synthetized photocatalysts were compared with commercial Degussa P25. The atenolol degradation was studied using different concentration of catalyst (50 and 1000 mg/L) showing a maximum removal efficiency of 65%. Although the new catalysts showed a lower efficiency when compared to commercial P25, they can be easily recovered from water being in the form of micro-aggregate, and then reused without remarkable changes. The experimental data were fitted using a pseudo first order kinetic model. © 2017 Elsevier Ltd. All rights reserved.

Magnetite nanoparticles (Fe3O4) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C2H5)4NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

Sintering of yttria (8 mol%)–zirconia ceramics assisted by one or two driving forces was performed using nanosized precursors hydrothermally synthesized. Two monophasic precursors, both containing 8 mol% of yttria, were hydrothermally synthesized from amorphous zirconia–yttria co-precipitate and from a mechanical mixture of amorphous zirconia with crystalline yttria, respectively. Two diphasic precursors, characterized by the same yttria content (8 mol%), were obtained mixing in an equal molar ratio two hydrothermally synthesized powders with yttria content of 2 and 14 mol%, respectively. By applying a same pressureless heating schedule, the different precursors, previously pressed by cold isostatic pressing, were sintered and characterized. The diphasic precursors assisted on sintering by the double driving force, the surface area and the composition gradient, show an exaggerated formation of the grain boundary interfaces in comparison to that of the monophasic precursors sintered in the presence of the single driving force, the surface area.

A method for determining the effective and long aging time of lime putty, a feature which favors better quality of the corresponding lime mortar, is proposed. Different quicklime precursors were slaked under an excess of water for different times ranging from 3 to 66 months. Each of resulting lime putty was dehydrated by lyophilization and after characterized by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), and surface area. Taking into account the impurity contents present in the starting quicklime, the mineralogical composition of each lime putty was determined from the weight loss related to the amount of adsorbed water and to the weight losses related to the decomposition of mineral phases present in the lime putty such as brucite, Mg(OH)2, portlandite, Ca(OH)2 and calcite, CaCO3, respectively. The total mineralogical composition of lime putties aged for a time higher than 12 months was close to the expected value of 100%, while such value resulted lower than 100% for lime putties aged for lower times. To justify such result, an incomplete hydration of the quicklime precursor must be considered for lime putties aged for lower times. The delayed hydration can be related to the presence of over burnt of some particles of lime present in the starting quicklime.

This paper reports significant results about the effects of repeated treatments to protect a mediaeval Italian mortar from capillarity-absorbed water, by using for the treatments, our no-commercial hydro-alcoholic suspensions ofcalcium hydroxidenanoparticles(nanolime). The mortars samples came from the historical site, where preliminary thermographic inspection were performed to detect the damp zones. Before treatments, the samples were analyzed from a mineralogical and chemical point of view, by means of several techniques, asoptical microscopy(OM), thin section observations (PFM), porosimetric investigations, X-ray fluorescence (XRF), X-ray diffraction (XRD),infrared spectroscopy(FT-IR) and thermal analysis (TG-DTA). The size-grading curve of the aggregate and the binder/aggregate ratio were examined too. Then, the efficacy of nanolime protective treatments on this mortar versus the nanolime concentrations was investigated. For this aim, capillarity tests as well as porosimetric investigations, before and after the treatments, were performed. The obtained results were remarkably promising both in terms of the reduction of water absorbed by capillarity (up to 60%) together with an adequate decrease of porosity (up to 23%), fixing the protective effect of such eco-friendly and very compatible approach.

Mixed titanium (IV) and zirconium (IV) alkoxides were co-hydrolyzed either at room temperature or at 140 °C in the presence of ammonium-containing catalysts such as hydroxide, carbonate, chloride or nitrate. Mesoporous aggregates of Zr-doped (5 mol%) titania have been obtained at 140 °C and in the presence of catalyzing NH 4 OH or NH 4 Cl, respectively, whereas only microporous products resulted in performing the remaining treatments. By calcination at 400 °C the microporosity of the products drastically was reduced while their mesoporosity was preserved, contemporaneously the crystallization of anatase-type TiO 2 was favoured. The formation mechanism of mesopores in the absence of a templating agent is a consequence of a thermal interconnection of the primary particles with packed inter-particle spaces responsible of the mesoporosity. Such formation is discussed in terms of nature of catalyzing agent, alcoholic media, temperature and treatment time of hydrolysis.

Adopting four different drying modalities on three single stocks of hydrous zirconia gel, 12 samples of pure zirconia xerogels were obtained. In particular, the following drying modalities were adopted: drying in air at room temperature, drying in air oven at 60° or 110°C, and, finally, drying by freeze-drying. The resulting xerogels showed, on heating, very different reactivity, affecting the structural phase transformations of pure zirconia. The kinetics feature could be the key to explain the formation mechanism of the metastable phases of zirconia at room temperature. The experimental results show, in fact, that the metastable phase is favored by a fast crystallization rate, whereas the stable one, by a slow crystallization rate. These findings could resolve the conflicting results on the metastability of zirconia reported in the literature.

This letter summarizes the literature data on the synthesis of layered double hydroxides (LDHs) in order to demonstrate that the preparation by reconstruction method is not based on the memory effect but it is simply a direct synthesis of these attractive solids.

This letter summarizes the literature data on the synthesis of layered double hydroxides (LDHs) in order to demonstrate that the preparation by reconstruction method is not based on the memory effect but it is simply a direct synthesis of these attractive solids.

The effects of an innovative hydrophobic treatment and moisture content on thermal conductivity of lightweight mortars were investigated. The aim of this study was to provide data on the insulating properties of the above mentioned mortars, that can be used in engineering practice, once properly processed. Various mortars were prepared by mixing Portland cement and/or lime with different granulated aggregates such as Neapolitan tuff, expanded clay or siliceous standard sand. After a curing time of 28 days, a set of mortars was directly tested in terms of thermal conductivity at different moisture content, comparing the results obtained from the corresponding mortars previously submitted to hydrophobic treatment. Finally, the effects of hydrophobic treatment on other physical properties such as water vapour permeability and capillary rise were also investigated.

A coprecipitated xerogel having the composition of 90 vol.% zirconia (3 mol% Y 2 O 3 ) and remaining 10 vol.% alumina was crystallized under hydrothermal conditions by adopting conventional (110 °C for 7 days) or microwave (250 °C for 2 h) routes. The hydrothermal treatments of crystallization were performed in the presence of (KOH+K 2 CO 3 ) (K), (CH 3 ) 4 NOH (TMA), or (C 2 H 5 ) 4 NOH (TEA) mineralizer solutions at different concentrations. The role of the two different hydrothermal routes, of the nature and the concentration of the mineralizer solution on the thermal behaviour of the resulting powders are discussed.

The thermal transformation of Ba- and (Ba+Li)-exchanged precursors of zeolites A and X into monoclinic celsian has been investigated by X-ray diffractometry, differential thermal analysis, and thermodilatometry. Upon the proper thermal treatment either Ba-exchanged zeolite A or X give rise to the following transformations: zeolite→amorphous phase→hexacelsian→monoclinic celsian. Zeolite A-based precursors are more reactive than zeolite X-based precursors allowing all the reported transformations to occur at far lower temperatures starting from Ba-exchanged zeolite A rather than from Ba-exchanged zeolite X. In particular, starting from zeolite X-based precursors, fully monoclinic celsian may be obtained after 24 h at 1550°C in the absence of Li and after 6 h at 1100°C in the presence of Li, whereas starting from zeolite A-based precursors it may be obtained after 6 h at 1100°C in the absence of Li and by slow heating (1°C/min) up to 900°C in the presence of Li.

A wide spectrum of mesoporous titania (TiO2) materials has been synthesized by co-hydrolysis of titanium tetraethoxide in mixture with zirconium tetraisopropoxide (5 mol%) by changing the hydrolysis temperature, from 110 °C to 140 °C, the reaction time, from 20 h up to 144 h, the catalyst, NH4OH or NH4Cl, and the alcoholic media, ethanol or isopropanol. For short reaction times and/or for low temperatures of hydrolysis, micrometer aggregates of amorphous and microporous products were obtained. By increasing both the reaction time and temperature, the crystallization of TiO2-anatase occurs with a strong change of micropores into mesopores. In this work are discussed the numerous parameters which affect the crystallization of TiO2, allowing to obtain a wide spectrum of mesoporous materials characterized by crystal sizes and average pore diameters ranging between 9 nm and 38 nm and from 2.5 nm to 16 nm, respectively.

The microstructure evolution of lime putty upon aging was investigated by slaking quicklime (CaO) with an excess of water for 3, 12, 24, 36, 48 and 66 months. The as-obtained lime putties were characterized in the water retention and in the particle size distribution using the static laser scattering (SLS). The same lime putties, dehydrated by lyophilization, were also investigated in the pore size distribution by mercury intrusion porosimetry, in the surface area by the BET method and, finally, in particle morphology by scanning electron microscopy (SEM). The effect of the extended exposure of quicklime to water confirms a shape change from prismatic crystals of portlandite, Ca(OH)(2), into platelike ones. Simultaneously a growth of larger hexagonal crystals at the expense of the smallest ones (Ostwald ripening) favours a secondary precipitation of submicrometer platelike crystals of portlandite. The shape change and the broader particles size distribution of portlandite crystals upon aging seem to contribute to a better plasticity of lime putty. (C) 2010 Elsevier B.V. All rights reserved.

Mechanical mixtures of zirconia xerogel with variable content of crystalline Y2O3 up to 25 mol%, were hydrothermally treated by microwave route at 110 °C for 2 hours in the presence of 0.2 M solution of (KOH+K2CO3) mineralizer. The resulting amorphous hydrated zirconia-yttria solid solutions with a maximum solubility of Y2O3 content between 20 ~ 25 mol%, showed a remarkable reduction of the surface area at the increasing Y2O3 content of the starting mixture. The as-synthesized products and the corresponding calcined powders at 400 °C were uniaxially pressed into pellets (10 x 7 x 2 ~ 4 mm, in width) at 150 MPa. Conductivities were measured at 25 °C by AC impedance method with a frequency range from 10 Hz to 1 MHz with the pellets equilibrated either under silica gel or under increasing relative humidity (RH) up to ~90 %. The effects of composition, surface area, calcination temperature and relative RH on the proton conductivity of the amorphous solid solutions are discussed.

Nanocrystalline ytterbia (10 mol%)-doped cubic zirconia powders were synthesized by hydrothermal treatment of either an amorphous co-precipitate of hydrated ytterbia–zirconia or of zirconia xerogel in mixture with crystalline Yb 2 O 3 . The treatments were performed at 110 °C in the presence of diluted (0.2 M) or concentrated (2.0 M) solution of (K 2 CO 3 + KOH) mineralizer and for different reaction times. The reaction times for the full crystallization of cubic-YbSZ-based products were determined for both the employed precursors and for each mineralizer solution. The various fully crystallized products were characterized in their degree of agglomeration and sintered at 1500 °C for 2 h. The best performance on sintering was achieved with the less agglomerated powder synthesized from the mechanical mixture and in the presence of the diluted solution of the mineralizer. The resulting density was the highest achieved with materials having the same composition.

Nanocrystalline powders of yttria (8 mol.%)-stabilized zirconia have been hydrothermally synthesized from mechanical mixture of ZrO 2 xerogel and crystalline Y 2 O 3 by conventional or microwave route, respectively. The treatments have been performed at 110 and/or 150 °C for 2 h up to 72 h, and in the presence of diluted (0.2 M) or concentrated solution (2.0 M) of (KOH + K 2 CO 3 ) mineralizer. To reduce the degree of agglomeration, the freshly synthesized powders has been treated under stirring with aqueous solution of poly(vinyl alcohol) (PVA 10 wt.%) for 15 h at pH 6.8, whereas to favour the formation of coating suspensions, the polymer absorbed powders and poly(ethylene glycol) (PEG) have been added to ethanol/water solution and stirred under ultrasonic agitation. With the different suspensions, various films have been deposited on glass substrates through withdrawal-coating. After drying at 60 °C and firing at 600 °C, the texture of the different films has been examined and compared with analogous films deposited by the sol–gel method. The effects of both the type of hydrothermal treatment, the concentration of the mineralizer, and the withdrawal-coating speed on the texture of the films are discussed.

Mechanical mixtures of zirconia xerogel and crystalline Y 2 O 3 were hydrothermally treated by microwave and traditional route, respectively. Some mixtures were used either as powders form or as cylindrical compacts isostatically pressed at 150 MPa. The microwave–hydrothermal treatments were performed at 110, 150 and 200 °C for reaction times up to 2 h, whereas the traditional hydrothermal treatments were performed at 110 °C at increasing reaction times up to 7 days. All the treatments were performed in the presence of diluted (0.2 M) or concentrated (2.0 M) solution of (K 2 CO 3 +KOH) mineralizer. The crystallization–stabilization mechanism of synthesized Y-based zirconia powders and the reaction times for the full crystallization at the low temperature of hydrothermal treatments are discussed.

Summary Mechanical mixtures containing zirconia xerogel and increasing amount of crystalline yttria up to 40 mol%, were hydrothermally treated by microwave route at 110°C for 2h. All the treatments were performed in the presence of (KOH+K2CO3) mineralizer solution at concentration 0.2 M. Amorphous and hydrated ZrO2-Y2O3 solid solutions with yttria content up to 33.3 mol% (corresponding to Zr/Y molar ratio equal to 1), resulted after the hydrothermal treatments. A remarkable reduction of the surface area has been detected at increasing yttria content of the amorphous phases with a corresponding increase of the exothermic peak of crystallization. A mechanism of reaction for the formation of the amorphous solid solutions has been proposed.

The zeolite 4A (Na12Al12Si12O48·27H2O) was subjected to cationic exchange with an aqueous solution of Li+ 0.5 M at 70 °C. After three exchanges for 24 h, about 100% of Na+ was removed obtaining the Li-exchanged form (Li)-A. Despite this quite complete exchange, some undesired and occluded NaAlO2 was detected in the typical structural cages of precursor. The partial exchange of Li with equivalent amounts of Ca or Mg, allowed the formation of (Li–Ca)- or (Li–Mg)-exchanged zeolitic forms characterized by different Ca or Mg contents, respectively. These various zeolitic precursors have been thermally treated at increasing temperatures up to 1170 °C. The transformations into other crystalline phases occur immediately after the formation of intermediate amorphous phases originating from the thermal collapse of zeolitic precursors. From the (Li)-A zeolite-based precursor, a small amount of nepheline (NaAlSiO4) and β-eucryptite (LiAlSiO4) crystallize, while during the thermal transformation of Li–Ca-containing precursors, anorthite [(Ca,Na)Al2Si2O8] and β-eucryptite-like phase are formed. Stuffed derivatives of quartz relatively richer in SiO2 crystallize from (Li–Mg)-containing precursors. The Mg content of the zeolitic precursor affects the type of secondary crystallized phases and consequently the composition of the corresponding stuffed derivative of quartz.

The thermal transformation of a sample of Ba-exchanged zeolite A, containing a residual Na content of 0.20 meq/g, into monoclinic celsian is thoroughly investigated. The samples were thermally treated at temperatures ranging from 200 to 1500 °C for times up to 40 h and subsequently were characterized by room-temperature X-ray diffraction. The following are the main results of this investigation:(1) Above 500 °C, the presence of small crystalline aggregates of monoclinic celsian dispersed in the amorphous phase arising from the thermal collapse of Ba-exchanged zeolite A is recorded.(2) Above 900 °C, crystallization of hexacelsian occurs.(3) Above 1100 °C, hexacelsian converts into monoclinic celsian. The conversion is complete with thermal treatments at 1300, 1400, and 1500 °C within 22, 15, and 22 h, respectively.The presence of monoclinic celsian nuclei above 500 °C appears to favor the conversion of hexacelsian into monoclinic celsian at temperatures higher than 1100 °C. The residual Na content of Ba-exchanged zeolite A was found to strongly affect the temperatures and times at which the transformations of amorphous phase → hexacelsian and hexacelsian → monoclinic celsian occur. Actually a higher Na residual content results in lower temperatures and times, ceteris paribus.