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An experimental study has been carried out to determine the compositions of the slag/matte/metal/tridymite phases in equilibrium in the Cu-Fe-O-S-Si system at 1200℃. The measurements covered the full range of matte compositions from copper-free mattes to white metal, i.e. from 0 to 80 wt% of copper in matte. The research methodology involved high-temperature equilibration, quenching of the samples and accurate measurement of the phase compositions by electron probe X-ray microanalysis. The oxygen concentrations in mattes were directly measured using the EPMA. A comprehensive set of experimental equilibrium data has been obtained for coexisting matte, slag, Cu-Fe metal alloy and Fe-Cu metal alloy phases. It has been shown that solid iron-copper alloys were present at matte grades below 56 wt% Cu, while liquid copper-iron alloys were formed for matte grades higher than 56 wt% Cu. The experimental measurements have been compared with data reported in the literature and the trends calculated using the thermodynamic model descriptions of the system.

Phase equilibria of the PbO-“FeO”-SiO2 and PbO-“FeO”-CaO-SiO2 slags with liquid Pb metal, solid or liquid Fe metal and solid oxides [cristobalite and tridymite SiO2, wustite (Fe,Ca)O1+x, olivine (Fe,Ca)2SiO4, dicalcium silicate (Ca,Fe)2SiO4, wollastonite (Ca,Fe)SiO3 and lime (Ca,Fe)O] were investigated at 1100-1689 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Ca, and Si concentrations in the phases with the electron probe x-ray microanalysis (EPMA) was used to accurately characterize the system. Present results provide important basis for improvement of the thermodynamic models for all phases in this system.

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was −0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper.

The formation of nanosized particles in pure silica glass irradiated in water in the reactor core with fast neutrons up to 1019 cm-2 and gamma radiation has been studied by optical spectroscopy and X-ray diffraction. Irradiation with neutrons leads to the destruction of the initial mesostructure of a - and β - quartz with dimensions of 1.7 and 1.2 nm and the formation of cristobalite and tridymite nanocrystallites with dimensions of 16 and 8 nm in displacement thermal peaks.

A combined experimental and thermodynamic study has been carried out to determine the CaO effect on the equilibria between slag/matte/metal (Fe or Cu)/tridymite phases in the Cu-Fe-O-S-Si-Ca system at 1473 K (1200 °C). The experimental methodology included equilibration of the mixtures at high temperatures on substrates made from the primary phase, followed by rapid quenching of the samples and direct measurement of the condensed phase compositions using the Electron Probe X-ray Microanalysis (EPMA) technique. New experimental results have been obtained for fixed concentrations of CaO in slag phase (1.5, 6, 9, and 18 wt pct). All results have been plotted as functions of the copper concentration in the matte phase and provides information about the effect of CaO on the oxygen and sulfur concentration in the matte phase; the Fe/SiO2 ratio in slag; and dissolved copper and sulfur in slag. The experimental research is part of integrated experimental and thermodynamic study aimed to development and optimisation a thermodynamic database for copper-containing systems of non-ferrous metallurgy.

This article provides data on cristobalite and tridymite from the Arsenatnaya active fumarole of the Tolbachik volcano, Kamchatka, Russia. The minerals occur in associations with fumarolic sylvite, sanidine, cassiterite, hematite, pseudobrookite, johillerite, tilasite, and badalovite. Fumarolic cristobalite is tetragonal (α-modification); the unit-cell parameters for one sample are: а = 4.975 (7) A, с = 6.944 (13) A, and V = 171.89 A3. There are two types of tridymite, that is, monoclinic (MC) and orthoorthorhombic (PO-10), in the Arsenatnaya fumarole. The unit-cell parameters of these tridymite modifications are: a = 18.553 (5) A, b = 5.006 (1) A, с = 25.952 (10) A, β = 117.68 (2)°, V = 2134.3 (11) A3 (MC); a = 9.941 (2) A, b = 17.165 (4) A, с = 82.362 (18) A, and V = 14053.4 (29) A3 (PO-10). Mineral assemblages of cristobalite and tridymite indicate high-temperature formation conditions of these minerals not lower 450–500°С with considerable participation of HCl and HF in process of basalt alteration by fumarolic gas. The surrounding basalt was a source of silicon. This element was probably transported in the form of SiX4, where X = F, Cl.

New experimental measurements have been made to determine liquidus isotherms, univariant and invariant equilibria in the FeO-Fe2O3-CaO-SiO2, CaO-SiO2 and FeO-Fe2O3-SiO2 systems in air at temperatures between 1190 °C and 1730 °C. The study was undertaken using equilibration/quenching and microanalysis techniques, enabling the compositions of the liquid and solid phases in equilibrium at temperature to be accurately measured. The data have been used to define liquidus in the primary phase fields of hematite (Fe2O3), spinel [(Fe,Ca)O·Fe2O3], lime (CaO), tridymite or cristobalite (SiO2), dicalcium ferrite (2CaO·Fe2O3, C2F), pseudo-wollastonite (CaO·SiO2, CS), rankinite (3CaO·2SiO2, C3S2), dicalcium silicate (2CaO·SiO2, C2S), tricalcium silicate (3CaO·SiO2, C3S) and the two liquids miscibility gap. These data obtained in the present study provide a more complete and more accurate description of the multi-component Fe-Ca-Si-O-Al-Mg-Cu-S system directly relevant to applications in the cement, the ferrous and non-ferrous metallurgical industries.

The distributions of arsenic, lead, tin and zinc between iron silicate slag and copper in equilibrium with tridymite in the Cu–Fe–O–Si system have been experimentally determined at selected oxygen partial pressures (P(O2)) at temperatures of 1 523 K and 1 573 K. The experimental technique involved high temperature equilibration in a sealed silica ampoule to minimize the vaporization of minor elements, rapid quenching of the condensed phases, and the direct composition measurements of the condensed phases using microanalysis techniques. The effective P(O2)s of the samples were determined based on the measured Cu2O concentrations in slag. The new experimental data resolve discrepancies found in previous studies and have been used in the development of a new thermodynamic database of the Cu–Fe–O–Si system containing minor elements.

The study of silica polymorphs in impactites is important for determining the pressure and temperature of impact rock formation. Silica modifications in impact melt rocks of the Janisjärvi impact structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite and coesite. Silica modifications were characterized and studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman and cathodoluminescent spectroscopy. Investigations were carried out in order to clarify polymorphs formation mechanisms and search for signs of the transition of certain structural modifications to others. For the first time, a description of tridymite with a ballen-like texture from impact melt rock is given. A sequence of silica modification and textural transformation in impact rocks after the impact event is suggested. We conclude that the pressure of 40 GPa and a temperature of more than 900 °C were achieved in the impact structure.

The main aim of this work was to perform low-temperature synthesis of glass-ceramics with YNbO4:Eu3+ crystallites and study the structural and luminescent properties of the samples synthesized. The inclusions crystallized in the ЅіО2–Na2О–K2O–Y2O3–Nb2O5–Eu2O3 (SiNaK) and B2O5–Na2О–Y2O3–Nb2O5–Eu2O3 (BNa) systems under the conditions of low-temperature synthesis were studied for the first time. It was shown that YNbO4:Eu3+ was crystallized in both systems under study. In the SiNaK system, SiO2 (quartz, cristobalite, and tridymite) was also crystallized under the chosen conditions. The BNa system was found to be most promising for the synthesis of doped glass-ceramics with YNbO4 because this system allows formation of only the desired crystallites. The luminescent properties of crystalline inclusions were studied by local cathodoluminescence. The glass-ceramics composition and structure were studied by X-ray spectral microanalysis and X-ray diffraction analysis.

International audience; The stuffed tridymite structure Ba(Zn/Co)1−xSi1−xM2xO4 (M=Al3+ and Fe3+) is explored for the possible multiferroic behavior and to develop new inorganic colored materials. The compounds were synthesized by employing conventional solid-state chemistry methods in the temperature range 1100–1175 °C for 24 h. The powder X-ray diffraction (PXRD) and Rietveld refinement studies indicate that the compounds stabilize in the P63 space group (no. 173). The refinement results were also rationalized by employing Raman spectroscopic studies. The compounds were found to be second harmonic generation (SHG) active and show weak ferroelectric behavior. The co-substitution of Co2+ and Fe3+ in the structure gives rise to a weak ferromagnetic behavior to the compound, BaCo0.75Si0.75Fe0.5O4, making it a multiferroic material. The optical studies on the prepared compounds exhibited blue color (Co2+ in Td geometry), purple color (Ni2+ in Td geometry), and simultaneous substitution of Co2+ and Fe3+ gives rise to blue-green color owing to metal-to-metal charge transfer (MMCT) effect.

The specific features of crystal chemistry and physical properties of phosphates (arsenates, vanadates) of alkali and transition metals, crystallized as derivatives of minerals ellenbergerite (Mg,Ti,Zr, $$\square $$ )2Mg6(A1,Mg)6(Si,P)2Si6O28(OH)10 and β-tridymite SiO2, have been analyzed in the aspect of flexibility of their radically different frameworks. The crystal chemical function of cations of transition metals in the structures of ellenbergerite- and tridymite-like analogs has been discussed. The data on their formation methods and thermodynamic and electrical properties are given. The reasons for the structural differences of tridymite-like phases and the relationship between the polymorphism and variations in the coordination polyhedra of transition metals, tending to the most stable configuration, have been investigated.

The conversion of rice crop residues into activated carbon (AC) and nanosilica was performed via an integrated procedure including successive carbonization, K2CO3 activation, and extraction steps. For the first time, rice husk and rice straw were utilized comparatively as the raw materials for parallel AC and silica production, and the main characteristics of the corresponding products were compared. However, AC produced from rice straw at 1000 °C and impregnation ratio of 1.5 showed a larger surface area and total pore volume (2229 m2/g and 1.6 cm3/g) than AC produced from rice husk (1941 m2/g and 1.5 cm3/g); no definite and general conclusion can be made about the superiority of rice straw as the raw material. This is attributed to the close characteristics of the products, the large variety of rice crop residues, and the strong influence of the operating conditions on the properties of products. The rice husk– and rice straw–based activated carbons had no significant difference in their functional groups and chemical characteristics. The amorphous silica nanosize particles (

The elusive structure of the mineral kaliophilite has been determined by 3D electron diffraction and refined using single-crystal X-ray data. Despite its simple formula, ideally KAlSiO4, the structure of this mineral remained a mystery for over a century as a result of pseudo-symmetry and twinning, which reduce the coherent crystalline domain size to a few hundreds of nanometres., Kaliophilite is a feldspathoid mineral found in two Italian magmatic provinces and represents one of the 12 known phases with composition close to KAlSiO4. Despite its apparently simple formula, the structure of this mineral revealed extremely complex and resisted structure solution for more than a century. Samples from the Vesuvius–Monte Somma and Alban Hills volcanic areas were analyzed through a multi-technique approach, and finally the crystal structure of kaliophilite was solved using 3D electron diffraction and refined against X-ray diffraction data of a twinned crystal. Results were also ascertained by the Rietveld method using synchrotron powder intensities. It was found that kaliophilite crystallizes in space group P3 with unit-cell parameters a = 27.0597 (16), c = 8.5587 (6) Å, V = 5427.3 (7) Å3 and Z = 54. The kaliophilite framework is a variant of the tridymite topology, with alternating SiO4 and AlO4 tetrahedra forming sheets of six-membered rings (63 nets), which are connected along [001] by sharing the apical oxygen atoms. Considering the up (U) and down (D) orientations of the linking vertex, kaliophilite is the first framework that contains three different ring topologies: nine (1-3-5) (UDUDUD) rings, six (1-2-3) (UUUDDD) rings and twelve (1-2-4) (UUDUDD) rings. This results in a relatively open (19.9 tetrahedra nm−3) channel system with multiple connections between the double six-ring cavities. Such a framework requires a surprisingly large unit cell, 27 times larger than the cell of kalsilite, the simplest phase with the same composition. The occurrence of some Na for K substitution (3–10%) may be related to the characteristic structural features of kaliophilite. Micro-twinning, pseudo-symmetries and anisotropic hkl-dependent peak broadening were also detected, and they may account for the elusive character of the kaliophilite crystal structure.

At production of hot-rolled product from middle-carbon and low-carbon steel, a surface defect “rolled-out bubble” is formed sometimes. To decrease rejections by surface defects like this one, it is necessary to know the mechanism of their origination. The comprehensive study by methods of micro-X-ray-spectral and X-ray-phase analysis on internal surface of the rolled-out bubbles and areas, located in the direct vicinity of the defects mentioned, allowed to determine the content of isolations, localized at the internal surface of the defects. The content was as follows (%, mas.): quartz - 24, tridymite - 28, magnetite - 48. By the method of differential scanning calorimetry the melting temperature of isolations on the internal surface of the rolled-out bubbles determined, amounted to 1178 dC, which corresponds to melting temperature of iron-silicon eutectic Fe 3 O 4 -SiO 2 . A mechanism of the defect “rolled-out bubble” formation proposed. According to the mechanism proposed, the inclusions of silicates, localized at the internal surface of the bubbles and complex inclusions based on silicon and iron oxides, form the low-melting eutectic of Fe 3 O 4 -SiO 2 type when interacting with oxygen of air during the heating before rolling. As a result of expanding forces during the rolling, in the surface metal layer, which has a liquid eutectic at the rolling temperatures, discontinuity flaws are formed. To avoid the defects it was proposed to keep the reheating and rolling temperature lower the melting temperature of the eutectic of Fe 3 O 4 -SiO 2 type. The corrected rolling regime allowed to exclude practically completely the rejections by defect “rolled-out bubble” and to decrease the metal consumption coefficient at production of rolled products from S355J2G3 and C45R steels.

To address the increasing complexity of feed materials to pyrometallurgical processes, an integrated experimental and thermodynamic modeling research program is in progress to accurately characterize the multi-phase gas-slag-matte-speiss-metal-solids 17-component Cu/Pb-(Cu2O-PbO-ZnO-CaO-FeO-Fe2O3-SiO2)-(Al2O3-MgO)-S-(As-Bi-Sb-Sn-Ag-Au-Ni) system. New experimental data are used to continuously improve the thermodynamic database using FactSage. An example is provided on the slag-matte distributions of Bi, Pb, and Zn in equilibrium with tridymite in the Cu-Fe-O-S-Si system under copper smelting conditions. A closed system equilibration experimental technique with rapid quenching was used. Major element concentrations in phases were measured with electron probe x-ray microanalysis. A laser ablation inductively coupled plasma mass spectrum technique was used for determination of Bi, Pb, and Zn concentrations in slag. New experimental data contributed to the optimization of thermodynamic model parameters. Improved thermodynamic databases can be used to accurately predict the elemental distributions in multi-component systems; an example is given for the minor element distributions between slag and matte for industrial conditions.

Experimental study on the phase equilibria between copper matte with silica-saturated iron silicate slags was conducted at 1300 °C and $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 = 0.5 atm. The high-temperature isothermal equilibration in silica crucibles under controlled flowing CO-CO2-SO2-Ar was followed by quenching in an ice–water mixture and direct phase composition analyses by an electron probe X-ray microanalyzer. The equilibrium compositions for matte and slag, as well as the distribution coefficients, were displayed as a function of matte grade. The data set obtained at $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 = 0.5 atm and the previous study at $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 = 0.1 atm by the authors enabled an investigation on the impacts of $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 as well as Al2O3 and CaO additions on phase equilibria in the multiphase copper matte smelting system. Thermodynamic calculations using MTDATA software were performed to compare the experimental results with modeling. The present results enrich the fundamental thermodynamic information for the matte/slag/tridymite/gas equilibria in the primary copper smelting process at high $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 .

The gas-slag-matte-tridymite equilibria in the Cu–Fe–O–S–Si system at 1200°C have been experimentally studied. An improved experimental technique was used, which includes high temperature equilibration of sulfide-oxide mixtures on silica substrates at p(SO) = 0.6 atm, preservation of the equilibrium phases by rapid quenching, and direct compositional analysis of the phases using microanalysis techniques. The new data have enabled the effects of sulfur dioxide partial pressure between 0.1 and 0.6 atm on the equilibria to be accurately determined. Whilst, for a given matte grade, the dissolved copper in slag is not sensitive to sulfur dioxide partial pressure, the Fe/SiO in slag in equilibrium with tridymite was found to increase with increasing p(SO). This latter observation has implications for fluxing practice in industrial copper smelting operations.

Experimental measurements have been made of the compositions of slag, matte and tridymite phases in chemical equilibrium in the Cu-Fe-O-S-Si system at 1300°C, p(SO) = 0.25 atm and selected oxygen partial pressures. The high temperature equilibration experiments were conducted using silica substrates under controlled CO-CO-SO-Ar gas atmospheres. The resulting phases obtained from the equilibrations were retained at room temperature through rapid quenching of the samples. The condensed phase compositions from the equilibrium experiments were measured by Electron Probe X-ray Microanalysis (EPMA). The data obtained in the present study, combined with those from previous studies, have enabled the liquidus slag temperature to be accurately described as a function of Fe/SiO ratio at p(SO) = 0.25 atm for temperatures between 1200 and 1300C and mattes containing from ∼44 to ∼ 78 wt pct Cu.

The new mineral fluorapophyllite-(NH4), ideally NH4Ca4(Si8O20)F⋅8H2O, was found at the Vechec andesite quarry located near Vechec village, Vranov nad Topľou Co., Prešov Region, Slovak Republic. It occurs in cavities of quartz–illite–saponite–tobelite xenolith embedded in pyroxene andesite. Fluorapophyllite-(NH4) is associated with calcite, tridymite, pyrite, chabazite-Ca and heulandite-Ca. It forms clusters, aggregates or crystalline crusts consisting of individual, well-developed crystals up to 4 mm in size, exhibiting the forms {110}, {101} and {001}. The mineral is colourless to light pink and translucent with white streak and vitreous to pearly lustre; it is non-fluorescent under ultraviolet radiation. The Mohs hardness is ~4½ to 5, tenacity is brittle, fracture is irregular, and there is perfect cleavage on {001}. The calculated density is 2.325 g cm–3. Fluorapophyllite-(NH4) is optically uniaxial (+) with ω = 1.5414(5) and ɛ = 1.5393(8) (λ = 589 nm). It is non-pleochroic. The empirical formula (based on 29 O + F apfu) is [(NH4)0.55K0.32Na0.07Ca0.06]Σ1.00(Ca4.01Mg0.02)Σ4.03Si7.97O20[F0.84(OH)0.16]Σ1.00⋅8H2O. Fluorapophyllite-(NH4) is tetragonal, space groupP4/mnc,a= 8.99336(9) Å,c= 15.7910(3) Å,V= 1277.18(3) Å3andZ= 2. The seven strongest X-ray powder diffraction lines are [dobsin Å,(I,%)(hkl)]: 7.897(32)(002), 7.812(13)(101), 4.547(14)(103), 3.946(100)(004), 2.985(39)(105), 2.4841(11)(215) and 1.5788(12)(00.10). The crystal structure of fluorapophyllite-(NH4), refined toR1= 0.0299 for 743 unique (I> 3σI) observed reflections, confirmed that the atomic arrangement is very similar to that of the other members of the apophyllite group. The new mineral is named according to the current nomenclature scheme for apophyllite-group minerals and is an NH4dominant analogue of fluorapophyllite-(K), fluorapophyllite-(Na) and fluorapophyllite-(Cs).

In this work, the peculiarities of xonotlite hydrothermal synthesis at 200 °C from lime and SiO2 materials with different pozzolanic activities (AP) were investigated: calcinated opoka (Ap = 170.1 mgCaO kg−1), granite sawing waste (Ap = 52.2 mgCaO g−1) and reagent SiO2·nH2O (Ap = 336.8 mgCaO kg−1). By XRD, DSC, TG, SEM, FT-IR methods have been shown that the formation of crystalline calcium silicate hydrates and the sequence of the intermediate phases existence are influenced not only by SiO2 component activity, but by other factors too. The use of the most active raw meal with SiO2·nH2O results in a very rapid formation of z-phase, C–S–H(I) and gyrolite, which hardly recrystallize into thermodynamically stable mineral—xonotlite. The impurities in the starting materials may promote the formation of some other compounds and retard the synthesis of stoichiometric ones: high content of Al-containing minerals in granite sawing waste (15.41% of Al2O3) predetermines that 1.13 nm tobermorite even after 72 h of hydrothermal curing did not recrystallize into xonotlite. Regardless of its average activity, calcinated opoka is an excellent material for the synthesis of crystalline calcium silicate hydrates. Amorphous SiO2 from opoka begins to react first, followed by tridymite and cristobalite. 1.13 nm tobermorite and xonotlite are formed at the beginning of the hydrothermal synthesis (4 h), and this greatly reduces the probability of the existence of amorphous phases.

The effect of temperature, CaO, MgO and Al2O3 on important technological copper smelting parameters, such as the chemically dissolved copper in slag and the composition of the liquid phase in equilibrium with tridymite, are experimentally characterised as a function of copper concentration in matte. Two series of experiments for the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at p(SO2) = 0.25 atm have been carried out. The effect of CaO at 1573 K (1300 °C), and the combined effect of Al2O3 + CaO + MgO at 1473 K (1200 °C) and 1573 K (1300 °C) have been measured in the first and second series of experiments respectively. The experimental methodology involves high temperature equilibration of samples on a substrate made from the primary phase under controlled gas atmosphere (CO/CO2/SO2/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using the Electron Probe x-ray Microanalysis. The resulting data are used in the optimization of the thermodynamic database for the copper-containing systems.

Phase equilibria in the ZnO-“CuO0.5”-SiO2 system have been investigated at 1403-1948 K (1130-1675 °C) for oxide liquid in equilibrium with Cu-Zn metal (> 99% Cu) and solid oxide phases: (a) tridymite or cristobalite SiO2; (b) willemite Zn2SiO4; (c) zincite ZnO; and (d) cuprite Cu2O. Two-liquid immiscibility range in the high-SiO2 slags has also been studied. High-temperature equilibration on primary phase (SiO2, Cu2O), inert metal (platinum-iridium wire), or ceramic (Al2O3 for high-Cu2O slags) substrates, followed by quenching and direct measurement of Zn, Cu, Si and possible impurities (Al, Pt, Ir) concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with metal. All results are projected onto the ZnO-“CuO0.5”-SiO2 plane for presentation purposes.

Experimental investigations have been undertaken to determine the effect of Al2O3in slag on the gas/slag/matte/tridymite equilibria in the multi-component Cu-Fe-O-S-Si-Al system at 1 200 8C, and P(SO2) = 0.25 atm. The experimental technique involves high temperature equilibration of synthetic samples on the open silica substrate in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching after a designated equilibration time followed by the compositional analysis of the condensed phases with electron probe X-ray microanalyzer. The experimental data of the present study provide information on the effect of alumina on the slag composition, such as the chemically dissolved copper, dissolved sulphur, and Fe/SiO2 ratio in slag at tridymite saturation at different Cu in matte. The new data have been used as inputs for the optimization of the thermodynamic databases for the copper-containing systems and can also be used to evaluate the fluxing strategy in the copper smelting operation.

Equilibria between gas/slag/matte/spinel phases in the Cu-Fe-O-S-Si system have been experimentally studied at 1523 K (1250 °C), P(SO2) = 0.25 atm, and a range of oxygen partial pressures. The experimental technique involved high temperature equilibration using spinel substrates in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of the equilibrated phases, and direct measurement of phase compositions using Electron Probe X-ray Microanalysis. The influence of temperature on the gas/slag/matte/spinel equilibria has been analyzed. Comparisons with previous studies on the gas/slag/matte/tridymite equilibria and the most recent thermodynamic database have been provided. This is the first systematic study on the influence of temperature on the gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si system at P(SO2) = 0.25 atm.

The ash fusion characteristics and co-gasification activities of different biomasses (corn straw (CS), rice straw (RS) and rice husk (RH)) are investigated in an ash fusion temperature (AFTs) analyzer and a thermo-gravimetric analyzer (TGA). Moreover, the transformation behaviors of mineral matters during CS/RH and RS/RH co-gasification processes are calculated by FactSage software. Results show that the ash fusion characteristic temperatures (AFTs) of CS/RH and RS/RH mixtures both increase with increasing RH ratio, and the maximum ratio of 75% CS and 55% RS in CS/RH and RS/RH mixtures can avoid the melting and slagging problems during co-gasification processes. Under the desirable RH ratio, the gasification activities of CS/RH and RS/RH mixtures increase with increasing CS or RS ratio. Besides, the increased AFTs of CS/RH and RS/RH mixtures are mainly ascribed to the increased contents of high-melting point quartz [SiO2] and tridymite [SiO2] and the decreased content of low-melting point silicate with the increase of RH ratio.

Fundamental experimental investigations have been conducted to study the effect of Al2O3 on the equilibria between the gas phase (CO-CO2-SO2-Ar) and slag-matte-tridymite phases in the Cu-Fe-O-S-Si-Al system at 1573 K (1300 °C) and P(SO2) = 0.25 atm. The experimental technique used is based on equilibration, rapid quenching and electron probe x-ray microanalysis. New experimental data have been obtained for the four-phase gas-slag-matte-tridymite equilibria system for a range of alumina concentrations up to 20.4 mass% in the slag phase as a function of matte grade, including the concentrations of dissolved sulphur and copper in slag, and Fe/SiO2 ratios in slag. The results obtained for 1573 K (1300 °C) are also used to analyse the effect of temperature on phase equilibria in the range of conditions investigated to that of reported for 1473 K (1200 °C) in the literature. The results obtained show that the concentrations of sulphur, copper and “FeO” in slag decrease with increase of Al2O3 concentration in slag while it has no detectable effect on concentration of sulphur in matte for a given matte grade. The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input for optimisation of the FactSage thermodynamic database for the copper-containing, multi-component multi-phase system.

Understanding the significance of magnesia as a common component in copper processing slags is essential for optimisation of the industrial copper production. Fundamental experimental studies have been undertaken to determine the effect of MgO on the equilibria between the gas phase (CO-CO2-SO2-Ar) and slag-matte-tridymite phases in the Cu-Fe-O-S-Si-Mg system at 1473 K (1200 °C) and 1573 K (1300 °C), and P(SO2) = 0.25 atm. The experimental methodology used was based on equilibration, quenching and microanalysis. New experimental data have been obtained for the four-phase gas–slag–matte–tridymite equilibria system for a range of MgO concentrations up to 3.1 wt pct in the slag phase as a function of matte grade, including the concentrations of dissolved sulphur and copper in slag, and Fe/SiO2 ratios in slag. The results are also used to analyse the effect of temperature on phase equilibria in the range investigated. The results obtained showed that dissolution of sulphur, copper and “FeO” in slag decreases with increase of MgO in slag while it has no detectable effect on concentration of sulphur in matte. Also, dissolved copper and sulphur in slag increases when temperature increases while the Fe/SiO2 ratio in slag is greater at 1473 K (1200 °C) than 1573 K (1300 °C). The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input for optimization of the FactSage thermodynamic database for the copper-containing multi-component multi-phase system.

The chemical reactions of dry-disposed ash dump, ingressed oxygen, carbon dioxide, and infiltrating rainwater affect mineralogical transformation, redistribution, and migration of chemical species. Composite samples of weathered coal fly ash taken at various depths and fresh coal fly ash were examined using organic petrographic, X-ray diffraction, X-ray fluorescence techniques, and successive extraction procedures. Results obtained show relative enrichment of glass, Al–Fe-oxides, calcite, and tridymite in the weathered CFA, but the fresh CFA is enriched in mullite, inertinite, maghemite, and ettringite. The enrichment of the weathered CFA in amorphous glass suggests higher reactivity when compared to fresh CFA. The evident depletion of soluble oxides in the weathered CFA is attributed to flushing of the soluble salts by percolating rainwater. Comparative enrichment of examined elements in water-soluble, exchangeable, reducible, and residual fractions of the weathered CFA is partly due to the slow release of adsorbed chemical species from the alumina-silicate matrix and diffusion from the deeper sections of the particles of coal fly ash. Sodium and potassium show enrichment in the oxidisable fraction of fresh CFA. The estimated mobility factor indicates mobility for Ca, Mg, Na, Se, Mo, and Sb and K, Sr, V, Cu, Cr, Se, and B in fresh and weathered CFAs, respectively.

Oil palm frond (OPF) was investigate in this study that aim to establish the potential of OPF as precursor for silica synthesis. OPF is one of abundance biomass produce in oil palm plantation during pruning and replanting phase that usually underutilized comparable to other oil palm-based waste. In this study, OPF was first combusted at 600 ℃ to produce the oil palm frond ash (OPFA) that subsequently followed with acid leaching treatment using 3% citric acid solution. The non-leached ash and leached ash was analysed and characterized using Fourier Transform Infrared Spectroscopy (FTIR) and AAS Atomic Absorption Spectroscopy (AAS). Combustion of OPF indicate that it produces approximately of 3.5% of ash out of total weight of OPF. The AAS analysis perform display a significant reduction of metal ions such as K+, Ca+ and Mg+ and total removal of iron from which proven the beneficial of acid leaching treatment in removing the undesired substance from OPFA. FTIR characterization display a significant different in spectra of treated and non-treated ash and it also successfully illustrate that the OPFA produce contain the required silica as well as the acid leached OPFA is in amorphous form due to the absence of band which indicating the presence of tridymite (crystalline phase).

The structure and dielectric properties of BaAl(2−2x)(Zn0.5Ti0.5)2xO4 ceramics were investigated. Single-phase solid solutions in space group P63 (No. 173) were confirmed when 0% ≤ x ≤ 1.6%. [Zn0.5/Ti0.5]3+ averagely occupied four symmetrically inequivalent Al sites, and Al1/(Zn,Ti)–O, Al2/(Zn,Ti)–O and Al3/(Zn,Ti)–O bond lengths increased with increased x. Two dielectric anomalous peaks existed, the first peak referred to second-order ferroelectric transition. Stability was significantly improved by moving the first dielectric abnormal peak from 123 °C to −22 °C due to the lower atomic shift amplitude Δz of B cations along the polar axis. The co-doping of Zn2+ and Ti4+ played a decisive role in realizing an ultrabroad temperature range (−100 °C–700 °C) of stability (−27 ppm/°C ≤ TCC ≤ +10 ppm/°C), which met the conditions of C0G or NP0 multilayer ceramic capacitors (±30 ppm/°C). Superior insulating properties were performed by high resistivity of > 1014 Ω cm.

Oligo–Miocene volcanic rocks cover large areas in Western Anatolia and pass laterally into terrestrial sediments, and they have economic occurrences formed by the effect of active tectonism. Alteration of these rocks developed by hydrothermal solutions reaching the surface along the active tectonic zones and formed important kaolin deposits for the ceramic industry in the region. The geological, mineralogical and technological properties of well-known kaolin deposits around Canakkale and Balikesir and their importance for the ceramic industry are discussed in this study. The XRD, XRF and SEM analyses, water absorption, firing colour, firing shrinkage, viscosity, Atterberg limits and grain size distributions were analysed for the characterization of chemical and technological properties of the samples. Mineralogical composition of the altered rocks comprised kaolinite, quartz (± tridymite and cristobalite), feldspar (mainly sanidine, rarely plagioclase) and small amounts of haematite and/or alunite. In light of these findings, Canakkale and Balikesir kaolin deposits are used in different sections of the ceramic industry such as for ceramic tiles, vitrified ceramics and insulators in terms of their industrial properties and the studied deposits developed with different degrees of alteration.

Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (− 16.67 mV), compared to the effects of acid-activation (− 6.60 mV) or non-activation method (− 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method.

Inhalation of respirable silica particles can cause serious lung diseases (e.g., silicosis and lung cancer), and the toxicity of respirable silica is highly dependent on its crystal form. Common combustion processes such as coal and biomass burning can provide high temperature environments that may alter the crystal forms of silica and thus affect its toxic effects. Although crystalline silica (i.e., quartz, tridymite, and cristobalite) were widely found at different temperatures during the burning processes, the sources and crystal transformation pathways of silica in the burning processes are still not well understood. Here, we investigate the crystal transformation of silica in the coal and biomass combustion processes and clarify the detailed transformation pathways of silica for the first time. Specifically, in coal burning process, amorphous silica can transform into quartz and cristobalite starting at 1100 °C, and quartz transforms into cristobalite starting at 1200 °C; in biomass burning process, amorphous silica can transform into cristobalite starting at 800 °C, and cristobalite transforms into tridymite starting at 1000 °C. These transformation temperatures are significantly lower than those predicted by the classic theory due to possibly the catalysis of coexisting metal elements (e.g., aluminum, iron, and potassium). Our results not only enable a deeper understanding on the combustion-induced crystal transformation of silica, but also contribute to the mitigation of population exposure to respirable silica.

The article presents the results of a study of the effects of the fractional composition of quartzite on the physical and mechanical properties of a fired shard of dinas refractory masses. As a result of the study of their chemical-mineralogical, fractional compositions and physicochemical characteristics, it was found that for the development of the composition of refractory dinas masses, it is necessary to use fractions of fine grinding of quartzite.

Phase equilibria of the ternary CaO-ZnO-SiO2 system have been investigated at 1170 °C to 1691 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2 (up to two immiscible liquids), pseudowollastonite (CS) CaSiO3, rankinite (C3S2) Ca3Si2O7, dicalcium silicate (C2S) (Ca, Zn)2SiO4, tricalcium silicate (C3S) (Ca, Zn)3SiO5, lime (Ca, Zn)O, zincite (Zn, Ca)O, willemite Zn2SiO4 and hardystonite (melilite) Ca2ZnSi2O7, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates followed by quenching and direct measurement of the Ca, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the CaO-ZnO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases.

Phase equilibria of the Pb-Cu-Si-O system have been investigated in the range 933-1938 K (660-1665 °C) for oxide liquid (slag) in equilibrium with solid Cu metal, liquid Pb-Cu alloy, or both solid and liquid metals, and solid oxide phases: (a) quartz, tridymite, cristobalite (SiO2); (b) cuprite (Cu2O); (c) lead silicates (PbSiO3, Pb2SiO4, Pb11Si3O17); (d) lead oxide (massicot, PbO); and (e) copper plumbite (Cu2PbO2). High-temperature equilibration on silica or copper substrates, followed by quenching and direct measurement of Pb, Cu and Si concentrations in the liquid and solid phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO0.5”-SiO2 plane for presentation purposes. The present study is a continuation of the previous investigation of this system by the authors in a part of the silica and cuprite primary phase fields. Present data were later used to develop the thermodynamic models for all phases in this system.

The presence of large quantities of agricultural waste directed our attention to how to benefit from them. The main concern of this article deals with the extraction of silica from rice husk and Peanut Peel. The material burning in large quantities can produce an environmental problem. Consequently, there is a need to waste disposal. In this study, all waste materials are subject to humidity removal at 200 °C then heat-treated at 900 °C for 7 h. The obtained powders were examined and described by FT-IR and XRD analysis. The Powder obtained from rice husk and Peanut Peel sources found to be SiO2 in Cristobalite and Tridymite phases. The crystal rice husk and Peanut Peel used as an alternative source of silica for the installation of glass samples. Glass samples prepared containing 40% substances produced, in addition to sodium and lithium oxide. The resulting glass studied and tested using a variety of analytical techniques, including x-ray diffraction (XRD), infrared spectroscopy for Fourier transform (FT-IR), differential thermal analyzes (DTA), UV / VIS / NIR spectroscopy. The thermal parameters from DTA data indicate the glass prepared from rice ash have more similarity of glass formed from chemical composition than the glass formed from the Peanut Peel. FTIR show that these glasses consist mainly of SiO4 vibration groups in addition to non-bridging oxygen units. From measurements and studies the visible UV, the optical band gap and intensity of absorption coefficient increase with SiO2 yield from rice husk.

The co-gasification of coal and biomass is of importance for coal clean conversion and biomass utilization on a large scale. To investigate the effecting behaviors of biomass on ash fusion characteristics of low ash-fusion-temperature (AFT) coal, the ash chemical properties of three materials (Shenmu coal (SM), chestnut shell (CS), and rice husk (RH)), the variations in SM mixed AFT with increasing CS or RH mass ratio and their mechanisms were explored through silicate-network structure theory, X-ray powder diffractometry, and FactSage software. The formations of anorthite, gehlenite and their eutectics caused SM with low AFT. An increased CS mass ratio led to the increasing contents of high melting-point (MP) kalsilite, lime and magnesia and the decreasing contents of low MP nepheline, olivine, and gehlenite, this made SM mixed AFTs increased gradually. Increasing high MP tridymite content led to SM mixed AFT mostly increased with increasing RH mass ratio. The temperature that all minerals changed into liquid phase based on FactSage calculation could reflect the AFT variation of samples.

Transformations of granules based on kaolin and phosphoric acid under conditions of vapor-phase crystallization in a mixture of water vapor and a structure-directing agent have been studied. It has been shown that silicoaluminophosphate granules obtained in the presence of dipropylamine, triethylamine, or tetramethylammonium hydroxide as a structure-directing agent consist of a shell formed by dense nonporous cristobalite, tridymite, and berlinite phases and the core made mainly of microporous crystalline silicoaluminophosphates. The formation of the shell, which ensures the strength of the silicoaluminophosphate granules, is due to the interaction of steam with the material of the granules at the initial stages of vapor-phase crystallization. It has been established that the selectivity of the structure-directing action of the amines under vapor-phase crystallization conditions basically corresponds to the template hydrothermal synthesis. It has been assumed that the specific features of the structure-directing action of dimethylamine during vapor-phase transport synthesis are due to its low boiling point, which ensures the primary contact of the granules with template, rather than water molecules. As a result, the products of the transformation of granules in the presence of a mixture of dimethylamine and water do not contain dense nonporous phases and are cocrystallized silicoaluminophosphate and calcium aluminosilicate with the gismondine structure.

An integrated experimental study and thermodynamic modelling approach has been used in the investigation of the distribution of As between slag and matte in equilibrium with tridymite in the Cu-Fe-O-S-Si system. The experimental technique involves high-temperature equilibration in sealed quartz ampoule, rapid quenching, and direct measurements of phase compositions using microanalysis techniques. Electron Probe X-ray Microanalysis (EPMA) was used to measure major and minor element concentrations in the matte, slag, and solid phases. The experimentally-determined distribution coefficient of As between slag and matte was found to decrease with decreasing P(SO ) from log L = 0.5 at P(SO ) = 25 kPa to approximately log L = −4.0 at lowest P(SO ), corresponding to metal saturation. Thermodynamic model parameters describing As distribution have been derived based on the present and previous data on the slag/matte, slag/metal, and slag/matte/metal equilibria. The thermodynamic model can be used for the evaluation of distribution of As between phases in the high-temperature pyrometallurgical production and refining of copper.

Structural characterization and X-ray reference powder pattern determination have been conducted for the Co- and Zn-containing tridymite derivatives Ba(Co1−xZnx)SiO4 (x = 0.2, 0.4, 0.6, 0.8). The bright blue series of Ba(Co1−xZnx)SiO4 crystallized in the hexagonal P63 space group (No. 173), with Z = 6. While the lattice parameter “a” decreases from 9.126 (2) Å to 9.10374(6) Å from x = 0.2 to 0.8, the lattice parameter “c” increases from 8.69477(12) Å to 8.72200(10) Å, respectively. Apparently, despite the similarity of ionic sizes of Zn2+ and Co2+, these opposing trends are due to the framework tetrahedral tilting of (ZnCo)O4. The lattice volume, V, remains comparable between 626.27 Å3 and 626.017 (7) Å3 from x = 0 to x = 0.8. UV-visible absorption spectrum measurements indicate the band gap of these two materials to be ≈3.3 and ≈3.5 eV, respectively, therefore potential UV photocatalytic materials. Reference powder X-ray diffraction patterns of these compounds have been submitted to be included in the Powder Diffraction File (PDF).

The effects of partial pressure of sulphur dioxide on the gas/slag/matte/tridymite equilibria in the Cu–Fe–O–S–Si system at 1 200 °C have been experimentally investigated and compared with the previous studies at various P(SO2). The experimental procedure includes equilibration of the sample and silica substrate at high temperature for the designated time, rapid quenching to preserve the equilibrium phases, followed by measuring the composition of the condensed phases with electron probe X-ray microanalysis. A set of graphs were constructed to present the compositions of slag and matte as a function of copper concentration in matte. The present study confirmed that the chemically dissolved copper and sulphur for the given Cu in matte are independent of the partial pressure of SO2. However, the experimentally measured liquidus (Fe/SiO2) are different for various P(SO2). The new data provide an important, accurate and reliable quantitative foundation for improvement of the thermodynamic databases for the chemical systems containing copper matte and slag. The present study is a part of a broader overall research program on the characterisation of the multi component (Cu–Fe–O–S–Si–Al–Ca–Mg), multi-phase (gas/slag/matte/metal/solids) systems with minor elements.

The distributions of Sb and Sn between slag and matte in equilibrium with tridymite in the Cu-Fe-O-S-Si system at 1200 °C (1473 K) have been measured. The experimental technique involves high-temperature equilibration in sealed quartz ampoule, rapid quenching, and direct measurement of phase compositions using Electron Probe X-ray Microanalysis (EPMA). The closed system equilibration approach was used to minimize the evaporation of Sb and Sn from the samples. The experimentally-determined distribution coefficients of Sb and Sn between slag and matte were found to increase with increasing Cu concentration in matte above 40 wt%. The new data have been used to refine the computational thermodynamics model for the system containing Sb and Sn at dilute concentrations. The molten slag phase is described using the Modified Quasichemical Model in the Quadruplet Approximation. Liquid matte and metal phases were modelled using single solution built within the Modified Quasichemical Model in the Pair Approximation. The thermodynamic model can be used to assess and predict the deportments of Sb and Sn between the slag and matte phases in the high-temperature pyrometallurgical production, refining and recycling of copper.

The properties of a molten slag play an important role in the separation of the slag from the matte during copper smelting. In this study, the viscosity, electrical conductivity, density, and surface tension of molten FeOt-SiO2-CaO-based slags were measured, and the effects of the common constituents, such as CaO, Fe3O4, and Cu2O, on various properties were investigated. The primary phases in the molten slags which are suitable for the copper recovery process were obtained, and they mainly correspond to fayalite and tridymite. The comparison of the static settling properties of molten industrial copper slag before and after modification is also discussed.

The wear mechanism of a quartzite lining of induction crucible furnaces during iron and steel smelting is presented. It is established that the main cause of lining wear is a decrease in its strength due to transition of the tridymite joints into cristobalite, which is more readily washed off crucible walls by moving metal and slag. The second important factor of wear is the choice of quartzite raw material, its substance and grain size compositions, firing regime, and melting technology during furnace operation. Silicon reduction from silica of the carburizer lining and within the cast iron composition is a subsidiary factor of crucible lining wear.

Cherty rocks, most abundant byproduct of mining industry, were used as adsorbent for the extraction of rare earth elements. Purified chert was characterized by various analytical methods (XRD, FX-ED, MEB, FTIR, laser granulometry). XRD patterns showed diffraction peaks of quartz, tridymite, cristobalite and clinoptilolite-Ca phases. SEM micrographs showed granular morphology of studied chert and particle size distribution was lower than 100 μm and unimodal. Adsorption behaviors of La(III) and Ce(III) ions on chert were investigated with various chemical methods and ICP-AES. Various experimental parameters were optimized such as contact time, initial rare earth concentration, temperature, agitation rate, and calcination of chert. Stable adsorption of Ce(III) and La(III) on chert were observed at stirring speed 400 and 200 rpm respectively. However the process of calcination does not affect the adsorption capacity of the two rare earths. The adsorption kinetics, the effect of various parameters influencing the adsorption capacity and adsorption isotherms were determined. Results showed instantaneous adsorption, fast kinetics and maximum percentages of adsorption ranged between 80 and ∼100%. Highest correlation coefficients were obtained for the pseudo-second order kinetic that are described satisfactorily by the Langmuir model. Thermodynamic parameters obtained indicate an endothermic and spontaneous adsorption process for lanthanum and exothermic and nonspontaneous adsorption process for cerium. Adsorption of rare earths on chert showed similar adsorption capacities to commercial diatomaceous earth and low matrix effect was observed when chert is used as an adsorbent of REE from a phosphogypsum leachate. Keywords: Chert, La(III), Ce(III), Adsorption/desorption, Kinetics, Thermodynamic

Three clinoptilolite-based materials, with Ba2+/NH4+ ratios of 2.27, 0.60 and 0.11, were prepared starting from a powder containing about 90% of NH4-clinoptilolite. The samples were submitted to thermal treatments of 2 h up to 1200 °C. Further treatments were carried out at 1100 and 1200 °C for 4, 8, 16 and 32 h. The sequence of reactions observed in heating (NH4, Ba)-clinoptilolite is: dehydration; de-ammoniation (along with residual dehydration); dehydroxylation; amorphization; crystallization of new phases. Amorphization temperature varied from 700 to 900 °C, and increased with barium content. Monocelsian, mullite and cristobalite/tridymite were obtained from all samples heated 32 h at 1100 °C, along with residual glass that never exceeded 9%. The Ba2+/NH4+ ratio resulted the main factor in determining type and quantity of the phases formed in the fired products, as well as their order of crystallization, but also temperature and duration of treatment affected the result. At 1100 °C mullite crystallized as last phase in the Ba-rich sample, and it did not form at 1200 °C. Similarly, celsian was never obtained at 1200 °C from the ammonium-rich material, and was the last phase to crystallize at 1100 °C. Transformations were faster at 1200 °C, but the amounts of residual glass were higher. Hexacelsian, the metastable polymorph of Ba-feldspar which is always formed during the heating of Ba-exchanged zeolites A and X, was never recorded among crystallization products obtained from (NH4, Ba)-clinoptilolite.