Impurities In Quartz Research Articles

Pozzolanic reactivity of a calcined interstratified illite/smectite (70/30) clay

Calcined clays can be potential supplementary cementitious materials if effects of heat-treatment on their structure and reactivity are understood. This work reports structural characterization of an interstratified illite/smectite clay, including a quartz impurity, upon heating using 27Al and 29Si MAS NMR spectroscopy and ICP-OES analysis. During dehydroxylation (600–900°C) the Q3-type SiO4 sites become disordered and octahedral AlO6 sites transform into tetrahedral sites, resulting in an amorphous material with substantial pozzolanic properties, as demonstrated by reactivity tests and hydration studies of a Portland cement–calcined clay blend. At higher temperatures (above 950°C), inert Q4-type phases crystallize which radically reduce the reactivity. At optimum calcination temperature (900°C), the amorphous material contains highly dissolvable elemental species as seen from complementary ICP-OES analysis. The quartz impurity exhibits a unique variation in 29Si spin–lattice relaxation times upon heat-treatment which is ascribed to changes in the concentration of impurity ions in quartz.

A simple hydrothermal approach to modify palygorskite for high-efficient adsorption of Methylene blue and Cu(II) ions

Silicate materials have been frequently used as stable, low-cost and efficient adsorbents for the removal of dyes and heavy metal ions from aqueous solution. Herein, at the aim of designing new adsorbent with higher adsorption capacity, natural palygorskite (PAL) was modified via a one-step hydrothermal process by introducing sodium silicate and magnesium salts. The effect of Si/Mg dosage ratio on the structure and physico-chemical features of the adsorbent was investigated, and its adsorption capability for Methylene blue (MB) and Cu(II) ions was intensively evaluated. It was found that Si/Mg dosage ratio is the key to control the adsorption properties of the adsorbent. The active magnesium silicate could be formed around PAL at the moderate Si/Mg dosage ratio, and even the undesirable quartz impurities without adsorption activity in the natural PAL minerals may transform as amorphous magnesium silicate with higher adsorption activity in this process. The adsorbent shows greater BET specific surface areas (407.3m2/g), ideal surface charge distribution and superior adsorption capacity to MB and Cu(II) ions, with the maximum adsorption capacity of 527.22mg/g for MB and 210.64mg/g for Cu(II) ions at the Si/Mg dosage ratio of 2:1. The MB molecules and Cu(II) ion could be almost completely removed from 100mg/L of MB solution and 25mg/L of Cu(II) solution by the adsorbent, respectively, which is far away higher than that of raw PAL. The electrostatic attraction, ion exchange and chemical association of –Si–O− groups contribute to the enhanced adsorption for MB or Cu(II) ions.

PHYSICOCHEMICAL CHARACTERIZATION OF A FEW CLAYS FROM ASSAM, INDIA

A few clay samples are collected from Karbi Anglong and North Cachar districts in Assam (India), were characterized with respect to moisture content, LOI, CEC, SiO 2 , Al 2 O 3 , Fe 2 O 3 , CaO, K 2 O, TiO 2 , P 2 O 5 , Na 2 O, MgO, and various trace elements and rare earth elements. The XRD measurement indicated that the predominant clay mineral present in the clays was kaolinite with some amount of quartz impurities. The IR measurements yielded appropriate frequencies expected for the OH and SiO stretching regions, and OH and SiO bending regions in kaolinite, and the data complemented the conclusions drawn from XRD analysis.

An Experiment Study on Flotation Process of Fine Scaly Graphite from Dandong in Liaoning

The aim of this study is to acquire graphite from the ore of 3.21%, a technological process including an open circuit experiment of six grinding and seven concentrating steps is testified and in the final concentrate the graphite with fineness (325-mesh) raise to 82.63%. The fine scaly graphite ore from low-grade mine in Dandong, Liaoning contains quartz, sericite, muscovite, feldspar and other impurities. As the only valuable element in the mineral, graphite with small grain size is closely symbiotic with gangue minerals. The technological process also includes a close circuit flotation experiment using sodium silicate as dispersing agent and depressant agent of gangues and using kerosene as inhibited agent and the final rate rises to 86.32% and recovery rate to 82.50%. This experimental study will provide support and guidance on process of graphite minerals with similar characters.

Study on CO<sub>2</sub> Adsorption of Halloysite Modified by Silane Coupling

The natural halloysite as the main raw material, removing the kaolinite, the quartz, feldspar and other impurities through purification. The purified halloysite was roasting activation pretreatment, in order to enhance surface porosity and reaction activity, and then was made of halloysite composite by modifying through the use of silane coupling agent. The samples were characterized by XRD、FESEM、BET、FT-IR and other chemical analysis method. The weight percentage of CO2 which were adsorbed by the modified halloysite increased from 3.13% to 13.92%.

Study on CO<sub>2</sub> Adsorption of Sepiolite Modified by Silane Coupling

The natural sepiolite as the main raw material, removing the quartz, calcium carbonate and other impurities through purification. The purified sepiolite was roasting activation pretreatment, in order to enhance surface porosity and reaction activity, and then was made of sepiolite composite by modifying through the use of silane coupling agent. The samples were characterized by XRD、SEM、BET、FT-IR and other chemical analysis method. The weight percentage of CO2 which were adsorbed by the modified sepiolite increased from 4% to 14.61%.

Giant g-factors of natural impurities in synthetic quartz

We report the observation of g-factors of natural paramagnetic impurities in a pure synthetic quartz crystal at milli-Kelvin temperatures. Measurements are made by performing spectroscopy using multiple high-Q whispering gallery modes sustained in the crystal. Extreme sensitivity of the method at low temperatures allows the determination of natural residual impurities introduced during the crystal growth. We observe g-factors that significantly differ from integer multiples of the electron g-factor in vacuum, and with values of up to 7.6, which reveals much stronger coupling between impurities and the crystal lattice than in previous studies. Both substitutional and interstitial ions are proposed as candidates for the observed interactions.

Characterization of Pakistani purified bentonite suitable for possible pharmaceutical application

The aim of this study is to assess the suitability of Pakistani bentonite for its possible pharmaceutical use in raw and purified forms. The purified samples were obtained by two different methods i.e. simple sedimentation and classical NaCl treatment. Prior to bentonite application in pharmacy, it is imperative that they must comply with some general features as high mineral, chemical and microbial purity. The physicochemical properties especially gel formation and swelling capacity are also important to be tested to investigate its specific use. The mineralogical study reveals that the raw sample is bentonite containing mainly montmorillonite with minor contents of kaolinite, illite and quartz. The quartz impurities were removed by the purification methods as confirmed by the X-ray diffraction patterns and the other properties were also improved. In view of the fundamentals of major pharmacopeias for use of bentonite in pharmacy and considering the chemical composition, microbiological results we could designate a pharmaceutical acceptable denomination for Pakistani purified bentonite samples. The two purified samples vary in interlayer cations, chemical composition and other properties that would present different behavior in pharmacy. The studied bentonite in purified form could be used as suspending and disintegrating agent because of its excellent swelling capacity and sedimentation volume. The high cation exchange capacity, high surface area and pore size distribution suggest their use as a good adsorbent of drugs and a drug carrier in controlled drug release system.

Genetic analysis of quartz from pegmatites of the Mama-Chuya mica belt based on distribuition of isomorphic impurities, Russia

The effect of the formation conditions of pegmatites in the Mama-Chuya mica belt on the distribution of isomorphic Al, Ti, and Ge impurities in quartz detected by electron paramagnetic resonance (EPR) has been estimated using the isogen method, which takes into account the relationship between this distribution and geological time. It has been revealed that each of the studied types of pegmatite veins is described by special isogens that reflect interrelations between concentrations of various isomorphic impurities. The typification of veins, enrichment of parental melt in water, and other factors affect the isogens. New potentialities of the isogen method for genetic analysis of quartz have been established.

Trace Elements in the Si Furnace. Part I: Behavior of Impurities in Quartz During Reduction

Quartz and carbonaceous materials, which are used in the production of silicon as well as electrodes and refractories in the silicon furnace, contain trace elements mostly in the form of oxides. These oxides can be reduced to gaseous compounds and leave the furnace or stay in the reaction products—metal and slag. This article examines the behavior of trace elements in hydrothermal quartz and quartzite in the reaction of SiO2 with Si or SiC. Mixtures of SiO2 (quartz or quartzite), SiC, and Si in forms of lumps or pellets were heated to 1923 K and 2123 K (1650°C and 1850°C) in high purity graphite crucibles under Argon gas flow. The gaseous compounds condensed in the inner lining of the tube attached to the crucible. The phases present in the reacted charge and the collected condensates were studied quantitatively by X-ray diffraction (XRD) and qualitatively by Electron Probe Micro Analyzer (EPMA). Contaminants in the charge materials, reacted charge and condensate were analyzed by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Muscovite in the mineral phase of quartz melted and formed two immiscible liquid phases: an Al-rich melt at the core of the mineral, and a SiO2-rich melt at the mineral boundaries. B, Mn, and Pb in quartz were removed during heating in reducing atmosphere at temperature above 1923 K (1650°C). Mn, Fe, Al and B diffused from quartz into silicon. P concentration was under the detection limit. Quartzite and hydrothermal quartz had different initial impurity levels: quartzite remained more impure after reduction experiment but approached purity of hydrothermal quartz upon silica reduction.

Trace Elements in the Si Furnace-Part II: Analysis of Condensate in Carbothermal Reduction of Quartz

Silicon feedstock for production of solar-grade silicon should be as pure as possible to decrease the cost of manufacturing of solar cells. Impurities in quartz, carbonaceous materials, electrodes, and refractories are mostly present in the form of oxides. These oxides can be reduced to volatile gaseous compounds in presence of SiO(g) and CO(g) atmosphere and potentially leave the furnace or stay in the condensed reaction products, metal, and slag. This work investigates the conditions under which volatile impurities report to the gas phase in laboratory experiments with lumpy and pelletized mixtures of SiO2, SiC, and Si at 1923 K and 2123 K (1650 °C and 1850 °C), respectively, were carried out. The volatile compounds were generated by the reduction of quartz and collected in the form of condensate. The effects of the reaction temperature, quartz type, charge composition, pellets, and lumps on the composition of the condensate were studied. The trace elements in the charge input, reacting charge, and condensate were analyzed using inductively coupled plasma (ICP)-mass spectroscopy (MS) and X-ray diffraction (XRD). CO(g) and SiO(g), which are the major components in reduction reactions, formed four types of condensate: white, brown, green, and orange. The condensate constituents were amorphous SiO2, 3C:SiC, Si, and α-quartz. Each impurity present in the quartz charge entered the gas phase during quartz reduction and was detected in the condensate. Al and Fe show limited volatility. The volatility of Mn, P, and B depends on the charge mix: a higher PCO enhances the concentration of these elements in the gas phase. Fluid inclusions, common in hydrothermal quartz, enhance the distribution of the contaminants to the gas phase. Industrial campaigns on Si and Fe-Si production confirm the experimental results.

Structural defects and polymorphic transformations in quartz

The influence of structural defects on the polymorphic transformations in quartz was studied by electron paramagnetic resonance and electron microscopy. It was established that the kinetics of the accumulation of the clusters of the β-phase depends on isomorphic impurities in quartz. It was confirmed that germanium ions and vacancies in quartz participate in the formation of the clusters. Obtained results allow the assumption that the amount of germanium required to preserve clusters increases with increasing temperature and vice versa. An explanation is presented for experimentally observed decomposition of clusters during artificial heating of some quartz samples. It was found that the clusters of the β-phase are autonomous units, i.e. may exist independently of host crystalline structure of quartz. The possible mechanism of influence of Ge impurity on the temperature of α-β-transition in quarts is discussed.

Investigation on non-optically bleachable components of ESR aluminium signal in quartz

Electron Spin Resonance (ESR) can be used as a method to estimate the age of sediment deposition using the paramagnetic centre related to aluminium impurities in quartz. This so-called Al-centre can be partially optically bleached and its signal intensity decreases in relation to time exposure to solar light, until it reaches a plateau value corresponding to a residual signal. This signal can be attributed to “Deep Aluminium Traps” (DAT) which cannot be reset by an exposure to sunlight. In this study, we have investigated the behaviour of the DAT signal in samples from different origins and ages. The intensity of the DAT signal has been isolated from the total aluminium signal by the exposure of different quartz samples to simulated solar light. We observed that the DAT intensities were sample dependant and therefore it should be determined for each sample. Moreover, DAT intensities of Pleistocene volcanic quartz increase with gamma laboratory irradiation, whereas DAT intensities of sedimentary quartz do not vary with added artificial doses. This suggests that DAT in quartz extracted from sediments must be inherited from the primary source of the quartz, and were saturated at the time of sedimentation. We thereby validate the ESR dating of quartz sediment protocol used so far.

The direct synthesis of pure zeolite-A using ‘virgin’ Kaolin

Here we demonstrate the conversion of a Nigerian Kaolin, straight from the source without any form of pre-treatment, directly into pure zeolite-A. The method involves a rapid and low temperature meta-kaolinization step followed by chemical conversion directly into pure zeolite-A. The synthesis step acts as the purification step removing the 80% quartz impurity simultaneously with zeolite growth. The whole process is designed to be both economical and straightforward to facilitate commercialisation.

Thermal behavior of calcite as an expansive agent

In this paper, thermal behavior of calcite as raw material of CaO-based expansive agent was investigated. The products were characterized by using differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD). DTA curves show that calcite has endothermic peak and impurity affects the onset of reactions. The more the impurity increases, the more energy changes increase. At 800-900?C, calcite was decomposed into solid calcium oxide (CaO) and gaseous CO2. Lime (CaO) used as the base of expandable material is the ultimate product of heated calcite. The calcium oxide phase, in reaction to water forms portlandite, at an onset temperature of about 900?C was also characterized by the appearance of the FT-IR mode at 867,3424 and 3644 cm-1. XRD results show that quartz impurity in calcite samples at 900?C forms larnite phase (Ca2SiO4). The expansions are mainly generated from the hydrations of CaO in the CaO-type expansive agent.

Flotação da mistura argila-quartzo com surfactantes e estudos de pilarização

Clay is often employed as a catalyst, but quartz impurities can decrease the catalytic efficiency. Fine particles of clay can be purified by flotation. We examined the cationic surfactant hexadecyltrimethylammonium bromide (HTAB), the anionic sodium dodecyl sulfate (SDS) and the non-ionic TRITON X-100 for separating the quartz impurities from clay. Using X-ray diffraction, the separation was monitored for changes in the peaks corresponding to clay and quartz. Cationic surfactant HTAB was most effective in separating the quartz-clay mixture and the selectivity can be explained by internal adsorption of the surfactant onto the clay and external adsorption onto the quartz.

Separation and purification of montmorillonite and polyethylene oxide modified montmorillonite from Vietnamese bentonites

Several granulometric treatments and chemical processes were tested to separate and purify montmorillonite (MMT) from the bentonite deposits of LamDong and ThuanHai (south and central Viet Nam) to obtain MMT for filler application in polymer nanocomposites. X-ray diffraction, laser granulometry, nitrogen adsorption at 77 K, cationic exchange capacity (CEC), and infra-red spectroscopy (IR) measurements showed that the purest fraction of MMT was separated from the raw material by sedimentation (55 h) combined with centrifugation and sonication, compared with a sonication coupled with sedimentation or a single centrifugation. The quartz impurities were totally removed by the more efficient granulometric separation whereas residual kaolinite particles were still observed by the IR spectra. The granulometric separation by sedimentation or centrifugation already tested on raw materials were also applied successfully on chemically purified LamDong bentonite sonicated in PEO (polyethylene oxide) aqueous solution, allowing the direct preparation of pure MMT/PEO intercalated compounds free from quartz impurities, suitable for filler application in polymer nanocomposites. The separated MMT (from LamDong or ThuanHai Clays) after granulometric separation was chemically purified by three steps: 1. the carbonates were dissolved with acetic acid; 2. organic molecules were oxidized by hydrogen peroxide; and 3. iron (hydr)oxides were removed by several complexation and redox reactions. The X-ray fluorescence (XRF) chemical analyses and X-ray microanalyses coupled with scanning electron microscopy (SEM) showed that the nitric acid and the dithionite-oxalic acid reaction were ways to remove the iron (hydr)oxides from the bentonites (respectively ∼ 2 mass % and ∼ 0.3 mass % iron content after purification). The combination of the four reactions involving successively complexation + reduction + acid reactions allowed to minimize the proportion of iron (hydr)oxides in the LamDong purified MMT (∼ 1.5 mass % of Fe).

Complex impedance spectroscopy of alkali impurities in as-grown, irradiated and annealed quartz

This work compares the dielectric relaxation properties of different crystalline quartz materials, according to their source (natural or synthetics). It is shown that these relaxation properties are due to a hopping process of alkaline (Li+, Na+, and K+) impurities located near [Al–O4]5− tetrahedra. A detailed analysis, in terms of the distribution function of the dielectric loss peak, allowed us to perfectly distinguish the different types of as-grown quartz. We show that (i) the natural quartz has less stable M+ charge carriers than the synthetic materials and that (ii) the homogeneity of the M+ trapping sites, created by the [Al–O4]5− tetrahedra, strongly depends on the crystal growth conditions. These features were then studied using quartz samples with different treatment conditions: as-grown, irradiated, or annealed at high temperature. We propose that the irradiation greatly facilitates the M+ relaxation, by creating additional low energy M+ hosting sites, whose number depends on the source of the quartz crystals. We also show that for 100krad irradiation, the saturation state of the defects is already reached for all the materials under consideration. Finally, we propose that the irradiation followed by annealing at 450°C improves the M+ stability and homogeneity in quartz materials, compared with the as-grown materials, this trend being much more relevant for the natural than for the synthetic quartz.

Mechanisms of isomorphic substitution in quartz

Mechanisms of the incorporation of isomorphic impurities of Al, Ti, and Ge into quartz were studied by EPR techniques. For this purpose, laboratory experiments were carried out on quartz annealing, which allowed us to model the processes of impurity atom introduction into the quartz lattice. The investigation of the kinetics of these processes showed that they are described by diffusion-controlled reactions. In many samples, a proportional relationship was observed between the concentrations of Al and Ti impurities incorporated into the quartz structure during laboratory annealing. A comparison of the experimental results with the character of the natural distribution of isomorphic impurities in quartz revealed their similarity. Based on the analysis of the results of our investigations, two main mechanisms were proposed for isomorphic substitutions in quartz. One of them is referred to as the capture mechanism and corresponds to the incorporation of isomorphic impurities during mineral formation. The second, diffusion mechanism operates after the crystallization of quartz. The isomorphic impurities incorporated into the quartz structure by this mechanism are either formed through the decomposition and transformation of composite complexes or as a result of diffusion from crystalline and gas-liquid inclusions. It was suggested that both mechanisms are responsible for the incorporation of Al and Ge impurities into the mineral lattice, whereas Ti is introduced mainly by the diffusion mechanism. The accounting for the mechanisms of isomorphic substitutions provides a means to significantly increase the reliability of the interpretation of genetic information recorded in the distribution of structural impurities in quartz.

Correlation of blue-thermoluminescence (BTL) properties with some impurities in synthetic quartz

In growth zones of synthetic quartz samples, BTL (blue-thermoluminescence) intensities were found to gradually decrease with Al-impurity concentrations beyond 13 ppm, except for - X zones. This tendency suggests the relevance of other impurities, which were identified by infrared (IR) spectrometry. In the IR spectrum, + X zones indicated a negative relationship between BTL and Al–OH absorbance, whereas the - X zones showed extremely weak BTL and high Al–OH absorbance. On the basis of low-temperature measurements we suggest that hydrogen radicals and other radicals due to OH or water molecule impurities cause the elimination of BTL-centers and that the BTL sensitivity of quartz at environmental temperature is influenced not only by Al-impurities, but also by OH groups and other types of center.