Impurities In Quartz Research Articles

Lattice defects in the disordered quartz structure of gold deposits of the Darasun ore field (Eastern Transbaikalia)

Research subject. The composition, properties, and connection of the lattice defects in the disordered s tructure of quartz with the conditions of its formation. Materials and methods. The quartz of the gold deposits of the Darasun ore field – Darasun, Teremkinskoye, and Talatuy – were studied. For the purpose of comparative analysis, gold-ore quartz from the deposits of Northern Kazakhstan was used. Registration of centers in quartz samples was carried out by the EPR method. When interpreting the obtained results, genetic information consisting in the distribution of substitutional Ge and Ti impurities in quartz was used. Results. Two groups of paramagnetic centers were identified in the quartz under study. One of them is associated with substitutional Al, Ti, and Ge impurities in quartz zones with an ordered crystal structure, while the other is associated with the lattice defects localized in the disordered crystal structure of quartz. The latter group includes several types of E'-centers formed in quartz glass and Al-X-centers caused by Al3+ ions associated with oxygen vacancies. In the case of stable thermodynamic conditions of mineral formation, a linear relationship was established between the concentrations of Al-X-centers (CAl-X) and E'-centers (CEs). Under a change in thermodynamic conditions, a deviation of the points from the CEs(CAl-X) dependence was observed. Conclusions. The type of CEs(CAl-X) dependence is determined by the thermodynamic conditions of mineral formation and can be used to identify cases of non-equilibrium solidification of quartz.

Removal of hydroxyl impurities in vein quartz by vacuum roasting

Removing hydroxyl impurities is the key to preparing high-purity quartz sand by replacing natural crystals with vein quartz. Water hydroxyl groups in inclusions (WHI) and Silanols groups in the crystal structure (SHCS) are the two main types of hydroxyl impurities. In this study, a vacuum roasting technique was used to eliminate volatile WHI and SHCS impurities from quartz. The mechanisms by which vacuum roasting accelerated the crystal transformation to remove WHIs and the intrinsic mechanism of vacuum roasting that promoted the diffusion of water to remove the SHCS were revealed. The results showed that under the same experimental conditions, the hydroxyl content in quartz decreased from 226.8 μg g−1 to 172.2 μg g−1 after atmospheric pressure roasting. It further decreased to 88.2 μg g−1 after vacuum roasting, satisfying the hydroxyl content requirement of high-purity quartz used for quartz crucibles. This study makes it possible to prepare high-purity quartz sand from vein quartz, which is important for the development of photovoltaics.

Forms of presence, interrelation and genetic significance of Al and Li impurities in quartz of gold deposits of the Darasunsky ore field (Eastern Transbaikalia, Russia)

Research subject. The distribution regularities of Al and Li impurities in gold-ore quartz. Materials and methods. The quartz of the Darasun, Teremkinskoye and Talatuy gold deposits of the Darasun ore field was studied. The gross contents of Al and Li impurities in quartz were determined by the LA-ICP-MS method; substitutional Al impurity concentrations were studied by the EPR method. The forms of Al impurity in quartz were determined based on the results of studying its behavior during material recrystallization. The genetic significance of Al and Li impurities in quartz was estimated taking into account the genetic information obtained during the study of the distribution of substitutional Al and Ti impurity concentrations. Results. It was found that Al is present in quartz in two main forms, i. e., as a substitutional Al impurity and Al complexes localized in the areas of high mineral defectiveness. Li+ ions are located in the structural channels of the mineral, serving as compensating ions for both Al impurity forms. The composition of Al complexes is assumed to include three Al3+ ions and one H+ or Li+ ion. Two stages of quartz recrystallization occurring at different temperatures of mineral formation were identified. The first, low-temperature stage leads to quartz enrichment with substitutional Al impurities. The second, high-temperature stage causes the decomposition of Al complexes. The recrystallization stages can be identified by the type of relationship between the gross concentrations of Al and Li. The increased content of Al impurity in ore quartz was found to be related to the presence of a large number of Al complexes. An assumption is made that these complexes formed during mineral crystallization from solutions with a high content of metal ions. Conclusions. The results obtained indicate that high Al impurity concentrations can serve as a genetic sign of ore quartz. At the same time, the decomposition of Al complexes during quartz recrystallization should be taken into account. A method for estimating the initial concentration of Al complexes is proposed, which is a more reliable genetic indicator.

Kaolinite structural modifications induced by mechanical activation

This study presents novel characterisation techniques to evaluate the effects of mechanical activation (MA) on the kaolinite structure. MA was achieved with a planetary ball mill at various times and rotation speeds to get different activation degrees. A thermal activation was performed for comparison purposes. The results of X-ray diffraction and selective area electron diffraction demonstrated that the kaolinite content was significantly reduced as the amorphous phase increased. Illite, K-feldspars, and quartz impurities were extensively modified as well. The morphology of kaolinite particles is altered. Furthermore, the mechanical treatments significantly affected the hydroxyls, losing bonding strength with the structure, as stated with 1H nuclear magnetic resonance. Thermogravimetric analysis and infrared spectroscopy also revealed that water molecules could be formed due to the reaction of hydroxyls between them or with the atmosphere. This work improves the comprehension of MA on kaolin by clearly confirming with new techniques that the mechanical treatments distort the kaolinite structure.

Assessment of Gold-Bearing Quartz Vein as a Potential High-Purity Quartz Resource: Evidence from Mineralogy, Geochemistry, and Technological Purification

High-purity quartz (HPQ) is an important material widely used in many high-tech industries. It is a product processed from pure natural quartz raw materials, so selecting suitable quartz raw material is the key to successfully processing HPQ. Hydrothermal quartz vein is one of the most likely raw materials to be purified into HPQ because of its high SiO2 content. This study focuses on the evaluation of HPQ raw material potential of the two gold-bearing quartz vein tailing resources in Chibougamau (CBG) and Tianjingshan (TJS). Petrography and the contents of impurity elements in the two vein quartz samples before and after processing were studied by optical microscope, SEM, Raman spectrometry, XRD, LA-ICP-MS, and bulk solution ICP-OES. Petrographic results reveal that major impurities in quartz are feldspar, mica, iron compounds, ankerite, rutile, silicate melt, and fluid inclusions. LA-ICP-MS analysis result shows that the SiO2 contents are between 99.953–99.971 wt.% in CBG raw quartz and 99.969–99.976 wt.% in TJS raw quartz, respectively, with very low contents of impurity elements, except for Ca. Bulk solution ICP-OES analysis demonstrates that the CBG processed quartz sand has total impurity contents of 56.8 µg·g−1, with 13.1 µg·g−1 Al and 6.6 µg·g−1 Ti, and the TJS processed quartz sand has the total impurity contents of 85.2 µg·g−1 with 29.4 µg·g−1 Al and 6.1 µg·g−1 Ti. Both the contents of Al and Ti fit with the lattice-bound criteria for HPQ. These results, for most of the impurities, are likely hosted by silicate melt, fluid, and mineral inclusions, indicating that these two hydrothermal raw vein quartz samples can be upgraded to HPQ after processing by more advanced methods. Therefore, the CBG and TJS quartz vein deposits would be considered as potential future resources for HPQ to realize efficient recovery and utilization of tailings resources and to improve mine economic benefits.

Aluminosilicates Catalysts Synthesis from Low-Grade Indonesian Kaolin for the Acetalization Reaction

Aluminosilicate and ZSM-5 catalyst were synthesized from local materials, low-grade Indonesian kaolin. High quartz impurities content in the low-grade kaolin was successfully reduced by the consecutive treatment process including washing, centrifugation, and Fe3+ treatment. All the synthesized catalyst showed mesoporous structure with pore diameter around 3.5 nm. The catalytic activity was investigated in the acetalization of 3,4-dimethoxybenzaldehyde and propylene glycol, then the effect of a different base (TPAOH and NaOH) and Fe3+ addition in the treatment process to the catalytic activity was discussed. The catalytic activity of the aluminosilicate catalyst outperforms the ZSM-5. Interestingly, it is found that the catalytic activity of the catalyst can be enhanced by addition of Fe3+ in the aluminosilicate, with enhanced the conversion from 32.2% to 81.6%, whereas Fe3+ addition to ZSM-5 showed slightly increased conversion value from 0% to 3.65%. All catalysts showed high selectivity of 100% of the reaction product 2-(3,4-dimethoxy-phenyl)-4-methyl-1,3-dioxolane.

Adsorption of Copper Ion from Acidic Wastewater by Local Natural Zeolite

Natural zeolites are available in Indonesia in very large quantities and are available in the market at very affordable prices. The use of zeolite has developed in various fields of industry, water treatment and wastewater treatment. The study on the ability of local natural zeolite to adsorb copper from acidic wastewater from a laboratory in Tangerang has been conducted. XRD data show that the local natural zeolite consists of mordenite as main mineral and quartz as an accessory mineral. Acid activation of zeolite with HCl 3 M could remove quartz impurities from natural zeolite based on XRD data. Mordenite is one of the most abundant zeolite minerals and commercially used for many purposes including adsorbents, catalyst, fertilizer, and gas separation. The crystallinity of mordenite decreases throughout the process of acid activation and calcination. The calcined zeolite has better copper adsorption ability compared to local natural zeolite without any treatment. The optimum copper adsorption percentage is 14.554% at solution pH of 0.3 by using 10 grams of calcined zeolite in 200 mL of wastewater solution.

Effect of Metakaolin and Lime on Strength Development of Blended Cement Paste

To develop a more reactive pozzolan for supplementary cementitious materials (SCMs), the co-calcination of kaolinite and limestone was investigated for its contribution to hydration of blended cement. Kaolinite (with ~50 wt% quartz impurity) was calcined at 700 °C, and a mixture of kaolinite and limestone was calcined at 800 °C. These activated SCMs were added to ordinary Portland cement (OPC), replacing ca. 30 wt% of the OPC. The compressive strength of these blended cement paste samples was measured after 28 and 90 days, while the hydration products and microstructural development in these blended cement pastes were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results revealed that adding free lime to OPC, together with metakaolin, led to enhanced compressive strength. The compressive strength of this new blended cement paste reached 113% and 112% of the compressed strength of pure OPC paste after 28 and 90 days of hydration, respectively. Furthermore, this study showed that the improvement was due to the increased consumption of Portlandite (CH), the formation of calcium aluminosilicate hydrate (CASH), and the reduction of porosity in the sample containing free lime and metakaolin.

Comparison of two purification methods of Algerian bentonite: chemical, mineralogical and physicochemical properties

The aim of this work is to evaluate the efficiency of two methods of purification on Algerian bentonite clay. The first method was performed by centrifugation treatment, using sodium hexametaphosphate (NaPO3)6 as a dispersing agent. The second method involves a chemical purification with NaCl, followed by sedimentation technique. The study concerns mineralogical, chemical, structural aspects and a series of physical testing. The results have shown that the raw bentonite (RBN) contain (~ 59%) of montmorillonite, illite (~ 5) and (~26%) of quartz, and feldspar (orthoclase + albite), with 5% of calcite. In the purified state by NaCl (RBN-2), the mineralogical and physicochemical properties including cation exchange capacity and specific surface area are higher than the purified samples by physical beneficiation (by centrifugation - RBN-1). Moreover, the treatment with NaCl increased the montmorillonite content of the bentonite from 56 % to 100%. The quartz impurities were totally removed in RBN-2, whereas impurities (quartz + feldspar) were still observed by the X-ray diffraction (XRD). Finally, the results obtained from the morphological, mineralogical and chemical characterization confirm that the bentonite RBN -2 was more effective , and it has promise as an engineering material compared to the RBN and RBN-1, indicating its possible application in various industrial applications.

Specific development features of secondary gold mineralization in mature tailings of gold processing plants

The paper studies the development of secondary gold mineralization driven by the interaction of gold-bearing solutions with primary minerals in sulfide and oxidized ore processing tailings, as well as with secondary limonite formed during their long-term storage. Lowtemperature gas adsorption was used to establish that such tailings are characterized by high specific surface areas of up to 20 m2/g. Material surface area may play an important role in the processes of sorption and reduction. Using X-ray photoelectron spectroscopy, it has been established that secondary mineralization gold predominantly occurs in its elemental form, with a subordinate amount of the occluded ionic form of Au(I). It has been shown that Au(III) ions selectively precipitate from solutions at 25 °C and pH 6.9–7.3 on pyrite, arsenopyrite, and limonite, forming individual metal particles of 30–1000 nm, as well as mineral aggregates of complex structure and composition, including oxidized antimony minerals, limonite, and nanodispersed gold. Gold precipitation on a mixture of hydrates of iron and manganese oxides was found in samples of oxidized ore processing tailings. The specific morphology and grain-size distribution of secondary gold particles on various carrier minerals and the composition of new formations have been studied. On the secondary limonite, containing calcite (up to 10 wt%) and quartz impurities, the gold particles are up to 500 nm and are uniformly distributed over the entire material surface. This is in contrast to the sulfide and oxidized ore processing tailings, where gold was selectively reduced on certain minerals. The paper considers the potential mechanisms of gold reduction on the surfaces of oxidized minerals.The work patially was carried out within the framework of the state assignment of the Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of Sciences (project No. 0287-2021-0014) using the equipment of the Federal Research Center «Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of Sciences».

Gemology, Mineralogy, and Coloration Mechanism of Pinkish-Purple Cobaltoan Dolomite from the Democratic Republic of Congo

A pinkish-purple cobaltoan dolomite from the Democratic Republic of Congo (DRC) has appeared on the Chinese gemstone market recently. In this study, Raman analysis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electron probe micro-analysis (EPMA), scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence (EDXRF), and fiber optic spectrometry were used to explore the gemology, mineralogy, and coloration mechanism of cobaltoan dolomite. Results indicate that cobaltoan dolomite is a mineral aggregate with a granular texture. The degree of fineness and luster differs due to mineral (quartz) impurities in the texture. The cobaltoan dolomites are typically associated with carbonates, such as azurite, malachite, spherocobaltite, and the rare species kolwezite, which were documented in this study. The natural presence of magnesite-spherocobaltite solid solution with distinct chemical zoning occurs as crystals in the country rock. The pinkish-purple dolomites are mainly colored by CoO, whose concentrations ranged from 0.966 to 6.111 wt.%. Based on UV-Vis spectroscopy, cobaltoan dolomite showed broad characteristic absorption bands at 531.5 nm, which varied as the concentrations of CoO increased. The origin of the color is related to the electronic transition of Co2+ and charge transfer between the ions.

Improved Natural Mordenite as Low-Cost Catalyst for Glycerol Acetalization into Solketal – An Effective Fuel Additive

The increase in biodiesel production results in an excessive amount of crude glycerol by-product. Therefore, production of solketal –an effective additive of gasoline fuel-from glycerol and acetone via catalytic acetalization could improve the added value of glycerol. This study investigates enhancement of natural mordenite catalytic properties through the hydrothermal recrystallization method for glycerol acetalization. The hydrothermal temperature was varied at 150, 170 and 190 oC to form ZT 150, ZT 170 and ZT 190, respectively. The samples were characterized using the x-ray diffraction and the scanning electron microscope-Energy dispersive X-Ray. They were later used as catalysts for glycerol acetalization with acetone. The best obtained catalyst was further studied to explore the effect of acetone on glycerol ration. The glycerol conversion was deter-mined using the ASTM D7637-10 titration method. Solketal product was identified by using the Fourier transform infrared spectroscopy. The results show that the recrystallization temperature affects the intensity of the mordenite phase and quartz impurity phase in the modified zeolites. A high recrystallization temperature led to a higher phase of mordenite, peaking at 170oC, beyond which the quartz impurity phase increased. Glycerol acetalization conversions over zeolite parent, ZT 150, ZT 170 and ZT190 with acetone to glycerol ratio of 3 were 16.1%, 30.4%, 33.9% and 32.5%, respectively. When the ratio of acetone to glycerol was increased to 12, the glycerol conversion over ZT 170 catalyst reached 59%, a good starting point for further modifications. Overall finding demonstrated a straight-forward fabrication of catalyst from natural resource to enhance glycerol as the biodiesel production by-product into a higher value end-product of solketal.

The use of lattice defects in quartz to determine provenance and conditions for the formation of sedimentary deposits (using the example of quartz from sedimentary rocks of the Central Kyzylkum)

Research subject. The composition and distribution patterns of lattice defects in the clastic quartz of sedimentary rocks.Material and methods. Quartz collected from the core of two wells uncovering the Neogene, Paleogene and Cretaceous deposits in the rocks of the Central Kyzylkum. The registration and determination of the concentrations of lattice defects in detrital quartz were carried out by the EPR spectroscopy. Their stability in quartz under natural conditions was evaluated by comparing the concentrations of lattice defects in the near-surface and deep zones of quartz grains. The etching of quartz grains in HF was used to study the spatial location of lattice defects in the mineral. The genetic analysis of detrital quartz was carried out using the methods tested in the study of quartz from crystalline rocks.Results. The presence of substitutional Al, Ti, and Ge impurities, radiation induced E1-, Al–O−- and Ti-centers, as well as other paramagnetic centers possessing genetic information was found in quartz. The distribution of substitutional impurities in clastic quartz is close to their original distribution formed at the time of the mineral formation. This creates the prerequisites for identifying genetically similar quartz samples and attributing them to the certain provenance. The formation of sedimentary rocks of the Central Kyzylkum occurred due to two main provenance sources of terrigenous material. The expediency of using radiation induced centers with different thermal stability for studying the radiation prehistory of quartz and the conditions for the formation of uranium deposits is demonstrated.Conclusion. The clastic quartz of sedimentary deposits retains the main part of the genetically significant lattice defects formed during crystallisation. The most important of them are Al, Ti, and Ge isomorphic impurities. The regularities of their distribution, along with the distribution of radiation induced lattice defects in quartz, are able to carry information about the provenance of detrital material and the conditions of sedimentation and associated formation of mineral deposits.

Effect of Beneficiation on the Characterization of Getso Kaolin

Abstract In their raw forms, clay minerals are found with a number of inherent impurities which make them unsuitable for most industrial applications. In order to overcome this problem and add value to clay minerals, beneficiation process is an indispensable solution. This study investigates effect of wet beneficiation process on the characteristics of a local clay mined from Getso village of Kano State, Nigeria. Mineralogical characterization of the clay was carried out using X-ray diffraction (XRD) analyzer. Chemical characterization of the clay was carried out using X-ray fluorescence analyzer. Physicochemical characterization of the clay was carried out using pH meter and density analysis conducted using density bottle. XRD analysis of Getso clay showed that the raw clay had 8 wt% kaolinite and 51% quartz. Wet beneficiation resulted into 53% improvement of the kaolinite content and 47% reduction of quartz impurity. The XRF analysis has shown that silica-alumina ratio of the raw Getso clay was 1.55 and this reduced to 1.49 after beneficiation. The physicochemical characterization of the clay has shown that Getso clay is neutral, the raw clay and beneficiated clay had average pH values of 7.5 and 7.3, respectively. Specific gravity values of the raw and beneficiated clay were 2.24 and 2.04, respectively. The beneficiation process had been effective as substantial increase in kaolinte content was observed and a reasonable decrese in the impurity contents was observed from the raw to the beneficiated clay. The Garnet content was completely reduced to zero while quartz, clinochlore and orthoclase were reduced by 24%, 9% and 13% respectively. The clay obtained after the beneficiation be serve as good raw material for production of whitewares, high grade ceramics in synthesis of zeolitic materials.

Gamma radiation effects on quartz Al and Ti center electron spin resonance signal intensity: Implications for quartz provenance discrimination

Abstract Quartz is one of the most common rock-forming minerals and crystallizes over a wide range of temperature and pressure conditions. This diversity of quartz crystallization environments is reflected by trace-element compositional variations, which can be used to distinguish between different source sediments. Trace elements that are incorporated into the quartz lattice form corresponding paramagnetic centers (impurity centers, such as Al and Ti centers), which can be detected using the electron spin resonance (ESR) method. However, whether the quartz impurity center ESR signal intensity (quartz ESR-SI) can be used for quartz sediment provenance tracing remains uncertain. In the present study, five present-day (modern) fluvial sediments from the Songhua, Yellow, Yangtze, Huai, and Pearl rivers in China and eight ancient fluvial sand lenses from the Yichang Gravel Layer (YGL) located in the middle Yangtze River were sampled for major- and trace-element determinations by ICP-OES and ICP-MS for the purpose of provenance discrimination. A total of 1404 ESR spectra were also collected to evaluate the effect of γ-ray dose (varying from 50 to 50 000 Gy) on quartz ESR-SI to establish the relationship between quartz element contents and quartz ESR-SIs and thereby to assess the potential utility of quartz ESR-SI for sediment provenance analysis. Results indicate that: (1) quartz collected from the different studied locations can be distinguished by element contents; (2) the quartz Al center ESR-SI increases with increasing γ-ray dose from 50 to 50 000 Gy; (3) the quartz Ti center ESR-SI increases within a γ-ray dose of 10 000 Gy and decreases beyond 10 000 Gy; (4) quartz Al and Ti center ESR-SIs are closely related to the contents of Al and Ti in quartz; and (5) a plot of quartz Ti center ESR-SI vs. Al center ESR-SI using data for a γ-ray dose range of 4000–7000 Gy is the best indicator of fluvial sediment provenance using the ESR method.

The effects of partially replacing amine collectors by a commercial frother in a reverse cationic hematite flotation

Iron ore froth flotation has recently been used to obtain pure minerals due to the depletion of high-grade deposits. Amine collectors have often been used in cationic reverse iron ore flotation to achieve the separation with quartz impurities. The main problem associated with these collectors is related to the control of frothing properties and the high cost of amine reagents. In this paper, we report the benefits of partial replacement of amine collectors with a frother in reverse cationic flotation of hematite. Surface tension and batch flotation experimental results indicated for the first time that replacing Flotigam EDA, an etheramine collector by more than 10% improved the flotation performance in both grade and recovery of hematite. It was also noted mild hematite entrainments for lower frother dosages whilst reagents cost estimation indicated profitability per ton of iron recovered. At higher frother dosage however, higher quartz recoveries were observed as a result of entrainment which led to satisfactory results in terms of iron grade in the sink, but results showed higher costs of reagents than when collector was used alone. From observed results, it was concluded that partially replacing amine collector by a frother does improve the performance of the flotation globally regardless of pronounced entrainment that was mainly due the mineralogy of the ore with notable amounts of locked particles in the lower sizes. Finally, it would be useful to investigate these findings with alternative reagents and on minerals with different mineralogical properties.

Повышение качества металлического кремния методом рентгеновского радиометрического разделения сырьевых и готовых продуктов

In this research, we investigate the process of X-ray radiometric separation of both raw materials (quartz, carbonaceous reducing agent) used for silicon smelting in ore-smelting furnaces and the resulting smelting products. The research objects were quartz from the Aktas field (Kazakhstan), coal from the Shubarkol field and silicon metal of various grades smelted at the Tau-Ken Temir LLP (Karaganda, Kazakhstan). X-ray diffraction analysis was performed using a Philips powder diffractometer. To determine the SiO2 and Fe2O3 content, an ARL PERFORM’X X-ray fluorescence spectrometer was used. To remove impurities, a СРF1-150М single-strand radiometric separator was used. We found that the radiometric separation of original quartz samples with the Fe2O3 content of ~ 0.1-0.15% produces pure quartz with the Fe2O3 content of ≤ 0.05% and a yield of 65-70%. Provided that the Fe2O3 content in the original quartz sample does not exceed 0.5%, concentrates with the Fe2O3 content of 0.05% and a yield of 35-55% can be obtained. The yield of pure quartz with the Fe2O3 content of 0.01% does not exceed 15-20%. The use of radiometric separation is established to reduce the amount of phosphorus in the final product by 2-3 times. This method is effective for obtaining coal concentrates of varying ash content (2.0, 4.1 and 7.3%); the resulting concentrated product obtained with a yield of 25% contains 1.5% of ash. Separation of silicon metal (with the initial iron content of 1.2-1.5%) yields a product matching silicon grade 773 (product yield ~ 50%), 553 (~ 35%) or 441 (20%). It is concluded that radiometric separation allows the content of impurities in quartz, silicon metal and coal ash to be reduced, thus facilitating the production of higher-grade silicon.

Efficient Iron Removal to Produce High Purity Quartz Sand by Micro-Inclusion Bursting Using Microwave Pretreatment Combined with Different Acid

The one of major impurities in quartz is iron, which has a great impact on the properties of the material and should be be strictly removed in many applications. In this study, a low-energy consumption, simple, fast processing is introduced by combination microwave treatment with different acid leaching. Selective heating of microwaves is used to process quartz, causing local phase changes to improve the purification effect. Acid leaching was used to remove the iron in the quartz matrix. Under optimized conditions, the iron content can be reduced to below 0.167 ppmw with one single purification pass.

A Critical Review on the Mineralogy and Processing for High-Grade Quartz

High-purity quartz (SiO2) is an important material widely used in many industries, including semiconductor technology, telecommunication, and optics. The content and distribution of impurities in quartz significantly affect the processing methods. This paper provides an insightful review on the processing of high-purity quartz, covering the analytical techniques, separation methods, and the critical procedures used to assess the quality of quartz ore. More importantly, the critical review of the thermal phase transition separation method for fine-grained mineral inclusions, micron-grade fluid inclusions, and lattice-bound trace elements is notably opened for the first time. It is proposed that the research field as a monopolized industry would benefit by expounding the critical problems that occur during the preparation of high-purity quartz.

Carbothermic Microwave Processing for the Enrichment of Iron Ore Fines

The current study investigates the beneficiation of iron ore fines by the carbothermal process using muffle and microwave furnace. The muffle furnace reduction was found useful for the separation of iron-bearing phases from the quartz impurities and concentrate with iron purity of ~ 64%, recovery of 98%, and a yield of 84.5% is achieved at 900 °C, 9% charcoal in 1 h. Incorporating coal as a reductant followed a similar trend as charcoal, although the leaner reduction rate leads to limited fayalite formation and, consequently, better magnetic property at a higher temperature. The microwave exposure of ore led to a temperature of ~ 750 °C in 15 min, and the ore-reductant mixture attained 960 °C with charcoal and ~ 800 °C with coal. The microwave reduction yielded comparable concentrate iron grade-recovery with muffle furnace reduction at comparatively lower carbon dosage (6%), suggesting better carbon utilization. Meanwhile, coal-based microwave reduction followed the opposite trend as muffle furnace reduction, and iron grade decreases with an increase in carbon dosage. The optimal conditions of 6% charcoal and 800 W yielded concentrate of 63.8% Fe, 99% recovery with 87.4% product yield. The maximum separation efficiency of the muffle furnace reduction is 80% at 1000 °C with 18% charcoal compared to 70% in the microwave at 6% charcoal, indicating the latter route is efficient and economical. The separation efficiency remains unaltered with carbon dosage suggesting minimal carbon required for achieving maximum separation is 6% C. The metallization of the product of microwave reduction was the functionality of reductant dosage and increases exponentially with carbon dosage. The ferrite formation is initiated at 12% C with maximum metallization of 38.5% at 27% charcoal and 900 W power. The maximum metallization in muffle furnace reduction is 16% at 1000 °C and 18% C. The techno-economic comparison indicates incorporating microwave reduction reduces processing time by 25%, and the carbon consumption is reduced by 35.5%.