High Impurity Concentration Research Articles

Impurity-induced step pinning and recovery in MOVPE-grown (100) β-Ga2O3 film

This study focuses on the impact of high-doping impurities (>1018 cm−3) on the morphology of homoepitaxially grown (100) 4° off β-Ga2O3 film, as well as incorporating insights from the Cabrera–Vermilyea model (C–V model). Using atomic force microscopy imaging, we reveal that under low-supersaturation conditions, dopant-induced impurities lead to irregular step formation and growth stalling, inducing the step-bunching formation consistent with C–V model predictions. Conversely, higher supersaturation conditions restore desired step-flow morphology, resembling low-impurity growth states. It is also shown that the step-bunching formed under lower supersaturation conditions and high-impurity concentration might induce unwanted structural defects and compensate the free carriers. These findings underscore the delicate interplay between dopant concentrations, growth morphology, and supersaturation in metalorganic vapor phase epitaxy-grown (100) β-Ga2O3 films, providing a comprehensive understanding of optimizing their electrical properties with respect to power electronics applications.

Effect of Major Impurity in the Vanadium‐Rich Solution on the Growth of NaV2O5 Crystals under Hydrothermal Conditions

NaV2O5 is a promising cathode material for ion batteries with high capacity and good cycle performance. The high concentration of vanadium and low impurity in vanadium‐rich solution makes it possible to be used as raw material for vanadium product preparation. Vanadium solution containing impurity was prepared to investigate its influence mechanism on NaV2O5 crystal precipitation. The influence of four major impurity elements on the precipitation of NaV2O5 following the order of P > Al > Si > Fe. With the increase of impurity concentrations, vanadium conversion rate and V content of the precipitates decreased to varying degrees, while impurity content increased. When concentrations of Fe, Al and Si were high, the resulting precipitate was still NaV2O5, but the crystal structure changed. The AlOH and SiOH hider the condensation between VOH and broke the rod into irregular flakes and blocks. As P concentration gradually increased, the precipitates changed from NaV2O5 to VO2(H2O) 0.5 and then to Na3.053((V5O9)(PO4)2(OH)0.1(H2O)8, meanwhile, the morphologies changed from rod to plate, then to cross‐like, and finally to cube. Revealing the influence of impurity in vanadium‐rich solution on the growth of NaV2O5 crystal is conducive to the popularization of the process.

基于 Adams 的间隙可调弹性低损玉米摘穗割台的设计与试验

To address the high damage rate and impurity content in corn ear picking, this study proposes the design of a gap-adjustable elastic low damage corn picking header. Theoretical analysis of the adaptive gap adjustment mechanism for the picking plate and the flexible picking mechanism will be conducted. Simulation experiments will be performed considering three factors: the stiffness coefficient of the compression spring, the rotational speed of the stalk-pulling roller, and the thickness of the flexible body. The test results indicate that the minimum collision force on the fruit cluster occurs when the stiffness coefficient of the compression spring is 36 N/mm, the rotational speed of the stalk-pulling roller is 700 r/min, and the thickness of the flexible body is 6 mm. When the header tilt angle was 25 degrees and the working speed was 3 km/h, using the stalk roller speed as the experimental variable, the collision force of the gap-adjustable elastic low-damage corn picking header was compared to that of the ordinary plate-type corn picking header. The results indicated that the collision force of the gap-adjustable elastic low-damage corn picking header was reduced by more than 25 % compared to the ordinary plate-type corn picking header.

Synergy effects of phosphogypsum on the hydration mechanism and mechanical properties of alkali-activated slag in polysilicon sludge solidification

Polysilicon sludge (PSS), due to its high organic impurity content, poses significant challenges in solidification using traditional cementitious materials, failing to meet engineering standards. As such, alternative solidification methods are urgently needed to enhance PSS resource utilization. This study explores the use of phosphogypsum (PG) to improve the alkali activation process in the solidification of PSS with slag. Given that calcium sulfate in PG promotes alkali activation, this research investigates the synergistic effects of PG, PSS, and slag as precursors in developing an eco-friendly, resource-efficient solidification approach. Comprehensive characterization techniques, including X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and solid-state magic-angle spinning nuclear magnetic resonance were employed to assess the influence of PG and PSS dosages on the hydration behavior, mechanical properties, and microstructure of the alkali-activated system. Results demonstrated that the addition of 5 wt% PG significantly improved slag dissolution promoted the formation of hydration products such as hydrated calcium aluminate, reduced sample porosity, and refined the pore size distribution. These effects mitigated the inhibitory impact of PSS on the alkali activation process. However, higher dosages of PG and PSS reduced the system's pH, which in turn hindered early slag solubility and compromised the early strength of the solidified product. In addition, the ternary alkali-activated system developed in this study effectively immobilized heavy metals present in both PSS and PG, thus enabling the synergistic utilization of these waste materials while enhancing environmental compatibility. The findings provide valuable theoretical insights into the use of alkali-activated systems for solidifying waste materials and promote the development of resource-efficient, sustainable waste management strategies. This study paves the way for future research into optimizing the composition of PG, PSS, and slag mixtures to further enhance mechanical performance, long-term stability, and environmental safety.

(Invited) Assessing Mechanical Properties of Multilayer Copper Foils for Secondary Batteries

As the mobile phone and electric vehicle industries grow, demand for mechanically reliable copper foils used as a current collector in secondary batteries is also increasing. In this study, the mechanical properties of copper foils were investigated using a microstructure control electroplating technique which controls the grain sizes of the foils by adjusting the concentration of JGB (Janus Green B) added into the electroplating solution. The JGB addition played a role in suppressing recrystallization, which was confirmed through changes of the sheet resistance and microstructure measured using an EBSD (Electron Backscatter Diffraction) technique. These phenomena are related to the amount of JGB-originated impurities in foil that are co-deposited on the copper surface during electroplating. Using the JGB-based process, the multilayered thin foils were fabricated by alternately stacking a thin layer with a high impurity concentration and a thick layer with a low impurity concentration. The σ0 and KY constants of the Hall-Petch equation were obtained from the stress-strain curves through the tensile testing. Through comparing the σ0 and KY of the multilayered foils and the bulk copper, we secured more reasonable σ0 and KY constants in the Hall-Petch relationship.

RECYCLING OF DOMESTIC AND INDUSTRIAL WASTEWATER USING VERMIFILTRATION TECHNOLOGY

One of the biggest problems of our time is the growing shortage of fresh water. According to the World Health Organization, by the middle of the 21st century, half of the planet's inhabitants will experience an acute shortage of fresh water. Simultaneously with the growing consumption of clean water, the annual volume of wastewater from municipal, agricultural and industrial enterprises also increases. At the same time, the volume of water used annually is more than an order of magnitude higher than the volume of treated wastewater. Untreated wastewater is characterized by a high content of organic impurities and pathogenic microorganisms capable of causing diseases that are dangerous for human life. In connection with the outlined extremely urgent task is to ensure effective purification of wastewater from pollution with subsequent recycling of purified effluents - their reuse for other purposes: in the circulating system of industrial enterprises, agricultural and landscape irrigation systems. From this point of view, the process of vermifiltration - wastewater treatment using earthworms - is of great interest. The technology is based on the ability of worms to work as "biofilters". Worms absorb organic and inorganic pollutants from wastewater, digest them and release them in the form of their excrement (coprolites) into the environment. With such processing, wastewater is cleaned, disinfected, and detoxified; treated effluents are suitable for reuse. There is also a transformation of organic and inorganic components into organo-mineral fertilizer - vermicompost and biomass of earthworms, which can serve as raw materials for the fodder and pharmaceutical industry.

Effect of H3PO4 coordination on vanadium extraction and iron separation in a H2SO4 leaching system.

The selectivity of the full wet leaching process for vanadium extraction using H2SO4 is low, resulting in a high impurity content in vanadium extracted from vanadium-bearing shale. This study focused on vanadium extraction and iron separation from vanadium-bearing shale, involving the coordination of H3PO4 in an H2SO4 leaching system. The effects of the ratio and quantity of H2SO4-H3PO4, leaching time, leaching temperature, and liquid-to-solid ratio on vanadium-bearing shale leaching were investigated. The dissolution processes of various minerals and the mechanism of iron coordination precipitation were analyzed. Results showed that vanadium leaching efficiency was 91.07% and iron leaching efficiency decreased from 84% to 23.86% under optimal leaching conditions-H2SO4-to-H3PO4 ratio of 2 : 1, H+ content of 8 mol kg-1, liquid-to-solid ratio of 0.8 L kg-1, and leaching time of 12 h at 95 °C. Leaching kinetics showed that the leaching process of vanadium shale was a mixed-control process in the H3PO4-H2SO4 leaching system; additionally, the leaching process was mainly controlled by a chemical reaction with an activation energy of 67 kJ mol-1. The preferential dissolution order of minerals in the vanadium-bearing shale was calcite, apatite, magnetite, muscovite, and pyrite. Under the H2SO4-H3PO4 leaching system, the iron content was reduced by inhibiting the dissolution of pyrite and coordination precipitation of Fe3+ with PO4 3-, thus separating iron and vanadium from the source. This provides guidance for vanadium extraction and impurity separation from vanadium-bearing shale using an all-wet method.

Preparation of TiCl4 from Ilmenite Concentrates via Carbothermal Reduction and Boiling Chlorination for Different Carbon Proportions.

Low-temperature boiling chlorination is the most common approach used to achieve a clean preparation of TiCl4 from ilmenite concentrates with high contents of calcium and magnesium impurities. However, this process did not systematically investigate the impact of the Ti/C ratio of the raw materials on the chlorination efficiency of Ti, Ca, and Mg elements. Thus, the influence of the carbon allocation proportion on the carbothermal reduction and boiling chlorination process of ilmenite concentrates with high contents of calcium and magnesium impurities was investigated in this study. The results show that the reduction products of ilmenite concentrates are mainly Mg-rich Ti2O3 impurities at a low carbon proportion. However, with increasing carbon proportion, Ti2O3 is gradually reduced to TiC x O1-x , and Mg2TiO4 appears. The Ti2O3 content in the acid-insoluble matter of the reduced products decreases after acid washing, while the TiC x O1-x content increases with increasing carbon allocation proportion. With increasing carbon proportion, the chlorination rate of the acid-insoluble matter increases, and the corresponding chlorination rates of titanium, magnesium, and calcium also increase. The residual carbon produced by acid-insoluble chlorination at high carbon proportions exacerbates the chlorination of Mg and Ca impurities.

Ethyl biodiesel production from crude soybean oil using enzymatic degumming-transesterification associated process

Brazil is one of the largest soybean producers in the world. Biodiesel production in Brazil (specially soybean oil biodiesel) has been growing every year and demanding more effective and sustainable technologies, which is the case of enzymatic processes. Enzymatic degumming could be an alternative to provide better quality products, before biodiesel production but also, in a one reaction step as a proposal to reduce time and costs. Therefore, this work was aimed at evaluating enzymatic degumming (previously optimized) of crude soybean oil using a phospholipase cocktail associated with transesterification using lipase from Aspergillus oryzae for ethyl biodiesel production. For this, transesterification was optimized for ethanol:oil (E:O) ratio, water and lipase % through a central composite rotatable design (CCRD). Optimal conditions were used to evaluate two degumming-transesterification associated processes: i) a one-pot reaction (OPR) where degumming and transesterification were performed at the same reactor; and ii) a two-pot reaction (TPR) where oil was first degummed, followed by transesterification. The optimal transesterification condition were achieved for E:O = 4.48:1, water = 3.41 % and lipase = 2.43 %, where 97 % fatty acid ethyl esters (FAEE) were obtained. Both OPR and TPR provided biodiesels with FAEE > 94 %: TPR was the best with 97.5 % and 99.98 % before and after biodiesel purification. Mineral elements (including phosphorus) and other impurities (anions) were low, and within quality standards. Glycerol produced also presented very low content of impurities which is quite advantageous. Although lipase achieves good conversion to FAEE (95.7 ± 0.29 %) using crude oil (Control), the final biodiesel carries many impurities (P=80.07 ± 0.1 mg/kg), thus requiring subsequent biodiesel purification steps. In addition, the high impurity content generates a biodiesel that does not comply with ANP legislative standards, P<10 mg/kg. The use of enzymatic degumming in the biodiesel production process generates a biodiesel with low impurities and higher final quality, in addition to being a process that generates less effluent. Enzymatic degumming was essential for obtaining high quality biodiesel and its association with transesterification showed to be a great option for decreasing time and costs for biodiesel production.

Development of a demulsifier and technological process study for the preparation of highly viscous heavy oils for refinement

One of the challenges in the petroleum industry is the production of highly viscous heavy oils, often accompanied by undesirable emulsion formation with very high aggregate stability. To prepare the crude oils for refinement, the oils must be destroyed. The destruction of aqueous emulsions containing highly viscous heavy oils is an intricate task owing to the comparatively small disparity in water and oil densities, as well as the high viscosity of the dispersive medium and its high content of mechanical impurities. The problem of the destruction of petroleum emulsions arises desperately during the desalination and dehydration of crude oils with a high content of emulsifiers (resins, asphalts, paraffin, etc.) The creation of a highly efficient demulsifier and the development of an optimal technological process for the preparation of highly emulsifying oils that are distinguished by the composition and quantity of emulsifiers of West Siberian oils, which are widely refined in Russia, are the ways to resolve this challenging and timely issue. This study focuses on the viscous heavy oil of the Verbliouje deposit in the Astrakhan region. It also explains the creation of an effective demulsifier for the destruction of petroleum emulsions characterized by a very high emulsifying power and the fundamental principles of the development of deep dehydration technology and desalination of such high-viscosity heavy oils.

Polycrystalline silicon photovoltaic cell defects detection based on global context information and multi-scale feature fusion in electroluminescence images

In photovoltaic (PV) cell inspection, electroluminescence (EL) imaging provides high spatial resolution for detecting various types of defects. The recent integration of EL imaging with deep learning models has enhanced the recognition of defects in PV cells. However, the high surface impurity content in polycrystalline silicon PV cells presents a challenge. Defect features can be similar to complex background textures, making highlighting features for small target defects difficult and leading to potential misclassification as background or other classes. To address these challenges, we propose a novel deep convolutional neural network (CNN) model for effectively identifying small target defects in polycrystalline PV cells. We first utilize a global context information (GCI) block to improve CNN’s modeling of global information, aiding in distinguishing PV cell defects with similar local details. Moreover, we design a channel weight feature pyramid (CWFP) that dynamically adjusts the channel weights of extracted features. We further achieve multi-scale feature fusion through the pyramid structure to enhance the resolution capability for small targets. The proposed model was evaluated on a publicly available dataset of 8 defect classes in polycrystalline PV cells, achieving an accuracy of 96.36 %. The experimental results show that the proposed model outperforms existing deep learning models in detecting small target defects with higher precision.

High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets

To realize room temperature ferromagnetic (FM) semiconductors is still a challenge in spintronics. Many antiferromagnetic (AFM) insulators and semiconductors with high Neel temperature TN are obtained in experiments, such as LaFeO3, BiFeO3, etc. High concentrations of magnetic impurities can be doped into these AFM materials, but AFM state with very tiny net magnetic moments was obtained in experiments because the magnetic impurities were equally doped into the spin up and down sublattices of the AFM materials. Here, we propose that the effective magnetic field provided by a FM substrate could guarantee the spin-dependent doping in AFM materials, where the doped magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM) materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM insulator LaFeO3 with FM substrate of Fe metal by the density functional theory (DFT) calculations. It is shown that the doped magnetic Mn impurities prefer to occupy one sublattice of the AFM insulator and introduce large magnetic moments in La(Fe, Mn)O3. For the AFM insulator LaFeO3 with high TN = 740 K, several FIM semiconductors with high Curie temperature TC > 300 K and the band gap less than 2 eV are obtained by DFT calculations when 1/8 or 1/4 Fe atoms in LaFeO3 are replaced by the other 3d, 4d transition metal elements. The large magneto-optical Kerr effect (MOKE) is obtained in these LaFeO3-based FIM semiconductors. In addition, the FIM semiconductors with high TC are also obtained by spin-dependent doping in some other AFM materials with high TN, including BiFeO3, SrTcO3, CaTcO3, etc. Our theoretical results propose a way to obtain high TC FIM semiconductors by spin-dependent doping in high TN AFM insulators and semiconductors.

Large-scale production of cefazolin in a microreactor with a low impurity content and high yield

Cefazolin is crucial in the field of healthcare because of its efficacy against bacterial diseases, but trace amounts of polymer impurities produced during synthesis may cause severe allergic reactions. In this work, an efficient system based on a membrane dispersion microreactor was designed for scalable cefazolin production with a high yield and low impurity content. At a production scale of 200 kg, the yield could reach 90 %, and the polymer impurity content could reach <0.008 %. Density functional theory calculations were used to investigate the formation mechanisms of the polymer impurities. The results revealed that the activation energy of cefazolin ring-opening and substitution reactions decreased by 22.4 kJ/mol and 6.4 kJ/mol respectively under alkaline conditions, resulting in increased polymer content. Computational fluid dynamics simulation indicates that the organic base in the substrate can be rapidly dispersed in the membrane dispersion microreactor, thus avoiding excessive local base concentration. In conclusion, the development of a membrane dispersion microreactor system offers a scalable and efficient method for cefazolin production with significantly lower polymer impurity content, thereby addressing a critical challenge in antibiotic synthesis and ensuring safer and more reliable healthcare applications.

The use of biofilters in the treatment of wastewater containing organic substances

Abstract The lack of sufficiently effective treatment of wastewater generated in industry and domestic life remains one of the most acute environmental problems. Domestic wastewater is characterized by a high content of organic impurities in its composition, which determines the specifics of the choice of treatment technologies. One of the most relevant and effective methods is biological purification carried out in biological filters. This article discusses the problems associated with wastewater treatment of a sanatorium compound. The analysis of the content of various components in the water supplied to the treatment was carried out, the efficiency of the treatment equipment was determined. The paper proposes and substantiates the expediency of using a modern type of synthetic ruff biofilter media to increase the cleaning efficiency of the wastewater and their compliance with regulatory requirements for discharge into a water body.

Characterization of residual-resistance-ratio of Cu stabilizer in commercial REBCO tapes

Residual-resistance-ratio (RRR) of Cu stabilizer in REBCO coated conductor is an important design parameter for REBCO magnets. Cu stabilizer with high RRR is especially beneficial for quench protections of REBCO magnets. In this work, we study RRR of electroplated Cu stabilizer in commercial REBCO tapes. We present RRR of over 180 samples measured for the quality assurance programs of REBCO magnet projects at the National High Magnetic Field Laboratory, USA (NHMFL). To investigate the factors that influence RRR, several samples were analyzed extensively by using scanning electron microscopy, secondary ion mass spectroscopy, and inductively coupled plasma mass spectroscopy. We found that RRR is strongly correlated with the grain size of Cu, which suggests that resistivity at low temperatures is dominated by grain boundary resistivity. In addition, low RRR corresponds to high concentration of chlorine impurity. This is explained by that higher chlorine impurity hindered the grain growth in the self-annealing process at room temperature which resulted in smaller grain size and low RRR. Annealing at 300C significantly enlarged the grain size and enhanced RRR. Due to the concern of critical current degradation, however, annealing is not recommended as a practical method to improve RRR of Cu in REBCO tapes.

Operation of downhole pumps under sanding conditions

One of the unfavourable factors of downhole pumping equipment operation at the fields at the final stage of development is high content of mechanical impurities in the pumped fluid. Similar problems are observed in fields with friable, weakly cemented formations, the fracture products of which flow downhole, resulting in lower extraction rates, equipment damage and higher operating costs. In oil production practice various technological measures and technical means are used to reduce the negative impact of sand penetration - regulation and optimisation of pumping equipment operation mode to ensure a rational rate of fluid withdrawal, application of technical devices in the form of sand filters and sand anchors and others. However, these measures and recommendations, for the most part, work successfully in the modes of continuous operation of wells. With the growing number of oil fields at the final stage of development, the issue of sanding becomes more and more urgent, as due to low flow rate wells at such fields are often switched to the mode of periodic operation, which favours the formation of sand plugs in tubing above the pump due to sufficient time for sedimentation of mechanical impurities. This can lead to pump jamming or rod breakage during subsequent well pump start-up. The experience of using sand filters (frame, slotted and others) in the arrangement of downhole pumps has shown that it does not always effectively solve the problem of sand penetration due to clogging of their cells with mechanical impurities and increased hydraulic resistance. This negatively affects the pumping equipment operation due to the shift of characteristics into the zone of suboptimal modes with associated problems for the electric drive. This makes it necessary to carry out underground well workover with removal of deep well pumping equipment for replacement or washing of the filter in surface conditions, as due to their peculiarities in the well pump layout (the filter is located at the intake of the pumping section), washing in well conditions is not always possible. These problems require not only the creation of effective downhole devices to prevent sand ingress to the pump intake or devices to prevent sand plugs above it, but also acceptable in practice calculation methods for predicting the sedimentation time of mechanical impurities in tubing or determining the minimum required speed of upward oil flow for stable sand removal. These calculation methods would also allow to reasonably regulate the time of technological interruptions while waiting for the wells to start up in periodic operation modes or to predict the time of activation of sand control devices for discharging the sand accumulated above the pump. This is the subject of this article. As a result of calculation analysis it was established that the main factors affecting the sedimentation process of mechanical impurities in the well are the speed and mode of fluid movement, its viscosity, density and size of the impurities themselves. Moreover, the most sensitive for the calculation accuracy is to take into account the change of fluid viscosity as it moves along the tubing as a result of heat exchange and the change of dissolved gas content due to pressure drop. Although at this stage the proposed methodology does not take into account some factors that can make additional adjustments to the process of sand sedimentation, however, it allows to predict with acceptable accuracy the time of technological interruptions in the well operation to prevent the formation of sand plugs, or the rational mode of operation of pumping equipment, providing the necessary speed of upward flow in the pipe for sand removal.

Spent Lithium-Ion Battery Recycling Using Flotation Technology: Effect of Material Heterogeneity on Separation Performance

In this study, two types of recycling scenarios are assessed for spent battery materials using froth flotation. The first is for a single cathode chemistry and would be considered as the most likely scenario for a large battery manufacturer, who takes back their own batteries for reprocessing. The second scenario is for mixed cathode chemistry, and this would be the most likely scenario for regional reprocessing. The mixed spent battery materials assessed in this work were sourced from such an industrial recycling operation in Australia. Good results were obtained for both recycling scenarios. The anode recovery and anode grade in the final concentrate for both materials evaluated were for the single spent battery material 80.1% and 90.3%, respectively, and for the mixed spent battery material, 77.4% and 82.0%, respectively. For the final tailings, the cathode grades for both materials tested were 93.9% and 87.1%, respectively, with the lower grade for the mixed spent battery attributed to the high content of impurities in the original material. These results highlight the importance of the preprocessing ahead of the flotation process. The results confirm froth flotation as a feasible technique that can be used to achieve the bulk of the separation.

A Review on the Zone Refining Process Technology toward Ultra‐Purification of Gallium for GaAs/GaN‐based Optoelectronic Device Applications

AbstractUltrapure gallium up to 99.9999%/ 99.99999% (6N/7N) purity level is a highly demanding material needed for the growth of gallium‐based group III–V semiconductor compounds and optoelectronic devices. However, general extraction of gallium from Bayer liquor contains high impurity content and ultra‐purification of the same cannot be accomplished by a single step. Thus, the purpose of this review is to assess various purification processes for the production of ultra‐pure gallium and to critically examine its applications in the optoelectronics industry. Through this research survey, it is found that zone refining of the zone melting process stands tall over other methods in purifying materials even up to 13N. Hence, scientists are adopting detailed mathematical models and simulation tools for designing unique zone refining systems for material purification. Current‐day technology even adopts intelligence methods such as machine learning, which sheds light on the importance of different zone refining parameters that influence the purification process. Here, the practical aspects of zone refining and how the feedback from the theoretical models or performance prediction through intelligence methods can be effectively incorporated into practice have also been emphasized

Waste‐derived low‐grade glycerol purification and recovery from biorefineries: an experimental investigation

AbstractA combination of different physio‐chemical treatment steps was applied to purify industrially derived crude glycerol at laboratory scale. The full process included acid–base treatments, phase separation, and adsorption, and the glycerol purity and recovery were optimized by varying the pH during saponification and acidification, the solvent‐to‐glycerol ratio, and type of base used in the process to enhance both. The testing campaign resulted in a final purity of up to 87% wt starting from a very low‐quality ‘end‐of‐life’ waste glycerol sampled from different refineries. The net glycerol recovery at laboratory scale reached 42% of the initial glycerol in the feedstock and the maximum ash removal exceeded 90% given the low quality of the feedstock and high content of impurities and the attempt to achieve high glycerol recovery. The experiment showed that mild operations such as saponification with KOH (pH of 8), acidification with H3PO4 (pH of 6), an ideal 2‐propanol to glycerol volume ratio equal to 3 and potassium hydroxide as a base for the neutralisation step were the optimum conditions despite the differences between samples. The sequence of the processes proposed was therefore considered a viable option to treat any kind of crude glycerol to make it profitable for fuel and chemical applications.

Circular economy as applied to refractory materials.

The closed-loop economy concerning refractory materials is implemented through systematic involvement in post-operational usage in thermal, including metallurgical, units as secondary (by-product) raw materials. This is one of today's trends in resource and energy economics, reducing carbon footprint and CO2 emissions, decreasing waste with subsequent disposal in landfills. Purified scrap of refractory materials is used as supplementary materials in metallurgical processes, commonly referred to as scrap utilization when used as fluxes to adjust slag composition in metallurgical units, molded materials for welding in converters, refractory fillers in the production of unformed materi-als for sections lining working outside the aggressive influence of molten metal and slag, etc. For these purposes, the scrap is sorted into grades, crushed and screened, occasionally incorporating other products. Refractory scrap after ser-vice in metallurgical units usually has higher impurity content, higher porosity, and contains fragmented remnants of the refractory structure. Recycling refractory scrap may additionally involve technological methods for extracting impurities (enrichment) with subsequent use of the recyclate directly in refractory production, partially replacing primary raw materials. In this case, research work with involvement of qualified specialists and the entire body of knowledge in creating new refractory materials is necessary. Practice has shown that qualified involvement of recyclate in manufacturing processes of high-quality refractories is accompanied by solving non-standard tasks and requires a special approach, including the issue of removing introduced or formed foreign materials in refractory material during its operation. Enrichment is an effective direction for cleaning refractory scrap, extracting quality materials during processing of waste from mining enterprises, materials of technogenic origin to obtain recyclate of necessary quality. The enrichment technology is selected based on the set tasks. Recyclate quality for use alongside primary raw materials must guarantee refractory manufacturers meet the corresponding requirements of end-users. An original technology of recyclate enrichment during its selective grinding with product separation using air-gravitational and centrifugal-air classification has been developed