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Untreated and pH-reduced red mud is used as a potential raw material in ceramic technology. During the alkalinity reduction process, CO2 is bubbled through the untreated red mud, which is particularly important as it can reduce the CO2 content of the atmosphere, and the pH of the red mud. Therefore, this method serves as a CO2 capture technique that utilizes waste as a raw material with low costs. Besides, reducing CO2 emission, it allows the production of material suitable for brick manufacturing from waste. In this study, treated and reduced alkalinity red mud was mixed with clay in the range of 5–30 wt%, and the physical, chemical, mechanical, and technologically important properties of the dried and sintered bricks were examined. The application of reduced alkalinity red mud as an additive offers advantages, as the resulting bricks require less water for processing, are less sensitive to drying, and their strength values exceed those of the commercially available bricks. Therefore, the technique presented in the study enables the production of bricks and roof tiles with advantageous properties using waste materials.

Numerous recent studies have shown that discharging colored wastewater into the environment causes contamination, which has adverse impact due to textile, dyeing, and food industries. The current study presents experimental research on the clathrate hydrate technique used for producing pure water from of wastewater contaminated by dyes. Under constant starting conditions, the clathrate formation for binary (water + refrigerant gas) and ternary (water + refrigerant gas + promotor) systems were studied. The R134a gas was used along with Cyclohexane (2.5 vol%), Tween 80 (100 ppm), and silica gel powder as promotors (100 ppm). Moreover, povidone-iodine (500, 2500, and 5000 ppm) and potassium permanganate (10, 50, and 100 ppm) were used as colored compounds in order to prepare synthetic wastewater (model wastewater). The production of hydrates, which rapidly captured the refrigerant gas molecules in the solid phase, was primarily responsible for the pressure drop. Both povidone-iodine and potassium permanganate have a negligible impact on the hydrate formation rates. It was found that the concentration of povidone-iodine and potassium permanganate in the produced water was decreased. As far as we know, the method of using clathrate hydrate to remove the dyes in water has never been investigated. The results showed that the povidone-iodine removal efficiency ranged between 86% and 92%, and the potassium permanganate removal efficiency ranged between 90% and 95%. The removal efficiency was improved by adding promotors, which increased the dissolved gas quantity and the amount of water hydrates. The maximum removal efficiency was accomplished using silica gel powder and cyclohexane, which are more significant than in pure water and Tween 80. This study demonstrated the viability of the clathrate hydrate technique as a green technology for the treatment of colored wastewater effluents from different industries.

During this research work, the wear and friction properties of TiN/TiC coatings produced with different manufacturing parameters were investigated against steel and zirconium counterparts. The coatings, which were deposited on WC–Co substrate, were characterized based on their microstructure, phase composition, and microhardness. The tribological behavior of the coatings was examined in accordance with ASTM G99 and ASTM G133 standards using pin-on-disc tests with steel and zirconium counterfaces, while the adhesion of the coatings was investigated with a modified scratch test. According to the results obtained from the experiments, the use of zirconium counterpart is advantageous even for coatings produced with different microhardness and layer thickness using the CVD method. The results show that the change in the friction coefficient can be well traced with properly chosen parameters, thereby determining the wear resistance of the coating.

We studied the fabrication of functionally graded Al2O3–CeO2-stabilized-ZrO2 (CTZ) ceramics by spark plasma sintering. The ceramic composite exhibits a gradual change in terms of composition and porosity in the axial direction. The composition gradient was created by layering starting powders with different Al2O3 to CTZ ratios, whereas the porosity gradient was established with a large temperature difference, which was induced by an asymmetric graphite tool configuration during sintering. SEM investigations confirmed the development of a porosity gradient from the top toward the bottom side of the Al2O3–CTZ ceramic and the relative pore volume distributed in a wide range from 0.02 to 100 µm for the samples sintered in asymmetric configuration (ASY), while for the reference samples (STD), the size of pores was limited in the nanometer scale. The microhardness test exhibited a gradual change along the axis of the ASY samples, reaching 10 GPa difference between the two opposite sides of the Al2O3–CTZ ceramics without any sign of delamination or cracks between the layers. The flexural strength of the samples for both series showed an increasing tendency with higher sintering temperatures. However, the ASY samples achieved higher strength due to their lower total porosity and the newly formed elongated CeAl11O18 particles.

Nowadays, global warming and the ensuing climate change are one of the biggest problems for humanity, but environmental pollution and the low ratio of waste management and recycling are not negligible issues, either. By producing alkali-activated cements (AACs), it is possible to find an alternative way to handle the above-mentioned environmental problems. First, with a view to optimizing experimental parameters, metakaolin-based AACs were prepared, and in it, waste tire rubber was used as sand replacement (5–45 wt %). Insufficient wetting between the rubber particles and the matrix was corrected through different surface treatments of the rubber. For improving the mechanical/strength properties of the specimens, fibrous waste kaolin wool (0.5–1.5 wt %) was added to the AAC matrix. Considering the results of model experiments with metakaolin, blast-furnace-slag-based AAC composites were developed. The effects of storage conditions, specimen size and cyclic loading on the compressive strength were investigated, and the resulting figures were compared with the relevant values of classic binders. The strength (44.0 MPa) of the waste-based AAC composite significantly exceeds the required value (32.5 MPa) of clinker saving slag cement. Furthermore, following cyclic compressive loading, the residual strength of the waste-based AAC composite shows a slight increase rather than a decrease.

Biocatalytic kinetic effect of a-chymotrypsin enzyme has been investigated in its free and pretreated forms (it was covered by a very thin, porous polymer layer, called enzyme nanoparticle) as well as its immobilized form into pores of polysulfone/polyamide asymmetric, hydrophilic membrane. Trimethoxysilyl and acrylamide-bisacrylamide polymers have been used for synthesis of enzyme nanoparticles. Applying Michaelis-Menten kinetics, the KM and vmax values of enzyme-polyacrylamide nanoparticles are about the same, as that of free enzyme. On the other hand, enzyme nanoparticles retain their activity 20&ndash, 80 fold longer time period than that of the free enzyme, but their initial activity values are reduced to 13&ndash, 55% of those of free enzymes, at 37 &deg, C. Enzyme immobilized into asymmetric porous membrane layer remained active about 2.3-fold longer time period than that of native enzyme (at pH = 7.4 and at 23 &deg, C), while its reaction rate was about 8-fold higher than that of free enzyme, measured in mixed tank reactor. The conversion degree of substrate was gradually decreased in presence of increasing convective flux of the inlet fluid phase. Biocatalytic membrane reactor has transformed 2.5 times more amount of substrate than the same amount of enzyme nanoparticles and 19 times more amount of substrate than free enzyme, measured in mixed tank reactor.