Phase Composition Research Articles

CHARACTERIZATION OF CLAYS FROM “MINES MARITSA IZTOK” AS RAW MATERIALS FOR CERAMIC INDUSTRY

The chemical and phase compositions of the clays from coal mining were evaluated by XRF and powder XRD method, respectively. Hot Stage Microscope was used to estimate the thermal behaviour. In addition, the thermal losses of the clays after 1 h thermal treatment at different temperatures were measured. This preliminary analysis elucidates potential prospects for using some of clays as raw materials for ceramic industry. It seems that samples which are montmorillonite type are more plastic, while the others, where higher sand content is observed, and the drying shrinkage is negligible could be characterized as less plastic. The initial results for the thermal behaviour and the structure of a brick sample (obtained by mixing two types of clays) and a foamed geopolymer are also reported. The first sample shows a beginning of the firing shrinkage at about 1000°C, while the second demonstrates intensive bloating after 950°C, leading to specimen with about 56 % closed porosity. Finally, X - ray Computed Tomography and SEM was used to highlight the structure of some test samples.

Advanced nano-composite coatings of ZrB₂/ZrC/SiC on carbon fibers via eco-friendly precursor synthesis

This study presents a comprehensive investigation into the synthesis and characterization of ZrB2/ZrC/SiC composite coatings on carbon fiber substrates via a solution-based process followed by high-temperature pyrolysis. The precursor solution was prepared using Gum Ghatti (GG), zirconyl chloride, tetraethyl orthosilicate, and boric acid. Optimization of precursor concentration and molar ratios was performed to achieve suitable viscosity and composition. The pyrolysis process was conducted in an argon atmosphere, resulting in the formation of well-defined ZrB2, ZrC, and SiC phases. XRD analysis confirmed the phase composition, while SEM imaging revealed spheroidal particle aggregates with a uniform distribution of composite phases. TG-DTA analysis reveals the thermal decomposition behavior, highlighting distinct stages of mass loss and phase transformations. Coated carbon fibers exhibited enhanced oxidation resistance, as evidenced by TGA analysis. SEM analysis confirmed the uniform distribution and adhesion of the composite matrix on the carbon fiber substrate. This study demonstrates the successful synthesis of ZrB2/ZrC/SiC composite coatings with promising thermal properties for advanced applications.

Corrosion resistance and biocompatibility of silica coatings on AZ31 magnesium alloy via magnetron sputtering

Magnesium alloys have promising prospects in biodegradable implants, but premature degradation is the main factor limiting their application. We prepared silicon coatings of different thicknesses on the surface of AZ31 magnesium alloy using the RF magnetron sputtering method. The phase, microstructure, and elemental composition of the coatings were characterized by XRD, SEM, and EDS, respectively. The corrosion resistance of the coatings in simulated body fluids was tested using immersion corrosion and electrochemical corrosion tests. Results showed that the silicon coating sputtered for 3 hours had the best corrosion potential and current, with a corrosion current density of 6.5614E-6 (A/cm2), which is two orders of magnitude lower than that of the AZ31 substrate. The extract of the sample in RPMI-1640 medium was co-cultured with human umbilical vein endothelial cells (HUVEC), and its cytotoxicity was evaluated by the CCK-8 assay. It was found that the silicon coating sputtered for 3 hours had the least toxicity, and the endothelial cells had a high proliferation rate. Therefore, the magnetron sputtered Si coating on AZ31 magnesium alloy exhibits good corrosion resistance and biocompatibility.

Novel Anodic TiO2 Synthesis Method with Embedded Graphene Quantum Dots for Improved Photocatalytic Activity

Photocatalytic degradation of pollutants have a high potential for sustainable and renewable uses. TiO2 is a widely studied photocatalyst due to its high chemical and photochemical stability and wide range of applications. However, the wide band gap and low capacity of photo-induced charge separation provide lower catalytic activity; thus, improvement of these properties must be found. The doping of TiO2 with other elements, such as carbon nanoparticles (CNP) in a quantum dot form, offers a promising pathway to improve the aforementioned properties. In addition, in situ doping methods should be investigated for practical scalability, as they offer the advantage of integrating dopants directly during material synthesis, ensuring a more uniform distribution and better interaction between the dopant and the host material, in turn leading to more consistent photocatalytic properties. Current technologies primarily involve nanoparticle combinations. This work focuses on the development of a novel in situ synthesis methodology by the introduction of three different graphene-based quantum nanodots into anodic TiO2 and the following investigation of structural, morphological, and photocatalytic properties. Results indicate that the introduction of CNP allows for the shift of a set of parameters, such as the optical band gap, increased photo-induced charge carrier density of TiO2/CNP composite, and, most importantly, the change of crystalline phase composition depending on added CNP material. Research indicates that not only a higher concentration of added CNP enhances higher photocatalytic activity as tested by the degradation of methylene blue dye, but also the type of CNP determines final crystalline phase. For the first time brookite and rutile phases were obtained in anodic titania synthesized in inorganic electrolyte by introducing hydrothermally treated exfoliated graphene.

Vapor–liquid phase equilibrium prediction for mixtures of binary systems using graph neural networks

AbstractVapor–liquid phase equilibrium (VLE) plays a crucial role in chemical process design, process equipment control, and experimental process simulation. However, experimental acquisition of VLE data is a challenging and complex task. As an alternative to experimentation, VLE data prediction offers great convenience and utility. In this article, an artificial intelligence network is proposed to predict the temperature and the vapor phase composition of binary mixtures. We constructed a graph neural network (GNN) and designed an uncertainty‐aware learning and inference mechanism (UALF) in the prediction process. The model was tested on both a self‐constructed dataset and a publicly available dataset. The results demonstrate that the proposed method effectively reveals the phase equilibrium properties of the target data. This work presents a novel approach for predicting vapor–liquid phase equilibrium in binary systems and proposes innovative ideas for investigating phase equilibrium mechanisms and principles.

Evaluation into the effect of lignocellulosic biochar on the thermal properties of shape stable composite phase change materials

Biochar is suitable for preparing shape stable composite phase change materials (sscPCMs) due to the advantages of cost-effective, environmentally, and sustainability. However, the heat properties of biochar-based sscPCMs were not consistent. To investigate how different types of biochar influence the thermal properties of sscPCMs, three types of sscPCMs were successfully prepared using peanut shell biochar (PSC), poplar wood biochar (PWC), and corn straw biochar (CSC) as framework materials and combined with stearic acid (SA). A comprehensive analysis of the thermal properties of three sscPCMs was performed, taking into account thermal conductivity, phase change latent heat, encapsulation efficiency, crystallization rate, and energy storage efficiency. The study indicated that among the three types of sscPCMs, SA/PWC sscPCMs demonstrated excellent comprehensive performance. The phase change latent heat of SA/PWC reached 100.13 J/g, and the thermal conductivity was 0.38 W/mK. Compared to SA/PSC, the phase change latent heat of SA/PWC increased by 45.96 %, with only a 28.30 % reduction in thermal conductivity. In comparison to SA/CSC, the thermal conductivity of SA/PWC improved by 18.75 %, while the phase change latent heat decreased by only 14.02 %. In addition, the proportions of cellulose, hemicellulose, and lignin played a crucial role in determining the thermal properties of sscPCMs. This study clarified the mechanism by which biochar influences the thermal characteristic of sscPCMs, offering valuable insights for choosing biochar framework materials.

Effect of the Activator Type on the Microstructure and Properties of the Vanadizing Layer on the Surface of GCr15 Steel

This research aims to replace the activator NH4Cl in a vanadizing agent and reduce air pollution and harm to the human body. This study adopts powder pack cementation to prepare the vanadizing layer on the surface of GCr15 steel, focusing on the influence of the activator types (NH4Cl, CuCl, CuCl+Cr powder, and CuCl+Ni powder) on the structure and properties of the vanadizing layer on the surface of GCr15 steel. The results show that the vanadizing layer is prepared on the surface of GCr15 steel with different activators and that they are closely bonded to the matrix. The main phase composition of the vanadizing layer is VCx, and it has a preferred orientation on the (111) crystal surface. When the type of activator is NH4Cl, the prepared vanadizing layer has a lower friction factor. When the activator type is CuCl+Cr powder, the prepared vanadizing layer has less inclusions, the thickness of the vanadizing layer is the highest at 10.87 μm, and the hardness is the highest at 2331.7HV. Considering the thickness of the layer, the hardness, and the wear resistance, the best performance of the vanadizing layer was obtained when the activators were CuCl+Cr powder.

The change of phase composition and the morphology of particles of hydrothermal titanosilicate precipitates during their aging

During the study of phase formation under conditions of hydrothermal synthesis of alkaline titanosilicate systems (NH₄)₂TiO(SO₄)₂⋅H₂O или TiOSO₄⋅H₂O-Na₂SiO₃-NaOH-H₂O it was found that the formed titanosilicate solid phases differ both in composition and structure. The process of their aging under conditions of long-term exposure without forced heating is accompanied mainly by the loss of free water without noticeable structural and morphological changes. The exposure to the temperature of 70–100°С significantly accelerates the process of solid phase transformation. In these conditions, a porous system of particles is formed, which is confirmed by an increase in their specific surface area and total pore volume, as well as by an increase in the activity of the powders to absorb single- and double-charged cations. The effectiveness of hydrochloric acid treatment of fresh and especially aged precipitates on the ordering of the structure with the formation of crystals of a clear frame shape, inherent in the minerals zorite and ivanyukite, which contributes to increasing the sorption capacity of the final product is shown. The obtained results are used to adjust the technological regulations, which are used to test the technology of titanosilicate sorbent on the pilot plant.

Mechanical, Durability, and Microstructure Characterization of Pervious Concrete Incorporating Polypropylene Fibers and Fly Ash/Silica Fume

Pervious concrete, because of its high porosity, is a suitable material for reducing the effects of water precipitations and is primarily utilized in road pavements. In this study, the effects of binder-to-aggregate (B/A) ratios, as well as mineral admixtures with and without polypropylene fibers (PPFs) (0.2% by volume), including fly ash (FA) or silica fume (SF) (10% by substitution of cement), on the mechanical properties and durability of pervious concrete were experimentally observed. The experimental campaign included the following tests: permeability, porosity, compressive strength, splitting tensile strength, and flexural strength tests. The durability performance was evaluated by observing freeze–thaw cycles and abrasion resistance after 28 d curing. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA-DTA), and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) were employed to investigate the phase composition and microstructure. The results revealed that, for an assigned B/A ratio identified as optimal, the incorporation of mineral admixtures and fibers mutually compensated for their respective negative effects, resulting in the effective enhancement of both mechanical/microstructural characteristics and durability properties. In general, pervious concrete developed with fly ash or silica fume achieved higher compressive strength (>35 MPA) and permeability of 4 mm/s, whereas the binary combination of fly ash or silica fume with 0.2% PPFs yielded a flexural strength greater than 6 MPA and a permeability of 6 mm/s. Silica fume-based pervious concrete exhibited excellent performance in terms of freeze–thaw (F-T) cycling and abrasion resistance, followed by fiber-reinforced pervious concrete, except fly ash-based pervious concrete. Microstructural analysis showed that the inclusion of fly ash or silica fume reduced the harmful capillary pores and refined the pore enlargement caused by PPFs in the cement interface matrix through micro-filling and a pozzolanic reaction, leading to improved mechanical and durability characteristics of pervious concrete.

Study on Microstructure and Properties of AlCoCrFeNi High-Entropy Alloys by Extreme High-Speed Laser Cladding

AlCoCrFeNi HEA powders were cladded onto AISI 1045 steel using EHLA and CLA, respectively. The phase composition, microstructure, micro/nanohardness, and corrosion resistance of the two coatings were compared and analyzed. The results show that the phase structure of AlCoCrFeNi HEA coatings prepared by EHLA and CLA was that of a BCC/B2 phase solid solution. From the bottom to the top, the EHLA-derived AlCoCrFeNi HEA coating experienced evolution in the microstructure of plane crystal, dendrite, and equiaxed crystal. The micro/nanohardness of EHLA-derived coating (~507 HV0.2, 6.716 GPa) is higher than that of CLA-derived coating (~429 HV0.2, 5.778 GPa). The electrochemical test results show that the Ecorr of CLA is −0.527 V and the Icorr of CLA is 1.272 × 10−7 A/cm2, while the Ecorr of EHLA is −0.454 V and the Icorr of EHLA is 1.588 × 10−8 A/cm2, which means that the corrosion resistance of EHLA is better.

Hydrogen production and elemental migration during supercritical water gasification of food waste digestate

The rapid growth of food waste (FW) is a huge challenge on a global scale, and anaerobic digestion is one of the most commonly used methods to deal with food waste, and the increasing amount of food waste digestate (FWD) produced by anaerobic digestion also poses a huge challenge to waste management. This paper explores supercritical water gasification (SCWG) as a valuable and innovative strategy for the conversion of FWD into H2-rich syngas. The research focuses on analyzing the effects of reaction temperature and residence time on syngas production, gas composition, element migration (C, N and P) during the SCWG process. Experimental results show that as the reaction temperature increases from 400 °C to 500 °C, the total syngas yield increases significantly, from 2.4 mol/kg to 9.7 mol/kg, especially the yields of H2, CO2, and CH4. As the reaction temperature increases and the residence time increases, the migration of carbon from the solid and liquid phases to the gas phase accelerates with increasing temperature and residence time, resulting in a higher proportion of carbon in the gas phase. In terms of liquid phase composition, nitrogenous compounds are significantly converted into ammonium (NH4+-N) at higher temperatures. In addition, the organic phosphorus is observed transferring into inorganic phosphorus, which are mainly apatite. This study explores the scalability of SCWG and its potential for the production of clean fuels, thereby contributing to the sustainable management of FWD.

Analysis of serum phase proteins and emulsifiers on the whipping capabilities of aerated emulsions: From the perspective of air-liquid interface rheology

In aerated emulsions, the serum phase plays a crucial role in determining whipping capabilities. However, the effects of serum phase components on emulsion properties remain largely unexplored and continue to be a mystery. This study takes a micro-level approach, focusing on the air-liquid interfacial rheology by incorporating different types of surfactants (proteins and emulsifiers) into the serum phase. It systematically explores the effects on the serum phase interface, emulsion properties, whipping capabilities, and foam stability in a stepwise manner. Proteins only slightly affect the strength of the air-liquid interface, primarily improving the capacity to trap bubbles at the initial whipping stage, thereby boosting the overrun of the aerated emulsion. The high viscoelastic modulus of the interface membrane is greatly influenced by the presence of solid lipid nanoparticles of glycerol monostearate (GMS SLN), leading to a reduction in whipping time and improved surface-mediated partial coalescence. This ultimately enhances the quality and stability of the foam system. Tween 80, due to its hydrophilic properties, is able to quickly adsorb at the air-liquid interface using the Gibbs-Marangoni mechanism. This helps to expedite the end of the whipping process and ultimately improves the foam quality. On the contrary, glycerol monooleate (GMO), a lipophilic emulsifier for liquids, struggles to effectively adsorb at the interface, leading to decreased stability of the air-liquid interface in the system and resulting in poor whipping capabilities. This paper delves into the mechanism by which different surfactants affect the whipping capabilities of aerated emulsions through an analysis of serum phase composition, laying the groundwork for enhancing formulation design.

Study on properties of pre-alloy powder of TiNiHf high temperature shape memory alloy for additive manufacturing by preheating treatment

In this work, pre-alloyed powder high-temperature shape memory alloy (Ti30Ni50Hf20) for additive manufacturing was preheated at 300–800°C and thermoscycled at 650°C to examine the influence of preheating temperature and thermal cycle number on the phase composition and phase transformation behavior. The results showed that the H phase precipitation occurred in the matrix with the rising preheating temperature within 300–600°C, and the phase transformation temperature of the pre-alloyed powders also increased. When the preheating temperature exceeded 600°C, the H phase dissolved back into the matrix, and the phase transformation temperature decreased. A total of 50 thermal cycles were conducted on the pre-alloyed powders at 650°C, and the phase transformation temperature and phase composition remained stable after cycling. It can be concluded that the preheating temperature greatly affected the phase composition and phase transformation behavior of Ti30Ni50Hf20 high-temperature shape memory alloy pre-alloyed powders, while the number of thermal cycles delivered a minor effect.

Effects of La2Ce2O7 on the phase composition, microstructure, wetting behaviour and corrosion resistance of magnesia refractory

The addition of rare earth oxides has a significant impact on the improvement of thermal properties of refractory materials. Magnesia refractory with La2Ce2O7 was prepared by high-temperature solid-phase synthetic sintering at 1873 K for 5h using fused magnesia as raw materials, CeO2 and La2O3 as addition, respectively. The effect of La2Ce2O7 on the phase composition, microstructure, apparent porosity, bulk density, wetting behaviour and corrosion resistance with steel of fused magnesia were investigated. When the content of La2Ce2O7 was 20wt%, the results showed that as-prepared samples from fused magnesia with an apparent porosity of 17.63% and a bulk density of 3.11g·cm-3 were obtained by high temperature solid-phase sintering reaction at 1873 K for 5h, respectively. Due to the addition of La2Ce2O7, and raw materials in the impurity phase CaO and SiO2 for the reaction, the generation of a small amount of CaLa4(SiO4)3O and La8.89Si6O25.9 high melting point phase, plugging the air holes, thus improving the bulk density of the fused magnesia and reduce its apparent porosity. The ability of steel corrosion of as-prepared samples from fused magnesia doped with La2Ce2O7 have better resistance than conventional fused magnesia, which the thickness of the corrosion layer was reduced by 42.1% compared to as-prepared samples without La2Ce2O7.

Unveiling trends in migration of iron-based nanoparticles in saturated porous media

Nanoscale zero-valent iron (nZVI) particles are routinely used for environmental remediation, but their transport dynamics in different settings remain unclear, hindering optimization. This study introduces a novel approach to predicting nZVI transport in saturated porous model environment. The method employs advanced long column devices for real-time monitoring via controlled magnetic susceptibility measurements. Numerical modeling with a modified version of the MNMs 2023 software was then used to predict nZVI and its derivatives mobility in field-like conditions, offering insights into the radius of influence (ROI) and shape factor (SF) of their distribution. A standard nZVI precursor was compared with its four major commercial derivatives: nitrided, polyacrylic acid-coated, oxide-passivated, and sulfidated nZVI. All these iron-based nanoparticles exhibited identical particle sizes, morphologies, surface areas, and phase compositions, isolating surface properties, dominated by charge, as the sole variable affecting their mobility. The study revealed optimal transport when the surface charge of nZVI and its derivatives was strongly negative, while rapid aggregation of nZVI derivatives due magnetic attraction reduced their mobility. Modeling predictions based on column scale-up, indicated that detectable concentrations of 20 g L⁻1 were found at distances ranging from 0.4 to 1.1 m from the injection well. Slightly sulfidated nZVI traveled farther than the nZVI precursor and ensured more homogenous particle distribution around the well. Organically modified nZVI migrated the longest distances but showed particle accumulation close to the injection point. The findings suggest that minimal sulfidation combined with organic modification of nZVI surfaces may effectively enhance radial and vertical nZVI distribution in aquifers. Such improvements increase the commercial viability of modified nZVI, reduce their adverse impacts, and boosts their practical applications in real-world scenarios.

Research on the multi environmental corrosion characteristics and mechanism of B4C doped Fe–Cr–Ni composite coating produced by laser cladding

Different Fe–Cr–Ni composite coatings doped with B4C were produced on the surface of Cr12MoV steel by laser cladding. Special attention was paid to the effects of B4C content on the phase composition, microstructure, and corrosion resistance of the cladded layers. The results indicated that the Fe–Cr–Ni composite coating was primarily composed of α-(Fe, Cr) and γ-(Ni–Cr–Fe) solid-solution phases, as well as Fe2B, M7C3, Fe3Si and M23C6 phases. Once the B4C content increased to 10 wt%, the microstructure of the cladding layer became coarse and exhibited the prominent carbide agglomeration. The composite coatings with different B4C contents exhibited superior corrosion resistance compared to the pure substrate in both 3.5 wt% NaCl and 1 mol/L HCl solutions. Furthermore, as the B4C content increased, the corrosion resistance of the coating initially increased and then declined. In particular, the Fe–Cr–Ni composite coating with an 8 wt% B4C content experienced the pronounced passivation in the corrosive media and possessed the optimal corrosion resistance due to the synergistic effect of the passive film and carbide barrier layer.

Phase transformation and metallurgical characterization of heat-treated nickel–titanium rotary instruments using differential scanning calorimetry, X-ray diffraction, and energy dispersive spectrometry

Objective: The present study aimed to evaluate the phase transformation behavior and elemental analysis of thermomechanical-treated nickel–titanium (NiTi) rotary instruments, TruNatomy (Dentsply Sirona), HyFlex CM (coltene, Whaledent), and Neoendo Flex (Orikam healthcare India), using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry. Materials and Methods: A total of 18 NiTi rotary instruments, TruNatomy, Hyflex CM, Neoendo Flex, taper. 04, size 25 (except TruNatomy, size 26) were selected and were divided into three groups (n = 6). Three NiTi files from each group were investigated for the DSC test (n = 3). The two segments of each sample were cut carefully by slow-speed water-cooling carborundum disc at 3 mm from the tip and then 4 mm from the previous section. The mass of the samples was measured on the electronic balance and samples that weighed 10–15 mg were loaded into a 40 µL aluminum crucible. The samples are then subjected first to a heating cycle from 0°C to 100°C and subsequently a cooling cycle from 100°C to 0°C in the differential scanning calorimeter (Mettler-Toledo, NIT Srinagar) at a rate of 10°C min−1. XRD (Make. Rigaku Japan, smart lab 3kW, NIT Srinagar.) was performed to verify the DSC results. The remaining two samples from each group (n = 2) were subjected to XRD analysis. The sample preparation for XRD analyses was done precisely with slow speed water cooled carborundum disc and samples were sectioned into three segments. Each segment was 5 mm long and grounded to obtain a uniform smooth plane. The data obtained from DSC and XRD were subjected to origin 8.5 software and graphs were obtained that depict the transformation temperature and phase composition, respectively. Alloy distribution and trace elements of the NiTi rotary instruments were done using energy dispersive spectrometry microanalysis. Results: The DSC results showed that the TruNatomy, Hyflex CM, and Neo Endo instruments had an Austenite finish (Af) temperature exceeding 37°C. The XRD graphs show the different intensity peaks that correspond to the various phases of NiTi rotary instruments. The TruNatomy is predominantly Austenite, Hyflex CM exists mainly in R-phase with a variable amount of austenite and martensite, while Neoendo flex endo mostly contains austenite phase. The elemental analysis revealed that all three file systems show Nickel and Titanium within their bulk structure in an equiatomic ratio. Conclusion: This study concluded that TruNatomy is predominantly martensite with a variable amount of austenite phase. There are differences in thermal transition temperature between the files.

Roles of Al/Ni ratio and solidification cooling rate in grain boundary engineering of AlxCrFeMnNi(2-x) high entropy alloy

In this work, the roles of Al/Ni ratio and solidification cooling rate in grain size, dendrite morphology and grain boundary characteristic of the AlxCrFeMnNi(2-x) (x = 0.3, 0.7 and1.0) high-entropy alloys (HEAs) were investigated. The results show that the increasing of Al/Ni ratio results in a transition from single-phase FCC to dual-phase BCC + B2 along with the reverse precipitation behavior of BCC phase. While the phase composition is not affected by solidification cooling rate. With the increasing of Al/Ni ratio and solidification cooling rate, a significant columnar-to-equiaxed transition (CET) behavior can be observed. That is, grain refinement and transition from columnar dendrites to equiaxial and cellular dendrites. This is mainly attributed to the constitutional supercooling (CS) caused by the solute interaction effect of Al and Ni, and which can be evaluated by P and Q parameters. In addition, in-situ formation of serrated grain boundaries (SGBs) can be also observed in solidification microstructures, and with the increasing of Al/Ni ratio, the proportion of SGBs increases gradually. Whether the B2 precipitated phase is present or not, the formation mechanism of SGBs is mainly attributed to the lattice strain energy caused by the segregation of Al and Ni. The strategy simultaneously achieving grain refinement, CET and in-situ forming SGBs during solidification by tailoring Al/Ni ratio opens new perspectives for grain boundary engineering.

An H3O-alunite method for production of smelter grade alumina from an ammonium alum solution after high-pressure acid leaching of coal fly ash

Precipitation of H3O-alunite from an ammonium alum solution using boehmite as a seed was studied. The ammonium alum solution was obtained after high-pressure leaching of mullite-type coal fly ash (CFA) with a mixture of 7.5 M H2SO4 + 40% NH4HSO4 at 200 °C. Fe(III) was extracted from the ammonium alum solution by ion exchange sorption using the Purolite S957 resin. Effects of temperature (70–90 °C), seed boehmite (100–400 g/l), ammonium alum (60–240 g/l), and precipitation duration (2–8 h) on the Al precipitation degree were evaluated. Calcination of the precipitate at 300–950 °C to obtain alumina powder was studied next. Concentration of impurities, specific surface area, phase composition, morphology, and the average particle size distribution of alumina powders were investigated. The results show that smelter grade alumina (SGA) can be obtained at optimized parameters of precipitation and calcination.

Multifunctional bacterium induced carbonate precipitation with low nitrogen effectively remediates cadmium polluted water

Microorganism Induced Carbonate Precipitation (MICP) has emerged as an efficacious approach to address the issue of cadmium (Cd) contamination in water bodies. However, the associated production of ammonium nitrogen (NH4+-N) poses a significant challenge to the MICP. To tackle this, our research has developed a novel bacterium (UN-1), with dual MICP and NH4+-N degradation capabilities. We have elucidated the biogeochemical pathways of Cd2+ precipitation and NH4+-N degradation, characterized the micromorphology, phase composition, and crystallization of the MICP products, and identified the key factors influencing the MICP reaction. Our findings indicate that The UN-1-mediated MICP effectively removes Cd2+ at concentrations below 20 mg/L, reducing NH4+-N levels to 50 mg/L within 120 h. The predominant strains in UN-1 are Sporosarcina (24.35 %), Bacillus (31.36 %), Tumebacillus (6.89 %), Nitrospira (11.09 %), and Alkaliphilus (8.16 %). The bacterium employs urea enzymes UreA, UreB, and UreC for urea hydrolysis, thereby facilitating carbonate production, while the degradation of NH4+-N is mediated by hydroxylamine oxidase (HAO), nitrite reductase (NIR), and nitrate reductase (NAR). The resultant MICP products after Cd2+ removal are irregular spherical minerals, 200–300 nm in diameter, exhibiting well-developed single-crystal structures and high crystallinity. Their X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) patterns align with the characteristics of cadmium carbonate (CdCO3) minerals. Optimal conditions for the UN-1-led MICP reaction are identified as a pH range of 5.0 to 9.0 and a temperature range of 20 to 40 °C, the dissolved oxygen (DO) concentration in the water does not significantly impact the MICP. Furthermore, the study demonstrates that NH4+-N concentrations can be maintained at low levels under most conditions. This research introduces an innovative solution to the NH4+-N by-product challenge during Cd removal via MICP, laying a solid theoretical foundation for the development of a rapid, efficient, and eco-friendly remediation technology for Cd-contaminated waters.