A novel process for making radiopaque materials using bauxite—Red mud

Red mud, which is an aluminum industry waste, has been utilized¹ for making X-ray radiation-shielding materials. A novel method for making radiation shielding materials utilizing red mud and barium compound has been developed by ceramic processing route using phosphate bonding. The red mud based shielding materials (RMSM) are characterized for their X-ray attenuation characteristics. The shielding, i.e. half value thickness (HVT) for different energies of X-ray photons for RMSM have been computed and compared with conventionally used shielding materials namely concrete and lead, it is found that the (HVT) of the red mud based shielding materials, in comparison to concrete, is significantly very less for the various energies of X-ray photons.The X-ray powder diffraction studies confirmed the presence of celsian, bafertiste and iron titanium oxide as the major shielding phases in the RMSM. Scanning electron microphotographs have revealed the compacted and continued integrated morphological characteristics of the various shielding phases in the matrix of shielding materials. The mechanical properties namely compressive strength and impact strength evaluation test showed that RMSM meets the standard specifications laid down for radiation shielding concrete and ceramic tiles. Based on the above studies, it is found that RMSM, can preferably be used for the construction of X-ray diagnostic and CT scanner room to provide adequate shielding against X-ray photons.     

氧化铝赤泥放射性及其屏蔽机制研究现状

分析了困扰赤泥资源化利用的主要原因,即高碱性和高放射性。着重讨论了赤泥放射性的来源和屏蔽技术的研究现状。指出赤泥的资源特性、赤泥中碱的富集和脱除机制、赤泥的天然放射性、赤泥的活性特征以及赤泥在建筑材料领域的安全应用途径等已经取得一些可喜的研究成果,而对于赤泥中放射性核素的富集机制和放射性屏蔽方法的研究仍处于起步阶段。为了从本质上解决赤泥放射性带来的应用困境,结合笔者的研究,提出了降低赤泥放射性的研究思路,以促进氧化铝赤泥在建筑材料领域的资源化利用。     

Development of celsian ceramics from fly ash useful for X-ray radiation-shielding application

For the first time the capability of fly ash to produce barium containing radiopaque materials has been demonstrated. Fly ash which is a waste generated in power plants due to combustion of pulverized coal, has been utilized^a for making X-ray radiation-shielding materials. A novel method for making radiation-shielding materials utilizing fly ash and barium compound has been developed by ceramic processing route using phosphate bonding. The fly ash based radiopaque materials (FARM), i.e. shielding materials are characterized for their X-ray attenuation characteristics. The shielding, i.e. half value thickness (HVT) for different energies of X-ray photons for FARM have been computed and compared with conventionally used shielding materials, namely concrete and lead, it is found that the HVT of the fly ash based shielding materials, in comparison to concrete, is significantly very less for the various energies of X-ray photons.The X-ray powder diffraction studies confirmed the presence of monoclinic and hexagonal celsian and sanbornite as the major shielding phases and potassium aluminosilicate, sodium aluminosilicate and silicophosphate as the binder phases in the FARM and are responsible for providing bonding to the ceramic matrix leading to the effective shielding and mechanical properties. Scanning electron microphotographs have revealed the compacted plate like particles with hexagonal morphological characteristics of the various barium silicate and barium aluminosilicate (BAS) shielding phases in the matrix of radiopaque materials. The mechanical properties, namely compressive strength and impact strength evaluation test showed that FARM meets the standard specifications laid down for radiation-shielding concrete and ceramic tiles. Based on the above studies, it is found that FARM, can preferably be used for the construction of X-ray diagnostic and CT-scanner room to provide adequate shielding against X-ray photons.     

Assessment of mechanical and microstructural properties of geopolymers produced from metakaolin,silica fume,and red mud

Geopolymers have been studied as viable alternative to traditional Portland cement-based products, given the use of industrial by-products as raw materials. This work evaluated the mechanical and microstructural properties of geopolymeric mortars produced with sodium hydroxide solution, metakaolin, silica fume, and red mud. The mixtures were produced by means of dosages with different molar ratios and curing conditions. The raw materials were characterized by granulometry, chemical, mineralogical, and thermal analysis. The characterization of mortars was performed by scanning electron microscopy (SEM) and axial compressive strength tests. The precalcination at 850°C of the red mud was sufficient to make it more reactive and suitable for use in geopolymers. Noteworthy, the best mechanical strengths of metakaolin mortars for curing at 50°C, and with the lowest SiO₂/Al₂O₃ ratios. In the mortars with incorporated red mud, there was a decrease of strength at thermal curing conditions and with the increase of residue content, whose microstructure indicates the formation of more pores in the geopolymer matrix. The thermal curing promoted the formation of sodalite crystals, and the significant presence of Na particles on the surface suggests that part of the added NaOH did not react with the precursors.     

Novel glass ceramic foams materials based on red mud

Glass ceramic foams were prepared using red mud and fly ash with added CaCO₃ as foaming agents. The aim of the present work was to investigate the possibility of adding red mud, an alkaline leaching waste, in the raw material for the preparation of glass ceramic foams. The results of mineralogical analyses as well as the microscopic examination showed that the use of the red mud affect the mineralogical characteristics and structures of the as produced foams. The influence of amount of red mud on the bulk density and compressive strength of samples was further evaluated. The experimental results showed that relatively low bulk density foams (0.33–0.41 g/cm³) could be obtained by using low sintering temperature (760–840 °C) when the red mud/fly ash ratio does not exceed 40:60. The reduction of sintering temperature or, above all, the reduction of the holding time, was found to limit the coalescence and significantly improve the compressive strength of the foams (0.33–2.74 MPa).     

Performance study of foam ceramics prepared by direct foaming method using red mud and K-feldspar washed waste

In this study, foam ceramics were prepared via a direct foaming method at high temperatures (1080–1120 °C), using red mud (RM) and K-feldspar washed waste (KFW) as the raw materials and SiC as the foaming agent, respectively. The chemical compositions and crystalline phases of the raw materials as well as the structural and mechanical properties of the foam ceramics were investigated. By adjusting the formulation and sintering process parameters, the porous structure of the foam ceramics could be effectively modulated. In addition to some residual crystalline phases in the raw materials, new phases, including rutile (TiO₂) and anorthite (CaAl₂Si₂O₈), were generated in foam ceramics. The compressive strength of the foam ceramics decreased with an increase in the KFW/RM ratio and sintering temperature, which was mainly related to the low density of the foam ceramics and the poor support of the pore walls to the structure. Among all the foam ceramics investigated, the foam ceramic with the KFW/RM ratio of 1:1, SiC content of 1 wt%, sintering temperature of 1100 °C and sintering time of 60 min showed the best overall performance with a bulk density, an apparent porosity, an average pore size and a compressive strength of 0.77 g/cm³, 61.89%, 0.52 mm, and 3.64 MPa, respectively. Its excellent porous structure and mechanical properties rendered it suitable for application as insulation materials or decorative materials for building partition walls.     

UHMWPVC/微细赤泥/炭黑复合导电材料的研究

使用超高相对分子质量的聚氯乙烯（UHMWPVC）,与微细赤泥、炭黑、增塑剂以及其他助剂共混制备复合导电材料。实验结果表明：微细赤泥可以提高复合体系的导电性能及加工稳定性能。讨论了炭黑和赤泥与材料导电性能、机械性能以及加工性能的关系。     

Experimental investigation and CFD simulation of liquid–solid–solid dispersion in a stirred reactor

For understanding the monosodium aluminate hydrate crystallization from the supersaturated aluminate solution containing red mud as the leaching liquor of bauxite, the liquid–solid–solid dispersion of a simulant system, i.e. glycerite, red mud and sand, in a stirred reactor has been experimentally investigated as well as simulated using computational fluid dynamics model (CFD) for the first time. The computational model is based on the Eulerian multi-fluid model along with RNG k–ε turbulence model, where Syamlal–obrien-symmetric drag force model (Syamlal, 1987) of the inter-phase momentum transfer between two dispersed solid phases is taken into account. A good agreement is obtained between the experimental data of solid distributions and the simulation results in the flow fields of liquid–solid–solid as well as liquid–solid systems. The solid suspension qualities of both liquid–solid and liquid–solid–solid systems in the stirred reactors with and without draft tube were also studied in detail based on mixing time, the standard deviation of solid concentration proposed by Bohnet and Niesmak (1980), the flow pattern and power number. The influence of the interaction between two dispersed solid phases on the suspension of red mud is found significantly greater than that of sand. The holdup of sand below the impeller is considerably larger than that above the impeller and the red mud dispersion approaches homogeneous in the reactor. The mixing time of liquid–solid–solid suspension is longer than that of liquid–solid suspension under the same conditions, and the mixing times of both systems in the stirred reactor with draft tube are longer than that in the reactor without draft tube. Furthermore, the distributions of sand and red mud in the reactor with draft tube were found less homogeneous than those without draft tube in most cases.     

Structural stability and neutron-shielding capacity of GdBO3-Al18B4O33 composite ceramics: Experimental investigation and numerical simulation

There is an urgent demand for advanced neutron-shielding materials that can be particularly used at extremely high temperatures in nuclear energy system. In this study, GdBO₃–Al₁₈B₄O₃₃ composite ceramics (GACCs) were successfully fabricated by the pressureless sintering of Al₄B₂O₉ and Al₂O₃ using different firing temperatures and varying quantities of Gd₂O₃ used as the neutron-shielding agent. The properties of the obtained samples, including the crystalline phases, microstructure, thermophysical properties, and neutron-shielding capacity, were studied systematically. The structural stability determined by thermal cycle tests is reassessed based on the thermal stress caused by the mismatch between the thermal expansion coefficients of multiple phases in the material system, and it is further verified via numerical simulations performed using the finite element method. Moreover, the influence of the sample thickness and dispersion density of Gd on the shielding capacity of the material were also investigated and parameterised to guide the design of borate-based shielding materials. The results suggest that GACCs are promising candidates for high-temperature structural materials and excellent neutron-shielding materials in novel nuclear systems.     

One‐Part Geopolymers Based on Thermally Treated Red Mud/NaOH Blends

In this study, one‐part “just add water” geopolymer binders are synthesized through the alkali‐thermal activation of the red mud which is relatively rich in both alumina and calcium. Calcination of the red mud with sodium hydroxide pellets at 800°C leads to decomposition of the original silicate and aluminosilicate phases present in the red mud, which promotes the formation of new compounds with hydraulic character, including a partially ordered peralkaline aluminosilicate phase and the calcium‐rich phases C₃A and α‐C₂S. The hydration of the “one‐part geopolymer” leads to the formation of zeolites and a disordered binder gel as the main reaction products, and the consequent development of compressive strengths of up to 10 MPa after 7 d of curing. These results demonstrate that red mud is an effective precursor to produce one‐part geopolymer binders, via thermal and alkali‐activation processes.     

Preparation and performance of ceramic filter material by recovered silicon dioxide as major leached component from red mud

In this study, a new ceramic filter material was prepared by recovering red mud from red mud at atmospheric pressure. The primary objective of this research was to investigate the effects of SiO₂ quantity and sintering temperature (ST) on the porosity, stability, microstructure, and performance of the resulting materials. The results demonstrated that after a two-step leaching process with 3 M HCl and 90% sulfuric acid, the recovery of SiO₂ from red mud exceeded 80%. The SiO₂ extracted from red mud was used as the main material and mixed with other materials including Na-bentonite, limestone and pulverized coal at a ratio of 65:25:8:2, resulting in a ceramic filter material with favorable chemical stability, high strength, and nontoxicity. The enhanced surface activity of the material can be attributed to the abundant Si-OH groups, which enable it suitable for the ammonia nitrogen removal from drinking water. Overall, silicon dioxide extracted from red mud will help solve the stockpile and pollution problems of it in China.     

Bauxite ‘red mud’ in the ceramic industry. Part 2: production of clay-based ceramics

Some potential uses of red mud as a raw component in clay mixtures for ceramic bodies production are presented. The influence of increasing amounts of red mud on the forming procedure, sintering and final properties was analyzed. Samples were produced by uniaxial pressing and slip casting. Two different clays are used as basic materials, the former being currently employed for the production of bricks by extrusion, the second — almost pure Kaolin — for high quality ceramic manufacturing. In both cases the addition of red mud led to more deflocculated solid–water systems and an increase of the critical moisture content. Mixtures prepared with the first clay and red mud loads up to 50% were fired at 850°C. The red mud content did not influence the sample porosity while determining a strength decrease attributed to the inertness of red mud at the working temperature. Samples produced using the second clay and red mud (0 – 20%) were fired at 950 and 1050°C. The addition of red mud determined increases of density and flexural strength which can be accounted for by the formation of a larger amount of glassy phase at higher red mud contents. The results of this work indicate excellent perspectives for using ‘red mud’ as raw material in mixtures with clay for the production of ceramic bodies.     

Mechanical and nuclear shielding properties of sodium cadmium borate glasses: Impact of cadmium oxide additive

In this study, highly effective radiation shielding glass materials with different amount of CdO additive were investigated in terms of nuclear shielding performance. Moreover, mechanical properties have been determined. The μ_m values were computed using XCOM and XMuDat program. The gamma and neutron shielding parameters such as μ_m, HVL, Z_eff, EBF, EABF, SAFE, b_co, b_ico, σ_co and σ_abs are calculated to understand the radiation shielding performances of investigated glasses. The results show that μ_m, Z_eff and σ_abs values increase as the CdO content increases. The S7 sample has the lowest HVL, MFP, EBF, EABF, SAFE, b_co, b_ico and σ_co values. Therefore, S7 glass sample (70 mol% of CdO) which has also the highest number of bonds per unit volume can be considered as a superior material for radiation shielding applications. The outcomes of this study can be very useful for future applications of investigated glass materials in medical and industrial radiation fields.     

赤泥中碱的分布特征与淋滤效果研究

赤泥中含有钠、钾等杂质,在堆存过程中不仅会造成环境污染,还会制约赤泥在水泥等建筑材料领域中的综合利用。利用电子探针、原位剥蚀等离子体质谱等微观分析手段分析研究了赤泥中钠、钾的分布特征。同时考察了不同pH的淋滤液对赤泥中钠、钾的淋滤效果。结果表明,pH为2、4、8这3种体系中,前10次取样共滤出拜耳法赤泥的钠分别大于17.6%、16.8%、19.6%;烧结法赤泥钠的滤出量分别为36.7%、53.1%、54.1%。pH为2、4、8的3种体系中,前10次取样共滤出拜耳法赤泥的钾分别为10.5%、10.1%、11.4%;烧结法赤泥钾的滤出量分别为40.0%、56.8%、57.5%。     

Bioactive glasses and direct effect of increased K2O additive for nuclear shielding performance: A comparative investigation

This study aimed to provide a large-scale investigation on direct effect of K₂O additive nuclear radiation shielding properties of calcium phosphate based bioactive quaternary P₂O₅–CaO–Na₂O–K₂O glasses. A gamma ray attenuation setup has been modeled in MCNPX (v-2.6–0) simulation code using Monte Carlo simulation technique. Next, all the bioactive glasses have been defined considering their chemical properties and material densities, respectively. The mass attenuation coefficients (MAC) have been calculated by using MCNPX code and obtained results have been used for determination of another vital gamma-ray shielding parameters. Moreover, a detailed calculation has been done for determination of exposure buildup factor (EBF) and energy absorption buildup factor (EABF) of investigated bioactive glasses which should be considered as important parameters for interaction properties of ionizing radiation with material environment. In addition, effective removal cross sections for fast neutrons have been calculated. To compare our results, obtained HVL values of the present investigation have been compared with copper oxide and cobalt oxide substituted bioactive glasses. Among the investigated bioactive glasses, the maximum MAC values were reported for PCNK60 sample with higher K₂O additive. It can be concluded that chemical structure of additive materials in the bioactive glasses is strongly related with the radiation attenuation properties of bioactive glasses.     

Radiation damage of MoAlB at elevated temperatures: Investigating MAB phases as potential neutron shielding materials

A new family of ternary nano-laminated compounds, MAB phases, are studied as a promising class of neutron shielding materials for applications within fusion reactors. The shielding capacity against high-energy neutrons was evaluated, and the damage tolerance of MoAlB against Si⁺ irradiation was investigated over the temperature range of RT- 600 °C. The linear attenuation coefficients of these materials over wide neutron-energy ranges imply that Mo(W)AlB have a high neutron shielding capacity. MoAlB shows a strong resistance to crack formation and excellent tolerance to amorphization under higher temperatures. The detailed thermal dynamic behaviors (reaction barrier and migration barrier) associated with the defects in MoAlB were studied through DFT calculations. Also, the lattice parameter changes are related to the formation of various point defects and the defect evolution evidenced by Rietveld refinement of the GIXRD and DFT calculations. MoAlB is confirmed to be a great candidate as a neutron shielding material.     

Hydrogenation of a model hydrogen-donor system using activated red mud catalyst

Hydrogenation of naphthalene to tetralin using activated red mud as catalyst was studied as a typical hydrogen-donor system. Under the chosen reaction conditions, unprocessed red mud resulted in a conversion of naphthalene of 3.55%. The most active catalyst, prepared by adding 20 wt% of Ti0₂ to the red mud, followed by acid digestion and re-precipitation, resulted in a 58% conversion of naphthalene. This technology may have an important bearing on processes such as coal hydrogenation or crude-oil-residue processing, where the rate of reaction and product quality may depend upon the rate at which a hydrogen-donor solvent can be re-hydrogenated.     

2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties

Electromagnetic shielding (EMI) materials are becoming more and more important because of the increasingly serious radiation pollution. The preparation of high mechanical strength, ultrathin, lightweight, flexible materials with excellent EMI shielding performance have so far been elusive. Here, we try to prepare an ultrathin, lightweight and flexible film with excellent EMI shielding performance using one-dimensional aramid nanofibers (ANFs) and two-dimensional few-layered Ti₃C₂T_x through a simple filtration method. The ultimate tensile strength and strain of the film are up to 116.71 MPa and 2.64%. The EMI shielding effectiveness and the specific EMI shielding efficiency are 34.71 dB and 21971.37 dB cm² g⁻¹, which will be no recession after 1000 times bending. Our results show that a practical EMI shielding material with excellent performances has been successfully prepared, which will be widely applied in wearable electronics, robot joints, and precision instrument protection and so on.     

Synthesis and properties of binary spinels in a NiO–CuO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The conditions for the formation of a spinel structure from a NiO–CuO–Fe₂O₃–Cr₂O₃ oxide mixture using several technological approaches have been examined. Addition of KCl is accompanied with the formation of two spinel-like phases, whereas in the absence of KCl just one solid solution of nickel–copper ferrite–chromite with the structure of a cubic spinel is formed. At the temperature of thermal treatment of 900°C, the presence of an admixture phase of the delafossite (CuCrO₂) type was established. The conditions for the fabrication of samples containing two spinel phases (cubic and tetragonal) characterized with the most developed surface and manifesting = increased catalytic activity in the reaction of the decomposition of an organic substance by hydrogen peroxide have been formulated. The studied features of spinel synthesis can be of interest for developing materials with an active surface promising for application as adsorbents of catalysts and sensors.     

Recycling of lime mud and fly ash for fabrication of anorthite ceramic at low sintering temperature

Lime mud is a kind of waste generated during causticization reaction of an alkali recycling process in paper industry. Lime mud and fly ash were reused as raw materials to fabricate anorthite ceramics through solid state reactions. Both sintering temperature and lime mud content influenced the crystalline phases in the prepared ceramics. Anorthite was the major phase in all samples (samples L36, L40, L50 and L60) and it was prominent in sample L36 (containing 36 wt% lime mud). The results also showed that anorthite ceramic can be synthesized at low sintering temperature (1100 °C). Gehlenite and wollastonite were formed in the samples possessing higher calcium (above 40 wt% lime mud) or at lower sintering temperatures. Bulk density, water absorption and compressive strength were measured. These ceramics were of light weight and had high water absorption. Recycling of lime mud and fly ash as raw materials of anorthite ceramic is a feasible approach to solve the solid wastes.