Na2O Content Research Articles

High-Iron Bauxite Residue (Red Mud) Valorization Using Hydrochemical Conversion of Goethite to Magnetite.

Bauxite residue (BR), also known as red mud, is a byproduct of the alumina production using the Bayer process. This material is not used to make iron or other iron-containing products worldwide, owing to its high content of sodium oxide and other impurities. In this study, we investigated the hydrochemical conversion of goethite (FeOOH) to magnetite (Fe3O4) in high-iron BR from the Friguia alumina refinery (Guinea) by Fe2+ ions in highly concentrated alkaline media. The simultaneous extraction of Al and Na made it possible to obtain a product containing more than 96% Fe3O4. The results show that the magnetization of Al-goethite and Al-hematite accelerates the dissolution of the Al from the iron mineral solid matrix and from the desilication product (DSP). After ferrous sulfate (FeSO4·7H2O) was added directly at an FeO:Fe2O3 molar ratio of 1:1 at 120 °C for 150 min in solution with the 360 g L-1 Na2O concentration, the alumina extraction ratio reached 96.27% for the coarse bauxite residue size fraction (Sands) and 87.06% for fine BR obtained from red mud. The grade of iron (total iron in the form of iron elements) in the residue can be increased to 69.55% for sands and 58.31% for BR. The solid residues obtained after leaching were studied by XRD, XRF, TG-DTA, VSM, Mössbauer spectroscopy, and SEM to evaluate the conversion and leaching mechanisms, as well as the recovery ratio of Al from various minerals. The iron-rich residues can be used in the steel industry or as a pigment.

A multiscale study on gel composition of hybrid alkali-activated materials partially utilizing air pollution control residue as an activator

This paper provides a detailed underlying mechanism of gel composition of hybrid alkali-activated fly ash/slag (AAFS) pastes prepared by utilizing the air pollution control residue (APCr, a highly alkaline waste containing 38.3% of Na2O content by mass) as a partial replacement (8%, 16% and 24% replacement by mass) of energy-intensive commercial sodium silicate (CSS) activator. AAFS pastes containing APCr as a partial replacement of CSS showed the strength, micromechanical and microstructure properties equivalent to the reference AAFS paste without APCr (R-0). SEM-EDS, FTIR spectral subtraction, and nanoindentation results showed that reaction products in AAFS pastes were composed of geopolymer gel (N-A-S-H), cross-linked gel (C–N-A-S-H) and alkali-activated gel (C-A-S-H) contributing to 60–66% of paste volume. Reaction products were more dominated by calcium-rich gels (C-A-S-H or C-(N)-A-S-H) as compared to N-A-S-H gel in all AAFS pastes. The heat of hydration and thermogravimetric results confirmed the slow rate of reaction of APCr-AAFS pastes at the early age but a higher rate of reaction at the silater stage which contributed to achieve a similar strength as control paste (R-0).

Constraints on Diagenetic Fluid Source and Genesis in Tight Dolostone Reservoir of Submember Ma55 of Ordovician Majiagou Formation in Northwestern Ordos Basin, China: Evidence from Petrology and Geochemistry

Diagenetic fluids is one of the most important reservoir modifiers, their differences can result in various petrography, storage capacity, and geochemical characteristics, so clarifying the diagenetic fluids is vital for understanding dolostone origin. Dolomitization is an important genetic type of dolostone reservoir, the fluid properties differ in different dolomitization, which may lead to reservoir storage capacity changes. Therefore, the identification of dolomitization fluid properties is critical for deeply understanding of dolomitization process and predicting storage capacity. Two types of dolostone are developed in submember Ma55 of Majiagou Formation in northwestern Ordos Basin, with obviously different petrological characteristics and reservoir properties. On the basis of petrological studies such as core and casting thin section observation and cathodoluminescence analysis, the diagenetic fluid properties of these two dolostone are characterized by geochemical analytical methods such as major and trace element tests. The results show that Type-1 dolostone is mainly composed of micritic dolomite, showing micritic structure and algae-rich lamina structure, and accompanied by evaporite minerals and moldic pores. This type of dolostone has a various Mn content, weak to medium cathodoluminescence intensity, high contents of TiO2, Al2O3, K2O+Na2O, Li, and U, and lower content of TFe2O3. The type-2 dolostone is composed of fine-grained dolomite with obvious residual texture of primary limestone, clear brim, and cloudy center structure, accompanied by the existence of intergranular pores. Most of this kind of dolostone have medium-strong cathodoluminescence, higher TFe2O3 content and lower TiO2, Al2O3, K2O+Na2O, Li, and U contents. Moreover, both the two types of dolostone have similar Fe/Ca and Mn/Ca ratios, and a low and concentrated CaO content, whose composition is similar to that of stoichiometric dolomite. The comprehensive analysis shows that the diagenetic fluid of Type-1 dolostone is mainly a high salinity fluid existed in plaster and calcareous sediments in a near surface environment with low temperature. The diagenetic fluid of Type-2 dolostone may be a high salinity brine formed by evaporation and concentration of seawater with normal salinity. The research results will provide a significant theoretical basis for the evaluation of dolostone reservoir quality and the prediction of favorable areas of reservoir distribution.

Geochronology and geochemistry of the granitoids in the Diancangshan-Ailaoshan fold belt: Implications on the Neoproterozoic subduction and crustal melting along the southwestern Yangtze Block, South China

The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771–762 Ma) and granites (ca. 767 Ma) have high SiO2 and low MgO contents. The trondhjemites have relatively high CaO, Na2O and Sr contents, but low K2O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na2O, and Sr contents, but higher K2O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to −3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ18O (4.37 ‰–7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf(t) (+1.24 to + 9.86) and higher δ18O (6.50 ‰–7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neoproterozoic (∼880–730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia.

Effect of active MgO on the hydration kinetics characteristics and microstructures of alkali-activated fly ash-slag materials

The effects of active S-MgO contents, MgO types, Na2O concentrations, and alkali activator modulus on the hydration kinetics, compressive strength, hydration products, pore structure, and microstructure of alkali-activated fly ash-slag (AAFS) were studied. The results showed that adding active S-MgO can reduce the total hydration heat of AAFS pastes, and the total hydration heat of samples incorporating 9% R-MgO increased significantly. Krstulovic-Dabic model was not completely suitable for the hydration reaction process of AAFS pastes. When the value of hydration degree α was small, the α value corresponding to the peak value of dα/dt can be used as the basis of evaluating the hydration kinetics of AAFS; When the value of hydration degree α was larger, the reaction process can be explained by the Krstulovic-Dabic model. The addition of active MgO reduced the amount of unreacted raw materials, and the volume of micropores, macropores, harmful pores and porosity increased. The addition of active MgO enriched the micromorphology of hydration products. The changes in hydration products, pore structure, and microstructure caused by the addition of MgO were the important reasons for the change in compressive strength.

Properties and Structure Evolution of CaO–Al2O3–La2O3 Slags with Various Alkali Metal Oxide Contents

To restrain the serious flux–steel reaction, CaO–Al2O3–La2O3‐based mold flux is designed for continuous casting of La‐bearing FeCrAl alloy. The properties and structure of slags with various alkali metal oxide contents are investigated. Results show that with the increase in Na2O or Li2O contents from 0 to 10 wt%, the melting temperature of slags decreased, and the fluxing effect of Li2O is improved. The addition of Na2O within 10 wt% reduces the slag viscosity at the temperature range of 1663–1823 K. While further increasing Na2O content to 15 wt%, the viscous behavior of the slag depends on the balance between the strong charge compensation effect of Na+ and the breaking network effect of O2−. Increasing Li2O contents from 0 to 15 wt% greatly reduces the slag viscosity, which is attributed to the reduction of the fraction of high‐polymerized QAl 4 units from 23.55% to 9.70% and the increase of [AlO6] octahedrons from 0 to 9.02% caused by more O2−. The NBO/Al and NBO fraction is calculated, which is consistent with the viscosity variations. In the melts, the structural roles of Na+, Li+, Ca2+, and La3+ are elucidated. Moreover, the relationship between the variations of crystalline phases and slag structure is discussed.

Geochronology and geochemistry of Early Cretaceous granitic plutons in northern Great Xing’an Range, NE China, and implications for geodynamic setting

AbstractEarly Cretaceous granitic rocks are widely distributed in the Great Xing’an Range, northeast China. However, their precise age and tectonic evolution remain controversial. This study presents new zircon U–Pb, Lu–Hf, and whole-rock geochemical data for the granitic plutons in the Yili area, Xing’an Massif, northern Great Xing’an Range. The aim of this study was to decipher the tectono-thermal history and obtain further understanding of the geodynamic setting of the large-scale Late Mesozoic magmatism in the Great Xing’an Range. Zircon U–Pb age dating indicated that the plutons were emplaced during the Early Cretaceous, with ages of 132.2–130.1 Ma. The plutons showed similar geochemical features, characterized by high concentrations of SiO2and Na2O + K2O and low concentrations of P2O5, CaO, MgO, and TFe2O3. The plutons were enriched in light rare earth elements and large ion lithophile elements and depleted in heavy earth elements and high-field-strength elements. Such features indicate that the plutons are highly fractionated with I-type granite affinity. These findings, combined with plutonεHf(t) values of + 5.25 to + 8.28 and two-stage model ages (tDM2) of 661–855 Ma, indicate that the primary magmas originated from partial melting of juvenile basaltic crustal material accreted during the Neoproterozoic. These results combined with regional geological evolution indicated that the generation of Early Cretaceous plutons in the northern Great Xing’an Range might be closely related to the post-collisional gravitational collapse and subsequent extension resulting from the closure of the Mongolia-Okhotsk Ocean. Their generation also superimposed the back-arc extension resulting from retraction of the Paleo-Pacific subduction plate.

An archaeometric assessment study of Seljuk period glazed tiles from Kılıçarslan Square (Konya, Turkey)

This study presents archaeometric analyses of glazed tiles produced with the cut-mosaic technique to reveal information about the Anatolian Seljuk period’s architecture and ceramic technology. The Persian Seljuk artists also used the same technique. For this purpose, physical, chemical, thermal, mineralogical, microstructural, and molecular analyses were carried out on the tiles from the Seljuk period unearthed in the Kılıçarslan Square excavation in Konya, the capital of the Anatolian Seljuk State from the twelfth-century to the beginning of the fourteenth-century. SEM, XRD, and Heat Microscopy analyses showed that the Seljuk period tiles were not fired at high temperatures like today’s tiles and were probably fired at temperatures below 1100 °C. WD-XRF analyses revealed that the glazes are classified into two categories, one being alkali varying the content of Na2O + K2O between 13 and 16 wt% (PbO between 0.5 and 2 wt%) and the other being lead-alkali type in which PbO content varies between 13 and 15 wt% and alkali content 10–14 wt%. The cobalt content in the blue color is around 0.2 wt%, and copper content in the turquoise-colored samples varies between 2.9 and 4.4 wt% depending on the lightness and darkness of the color (higher amount for tile 1 and tile 3, which are darker than the others). The brown color is obtained by the presence of MnO (3.3 wt%). Raman analysis showed that the difference in sintering temperature caused the color tone difference in Seljuk period tiles, and glazes were formed in the range of 800–1000 °C depending on the Ip values.

Study on Mechanical Properties of Heap Deposited Fly Ash Based Geopolymers with Different Alkaline Activator Properties

Geopolymers can improve environmental protection and are therefore considered a 21st-century material that requires special attention. The main objective of this study was to examine the utilization of fly ash deposited on a heap as a potential raw material for the geopolymerization process. In this work, flexural and compressive strengths, as well as water absorption of geopolymers, were evaluated based on alkaline activator properties. Na2O content, SiO2/Na2O molar ratio and fly ash-to-water ratio were key observed factors. Mechanical strengths tests were conducted after 7, 28, 90, 180, and 360 days. The research findings showed that geopolymer cured at appropriate conditions and with a suitable alkaline activator can reach a compressive strength of more than 55 MPa. The presented study highlighted the possibility of the efficient use of fly ash to produce useful materials, i.e., geopolymers, which contribute to environmentally friendly solutions. This approach is fully in line with the principles of sustainable development.

Performance study and environmental evaluation of alkali-activated materials based on waste photovoltaic glass

To alleviate the problems of energy shortage and environmental pollution, 15 alkali-activated materials (AAM) were designed and prepared based on slag and waste photovoltaic glass powder (WPGP). The setting time, fluidity, compressive strength, drying shrinkage rate and mass loss rate of AAM were tested. The effects of Na2O content, the modulus of water glass and the mass ratio of slag to WPGP (S/W) on the above properties were discussed. The properties and microstructure of AAM were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). The economic and environmental benefits of AAM were evaluated using a simplified method. The compressive strength prediction model of AAM under different curing time was established. The results show that the effects of Na2O content and the modulus of water glass on the properties of AAM are complementary. The maximum compressive strength at 28 d can reach 75.3 MPa. The predicted value of compressive strength is in good agreement with the test value, indicating that the established model has a high accuracy. The more encouraging result is that compared with traditional Portland cement, AAM shows significant environmental friendliness. The energy consumption and CO2 emission of 1 m3 AAM were 20.06%-42.45% and 49.01%-71.79% lower than those of the same volume Portland cement respectively. The above results show that the developed AAM can be used as a promising cementitious material to replace Portland cement.

Olivines and Their Melt Inclusions in Potassic Volcanic Rocks Record Mantle Heterogeneity beneath the Southern Tibet

Abstract Constraints on mantle heterogeneity are important for understanding geochemical differentiation and recycling in Earth’s interior. Alkali basalts are of particular interest in this context due to the clear signatures of recycled components that they yield. Previous studies have focused more on oceanic basalts than on continental mafic rocks because the chemical and isotopic characteristics of the latter are often modified by crustal contamination; however, high-forsterite olivine crystals and olivine-hosted melt inclusions may record the compositions of primitive melts before extensive crustal contamination, providing valuable insights into mantle heterogeneity. Here we report the results of high-precision major-, minor-, and trace-element and Pb isotope analyses of olivine phenocrysts and melt inclusions from the Sailipu potassic alkali basalts from southern Tibet, which constrain the mantle source of continental potassic alkali basalts. The minor- and trace-element compositions of the olivine phenocrysts (e.g. Ni and Ca contents and 100 × Mn/Fe, 10 000 × Zn/Fe, and Ni/Co ratios) suggest that the primary magmas were derived from a phlogopite-bearing pyroxenite source in which peridotite residues were also present. The low- and high-Li contents of the olivine phenocrysts suggest the recycling of continental crustal material in their mantle source. Comparing the major-element compositions (e.g. SiO2, TiO2, Al2O3, MnO, CaO, and Na2O contents), FCMS and FCKANTMS parameters, and pseudo-ternary projections of the primary Sailipu magmas with experimental data suggests that the primary magmas were partial melts of olivine-poor or carbonated olivine-poor lithologies with a small amount of peridotite residue. The negative Nb and Ta and positive Pb anomalies seen in primitive mantle-normalized trace-element patterns and the extremely low Nb/U ratios of the melt inclusions suggest that recycling of continental crust was the main process involved in enriching the mantle source of the Sailipu magmas. The heterogeneous Pb isotopic compositions of the melt inclusions (208Pb/206Pb = 2.089 – 2.158; 207Pb/206Pb = 0.851 – 0.858) are consistent with the presence of peridotite residue in this source. The subduction of Indian continental crust introduced enriched material (including carbonatites) into the mantle.

Türkiye'deki Muskovit Ocaklarının Elementel Bileşimlerinin Dağılımı

In this study, the contents of thirty-five elements (nine major-minor oxides, twenty-one heavy metals, and five other elements) in eighty-four muscovite samples collected from three commercially operated quarries in Manisa province of Turkey were determined using an energy dispersive X-ray fluorescence (EDXRF) spectrometer. The mean concentrations of SiO2, Al2O3, K2O, MgO, Na2O, Fe2O3, P2O5, TiO2 and CaO analyzed in mica samples were determined as 57.1, 32.8, 8.7, 2.9, 1.4, 0.8, 0.3, 0.3 and 0.3%, respectively. The mean concentrations of Cr, Zr, Mn, Zn, Ni, Co, Pb, Cu, Cd and Hg analyzed as primary toxic trace heavy metals in mica samples were found as 136.2, 124.6, 58.7, 19.2, 14.8, 6.8, 6.3, 2.6, 2.0 and 1.2 mg kg-1, respectively.

Effect of Na2O Content on the Structure and Properties of LAS Glass-ceramics Prepared by Spodumene

Effect of Na2O Content on the Structure and Properties of LAS Glass-ceramics Prepared by Spodumene

Enhancement of electrical conductivity and thermal stability of Iron- or Tin- substituted vanadate glass and glass-ceramics nanocomposite to be applied as a high-performance cathode active material in sodium-ion batteries

To explore novel vanadate formulations, i.e. newly effective cathode active material for sodium-ion battery (SIB), relationships among the local structure, electrical conductivity, and cathode performance of xNa2O•10 P2O5•(85-x)V2O5•5Fe2O3 and xNa2O•10 P2O5•(85-x) V2O5•5SnO2 (5 <x < 45 mol%) glasses and glass-ceramics nanocomposite abbreviated as xFeV and xSnV, respectively, were systematically investigated before and after heat treatment at 500 ℃ for 100 min. Measurements of 57Fe- and 119Sn Mössbauer spectra (FeMS, SnMS, respectively), X-ray absorption fine structure (XAFS), X-ray diffraction patterns (XRD), Fourier Transform Infrared spectroscopy (FTIR), differential thermal analysis (DTA), electrochemical impedance spectra (EIS) and charge-discharge capacity were carried out in this study. From DTA curves, decreases in glass transition temperature (Tg) and crystallization temperature (Tc) were observed for xFeV and xSnV glasses as ‘x’ increased from 5 to 45 mol% Na2O content. This indicates that the introduction of Na2O reduces thermal stability. Furthermore, the DC conductivity for xFeV and xSnV glasses and glass-ceramics nanocomposite, decreases from 2.82 • 10−5 to 6.61 • 10−7 S cm−1 and from 1.26 • 10−5 to 4.27 • 10−7 S cm−1, respectively, with increasing Na2O content from 5 to 45 mol%. The values of electrical conductivity of xFeV and xSnV are higher than that of xNa2O•10 P2O5•(90-x)V2O5, abbreviated as xV glasses. This indicates that the introduction of Fe2O3 and SnO2 produces an increase in electrical conductivity. 57Fe-Mössbauer spectra of xFeV glass showed decreased quadrupole splitting from 0.73 to 0.63 mm s−1, indicating that FeIII ion forms less distorted tetrahedra upon increasing ‘x’ from 5 to 45 mol%. Additionally, a high capacity of about 200 mAh g−1 was achieved for the SIB made of 5FeV glasses as a cathode. This capacity was larger than the previously reported value of 158 mAh g−1 in Na1.25V3O8. It can be concluded that the introduction of Fe or Sn ions into the phospho-vanadate glass as a cathode causes an increase in durability and conductivity, so these glasses can be considered promising for a high-performance cathode active material with significant improvement of cyclability in SIBs.

Geochemical and Cathodoluminescence Properties as Discriminators to Characterize K-Feldspar in Different Genetic Settings

ABSTRACTPotassic alteration is a common feature in hydrothermal ore systems, and both its occurrence and degree can be important features applicable to ore deposit exploration. Here we report results from optical cathodoluminescence (CL) and chemical composition investigations on K-feldspar of different origins in and around the Early Cretaceous lode gold deposits in the Xiaoqinling area, located along the southern margin of the North China Craton.We focus on K-feldspars from an Early Cretaceous biotite monzogranite (G-Kfs), a Paleoproterozoic migmatite (M-Kfs), and a hydrothermal alteration zone of Early Cretaceous gold deposits (H-Kfs). The grain size of G-Kfs ranges from 1 to 4 mm, usually exhibits tartan twinning, and occasionally shows evidence of exsolution. Part of the M-Kfs exhibits tartan twinning, and the grain size shows wide variation (from tens of microns to several centimeters), while the H-Kfs shows no twinning, and the grain size is generally less than 0.5 mm.Optical CL analyses show that the G-Kfs exhibits two emission bands at around 466–472 and 708–713 nm which occur in multiple, alternating dark red and blue zones. The M-Kfs exhibits blue, red, and/or violet-red luminescence resulting from two emission bands at 446–465 and 694–701 nm. The H-Kfs displays a distinct greenish-yellow luminescence resulting from an emission band at 545–550 nm.Electron probe microanalyses show that among the three K-feldspar types, the G-Kfs contains higher Na2O (average: 0.71 wt.%) and Al2O3 (average: 18.79 wt.%) and lower K2O (average: 15.62 wt.%), whereas the H-Kfs shows higher K2O (average: 16.31 wt.%) and lower Na2O (average: 0.45 wt.%) and Al2O3 (average: 18.61 wt.%). The K2O, Na2O, and Al2O3 contents of the M-Kfs are intermediate between those of the G-Kfs and H-Kfs. In transitioning from the G-Kfs, M-Kfs, to H-Kfs, it is noted that the concentrations of Sr, Ba, and Pb decrease progressively, whereas W, V, Zn, Mn, Sc, Ge, and Ga gradually increase. Concentrations of La, Ce, and Eu in the H-Kfs are lower than in the G-Kfs and M-Kfs, and the Cr and Cu concentrations in the G-Kfs are the lowest. Scatter diagrams constructed with Sr, Ba, Pb, and Rb concentrations show that the three types of K-feldspars fall into different fields. These, as well as the CL and spectral properties of K-feldspar, can clearly distinguish the K-feldspars of magmatic, metamorphic, and hydrothermal origin in the study area.

Mechanical Properties and Microstructure of Alkali-Activated Soda Residue-Blast Furnace Slag Composite Binder

This study prepared an alkali-activated soda residue (SR)-blast furnace slag (BFS) composite binder by adding a large amount of SR to the alkali-activated material system. Considering many factors, such as the Na2O content, ratio of SR to BFS and the water-binder ratio, the variation patterns in the new binder’s mechanical properties and its micro-evolution mechanisms were assessed. The results show that the compressive strength first grew and then dropped with the Na2O content, with an optimal level at 3.0%. At this level, the strength values of the 3d and 28d samples were 10.5 and 27.8 MPa, respectively, exceeding those in the control group without Na2O by 337.5 and 69.5%, respectively. As the Na2O admixture increased from 0 to 3%, the fluidity of the mortar decreased from 156 mm to 127 mm due to the high frictional resistance caused by the faster generation of hydration products, and the high water absorption of SR also led to reduced fluidity. The new binder’s hydration process mainly generated C-(A)-S-H gel, ettringite (ET), hydrocalumite (HC), calcium hydroxide (CH), and other crystalline hydrates. A 3% Na2O content inhibited the ET growth but significantly promoted the formation of uniformly distributed C-(A)-S-H gel and HC. Crystals grew in the pores or were interspersed in the gel, filling microcracks and significantly increasing the structure density and strength. Excessive Na2O (&gt;3%) could promote the generation of non-uniformly distributed gel, producing more macropores in the matrix and reducing its strength. Additionally, the increased SR content was not conducive to C-(A)-S-H gel formation, but significantly promoted ET formation, which would inhibit strength development. This study provides a theoretical basis for replacing cement with this new binder in pavement bricks and other unreinforced products.

Composition design and characterization of alkali-activated Slag–Metakaolin materials

This study explores the effects of the interactions among Na2O content, metakaolin content and activator modulus on the compressive strength and autogenous shrinkage of alkali-activated slag–metakaolin (AASM) materials. The Box–Behnken RSM design was used to create an experimental scheme, establish a model, and optimize the mix proportions. Fourier transform infrared spectroscopy, scanning electron microscopy, and Mercury intrusion experiments were used to analyze the compositions, microstructures, and pore structures of the hydration products of the AASM, respectively. Results showed that the interactions between the activator modulus and metakaolin content, as well as Na2O content and metakaolin content, are the key factors affecting the compressive strength and autogenous shrinkage, respectively, of the AASM. Under the optimal conditions of Na2O content of 6%, sodium silicate modulus of 1.5, and metakaolin/slag ratio of 1: 3, the relative errors in the model verification test for compressive strength and autogenous shrinkage are 0% and 0.18%, respectively. In the water glass modulus and metakaolin content interaction, Ca2+, A13+, and Si4+ ions in the composite system react with several [SiO4]4− groups to form C-A-S-H and N-A-S-H gels, which fill each other to make the composite structure denser. When Na2O interacts with metakaolin, the OH− and Na+ in the solution react with A13+ and Si4+ to generate additional N-A-S-H, thereby reducing the compressive strength of the composite system, mitigating autogenous shrinkage, and increasing volume stability.

Research on the mechanism of sodium separation in bauxite residue synergy preparation of potassium-containing compound fertilizer raw materials by the hydrothermal method.

Bauxite residue poses an increasingly serious ecological safety problem in the alumina industry. A novel process for removing sodium in bauxite residue synergistic preparation of potassium-containing compound fertilizer raw materials was proposed to relieve pressure on the fertilizer industry. In this paper, synthetic sodalite and katoite were used to simulate the main mineral phases of bauxite residue to determine the suitable conditions for the method, and the transformation mechanism of the process was researched by analyzing the phase structure and microscopic morphology of the samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and specific surface area detection. The results show that the ideal reaction condition is 320g/L K2O with solid reactants at 200°C for 1h. The separation rate of Na in the sodalite-katoite mixture reached 93.60%, with potassium aluminum silicate and katoite being the primary phases of the product, with a mesoporous structure and easy to be absorbed by crops. The bauxite residue transformation residue consisted of katoite and kaliophilite. With a total effective K2O, CaO, and SiO2 content of 38.22%, the Na2O content was 0.54%, meeting the requirements of compound fertilizer content on the market. The transformation mechanism is a dissolution-precipitation controlled sodium-potassium ion replacement reaction. This study provides theoretical guidance for the preparation of mineral fertilizer from bauxite residue and has practical production potential, opening up a new perspective for bauxite residue resource usage in the agricultural field.

Selective recovery of scandium with acid solutions of magnesium sulphate from ESP dust generated by bauxite sintering plants

Among potential sources of scandium and other rare earth elements (REEs) there are semiproducts generated by the alumina industry. They include red mud and ESP dust generated by sintering plants. Most of the previous research studies focused on red mud leaching using a variety of strong acids. However, because of the need to neutralize the caustic alkali present in red mud, as well as to dissolve iron and other macrocomponents, the above process is associated with a high consumption of reagents. This paper examines the possibility to selectively recover REEs from ESP dust at high pH values in the presence of magnesium cations. It is shown that the prior water leaching of ESP dust helps achieve a double rise in the REE concentration and considerably lower the concentration of Na2O in the solid residue. For selective recovery of REEs, the authors used weak solutions (pH = 2&divide;5) of sulphuric acid with magnesium sulphate. The latter help to desorb REEs from the surface of minerals contained in the solid residue. Over 75% Sc was recovered through solid residue leaching conducted at the temperature of 80 oC, liquid-to-solid ratio of 10:1 and duration of 60 min at pH = 2. The recovery of iron and titanium did not exceed 1&ndash;5%. With all other conditions being equal, raising pH to 3.5 would lead to a drop in the scandium recovery to 63% while the recovery of iron and titanium would drop to 0.2%. It was also found that, as the result of sulphuric acid leaching, the calcium that is present in the initial ESP dust gets precipitated in the form of gypsum and a certain amount of REEs may get carried away. This research was carried out as part of Grant No. 22-29-01515 of the&nbsp;Russian Science Foundation; the concentration of rare earth elements in&nbsp;the solid residue was determined through inductively coupled plasma mass&nbsp;spectrometry, supported through an assignment of the Government of the&nbsp;Russian Federation under Grant No. 075-03-2021-051/5.

Multi-element comprehensive utilization of high-silicon bauxite by roasting pretreatment and two-stage leaching

As a potential ore resource to produce alumina in industry, the complex symbiotic relationship between the aluminum-, silicon- and iron-bearing minerals in the high-silicon bauxite and severe desilication reactions during digestion process restrict its application. In this paper, a novel zero-waste process consisting of a roasting pretreatment and two-stage leaching was proposed to comprehensively utilize the high-silicon bauxite, and the phase transition mechanism and leaching properties of the roasting solid were systemically studied. When the roasting temperature is over 310 °C, the diaspore and kaolinite in the bauxite lose the crystal water, and gradually transform to alumina and metakaolin respectively. As the roasting temperature rises to above 950 °C, the metakaolin decomposes to an amorphous aluminosilicate phase and silica. The crystallinity of decomposed alumina and silica increases with the increase of roasting temperature and duration, but the excessive temperature and duration deteriorate the extraction property of the roasted bauxite. The optimal roasting conditions for the atmospheric-pressure leaching of silica and high-pressure leaching of alumina are 1050 °C for 30 min, and the corresponding extraction efficiencies of Al2O3 and SiO2 are above 94 % and 88 % respectively. The Fe2O3 and Na2O contents in the final leaching product are 55.23 % and 0.23 %, and can be directly used as iron concentrate in the ironmaking process.