Search Results (359)

The aim of this study was to improve the efficiency of in situ uranium leaching by developing a specialized methodology for selecting rational parameters for the chemical treatment of production wells. This approach was designed to enhance the filtration properties of ores and extend the uninterrupted operation period of wells, considering the clay content of the productive horizon, the geological characteristics of the ore-bearing layer, and the composition of precipitation-forming materials. The mineralogical characteristics of ore and precipitate samples formed during the in situ leaching of uranium under various mining and geological conditions at a uranium deposit in the Syrdarya depression were identified using an X-ray diffraction analysis. It was established that ores of the Santonian stage are relatively homogeneous and consist mainly of quartz. During well operation, the precipitates formed are predominantly gypsum, which has little impact on the filtration properties of the ore. Ores of the Maastrichtian stage are less homogeneous and mainly composed of quartz and smectite, with minor amounts of potassium feldspar and kaolinite. The leaching of these ores results in the formation of gypsum with quartz impurities, which gradually reduces the filtration properties of the ore. Ores of the Campanian stage are heterogeneous, consisting mainly of quartz with varying proportions of clay minerals and gypsum. The leaching of these ores generates a variety of precipitates that significantly reduce the filtration properties of the productive horizon. Effective compositions and concentrations of decolmatant (clog removal) solutions were selected under laboratory conditions using a specially developed methodology and a TESCAN MIRA scanning electron microscope. Based on a scanning electron microscope analysis of the samples, the effectiveness of a decolmatizing solution based on hydrochloric and hydrofluoric acids (taking into account the concentration of the acids in the solution) was established for the destruction of precipitate formation during the in situ leaching of uranium. Geological blocks were ranked by their clay content to select rational parameters of decolmatant solutions for the efficient enhancement of ore filtration properties and the prevention of precipitation formation. Pilot-scale testing of the selected decolmatant parameters under various mining and geological conditions allowed the optimal chemical treatment parameters to be determined based on the clay content and the composition of precipitates in the productive horizon. An analysis of pilot well trials using the new approach showed an increase in the uninterrupted operational period of wells by 30%–40% under average mineral acid concentrations and by 25%–45% under maximum concentrations with surfactant additives in complex geological settings. As a result, an effective methodology for ranking geological blocks based on their ore clay content and precipitate composition was developed to determine the rational parameters of decolmatant solutions, enabling a maximized filtration performance and an extended well service life. This makes it possible to reduce the operating costs of extraction, control the geotechnological parameters of uranium well mining, and improve the efficiency of the in situ leaching of uranium under complex mining and geological conditions. Additionally, the approach increases the environmental and operational safety during uranium ore leaching intensification. Full article

Phosphogypsum, a by-product of phosphate fertilizer production, was predominantly used as a supplementary additive in recycled construction materials. However, there are few detailed studies on utilizing phosphogypsum as the primary component in inorganic cementing materials while achieving cost-effective detoxification. This study aimed to develop a harmless phosphogypsum-based inorganic cementing material (PICM) mainly based on phosphogypsum, in which cement, quicklime, and a stabilizer were used as additives. Harmful ions and acidity were first detected through X-ray fluorescence and ion chromatography and then harmlessly treated with quicklime. Compaction parameters, mechanical performance, X-ray diffraction analysis, moisture, and freezing resistance were characterized successively. The results illustrated that fluoride and phosphate ions were the primary soluble contaminants, whose leaching solution concentration can be reduced to 15.31 mg/L and undetectable with 2% quicklime through the mass proportion of phosphogypsum added and mixed. Meanwhile, the corresponding pH value was also raised to over 8. Cement content and quicklime were positively correlated with PICM’s maximum dry density. PICM with 25% cement and 2.5% stabilizer presented the highest unconfined compression strength, and flexural strength did not show significant regularity. PICM was mainly composed of quartz, gypsum, ettringite, and calcite, whose content decreased as cement content and quicklime content increased. Stabilizer, quicklime and cement content were positively correlated with PICM’s freezing and moisture resistance. Full article

Circulating fluidized bed fly ash (CFBFA) stockpiles release alkaline dust, high-pH leachate, and secondary CO₂/SO₂—an environmental burden that exceeds 240 Mt yr⁻¹ in China alone. Yet, barely 25% is recycled, because the high f-CaO/SO₃ contents destabilize conventional cementitious products. Here, we presents a pressurized flue gas heat curing (FHC) route to bridge this scientific deficit, converting up to 85 wt% CFBFA into structural lightweight gravel. The gypsum dosage was optimized, and a 1:16 (gypsum/CFBFA) ratio delivered the best compromise between early ettringite nucleation and CO₂-uptake capacity, yielding the highest overall quality. The optimal mix reaches 9.13 MPa 28-day crushing strength, 4.27% in situ CO₂ uptake, 1.75 g cm⁻³ bulk density, and 3.59% water absorption. Multi-technique analyses (SEM, XRD, FTIR, TG-DTG, and MIP) show that FHC rapidly consumes expansive phases, suppresses undesirable granular-ettringite formation, and produces a dense calcite/needle-AFt skeleton. The FHC-treated CFBFA composite gravel demonstrates 30.43% higher crushing strength than JTG/TF20-2015 standards, accompanied by a water absorption rate 28.2% lower than recent studies. Its superior strength and durability highlight its potential as a low-carbon lightweight aggregate for structural engineering. A life-cycle inventory gives a cradle-to-gate energy demand of 1128 MJ t⁻¹ and a process GWP of 226 kg CO₂-eq t⁻¹. Consequently, higher point-source emissions paired with immediate mineral sequestration translate into a low overall climate footprint and eliminate the need for CFBFA landfilling. Full article

In the artificial cultivation of Morchella sextelata (Black Morel), exogenous nutrient bags (ENBs) commonly employ wheat grains as the primary substrate raw material. However, this approach is costly and runs counter to the “non-grain” development direction advocated by the edible mushroom industry. Under controlled field conditions, twelve self-made formulations were set up and compared with a conventional market formulation to comprehensively analyze their impacts on the agronomic traits, yield, soil physicochemical properties, and economic benefits of M. sextelata fruiting bodies. The research findings indicate that the nutrient bag formulations have a significant effect on soil available nutrients. Specifically, the contents of alkali-hydrolysable nitrogen (AN) and available potassium (AK) exhibit a significantly negative correlation with M. sextelata yield (r = −0.60, p < 0.05; r = −0.72, p < 0.01, respectively). Among all the treatment groups, the KY1 formulation (comprising 30% wheat grains, 5% rice bran, 60% corncobs, 2% rice husks, 1% lime, and 1% gypsum) achieved the highest yield of 915.13 kg per 667 m², which was 16.1% higher than that of the control group. The net economic benefit per unit area (667 m²) reached CNY 75,282.15, representing a 20.7% increase compared to the traditional wheat grains-based formulation. In conclusion, partially substituting wheat grains with rice bran in ENBs can not only reduce reliance on staple food resources but also enhance yield and economic efficiency. Due to the differences in cultivated strains and environmental conditions, the impact on morel yield is substantial; therefore, the results of this study need further validation through pilot trials. Full article

In order to elucidate the high-temperature reaction process of solid waste-based high belite sulphoaluminate cement containing residual gypsum in clinker (NHBSAC) and obtain the formation laws of each mineral in clinker, this article studied its high-temperature reaction kinetics. Through QXRD analysis and numerical fitting methods, the formation of C₄A₃$\overline{\mathrm{S}}$, β-C₂S, and CaSO₄ in clinker under different calcination systems was quantitatively characterized, the corresponding high-temperature reaction kinetics models were established, and the reaction activation energies of each mineral were obtained. The results indicate that the content of C₄A₃$\overline{\mathrm{S}}$ and β-C₂S increases with the prolongation of holding time and the increase in calcination temperature, while CaSO₄ is continuously consumed. Under the control mechanism of solid-state reaction, the formation and consumption of minerals follow the kinetic equation. C₄A₃$\overline{\mathrm{S}}$ and β-C₂S satisfy the D₄ equation under diffusion mechanism control, and CaSO₄ satisfies the R₃ equation under interface chemical reaction mechanism control. The activation energy required for mineral formation varies with different temperature ranges. The activation energies required to form C₄A₃$\overline{\mathrm{S}}$ at 1200–1225 °C, 1225–1275 °C, and 1275–1300 °C are 166.28 kJ/mol, 83.14 kJ/mol, and 36.58 kJ/mol, respectively. The activation energies required to form β-C₂S at 1200–1225 °C and 1225–1300 °C are 374.13 kJ/mol and 66.51 kJ/mol, respectively. This study is beneficial for achieving flexible control of the mineral composition of NHBSAC clinker, providing a theoretical basis and practical experience for the preparation of low-carbon cement and the optimization design of its mineral composition. Full article

The accelerated industrialization in China has precipitated a dramatic surge in solid waste generation, causing severe land resource depletion and posing substantial environmental contamination risks. Simultaneously, the cement industry has become characterized by the intensive consumption of natural resources and high carbon emissions. This review aims to investigate the current technological advances in utilizing industrial solid waste for cement production, with a focus on promoting resource recycling, phase transformations during hydration, and environmental management. The feasibility of incorporating coal-based solid waste, metallurgical slags, tailings, industrial byproduct gypsum, and municipal solid waste incineration into active mixed material for cement is discussed. This waste is utilized by replacing conventional raw materials or serving as active mixed material due to their content of oxygenated salt minerals and oxide minerals. The results indicate that the formation of hydration products can be increased, the mechanical strength of cement can be improved, and a notable reduction in CO₂ emissions can be achieved through the appropriate selection and proportioning of mineral components in industrial solid waste. Further research is recommended to explore the synergistic effects of multi-waste combinations and to develop economically efficient pretreatment methods, with an emphasis on balancing the strength, durability, and environmental performance of cement. This study provides practical insights into the environmentally friendly and efficient recycling of industrial solid waste and supports the realization of carbon peak and carbon neutrality goals. Full article

To address the practical limitations of conventional alkaline activators (e.g., handling hazards, cost) and promote the resource utilization of industrial solid wastes, this study developed a novel all-solid-waste activator system comprising soda residue (SR) and carbide slag (CS). The synergistic effects of SR-CS activators on the hydration behavior of blast furnace slag (GGBS)–fly ash (FA) cementitious composites were systematically investigated. Mechanical performance, phase evolution, and microstructural development were analyzed through compressive strength tests, XRD, FTIR, TG-DTG, and SEM-EDS. Results demonstrate that in the SR-CS activator system, which combines with desulfuriation gypsum as sulfate activator, increasing CS content elevates the normal consistency water demand due to the high-polarity, low-solubility Ca(OH)₂ in CS. The SR-CS activator accelerates the early hydration process of cementitious materials, shortening the paste setting time while achieving compressive strengths of 17 MPa at 7 days and 32.4 MPa at 28 days, respectively. Higher fly ash content reduced strength owing to increased unreacted particles and prolonged setting. Conversely, desulfurization gypsum exhibited a sulfate activation effect, with compressive strength peaking at 34.2 MPa with 4 wt% gypsum. Chloride immobilization by C-S-H gel was confirmed, effectively mitigating environmental risks associated with SR. This work establishes a sustainable pathway for developing low-carbon cementitious materials using multi-source solid wastes. Full article

To reduce the cost of coal mine filling materials, a novel composite cementitious material was developed by utilizing coal-based solid waste materials, including fly ash, desulfurized gypsum, and carbide slag, along with cement and water as raw materials. Initially, a comprehensive analysis of the physical and chemical properties of each raw material was conducted. Subsequently, proportioning tests were systematically carried out using the single-variable method. During these tests, multiple crucial performance indicators were measured. Specifically, the fluidity and bleeding rate of the slurry were evaluated to assess its workability, while the compressive strength and chemically bound water content of the hardened sample were tested to determine its mechanical properties and hydration degree. Through in-depth analysis of the test results, the optimal formulation of the composite cementitious material was determined. In the basic group, the mass ratio of fly ash to desulfurized gypsum was set at 70:30. In the additional group, the carbide slag addition amount accounted for 20% of the total mass, the cement addition amount was 15%, and the water–cement ratio was fixed at 0.65. Under these optimal proportioning conditions, the composite cementitious material exhibited excellent performance: its fluidity ranged from 180 to 220 mm, the bleeding rate within 6 h was less than 5%, and the 28-day compressive strength reached 17.69 MPa. The newly developed composite cementitious material features good fluidity and high strength of the hardened sample, fully meeting the requirements for mine filling materials. Full article

This study investigates the use of gypsum waste from civil construction as a partial substitute for cement in soil–cement formulations, aiming to produce eco-friendly bricks aligned with circular economy principles. Formulations were prepared using a 1:8 cement–soil ratio, with gypsum replacing cement in proportions ranging from 5% to 40%. The raw materials were characterized in terms of chemical composition, crystalline phases, plasticity, and thermal behavior. Specimens, molded by uniaxial pressing into cylindrical bodies and cured for either 7 or 28 days, were evaluated for compressive strength, water absorption, durability, and microstructure. Water absorption remained below 20% in all samples, with an average value of 16.20%. Compressive strength after 7 days exhibited a slight reduction with increasing gypsum content, ranging from 16.36 MPa (standard formulation) to 13.74 MPa (40% gypsum), all meeting the quality standards. After 28 days of curing, the formulation containing 10% gypsum achieved the highest compressive strength (26.7 MPa), surpassing the reference sample (25.2 MPa). Mass loss during wetting–drying cycles remained within acceptable limits for formulations incorporating up to 20% gypsum. Notably, samples with 5% and 10% gypsum demonstrated superior mechanical performance, while the 20% formulation showed performance comparable to the standard formulation. These findings indicate that replacing up to 20% of cement with gypsum waste is a technically and environmentally viable approach, supporting sustainable development, circular economy, and reduction of construction-related environmental impacts. Full article

This study investigated the distribution and source of heavy metals and dispersed elements in the high-salinity brine of Qarhan Salt Lake. The brine with an average total dissolved solid content of 332.22 g/L, dominated by Cl⁻ (216.41 g/L) and Mg²⁺ (44.76 g/L), indicated strong evaporation and dolomite dissolution. As (6.57 ± 3.59 μg/L) and Hg (0.48 ± 0.14 μg/L) showed uniform distribution while Li (69.66 mg/L), B₂O₃ (317.80 mg/L), and Zn (5.69 mg/L) were highly enriched, highlighting the resource potential and geochemical complexity. Correlation analysis revealed that water–rock interaction played a key role in element differentiation, with Sr and Ca²⁺/Cl⁻ showing strong positive correlations (r = 0.693/0.768), reflecting isomorphic substitution and dissolution. Meanwhile, Na⁺ and Mg²⁺/Ca²⁺ showed negative correlations (r = −0.732/−0.889), suggesting cation exchange and gypsum precipitation. The self-organizing map yielded four clusters of elements and positive matrix factorization model identified four sources; the elements in the Salt Lake brine mainly came from the river water supply, weathering and leaching of minerals, and dissolution of salt-bearing layers and were locally influenced by human activities. The research provided valuable insights for future sustainable development and the environmental protection of the region. Full article

The aim of this study is to determine the characteristics of the chemical and mineral composition of sediment layers in a technogenic settling pond. This pond is located on urban land in Berezniki (Perm Krai, Russia), outside the territory of operating industrial facilities, and contains alkaline saline industrial wastes. The origin of this waste was related to sludge from the Solvay soda production process, which had been deposited in this pond over a long period of time. However, along with the soda waste, the pond also received wastewater from other industries. As a result, the accumulated sediment is characterized by variation in morphological properties both in depth and laterally. Five undisturbed columns were taken to study the composition of the accumulated sediment. The obtained samples were analyzed by X-ray diffraction (XRD), synchronous thermal analysis (STA), and X-ray fluorescence (XRF) analysis. The results showed that the mineral composition of bottom sediments in each layer of all studied columns is characterized by the predominance of calcite precipitated from wastewater. Along with calcite, due to the presence of magnesium and sodium in the solution, other carbonates precipitated—dolomite and soda (natron), as well as complex transitional carbonate phases (northupite and trona). Together with carbonate minerals, the chloride salts halite and sylvin, sulfate minerals gypsum and bassanite, and pyrite and nugget sulfur were established. The group of terrigenous mineral components is represented by quartz, feldspars, and aluminosilicates. The chemical composition of sediments in the upper part of the section generally corresponds to the mineral composition. In the lower sediment layers, the role of amorphous phase and non-mineral compounds increased, which was determined by the results of thermal analysis. The content of heavy metals and metalloids also increases in the middle and lower sediment layers. When categorized according to the Igeo value, an excessive degree of contamination (class 6) was observed in all investigated columns for copper content (Igeo 5.2–6.1). Chromium content corresponds to class 5 (Igeo 4.1–4.6), antimony to class 4 (Igeo 3.0–4.0), and lead, arsenic, and vanadium to classes 2 and 3 (moderately polluted and highly polluted). The data obtained on variations in the mineral and chemical composition of sediments represent the initial information for the selection of methods of accumulated waste management. Full article

Soil salinization in coastal areas is a serious problem restricting agricultural development. This field study aimed to explore the effects of flue gas desulfurization gypsum (FGDG) and coal fly ash (CFA) in combination with irrigation on coastal saline soils in China. Six different treatments (C1–C4: FGDG 4.5–15.0 t/hm²; C5 and C6: FGDG 4.5 t/hm² combined with CFA 2.0 and 3.5 t/hm²) were established, and soil properties such as pH, electrical conductivity (EC), and organic matter (OM) content were analyzed. The results showed that compared with the control group, the addition of FGDG (4.5 t/hm² to 15 t/hm²) slightly increased the soil pH, and the combined application of FGDG and CFA made the soil pH closer to neutral. The application of FGDG combined with two rounds of irrigation could reduce the soil EC, and the mixed application of FGDG and CFA further reduced the soil EC by about 6.7% in the 0–20 cm layer. The application of FGDG combined with irrigation showed no significant effect on the soil OM content. In general, the moderate application of FGDG and CFA can effectively improve the physicochemical properties of soil, potentially contributing to more sustainable agricultural practices in coastal regions. Full article

This study investigates the performance of alkali-activated mortar incorporating slag, fly ash, and desert sand, with a focus on flowability, mechanical properties, sulfate resistance, and microstructural characteristics. A four-factor, three-level orthogonal experimental design was used to analyze the effects of the fly ash substitution rate, alkali content (Na₂O/b), activator modulus, and desert sand replacement rate for natural sand. The results indicate that increased slag and desert sand contents reduce mortar flowability. Despite this, the mortar exhibits excellent mechanical strength, with compressive strength reaching 77.7 MPa at 28 days and increasing to 89.34 MPa under sulfate exposure. However, after 120 days of sulfate erosion, a decline in strength is observed due to the formation of expansive products such as gypsum and caliche, leading to cracking. Microstructural analyses (XRD, SEM/EDS, MIP) reveal partial dissolution of desert sand under alkali activation, enhancing gel formation and reducing cumulative porosity. The pore structure predominantly consists of harmless pores. These findings demonstrate the potential of slag–fly ash–desert sand alkali-activated mortar as a durable and sustainable material for structural and construction engineering applications, especially in sulfate-rich environments or arid regions where desert sand is abundant. Full article

The aim of the conducted research was to assess the impact of gypsum deposit development on changes in the radiation levels of the abiotic components of the environment. For this purpose, a study of the radioactivity of water, bottom sediment, soil, gypsum and loam samples was performed. Ground-based studies of the distribution of the values of the ambient dose equivalent rate of gamma radiation and radon flux density were also carried out. It was shown that due to the high solubility of gypsum, the degree of karstification of the territory increases under the influence of meteoric waters, and as a result of the intensification of anthropogenic impact, the degree of chemical weathering of rocks increases. This leads to a coordinated change in not only the chemical but also the radiation conditions. In particular, radioactive contamination of quarry waters and areas of increased radon flux density in soil air were established. In bottom sediments, the significant correlations of ¹³⁷Cs, ²³⁸U and ²³⁴U activity concentrations with carbonates, organic matter and soluble salts contents, as well as Fe, Zn, Cu, Cr, Pb, Ni, Mo, Cd, Co, Ti and V, indicate a significant role of the anthropogenic factor in the accumulation in bottom sediments. This factor is associated with both regional atmospheric transport (¹³⁷Cs) and the activity of the mining enterprise in the study area (²³⁸U and ²³⁴U). Full article

Circulating fluidized bed combustion (CFBC) ash, a byproduct typically generated from coal-fired CFBC power plant boilers, contains high content of free lime and anhydrite. Due to its chemical composition, CFBC ash exhibits self-cementing properties; however, its performance is limited. One approach to enhancing the self-cementing properties of CFBC ash is through the incorporation of mineral admixtures such as gypsum. This study investigated the influence of desulfurization gypsum (DG) on the self-cementing behavior of CFBC ash. To this end, paste and mortar specimens were prepared and evaluated for their hydration and mechanical characteristics. The hydration behavior was analyzed using isothermal calorimetry, thermogravimetric analysis (TGA), setting time measurements, and X-ray diffraction (XRD) analysis. Mechanical properties were assessed by measuring the compressive strength at various curing ages. Additionally, changes in microstructure were examined by evaluating the pore size distribution through mercury intrusion porosimetry (MIP). The experimental results indicate that the appropriate incorporation of DG enhances the hydraulic reactivity of CFBC ash and significantly improves the compressive strength. Full article