Search Results (467)

The agricultural and environmental application of Miscanthus × giganteus biomass ash (MBA) as a soil amendment requires a thorough assessment of its properties, nutrient potential, and associated risks. This study characterizes the elemental composition, pH, cation exchange capacity (CEC), and polycyclic aromatic hydrocarbons (PAHs) content of MBA in comparison with other common biomass ashes (crops, wood, and sewage sludge) referred to the international regulatory standards. The ash exhibits a strong alkaline pH (11.03), suggesting potential to improve soil pH in acid soils, but requires careful controlled application to prevent excessive alkalization. The main nutrients detected include K (5.54%), Ca (2.07%), Mg (0.37%), and P (0.86%), indicating its potential as a soil amendment, though long-term use may cause nutrient imbalances. Micronutrients such as Zn (240.67 mg·kg⁻¹), Mn (297 mg·kg⁻¹), and Cu (33.5 mg·kg⁻¹) are found in concentrations suitable for agricultural use, while potentially toxic elements (PTEs), including Cd, Cr, Ni, and Pb, are below detection limits, thereby reducing the risk of pollution. As (8.3 mg·kg⁻¹) and ΣPAHs (1.63 mg·kg⁻¹) remain within safety thresholds, suggesting a low environmental toxicity of MBA. The low Na content (0.12%) indicates a minimal risk of salinity accumulation, distinguishing MBA from high-sodium biomass ashes. Soil alkalization, disruptions in nutrient balance, and element leaching are risks to be considered. Despite these concerns, its composition is in agreement with established safety guidelines, supporting its feasibility for valorization as a sustainable soil amendment and remediation material. To maximize agronomic benefits and mitigate environmental risks, it is important to utilize the ash, considering site conditions and carry out regular monitoring of the soil. Full article

In Chile, Eucalyptus globulus stands out as a significant forest species, yielding around 2 million tonnes of bark; this by-product is a valuable source of phenolic compounds. This research evaluated the valorization of E. globulus bark using alkali-assisted extraction (AAE) and obtained extracts intended to protect the wood against fungal degradation and ultraviolet (UV) radiation. The chemical and thermal properties of the extracts were characterized using total phenolic content (TPC), antioxidant capacity, FTIR spectroscopy, LC-LTQ-Orbitrap-MS, and thermal analyses (TGA and DSC). Pine wood samples were impregnated using the Bethel process, and their absorption, retention, leaching, UV resistance, gloss, and antifungal efficacy were evaluated. The AAE showed an extraction yield of 8.79%, almost double that of aqueous extraction, with a phenolic content of 970 mg GAE/100 g dry bark and good antioxidant capacity. The MS/MS analysis tentatively identified low-molecular-weight organic acids, phenolic acids, a hydrolyzable tannin derivative, ellagic acid, methylated flavonol glycosides, and an iridoid non-phenolic metabolite. Thermal analysis indicated greater stability of the alkaline extracts, with a mass loss of less than 10% up to 200 °C, and significant degradation between 220 and 300 °C. Leaching tests showed a lower release of polyphenols from alkali-treated wood, indicating reduced mobility and/or greater retention of the extractives within the wood structure. Biological assays demonstrated effective inhibition of stain fungi and strong resistance to brown rot. Furthermore, UV aging tests showed less color change (Delta E*) and greater resistance to surface degradation. These results demonstrate the potential of alkaline extracts from E. globulus bark as sustainable additives for wood protection. Full article

Simultaneous multi-ion detection is important for interpreting leaching, corrosion, hydration, and solidification processes in cement-based materials, because these processes are controlled by coupled ion migration, binding, and precipitation–dissolution reactions. Conventional methods such as pore-solution extraction, ion chromatography, inductively coupled plasma optical emission spectroscopy, and single-ion potentiometric measurements provide useful chemical information, but they generally rely on discrete sampling or isolated ion channels and therefore have limited ability to capture time-aligned multi-ion evolution. In this study, an IoT-based in situ multi-ion detection system was developed by integrating ion-selective electrodes for Cl⁻, Ca²⁺, F⁻, and H⁺ with an ADS1115 analog-to-digital converter, an ESP32 microcontroller, and a voltage amplification module. The system achieved minimum resolvable concentrations of 10⁻⁵ M for Cl⁻ and F⁻ and 10⁻⁴ M for Ca²⁺, while maintaining pH measurement over the range of 2–12. Ten consecutive measurements at 0.01 M showed relative standard deviations below 0.12%, indicating good short-term repeatability under laboratory calibration conditions. Interference and temperature tests showed that Br⁻ and NO₃⁻ affected the chloride channel at high concentrations, Ca²⁺ reduced free F⁻ activity through Ca–F precipitation equilibrium, and the temperature drift of Cl⁻ and F⁻ electrodes changed direction with concentration, whereas the Ca²⁺ response decreased monotonically with increasing temperature. When applied to phosphogypsum–cement hardened pastes, the system captured rapid Ca²⁺ release, low-level F⁻ fluctuation controlled by Ca–F interaction, non-monotonic Cl⁻ release, and alkaline pH evolution on the same time axis. Compared with existing single-ion or offline methods, the proposed system provides synchronized in situ evidence for interpreting coupled ion leaching in cement-based solid-waste systems. Full article

Steel dust is a waste generated during steelmaking in an electric arc furnace (EAF), which contains a high proportion of iron-bearing compounds, leading to the inclusion of this waste as a resource in the circular economy for steelmaking. In addition to the limitation related to granulation (the waste must be processed to obtain larger particle sizes), a limiting factor is the increasingly high Zn content due to the low-quality ferrous charge. For the recycling of steelmaking dust, preliminary processing is necessary to reduce zinc. The paper presents, in addition to qualitative characterization of steel dust, laboratory experiments on the compositional changes associated with zinc redistribution applying the hydrometallurgical leaching process in an alkaline environment, using sodium hydroxide (NaOH). The changes in the chemical composition were identified and evaluated using X-ray fluorescence (XRF) and energy-dispersive X-ray spectroscopy (EDX). The experiments consisted of treating steel dust samples with 5 M NaOH at 25, 70, 80 and 90 °C for 60 min, using solid-to-liquid ratios of 10, 15, and 25 g/L. The results indicate a reduction in ZnO content ranging from 4.52% to 16.82%, as determined from Na₂O-free normalization data. Room-temperature samples show only marginal changes in ZnO content. The XRF and EDX analyses indicate a moderate and condition-dependent redistribution of zinc in the solid phase after alkaline treatment, as evaluated using Na₂O-free normalized data. These values are derived exclusively from solid-phase measurements (XRF/EDX) and do not include zinc in the leachate; therefore, true zinc extraction efficiency cannot be determined. The research results attest to the viability and efficiency (as a solid-phase compositional transformation process) using NaOH as a leaching agent for the studied steel dust, thus providing a potential pathway for improved waste recycling in the steel industry. Full article

This study investigated the kinetics of chalcopyrite dissolution in an alkaline monosodium glutamate (MSG) solution using H₂O₂ and KMnO₄. The aims were to optimize process conditions for maximum copper dissolution and to study the kinetic mechanism of dissolution under varying conditions, such as particle size, oxidant type and concentration, temperature, and the presence of gangue minerals. Results showed that KMnO₄ exhibited better oxidative efficiency and stability than H₂O₂, yielding copper recoveries above 90% in most conditions while keeping the dissolution of some gangue metals, such as calcium, magnesium, and iron, lower, thereby reducing MSG consumption. Temperature and particle size were the most important factors in the effects on leaching kinetics; smaller particles allow higher initial reaction rates, while larger particles allow prolonged dissolution. The shrinking core model (SCM) was thus used to perform kinetic analysis and determine that diffusion controls the leaching process through the product layer. The calculated activation energies of 18.2 kJ/mol of MSG-H₂O₂ and 17.3 kJ/mol of MSG-KMnO₄ confirm the diffusional mechanism. Full article

Soil salinity and alkalinity are major constraints to agricultural productivity in arid regions, particularly where treated wastewater (TWW) is used for irrigation. This study evaluated the spatial variability of water and soil physicochemical properties along Wadi Hanifa, Saudi Arabia, and compared soils from two farms irrigated with TWW for approximately 5 and 15 years to assess the effects of irrigation duration on soil properties. Soil samples were collected from 25 locations along the Wadi using a handheld Global Positioning System (GPS), and water and soil properties were analyzed using standard laboratory procedures. The treated wastewater exhibited moderate electrical conductivity (EC = 2.0 dS m⁻¹) and low sodicity hazard (SAR = 1.55), indicating its suitability for irrigation under appropriate management practices. Soils were predominantly coarse-textured and showed considerable spatial variability in salinity and chemical composition. Soil pH remained relatively stable (7.33–8.07), while EC ranged from 0.88 to 2.64 dS m⁻¹, indicating non-saline to moderately saline conditions across the study area. Comparison of soil profiles from the two farms revealed greater salinity in subsurface layers, particularly at the farm irrigated with TWW for 15 years, where EC reached 4.15 dS m⁻¹ and Na⁺ concentrations reached 16.4 meq L⁻¹. These observations suggest salt redistribution and accumulation within deeper soil horizons under prolonged irrigation. Overall, soil and water quality in Wadi Hanifa are strongly influenced by spatial variability, coarse soil texture, and arid climatic conditions. The findings highlight the importance of regular monitoring of salinity and sodicity indicators, together with adequate leaching and drainage practices, to ensure the sustainable use of treated wastewater for agricultural production in arid environments. Full article

Soil salinization threatens agricultural production, and increasing extreme rainfall may alter natural leaching processes in coastal saline–alkaline soils. However, the relationships among salt ion migration, alkalinity changes, nutrients, and bacterial communities under natural rainfall leaching remain unclear. Therefore, a phased natural rainfall leaching experiment was conducted from June to September 2025 using moderate to severe NaCl-type saline–alkaline soil from Dongying in the Yellow River Delta. The results showed that natural rainfall leaching significantly reduced soluble salt ions, especially Na⁺, Cl⁻, and SO₄²⁻, and rapidly alleviated early salt stress. However, soil pH did not decline continuously with salt reduction, but fluctuated under the buffering effect of the carbonate system, indicating that desalination was not necessarily accompanied by alkalinity alleviation. Available nutrients showed stage-dependent changes, with HN and AK increasing around the middle leaching stage. Bacterial community composition and co-occurrence networks also changed during leaching, and these changes were more closely associated with salt ions and HCO₃⁻/pH than with available nutrients. These results suggest that post-rain management of saline–alkaline soils should not rely only on total salinity, but should also consider major salt ions, pH/HCO₃⁻, and nutrient availability. Full article

Rural road construction in the loess region of Gansu Province is constrained by aggregate shortage, high material transportation costs, and the limited early performance of cement-stabilized soil. In this study, KDJ-II stabilizer and cement were used to prepare KDJ-II–cement composite-stabilized soil for potential use as a base-course material. Compared with cement-stabilized soil, the addition of 0.02% KDJ-II increased the 7-day unconfined compressive strength, splitting tensile strength, and resilient modulus by 16.7%, 17.6%, and 12.1%, respectively. Leaching-based ion concentration analysis, XRD, FTIR, and SEM were used to interpret the early strength development mechanism. The results suggest that KDJ-II influenced the leachable ion release and retention behavior of the cement-stabilized soil and helped form a sulfate-rich, alkaline, and soluble-silica-bearing reaction environment under the tested conditions. This environment may favor the development of sulfate-bearing hydration products, the activation of primary aluminosilicate minerals, and the formation of C–S–H-like gels. The coupled variations in leachable Ca²⁺, SO₄²⁻, and Na⁺, together with the increase in calcite, decrease in albite, broadening of the absorption band at approximately 1018 cm⁻¹, and the SEM-observed needle/fibrous products, flocculent gels, and reduced visible pores, collectively support the interpretation that KDJ-II promotes particle cementation, pore filling, and microstructural densification. Overall, this study indicates that, under the selected mixture proportion and curing condition, KDJ-II can improve the early strength and stiffness of cement-stabilized loess by modifying the early reaction environment and promoting the coordinated development of hydration-related products and a denser microstructure. Full article

Vanadium extraction tailings, as a highly alkaline and hazardous solid waste, pose not only serious environmental risks but also severely hinder the large-scale recycling of secondary iron resources. This study proposes an innovative process of “mild alkali leaching for vanadium extraction coupled with deep calcification and dealkali removal”. The vanadium extraction slag from a steel plant in China was used as a raw material to carry out the experimental and pilot study of alkali leaching of vanadium and calcification dealkalization. Experimental results show that under the conditions of 120 °C, 1% NaOH solution, liquid-solid ratio of 4:1 to 6:1, and reaction time of 1 h, vanadium leaching rate can reach 50%, which can be effectively used as a high-value-added economic hedge. Subsequently, under the conditions of 200 °C, calcium oxide concentration of 19.29%, stirring speed of 800 rpm, liquid-solid ratio of 4:1, and reaction time of 1 h, the Na₂O content in the tailings was successfully reduced to below 1%. A large number of tailings can be converted into high-quality secondary iron ore resources, which are suitable for subsequent iron-bearing briquette preparation and blast furnace ironmaking. Furthermore, pilot-scale testing in a 200 L reactor verified the engineering scalability of this combined process, maintaining a vanadium extraction rate of over 50% and an alkali removal rate of over 80%. This study provides a robust, scalable, and highly profitable pathway for the comprehensive utilization of high-alkali metallurgical solid waste. Full article

Mining activities generate large volumes of waste that pose both environmental liabilities and potential secondary resource value. A significant fraction of these materials still contains recoverable copper, making leaching a promising strategy for reprocessing and valorization, given the natural decline in ore grade. This study presents a PRISMA-based systematic review of recent literature on leaching technologies applied to mining waste, with emphasis on technical performance, environmental implications, and economic feasibility. The reviewed residues include tailings, slags, copper smelter dusts, sludges, waste rock, leaching residues, and other secondary mining and metallurgical wastes. The main leaching routes identified were acidic, biological, alkaline, and hybrid systems, including conventional H₂SO₄ leaching, pressure oxidative leaching, chloride-based systems, glycine- and ammonia-based alkaline media, organic acids, deep eutectic solvents, and biologically mediated processes. Reported Cu recoveries ranged from low values in refractory systems to near-complete extraction under optimized conditions. Overall, copper recovery was controlled primarily by the mineralogical occurrence of Cu rather than by leaching category alone. In contrast, the highest recoveries were generally associated with intensified conditions capable of overcoming sulfide- and silicate-related constraints. Environmental and circular economy benefits were frequently claimed but less often demonstrated through direct evidence, while economic assessment remained limited. Future research should better integrate mineralogical interpretation, environmental verification, and economic feasibility. Full article

As lithium demand surges and primary resources face depletion, lithium-bearing wastewater from urban mines has become a crucial secondary resource. For highly alkaline (pH 9–12), low-lithium (Li⁺ 0.5–5 g/L), high-sodium (Na/Li mass ratio > 30) wastewater generated from the alkaline leaching-washing of spent lithium-ion batteries in urban mining, a single-component, synergist-free extraction process employing HBL121 in sulfonated kerosene was developed, and its extraction stoichiometry, reaction mechanism, and industrial feasibility were elucidated. Saponification significantly enhanced extraction under moderate alkalinity: the saponified system achieved over 99% extraction efficiency at pH 11.0, whereas the non-saponified system required pH > 13.5 for comparable performance, thereby lowering alkali consumption by 81%. Under optimal conditions (saponification degree 40%, 30% (v/v) HBL121 and 70% (v/v) sulfonated kerosene, organic-to-aqueous phase ratio O/A = 1:1, extraction time 5 min), single-stage extraction efficiency exceeded 99%. A McCabe-Thiele diagram was used to determine the theoretical stage number for lithium stripping, showing that essentially all lithium ions can be stripped via a three-stage countercurrent process. Using 3.0 mol/L H₂SO₄ at an aqueous-to-organic phase ratio of 1:4, the stripping efficiency exceeded 99% from the loaded organic. Slope analysis, FT-IR, and ESI-MS confirmed a coordination mechanism between HBL121 and metal ions, forming a stable anionic bisphosphonate complex [LiNa₂(C₂₈H₄₄O₇P₂)]⁻, whose neutral parent form is HLiNa₂(C₂₈H₄₄O₇P₂). Full article

Liquid-phase mineralization of CO₂ using coal fly ash (CFA) is an efficient approach to permanent CO₂ sequestration. To address the low leaching efficiency of calcium ions (Ca²⁺) in carbon mineralization, this study systematically investigates the leaching performance and leaching mechanism of calcium ions from CFA by using a sequential alkaline-acid processing (i.e., alkaline activation followed by acid leaching). The effects of NaOH concentration, acid concentration, acid type (HCl/CH₃COOH), reaction time, and grinding duration on leaching efficiency are studied. The reaction products are characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). A kinetic model is proposed to analyze the reaction dynamics and leaching mechanisms. The results show that the maximum Ca²⁺ leaching efficiency for untreated CFA is 43.7% after 40-min acid leaching with 7 mol/L HCl and 1:1.5 S/L ratio. The leaching efficiency can be enhanced to 72.1% after 50-min alkaline activation with 11 mol/L NaOH. Grinding the CFA can further increase the leaching performance of Ca²⁺. It is shown that the leaching efficiency can be enhanced to 58.75% and 82.3% after 90-min grinding, respectively, for cases without and with 50-min alkaline activation using 9 mol/L NaOH. It is also shown that a peak leaching efficiency of 86.51% can be obtained when 8 mol/L CH₃COOH is used for the acid system. The mechanism for the enhancement of leaching efficiency is that both NaOH activation and mechanical grinding can break down the calcium and aluminum silicate vitreous matrix of CFA, facilitating calcium release. Ca²⁺ leaching performance exhibits two regimes. The leaching efficiency is significantly time-dependent in the first regime, and it remains almost constant in the second regime after the efficiency reaches a pseudo-maximum value. The contribution of this study is that a theoretical foundation is provided for enhancing the Ca²⁺ recovery from CFA, which makes it practical for large-scale CFA utilization and permanent CO₂ sequestration in industry applications. Full article

Ningbo City is endowed with abundant mineral water resources. Investigating their chemical characteristics and formation mechanisms is essential for understanding hydrochemical evolution and supporting sustainable resource utilization. Based on hydrochemical data from 12 drinking natural mineral water sources in Ningbo City, this study investigates the hydrochemical features and genesis of mineral water by integrating statistical analysis, hydrochemical diagrams, ionic ratios, and mineral equilibrium modeling. The results indicate that metasilicic acid (as H₂SiO₃) and strontium (Sr) are the principal characteristic components of the drinking natural mineral water in Ningbo City, with concentrations of 32.87–60.8 mg/L and 0.05–4.59 mg/L, respectively. The mineral waters are neutral to slightly alkaline and weakly mineralized, with the pH values ranging from 6.70 to 8.16, and total dissolved solids (TDS) contents of 76.8–767.2 mg/L. The predominant hydrochemical facies are HCO₃-Ca-Na, HCO₃-Ca, HCO₃-Na-Ca. Their chemical composition is mainly governed by rock weathering, whilst also being influenced by cation exchange and mineral dissolution–precipitation equilibrium. H₂SiO₃ is mainly derived from the weathering and hydrolysis of silicate minerals such as plagioclase. Sr enrichment is associated with the dissolution of Sr-bearing silicate minerals and certain sulphate minerals, as well as prolonged water–rock interaction. The Sr- and Si-rich aquifers provide the material basis for the enrichment of Sr and H₂SiO₃ in groundwater. Structural fractures and weathering fractures provide transport pathways and storage spaces for groundwater, facilitating the migration and enrichment of these characteristic components. The mechanism of mineral water emergence can be summarized as of the tectonic fracture-controlled circulation-leaching type. Full article

Magma-heated geothermal systems have garnered significant attention in academia due to their unique formation mechanisms and vast potential. This paper focuses on the Rehai, Ruidian, and Banglazhang geothermal fields in the Tengchong area. We present the element geochemistry and isotope compositions of hot springs, cold springs, and surface water to explore magmatic fluid input into geothermal systems and investigate the release of deep mantle-derived components. Based on our findings, we propose a conceptual model and theoretical framework for geothermal system genesis constrained by magmatic heat source influences. Results indicate that magma-heated geothermal systems coexist with three types of geothermal water: neutral chloride-rich water, acidic sulfate-rich water, and alkaline bicarbonate-rich water. The infusion of magmatic fluids into geothermal systems. The enrichment of trace elements in hot springs is jointly controlled by magmatic fluid input and host rock leaching. The magma chamber is the primary factor influencing the reservoir temperature. The parent geothermal fluid can be identified within the geothermal system. During circulation, the parent geothermal fluid undergoes three cooling processes: adiabatic cooling, conductive cooling, and mixing with cold water. We propose that the release of mantle-derived materials is a key factor in element enrichment within magma-heated geothermal systems, and mantle-derived components are more enriched in areas with active magma chambers. The findings of this study provide insights into magmatic fluid input into geothermal systems and highlight the critical role of the release of mantle-derived components in the formation of high-temperature geothermal resources. Full article

The red mud generated during the alumina production process is a highly alkaline solid waste, with a global stockpile exceeding 4 billion tons. Reducing red mud at the source and enhancing its comprehensive utilization are significant global challenges. Herein, we propose a pre-treatment method utilizing co-roasting of bamboo powder and diaspore bauxite. Characterization techniques, including XRD, SEM-EDS, and TESCAN Integrated Mineral Analyzer (TIMA), have demonstrated that roasting modifies the composition and structure of the bauxite. After roasting, diaspore undergoes dehydroxylation and transforms into alumina, while hematite is transformed into magnetite by reducing gases such as CO and CH₄ produced from the pyrolysis of bamboo powder. Simultaneously, the roasting process created cracks in the alumina, resulting in an increased specific surface area and leaching rate of alumina. Under the optimal roasting conditions (diaspore bauxite to bamboo powder ratio of 30:1, 650 °C, 25 min), the roasted bauxite can be subjected to Bayer digestion at 260 °C with the addition of 4% calcium oxide, achieving a relative leaching rate of alumina of 98.8% and reducing red mud production by 17.3% at the source. Magnetic separation enabled the recovery of iron resources from red mud, with the iron concentrate obtained exhibiting a grade of 58.8% and an iron recovery rate of 85.6%, and the final red mud production was reduced by 63.6%, which is beneficial to the sustainable development of the alumina industry. Full article