Alkali-activated geopolymers based on calcined phosphate sludges and metakaolin.

The extraction of phosphorite ore in Tunisia has resulted in the discharge of substantial amounts of phosphatic sludge into the region's water system. To mitigate this environmental issue and prevent heavy metal leaching, a geopolymerization process was employed using two types of Tunisian calcined phosphate sludges (Cal-PS1 and Cal-PS2) as substitutes for alkali-activated metakaolin. This study aimed to investigate and compare the physical and mechanical properties of the resulting geopolymers. The optimal substitution ratio of metakaolin with calcined phosphate sludge was determined to be 1.5, equivalent to 20 wt.% of calcined phosphate sludge. Compressive strength tests conducted after 28 days of curing revealed values of 37 MPa for Cal-PS1 specimens and 28 MPa for Cal-PS2 geopolymers while compressive strength of geopolymers soaked in water for 28 days showed a decrease with the addition of phosphate sludges. The specific surface areas of Cal-PS1 geopolymers ranged from 16.3 to 16.9 m2/g and from 17.62 to 18.73 m2/g for Cal-PS2 specimens exhibiting a mesoporous structure. The elasticity modulus of the geopolymers was found to increase with the increase of the apparent density of geopolymers and with the sludges content but it tended to be lower than the Portland cement elasticity modulus. Leaching test was conducted to evaluate the potential environmental applications of the geopolymers. This test demonstrated effective containment of heavy metals within the geopolymers' network, except for low levels of arsenic.

Design and properties of ternary alkali-activated binder based on blast furnace slag, recycled powder and waste glass powder.

Ternary alkali-activated binder was prepared by blast furnace slag (GGBS), recycled powder (RP) and waste glass powder (WGP) using simplex centroid design method. By measuring the fluidity, setting time, drying shrinkage and mechanical property of specimen, the complementary effect of GGBS, RP and WGP was discussed. The reaction mechanism and microstructure were explored by X-ray diffraction and scanning electron microscopy. The results reveal that the addition of RP could significantly reduce the fluidity and setting time of paste, while WGP can obviously improve the rheological property and play a retarding role. The workability of paste can be effectively regulated by mixing RP and WGP together. Whether added alone or in combination, RP and WGP can effectively improve the shrinkage performance. In the ternary system, GGBS can be rapidly activated and form a skeleton structure. The fine RP particles can play a good role in filling the structure, and the pozzolanic reaction of WGP gradually occurs, which makes the microstructure more compact. The incorporation of GGBS, RP and WGP can promote the growth of hydration products, improve the density of microstructure, and form a certain complementary effect.

Enhanced anaerobic digestion of waste-activated sludge by thermal-alkali pretreatment: a pilot-scale study.

The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal-alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4-8 h, and the optimal alkali concentration range was 0.0125-0.015 kg NaOH/kg dry-sludge. Thermal-alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge.

Facilely Fabricated Single-Site Ptδ+-O(OH)x- Species Associated with Alkali on Zirconia Exhibiting Superior Catalytic Oxidation Reactivity.

Fabrication of robust isolated atom catalysts has been a research hotspot in the environment catalysis field for the removal of various contaminants, but there are still challenges in improving the reactivity and stability. Herein, through facile doping alkali metals in Pt catalyst on zirconia (Pt-Na/ZrO2), the atomically dispersed Ptδ+-O(OH)x- associated with alkali metal via oxygen bridge was successfully fabricated. This novel catalyst presented remarkably higher CO and hydrocarbon (HCs: C3H8, C7H8, C3H6, and CH4) oxidation activity than its counterpart (Pt/ZrO2). Systematically direct and solid evidence from experiments and density functional theory calculations demonstrated that the fabricated electron-rich Ptδ+-O(OH)x- related to Na species rather than the original Ptδ+-O(OH)x-, serving as the catalytically active species, can readily react with CO adsorbed on Ptδ+ to produce CO2 with significantly decreasing energy barrier in the rate-determining step from 1.97 to 0.93 eV. Additionally, owing to the strongly adsorbed and activated water by Na species, those fabricated single-site Ptδ+-O(OH)x- linked by Na species could be easily regenerated during the oxidation reaction, thus considerably boosting its oxidation reactivity and durability. Such facile construction of the alkali ion-linked active hydroxyl group was also realized by Li and K modification which could guide to the design of efficient catalysts for the removal of CO and HCs from industrial exhaust.

Development of innovative alkali activated paste reinforced with polyethylene fibers for concrete crack repair.

Concrete structures are susceptible to cracking, which can compromise their integrity and durability. Repairing them with ordinary Portland cement (OPC) paste causes shrinkage cracks to appear in the repaired surface. Alkali-activated binders offer a promising solution for repairing such cracks. This study aims to develop an alkali-activated paste (AAP) and investigate its effectiveness in repairing concrete cracks. AAPs, featuring varying percentages (0.5%, 0.75%, 1%, 1.25%, 1.5%, and 1.75%) of polyethylene (PE) fibers, are found to exhibit characteristics such as strain hardening, multiple plane cracking in tension and flexure tests, and stress-strain softening in compression tests. AAP without PE fibers experienced catastrophic failure in tension and flexure, preventing the determination of its stress-strain relationship. Notably, AAPs with 1.25% PE fibers demonstrated the highest tensile and flexural strength, exceeding that of 0.5% PE fiber reinforced AAP by 100% in tension and 70% in flexure. While 1% PE fibers resulted in the highest compressive strength, surpassing AAP without fibers by 17%. To evaluate the repair performance of AAP, OPC cubes were cast with pre-formed cracks. These cracks were induced by placing steel plates during casting and were designed to be full and half-length with widths of 1.5 mm and 3 mm. AAP both with and without PE fibers led to a substantial improvement in compressive strength, reducing the initial strength loss of 30%-50% before repair to a diminished range of 2%-20% post-repair. The impact of PE fiber content on the compressive strength of repaired OPC cube is marginal, providing more flexibility in using AAP with any fiber percentage while still achieving effective concrete crack repair. Considering economic and environmental factors, along with observed mechanical enhancements, AAPs show promising potential for widespread use in concrete repair and related applications, contributing valuable insights to the field of sustainable construction materials.

Insights into digestibility, biological activity, and peptide profiling of flaxseed protein isolates treated by ultrasound coupled with alkali cycling.

This study aims to investigate the effects of ultrasound coupled with alkali cycling on the structural properties, digestion characteristics, biological activity, and peptide profiling of flaxseed protein isolates (FPI). The digestibility of FPI obtained by ultrasound coupled with pH 10/12 cycling (UFPI-10/12) (74.56 % and 79.12 %) was significantly higher than that of native FPI (64.40 %), and UFPI-10 showed higher hydrolysis degree (35.76 %) than FPI (30.65 %) after intestinal digestion. The combined treatment induced transition from α-helix to ß-sheet with an orderly structure. Large FPI aggregates broke down into small-sized FPI particles, which induced the increase of specific surface area of particles. This might expose more cutting sites and contact area with enzymes. Furthermore, UFPI-10 showed high antioxidant activity (29.18 %) and lipid-lowering activity (70.52 %). Peptide profiling revealed that UFPI-10 exhibited a higher proportion of 300-600 Da peptides and significantly higher abundance of antioxidant peptides than native FPI, which might promote its antioxidant activity. Those results suggest that the combined treatment is a promising modification method to improve the digestion characteristics and biological activity of FPI. This work provides new ideas for widespread use of FPI as an active stabilizer in food systems.

Alkali Extraction of Arsenic from Groundwater Treatment Sludge: An Essential Initial Step for Arsenic Recovery.

Arsenic (As)-bearing Fe(III) precipitate groundwater treatment sludge has traditionally been viewed by the water sector as a disposal issue rather than a resource opportunity, partly due to assumptions of the low value of As. However, As has now been classified as a Critical Raw Material (CRM) in many regions, providing new incentives to recover As and other useful components of the sludge, such as phosphate (P) and the reactive hydrous ferric oxide (HFO) sorbent. Here, we investigate alkali extraction to separate As from a variety of field and synthetic As-bearing HFO sludges, which is a critical first step to enable sludge upcycling. We found that As extraction was most effective using NaOH, with the As extraction efficiency increasing up to >99% with increasing NaOH concentrations (0.01, 0.1, and 1 M). Extraction with Na2CO3 and Ca(OH)2 was ineffective (<5%). Extraction time (hour, day, week) played a secondary role in As release but tended to be important at lower NaOH concentrations. Little difference in As extraction efficiency was observed for several key variables, including sludge aging time (50 days) and cosorbed oxyanions (e.g., Si, P). However, the presence of ∼10 mass% calcite decreased As release from field and synthetic sludges considerably (<70% As extracted). Concomitant with As release, alkali extraction promoted crystallization of poorly ordered HFO and decreased particle specific surface area, with structural modifications increasing with NaOH concentration and extraction time. Taken together, these results provide essential information to inform and optimize the design of resource recovery methods for As-bearing treatment sludge.

[Estimation of soil moisture and organic matter content in saline alkali farmland by using CARS algorithm combined with covariates]. / 利用CARS算法联合协变量估算盐碱农田土壤水分和有机质含量.

Rapid acquisition of the data of soil moisture content (SMC) and soil organic matter (SOM) content is crucial for the improvement and utilization of saline alkali farmland soil. Based on field measurements of hyperspectral reflectance and soil properties of farmland soil in the Hetao Plain, we used a competitive adaptive reweighted sampling algorithm (CARS) to screen sensitive bands after transforming the original spectral reflectance (Ref) into a standard normal variable (SNV). Strategies Ⅰ, Ⅱ, and Ⅲ were used to model the input variables of Ref, Ref SNV, Ref-SNV+ soil covariate (SC), and digital elevation model (DEM). We constructed SMC and SOM estimation models based on random forest (RF) and light gradient boosting machine (LightGBM), and then verified and compared the accuracy of the models. The results showed that after CARS screening, the sensitive bands of SMC and SOM were compressed to below 3.3% of the entire band, which effectively optimized band selection and reduced redundant spectral information. Compared with the LightGBM model, the RF model had higher accuracy in SMC and SOM estimation, and the input variable strategy Ⅲ was better than Ⅱ and Ⅰ. The introduction of auxiliary variables effectively improved the estimation ability of the model. Based on comprehensive analysis, the coefficient of determination (Rp2), root mean square error (RMSE), and relative analysis error (RPD) of the SMC estimation model validation based on strategy Ⅲ-RF were 0.63, 3.16, and 2.01, respectively. The SOM estimation models based on strategy Ⅲ-RF had Rp2, RMSE, and RPD of 0.93, 1.15, and 3.52, respectively. The strategy Ⅲ-RF model was an effective method for estimating SMC and SOM. Our results could provide a new method for the rapid estimation of soil moisture and organic matter content in saline alkali farmland.

[Effects of Different Modified Materials on Soil Fungal Community Structure in Saline-Alkali Soil].

Studying the effects of different modified materials on the physicochemical properties and fungal community structure of saline-alkali soil can provide theoretical basis for reasonable improvement of saline-alkali soil. High-throughput sequencing technology was used to explore the effects of five treatments, namely, control (CK), desulfurization gypsum (T1), soil ameliorant (T2), organic fertilizer (T3), and desulfurization gypsum compounds soil ameliorant and organic fertilizer (T4), on soil physicochemical properties and fungal community diversity, composition, and structure of saline-alkali soil in Hetao Plain, Inner Mongolia. The results showed that compared with those in CK, the contents of available phosphorus, available potassium, organic matter, and alkali hydrolysis nitrogen were significantly increased in modified material treatments, and the T4 treatment significantly decreased soil pH. Modified treatments increased the Simpson and Shannon indexes of fungi but decreased the Chao1 index. The dominant fungi were Ascomycota, Basidiomycota, and Mortierellomycota, and the dominant genera were Mortierella, Conocybe, Botryotrichum, Fusarium, and Pseudogymnoascus. The application of modified materials increased the relative abundance of Ascomycota, Basidiomycota, Fusarium, and Pseudogymnoascus, while decreasing the relative abundance of Mortierellomycota, Chytridiomycota, and Mortierella. LEfSe analysis showed that modified treatments altered the fungal community biomarkers. Correlation analysis showed that pH and available potassium were the main environmental factors affecting fungal community structure. The results can provide scientific basis for improving saline-alkali soil and increasing soil nutrients in Hetao Plain, Inner Mongolia.

Strengthen sunflowers resilience to cadmium in saline-alkali soil by PGPR-augmented biochar.

In the center of the Nile Delta in Egypt, the Kitchener drain as the primary drainage discharges about 1.9 billion m3 per year of water, which comprises agricultural drainage (75 %), domestic water (23 %), and industrial water (2 %), to the Mediterranean Sea. Cadmium (Cd) stands out as a significant contaminant in this drain; therefore, this study aimed to assess the integration of biochar (0, 5, and 10 ton ha-1) and three PGPRs (PGPR-1, PGPR-2, and PGPR-3) to alleviate the negative impacts of Cd on sunflowers (Helianthus annuus L.) in saline-alkali soil. The treatment of biochar (10 ton ha-1) and PGPR-3 enhanced the soil respiration, dehydrogenase, nitrogenase, and phosphatase activities by 137 %, 129 %, 326 %, and 127 %, while it declined soil electrical conductivity and available Cd content by 31.7 % and 61.3 %. Also, it decreased Cd content in root, shoot, and seed by 55.3 %, 50.7 %, and 92.5 %, and biological concentration and translocation factors by 55 % and 5 %. It also declined the proline, lipid peroxidation, H2O2, and electrolyte leakage contents by 48 %, 94 %, 80 %, and 76 %, whereas increased the catalase, peroxidase, superoxide dismutase, and polyphenol oxidase activities by 80 %, 79 %, 61 %, and 116 %. Same treatment increased seed and oil yields increased by 76.1 % and 76.2 %. The unique aspect of this research is its investigation into the utilization of biochar in saline-alkali soil conditions, coupled with the combined application of biochar and PGPR to mitigate the adverse effects of Cd contamination on sunflower cultivation in saline-alkali soil.

Enhancing the Thermal Mineralization of Perfluorooctanesulfonate on Granular Activated Carbon Using Alkali and Alkaline-Earth Metal Additives.

Thermal treatment has emerged as a promising approach for either the end-of-life treatment or regeneration of granular activated carbon (GAC) contaminated with per- and polyfluoroalkyl substances (PFAS). However, its effectiveness has been limited by the requirement for high temperatures, the generation of products of incomplete destruction, and the necessity to scrub HF in the flue gas. This study investigates the use of common alkali and alkaline-earth metal additives to enhance the mineralization of perfluorooctanesulfonate (PFOS) adsorbed onto GAC. When treated at 800 °C without an additive, only 49% of PFOS was mineralized to HF. All additives tested demonstrated improved mineralization, and Ca(OH)2 had the best performance, achieving a mineralization efficiency of 98% in air or N2. Its ability to increase the reaction rate and shift the byproduct selectivity suggests that its role may be catalytic. Moreover, additives reduced HF in the flue gas by instead reacting with the additive to form inorganic fluorine (e.g., CaF2) in the starting waste material. A hypothesized reaction mechanism is proposed that involves the electron transfer from O2- defect sites of CaO to intermediates formed during the thermal decomposition of PFOS. These findings advocate for the use of additives in the thermal treatment of GAC for disposal or reuse, with the potential to reduce operating costs and mitigate the environmental impact associated with incinerating PFAS-laden wastes.

Development of an injectable oxidized dextran/gelatin hydrogel capable of promoting the healing of alkali burn-associated corneal wounds.

The cornea serves as an essential shield that protects the underlying eye from external conditions, yet it remains highly vulnerable to injuries that could lead to blindness and scarring if not promptly and effectively treated. Excessive inflammatory response constitute the primary cause of pathological corneal injury. This study aimed to develop effective approaches for enabling the functional repair of corneal injuries by combining nanoparticles loaded with anti-inflammatory agents and an injectable oxidized dextran/gelatin/borax hydrogel. The injectability and self-healing properties of developed hydrogels based on borate ester bonds and dynamic Schiff base bonds were excellent, improving the retention of administered drugs on the ocular surface. In vitro cellular assays and in vivo animal studies collectively substantiated the proficiency of probucol nanoparticle-loaded hydrogels to readily suppress proinflammatory marker expression and to induce the upregulation of anti-inflammatory mediators, thereby supporting rapid repair of rat corneal tissue following alkali burn-induced injury. As such, probucol nanoparticle-loaded hydrogels represent a prospective avenue to developing long-acting and efficacious therapies for ophthalmic diseases.

Mild alkaline conditions affect digester performance and community dynamics during long-term exposure.

This paper examines the adaptive responses of microbial communities to gradual shifts in pH toward the mild alkaline range in anaerobic digestion (AD) systems. The results indicate that a pH of 8.0 serves as a critical upper limit for stable AD operation, beyond which microbial efficiency declines, underscoring the importance of microbial resilience against elevated pH stress. Specifically, hydrolysis genera, e.g. Eubacterium and Anaerobacterium, and syntrophic bacteria were crucial for reactor stability. Fibrobacter had also been shown to play a key role in the accumulation of propionate, thus leading to its dominance in the volatile fatty acid profile throughout the experimental phases. Overall, this investigation revealed the potential adaptability of microbial communities in AD systems to mild alkaline pH shifts, emphasizing the hydrolysis bacteria and syntrophic bacteria as key factors for maintaining metabolic function in elevated pH conditions.

An antifouling supramolecular polymer ophthalmic ointment alleviates symblepharon in rat alkali burn eyes.

Symblepharon is an adverse ocular disease resulting in ocular discomfort and impaired vision, severely dragging down a patient's quality of life. Due to the specificity of the ocular surface, the retention time of drugs on it is short, leading to limited therapeutic effects for ocular diseases. Therefore, it is imperative to design a novel drug delivery system, which can not only prolong the retention time of a drug but also play an anti-fibrosis role in symblepharon. Herein, an antifouling supramolecular polymer ophthalmic ointment consisting of poly(N-acryloyl alaninamide) (PNAAA), vitamin C (VitC) and levofloxacin (Levo) was developed (termed PNAVL ophthalmic ointment), which acted as a mucoadhesive and long-acting ocular delivery system. This antifouling PNAVL ophthalmic ointment improved the retention time of VitC and Levo, and simultaneously provided anti-inflammation and anti-fibrosis effects for mitigating symblepharon after ocular alkali burn injury.

Alkali-Induced Protein Structural, Foaming, and Air-Water Interfacial Property Changes and Quantitative Proteomic Analysis of Buckwheat Sourdough Liquor.

In this study, the protein structural, foaming, and air-water interfacial properties in dough liquor (DL) ultracentrifugated from buckwheat sourdough with different concentrations of an alkali (1.0-2.5% of sodium bicarbonate) were investigated. Results showed that the alkali led to the cross-linking of protein disulfide bonds through the oxidation of free sulfhydryl groups in DL. The alterations in protein secondary and tertiary structures revealed that the alkali caused the proteins in DL to fold, decreased the hydrophobicity, and led to a less flexible but compact structure. The alkali accelerated the diffusion of proteins and decreased the surface tension of DL. In addition, the alkali notably improved the foam stability by up to 34.08% at 2.5% concentration, mainly by increasing the net charge, reducing the bubble size, and strengthening the viscoelasticity of interfacial protein films. Quantitative proteomic analysis showed that histones and puroindolines of wheat and 13S globulin of buckwheat were closely related to the changes in the alkali-induced foaming properties. This study sheds light on the mechanism of alkali-induced improvement in gas cell stabilization and the buckwheat sourdough steamed bread quality from the aspect of the liquid lamella.

Optimizing fertilizer usage for source reduction of salt and fluoride ion runoff discharge from a soda saline-alkali paddy field.

Planting rice is a beneficial strategy for improving soda saline-alkali soil, but it comes with the challenge of increased runoff discharge of salt and fluoride (F-) ions. The use of different nitrogen (N) fertilizers can impact this ion discharge, yet the specific characteristics of ion runoff under different N-fertilizer applications remain unclear. A field experiment was conducted in this study, applying five commonly used N-fertilizer types to monitor the ion runoff throughout an entire rice growing season. Salt ions and F- runoff discharge was significantly affected by N-fertilizer type, runoff event, and their interaction (p < 0.001). Regardless of N-fertilizer types, sodium (Na+) and bicarbonate (HCO3-) ions were consistently discharged from runoff in soda saline-alkali fields, constituting 20.55-25.06 % and 47.57-50.49 % of total ion discharges, respectively. Compared to no N-fertilizer (CK) and other N-fertilizer treatments, the organic-inorganic compound fertilizer (OCF) application significantly reduced Na+ and HCO3- runoff discharge, causing a decrease in the competitive adsorption capacity between HCO3- and F- (p < 0.05). The use of OCF and inorganic compound fertilizer (ICF) lowered pH in runoff water, resulting in reduced dissolution capacity of calcium fluoride in the soil and thereby decreasing total F- runoff discharge. In conclusion, OCF proves to be an effective N-fertilizer in mitigating salt ions and F- runoff discharge in soda saline-alkali paddy fields. Additionally, ICF demonstrates the ability to control F- runoff discharge.

Extraction of rare earth Eu from waste blue phosphor strengthened by microwave alkali roasting.

Spent phosphor is an important secondary resource for extracting rare earth elements. Microwave absorption properties and enhanced extraction of Eu from blue phosphor by microwave alkali roasting were studied. Dielectric properties of alkali roasting system were measured by resonator perturbation method. Dielectric constant increases linearly from 250 °C until it reaches a peak at 400 °C. The dielectric loss reaches a higher value at 400-550 °C, due to the strong microwave absorption properties of molten alkali and roasted products. Effects of roasting temperature, roasting time and alkali addition amount on Eu leaching were investigated. The phosphor was completely decomposed into Eu2O3, BaCO3 and MgO at 400 °C. The alkaline decomposition process of phosphor is more consistent with diffusion control model with Eα being 28.9 kJ/mol. Effects of the main leaching conditions on Eu leaching were investigated. The leaching kinetic of Eu was in line with diffusion control model with Eα being 5.74 kJ/mol. The leaching rules of rare earths in the mixed phosphor were studied. The results showed that the presence of red and green phosphor affected the recovery of blue phosphor. The optimum process parameters of rare earth recovery in single blue phosphor and mixed phosphor were obtained, and the recovery of Eu were 97.81% and 94.80%, respectively. Microwave alkali roasting promoted the dissociation of phosphor and leaching of rare earths. The results can provide reference for the efficient and selective recovery of rare earths in phosphors.

Changes of the Physicochemical Properties and Structural Characteristics of Alkali-Extracted Polysaccharides from Agrocybe cylindracea Across the Growth Process.

Polysaccharides derived from Agrocybe cylindracea have been demonstrated to exhibit various bioactivities. However, studies on their structural characteristics during the growth process are limited. This study aimed to compare the physicochemical properties and structural characteristics of alkali-extracted polysaccharides from A. cylindracea fruiting bodies (JACP) across four growth stages. Results showed that the extraction yields and protein levels of JACP declined along with the growth of A. cylindracea, while the contents of neutral sugar and glucose increased significantly. However, JACP exhibited structural characteristics similar to those across the four stages. Four polysaccharide subfractions were isolated from each growth stage, including JACP-Et30, JACP-Et50, JACP-Et60, and JACP-Et70. JACP-Et30 from the four stages and JACP-Et50 from the initial three stages were identified as heteroglucans with ß-1,3-d-Glcp and ß-1,6-d-Glcp residues as main chains, respectively. However, other subfractions were considered as ß-1,6-d-glucans containing minor glucuronic acid. These subfractions were predominantly replaced by Glcp residues at the O-3 and O-6 positions. Overall, while JACP exhibited variable physicochemical properties, its structural characteristics remained stable during the growth process, offering new insights into its potential applications in the food and medicinal industries.

Solidification/stabilization of lead-contaminated soil using alkali-activated volcanic ash.

The bioaccumulation of lead in soil poses a significant human health risk. The solidification/stabilization (S/S) technique, employing binders like Portland cement or lime, is a common method for remediating lead-contaminated soil. However, cement production has adverse environmental impacts, prompting the exploration of eco-friendly alternatives like alkali-activated materials (AAMs). This study assesses AAM efficacy in the S/S of lead-contaminated soil. The effects of several factors, including varying amounts of volcanic ash (VA), lead concentration, curing temperatures, and curing times are investigated. Unconfined compressive strength (UCS), toxicity characteristic leaching procedure test (TCLP), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscope-energy-dispersive spectroscopy-mapping analyses (FESEM/EDS/mapping) analyses are used to study the specimens. The findings indicated a substantial increase in the UCS of lead-contaminated soil treated with 15% VA (under oven curing (OC) conditions), and 10% VA (under ambient curing (AC) conditions) exhibited remarkable increases of up to 600% and 458%, respectively. Moreover, the leaching of Pb2+ ions from samples contaminated with 10,000 mg/kg (under OC conditions) and 2500 mg/kg (under AC conditions) experienced significant reductions of 87% (from 135.14 to 13.36 ppm) and 91% (from 26.32 to 2.21 ppm), respectively. The S/S process in these samples operated through three primary mechanisms of chemical bonding, physical encapsulation, and the formation of insoluble silicate. The formation of N-A-S-H and hydroxy sodalite structures played a vital role in facilitating these mechanisms. Therefore, alkali-activated VA demonstrated excellent performance in the remediation of lead-contaminated soil.

High-efficient stabilization and solidification of municipal solid waste incineration fly ash by synergy of alkali treatment and supersulfated cement.

Municipal solid waste incineration fly ash (IFA) designated as hazardous waste poses risks to environment and human health. This study introduces a novel approach for the stabilization and solidification (S/S) of IFA: a combined approach involving alkali treatment and immobilization in low-carbon supersulfated cement (SSC). The impact of varying temperatures of alkali solution on the chemical and mineralogical compositions, as well as the pozzolanic reactivity of IFA, and the removal efficiency of heavy metals and metallic aluminum (Al) were examined. The physical characteristics, hydration kinetics and effectiveness of SSC in immobilizing IFA were also analyzed. Results showed that alkali treatment at 25 °C effectively eliminated heavy metals like manganese (Mn), barium (Ba), nickel (Ni), and chromium (Cr) to safe levels and totally removed the metallic Al, while enhancing the pozzolanic reactivity of IFA. By incorporating the alkali-treated IFA and filtrate, the density, compressive strength and hydration reaction of SSC were improved, resulting in higher hydration degree, finer pore structure, and denser microstructure compared to untreated IFA. The rich presence of calcium-aluminosilicate-hydrate (C-(A)-S-H) and ettringite (AFt) in SSC facilitated the efficient stabilization and solidification of heavy metals, leading to a significant decrease in their leaching potential. The use of SSC for treating Ca(OH)2- and 25°C-treated IFA could achieve high strength and high-efficient immobilization.