Alkali Concentration Research Articles

Bond performance of reinforcing bars in fly ash-based engineered geopolymer composites under uniform and nonuniform corrosion conditions

While concrete is the most popular building material in the world, corrosion of the steel reinforcement in reinforced concrete (RC) structures poses ongoing durability issues. In this study, the effects of alkali activator modulus, concentration, and different corrosion periods are rigorously investigated utilizing accelerated electrochemical corrosion techniques under both uniform and nonuniform corrosion conditions. Bond stress and bond stress deterioration are evaluated to provide a thorough examination of corrosion-induced fracture formation through pull-out experiments. X-CT 3D imaging is also used to understand the spread of rust in both corrosion scenarios. Results show that mixes with lower alkali activator modulus and higher alkali activator concentration might result in better bond stress preservation and higher ultimate bond stress under corrosion. High bond stress, however, usually corresponds to a more brittle failure when subjected to pull-out force. Nonuniform corrosion treatment can result in differential rust formation and a quicker bond breakdown between steel bars and engineered geopolymer composites (EGCs) than uniform corrosion. Furthermore, under corrosion, EGCs with high alkali activator modulus tend to form more penetrating cracks with limited width and depth. Both narrow and deep penetrating fractures can arise from EGCs with low alkali activator concentration.

A Performance-Based Test for Mitigating the Risk of Geopolymer Concrete Surface Efflorescence Due to Alkali Leaching.

Geopolymer concretes are considered to be a potential sustainable, low-embodied carbon alternative for Ordinary Portland Cement (OPC) concrete. Alkali leaching is considered to be a major esthetic concern for Na-silicate-based geopolymers as it can lead to the formation of efflorescence products on the surfaces of concrete members exposed to humidity. In this context, this research aims to investigate the effect of the alkali content and the FA/GGBS mass ratio on the alkali leaching and formation of the efflorescence products. Paste cylinders were fabricated and cured in ambient conditions. Samples were submerged in deionized water and the concentration of the leached-out ions was measured. Efflorescence potential was also investigated by partial immersion of the samples in deionized water. The results highlight the complexity of the interacting parameters governing the formation of efflorescence products in geopolymer materials. Establishing relationships between the concrete mix variables and the risk of efflorescence seems unfeasible particularly because of the wide range of possible precursors and activators available to design geopolymer concrete mixes. To overcome this barrier, a practical performance-based testing method is developed. For the first time, by testing a wide range of geopolymer materials, performance-based requirements associated with the risk of efflorescence for geopolymer concrete surfaces exposed to humidity are calibrated. Four categories of risk are proposed and typical suitable exposure conditions for geopolymer concrete surfaces are suggested for each risk category.

Chloride transport in alkali-activated materials influenced by different reaction products: a review

Alkali-activated materials (AAMs) are regarded as a substitute for Portland cement. They have high chloride resistance and a low carbon dioxide footprint. The aim of this review is to provide a multi-scale perspective to understand material–product–microstructure–property relationships in terms of the chloride binding behaviour of AAMs. The physical and chemical chloride stability of different reaction products is summarised from nanostructure, to microstructure to macro properties. An analysis of studies in the literature gives an overview of recent progress in chloride transport in AAMs influenced by different reaction products. Results show that a higher calcium/silicon, aluminium/silicon molar ratios and alkali content increase the formation of amorphous phases, leading to a denser microstructure and lower chloride penetration in AAMs. Higher magnesium oxide and aluminium oxide contents result in increased formation of hydrotalcite. The enhanced physical and chemical absorption of chloride by hydrotalcite leads to higher resistance of chloride penetration in AAMs. Investigation of increasing chloride resistance could potentially focus on increasing gel and hydrotalcite formation.

Investigation of superparamagnetic iron oxide nanoparticles in air environment for elevated saturation magnetization

Iron oxide nanoparticles have garnered interest for their unique properties and wide application areas. For applications, superparamagnetic nanoparticles are required so that they can be magnetized by an external magnetic field and rapidly demagnetize again when the field is removed. High saturation magnetization, Ms is also required for applications to provide easy magnetic control over separation and targeting. For magnetically controlled applications, superparamagnetic iron oxide nanoparticles with a high Ms are important. In this study, superparamagnetic iron oxide nanoparticles were co-precipitated under air atmosphere and the effects of alkali concentration, stirring rate and reaction time on the structural and related magnetic properties were investigated to obtain the high Ms for each parameter. According to the structural results, it is challenging to obtain magnetite nanoparticles under air atmosphere due to oxidizing effect. The increase of Ms values with the increase of alkali concentration may come from the phase of the samples although the crystal size of the nanoparticles is getting smaller. It can be said that there is an optimum stirring rate to obtain the highest Ms under air atmosphere rather than an uptrend/downtrend. The maximum Ms of 69.2 emu g−1 was obtained for superparamagnetic iron oxide nanoparticles synthesized at 700 rpm. With the increase of reaction time, magnetic size of the nanoparticles is observed to decrease in contrast with the increase of physical particle size. The maximum Ms value for the reaction time parameter is 67.3 emu g−1 at 15 min. Due to their high Ms values and superparamagnetic nature, the nanoparticles synthesized under study may find use in magnetic separation, water purification, and other related fields.

Determining the Pulping Conditions and Properties of Unbleached Pulp from Uruguayan Pinus Taeda

Context: In Uruguay, numerous Pinus taeda plantations are at final-turn age, but they still do not have commercial destination and are exported as green-wood logs. For the development of this sector, it is necessary to strive towards a comprehensive processing of this resource. Method: This work focused on analyzing the use of Pinus taeda wood available in the country to produce brown kraft pulp with a kappa number of 80, which can be used to make packaging paper. As raw materials, we employed by-products from the mechanical wood-transformation industry (wood chips and thinning wood) and final-turn wood. Pulping tests were carried out, varying the alkali charge and the H-factor while aiming for a kappa number of 80. The viscosity, pulping, and rejection yield were measured in the pulps, and the pH and residual alkali content were evaluated in black liquor. Results: Based on the results, the best pulping conditions were an active alkali charge of 14% (Na2O) and an H-factor of 1260 for sawmill chips and thinning wood, as well as an active alkali charge of 14% (Na2O) and an H-factor of 1080 for final-turn wood. The pulp obtained with sawmill chips exhibited the most resistant fibers, and the final-turn wood pulp was the most sensitive to the refining process. Under the aforementioned conditions, the paper properties of laboratory-produced pulp are comparable with those of commercial pulp. Conclusions: This indicates that it is technologically possible to produce brown kraft pulp from Uruguayan Pinus taeda wood, with adequate quality to produce packaging paper

Optimizing Seed‐Induced Nucleation for Enhanced Al(OH)3 Crystal Precipitation from Supersaturated Potassium Aluminate Solution

AbstractPotassium alunite is a potential mineral resource of potassium and aluminum that can serve as a valuable resource. An effective potassium and aluminum recovery method is developed using gradient leaching with a KOH sub‐molten salt. The key part of this process is seeded precipitation of the potassium aluminate leach solution. Therefore, this study aims to optimize the seeded precipitation process by investigating the effects of alkali concentration, molecular ratio, stirring rate, temperature, and seed coefficient on the precipitation ratio and particle size of Al(OH)3. The results show that alkali concentration, molecular ratio, temperature, and seed coefficient are key factors influencing seeded precipitation. Furthermore, the process is optimized by using these four identified factors as variables. A 9L(34) orthogonal experiment determines optimal conditions for maximizing the precipitation ratio and achieves the desired average particle size. Under the optimal condition of 200 g L−1 alkali concentration, 1.5 molecular ratio, 1.0 seed coefficient, and 343.15 K temperature, the precipitation ratio reaches 54% and the average Al(OH)3 particle size is 114 µm. Further work is required to scale up this optimized seeded precipitation process and evaluate applications of the Al(OH)3 product.

Study on recycling and utilization of phosphogypsum and lithium slag in vertical barrier materials

Traditional vertical barrier materials typically have a large carbon footprint and high cost. Phosphogypsum (PG) and lithium slag (LS), possess latent cementitious activity. This study investigated the potential use of PG and LS in vertical barrier materials. The basic characteristics of the system were studied for LS:PG (mass ratio) ranging from 1:1–1:9, with a bentonite content of 10 % and a water-to-solid ratio of 0.5. The PG-LS matrix was microscopically characterized using XRD, TG, FT-IR, and SEM analysis. Additionally, an economic and sustainability assessment was performed. The results indicated that when LS:PG was in the range of 1:3–1:1, the flowability and setting time ranged from 16.15 to 21.00 cm and 51–87 hours, respectively. The bleeding rate within 12 hours was consistently below 5 %. Furthermore, the compressive strength and permeability coefficient at 28 days were within the ranges of 1.81–7.99 MPa and 2.91×10−8 to 7.98×10−9 cm/s, respectively. Excessive addition of PG was found to be unfavorable for the formation of C-(A)-S-H gel, resulting in an increase in free alkali content in the system and promoting the carbonation-induced formation of Calcite, thereby reducing the compressive strength and increasing the permeability. Compared to traditional barrier materials, the PG-LS-based barrier material exhibited a 61 % reduction in CO2 emissions and a cost reduction of 75–82 %. Additionally, the leaching concentrations of Zn, Cr, Ni, Cu, Pb, Cd, and As were below the standard limits. Therefore, the utilization of PG and LS in vertical barrier systems demonstrated excellent performance, economic feasibility, and environmental benefits, indicating significant potential for widespread application.

Petrology and geochemistry of Mount Lurus lavas: evidence for alkaline to subalkaline transition in the rear arc of Java, Sunda Arc

Abstract Mount Lurus, a small Quaternary volcanic center in the rear of Java Island, Sunda arc, has erupted both alkaline and subalkaline lavas in a short span of active period. Furthermore, this small volcanic edifice, together with its neighboring alkaline volcanic center of Ringgit-Beser, corresponds to a shallower slab depth (∼160 km) than Muria in Central Java (270 km). We report the mineralogical and geochemical characteristics of Lurus lavas and compare them to the Ringgit-Beser lavas. All Lurus lavas show typical characteristics of island arcs with elevated Ba, Sr, Pb, and K and negative anomalies of Nb and Ti. The older Lurus edifice (Old Lurus) produces alkaline lavas with high alkalinity, which are trachyandesite and phonotephrite in composition. The younger Lurus (Young Lurus) generates calc-alkaline lavas with basaltic andesite composition. Both groups have plagioclase, clinopyroxene, olivine, and opaque minerals as phenocrysts phase. Leucite is found in one sample of Old Lurus with the lowest SiO2 content (48.92 wt%) and highest alkali content (5.38 wt%). Old Lurus lavas tend to show higher contents of incompatible elements (Pb, Ba, Nd, and Rb) than Young Lurus. The mineralogical and compositional differences between these lavas suggest that these magmas are sourced from at least three magma chambers of distinct composition: highly potassic magma chamber (comparable to the evolved-K series of Ringgit-Beser) and hydrous-potassic magma which fed Old Lurus edifice; and calc-alkaline magma chamber which fed Young Lurus edifice.

Experimental Insights Into the Petrogenesis of Plume‐Related Magmas: Tholeiite‐Harzburgite Interaction at 2–3 GPa and 1,400–1,500°C

AbstractHow eclogite/pyroxenite‐derived melts evolve through the refractory lithosphere above a plume remains poorly understood. Here we conducted layered experiments of reaction between tholeiitic melts and harzburgite at 2–3 GPa, 1,400–1,500°C, with a run duration ranging from 2 to 24 hr. The resulting residual melts exhibit lower SiO2, TiO2, Al2O3, FeO, CaO, and total alkali contents, higher Ni, MgO, and Mg#, and almost constant CaO/Al2O3 compared to the initial tholeiitic melts. The compositions of the residual melts are influenced by factors such as the melt/harzburgite mass ratio, temperature, and run duration. Decreasing the melt/rock ratio or increasing temperature and run duration leads to a greater extent of assimilation. Under disequilibrated conditions (2 hr), the residual melts have higher SiO2, FeO, and MgO, and lower CaO, Al2O3, and total alkali contents compared to those under equilibrated conditions. The results suggest that interface reactions involving olivine dissolution and orthopyroxene precipitation, and chemical diffusion occur simultaneously during the interaction process. The compositions of the residual melts are largely controlled by interface reactions within 2 hr, followed by dominant chemical diffusion between the melts and refertilized harzburgite from 2 to 24 hr. Based on the experimental results, we propose a two‐stage model for the origin of Hawaiian shield stage parental magmas. Eclogite/pyroxenite‐derived tholeiitic melts first react with harzburgite, with varying melt/rock ratios, to produce residual melts in the deep lithosphere. These residual melts subsequently mix with plume peridotite‐derived melts at shallow depths, contributing to the geochemical diversity observed in Hawaiian shield stage lavas.

Investigation of the mechanism of sediment formation in sedimentary rock-forming compounds

For the successful application of water-limiting technologies and methods of regulating the extraction process, which increase the effectiveness of anti-flooding measures, it is necessary to conduct a comprehensive study, including analysis of the geological and physical condition, development of rheological and filtering characteristics of the compositions used. This article presents the indicators selected as criteria for the effectiveness of isolation of aquifers with polymer solutions - with a change in one group of geological– physical, technical and technological factors characterizing the well and processing technology. Thus, the conducted studies have shown that the amount of sediment formed can be adjusted by choosing the appropriate concentration of polymer and alkali for each specific case of treatment of the bottomhole zone of the well, and thereby the effectiveness of limiting using sedimentary gel-forming compounds is achieved. In the article, we have processed the results of experimental studies using methods of mathematical statistics. At the same time, we have established the dependence of the amount of sediment on the concentration of alkali at a stable value of the polyacrylamide concentration.

Micromechanical and chemical characteristics of interfacial transition zone in alkali-activated slag concrete containing lightweight iron-rich aggregates

This study explored the time-varying alkali-activation effects of the lightweight aggregates (LWA) on the interfacial transition zone (ITZ) of the alkali-activated slag concrete with different curing ages, molar ratios, and alkali concentrations from 28 to 300 d. The improved micromechanical performance of the ITZ at 28 d stemmed from the early-age internal curing effect of the porous LWA. However, the post-28 d internal curing effect diminished, with the alkali-activation dominating the performance of the ITZ from 28 to 300 d. Although alkali-activated cement possessed early strength characteristics, the deconvolved phase results illustrated that alkali activation persisted in the ITZ between the LWA and cement from 28 to 300 d, leading to a high proportion of calcium silica aluminate hydrate. As a marker, Fe from the lightweight iron-rich aggregates mitigated into the alkali-activated cement, demonstrating the alkali-activated reaction between the LWA and alkali-activated slag matrix. Molecular dynamics simulations further characterized that the low content of Fe did not decrease the overall strength of the ITZ. The interfacial interaction energy revealed the alkali-activation between the LWA and cement compensated for the weakening of mechanical properties caused by Fe ions on the ITZ.

Mechanical Properties and Mesoscopic Numerical Simulation of Local Weakening in High-Performance Concrete after 10 Years of Alkali Solution Immersion

The natural environment in the high-altitude regions of Northwest China is extremely harsh, characterized by numerous salt lakes. The high concentrations of chloride salts, sulfates, and alkali metal ions in these areas can induce alkali–silica reactions (ASRs) in concrete. These reactions generate harmful gel within the concrete, causing expansion and cracking, which significantly impacts the durability of concrete structures. This study investigates the evolution of the mechanical properties in high-performance concrete (HPC) under long-term ASR by incorporating different admixtures and varying the equivalent alkali content. A three-dimensional random aggregate mesoscopic model was used to simulate static compression tests under various operational conditions. Non-destructive testing methods were utilized to determine the expansion rate, internal, and surface damage variables of the concrete. The experimental results indicate that the 10-year expansion rate differs from the 1-year rate by approximately 1%, and under long-term ASR mitigation measures, the internal damage in the HPC is minimal, though the surface damage is more severe. As the equivalent alkali content increases, the compressive strength of the concrete cubes decreases, initially rising before falling by 5–15% over time. The HPC with only air-entraining agent added exhibited better mechanical performance than the HPC with both air-entraining and corrosion inhibitors added, with the poorest performance observed in the HPC with only a corrosion inhibitor. A relationship was established between the surface and internal damage variables, with the surface damage initially increasing rapidly before stabilizing as the internal damage rose. Numerical simulations effectively describe the damage behavior of HPC under static uniaxial compression. Comparisons with actual failure morphologies revealed that, in the cube compression tests, crack propagation directly penetrated both coarse and fine aggregates rather than circumventing them. The simulations closely matched the experimental outcomes, demonstrating their accuracy in modeling experiments. This study discusses the compressive mechanical properties of concrete under prolonged ASR through a combination of experimental and simulation approaches. It also delves into the impact of surface damage on the overall mechanical performance and failure modes of concrete. The findings provide experimental and simulation support for the concrete structures in regions with high alkali contents.

Understanding the Competition Mechanism between Na2O and CaO for the Formation of the Initial Layer of Zhundong Coal Ash

The contents of alkali and alkaline earth metals are higher in Zhundong coal, and there are serious problems of slagging and fouling during the combustion process. Therefore, it is of great significance to reveal the mechanism of slagging and fouling in the boiler of Zhundong coal. In this paper, first-principle calculations based on density functional theory are used to study the competition mechanism of alkaline metal oxides during the combustion process in Zhundong coal by establishing the Na2O(110)/CaO(100)-SiO2(100) double-layer interface model. The results show that the bond lengths of the surface of Na2O(110) and CaO(100) with SiO2(100) after adsorption were generally lengthened and the value of bond population became smaller, which formed a stable binding energy during the reaction. The electron loss of Na is 0.05 e, the electron loss of Ca is 0.03 e, and the electron loss of Na2O is greater than that of CaO. The charge transfer on the surface of Na2O with SiO2 is obviously higher than that of CaO and the orbital hybridization on the surface of CaO with SiO2 is weaker than that on the surfaces of Na2O with SiO2. Na2O is easier to react with SiO2 than CaO. The adsorption energies on the surface of Na2O and CaO with SiO2 are −5.56 eV and −0.72 eV, respectively. The adsorption energy of Na2O is higher than that of CaO, indicating that Na2O is more prone to adsorption reactions and formation of Na-containing minerals and other minerals, resulting in more serious slagging. In addition, the XRD analyses at different temperatures showed that Na-containing compounds appeared before Ca-containing ones, and the reaction activity of Na2O is stronger than that of CaO in the reaction process. The experimental results have good agreement with the calculation results. This provides strong evidence to reveal the slagging and fouling of Zhundong coal.

The coupling action mechanism of NaOH/NaNO3 on the hydrothermal synthesis of fly ash-based zeolites and the Sr-Na exchange capacity

The treatment of low- and intermediate-level radioactive waste from nuclear power plants using fly ash-based zeolite involves issues related to product evolution and cation exchange. This study aims to elucidate the evolution of hydration products and the interaction mechanism between Sr²⁺ and Na⁺ in fly ash-based zeolite under the regulation of NaOH/NaNO₃. The fly ash-based zeolites were characterized using XRD, IR, and SEM. The adsorption capacity and chemical binding energy before and after Sr²⁺ adsorption were analyzed using ICP and XPS, respectively. The results demonstrated that the main products in fly ash-based zeolite influenced only by NaOH undergo a transformation from Faujasite to Na-P1 zeolite, and finally to Sodalite. However, when NaOH/NaNO₃ were added simultaneously, the main product first transformed from Faujasite to Na-P1 zeolite, and then into Sodalite or Cancrinite as the Na/Al ratio increased. Furthermore, the adsorption process of fly ash-based zeolite influenced solely by NaOH followed the Langmuir isotherm model, while the adsorption process affected by both NaOH /NaNO₃ followed the Freundlich isotherm model. Among these, Na-P1 zeolite showed the most favorable adsorption performance for Sr²⁺. As Sr²⁺ adsorption increases, the fly ash-based zeolites exhibit the appearance of Sr-O bonds. These findings offer a new perspective for enhancing the nuclide immobilization capacity of fly ash-based geopolymers through the adjustment of salt and alkali concentrations.

Petrogenesis of the Dalaku’an Mafic–Ultramafic Intrusion in the East Kunlun, Xinjiang: Constraints from the Mineralogy of Amphiboles

The Dalaku’an mafic–ultramafic intrusion, located in the western segment of the East Kunlun, presents conducive conditions for the magmatic Cu-Ni sulfide deposits. According to the detailed petrographic observation, the amphiboles within distinct rock types were analyzed by EPMA analysis. The crystallization conditions, such as temperature, pressure, oxygen fugacity, and water content of the magma, were calculated to explore the genesis of the intrusion. The amphiboles were divided into three types: Amp-I, characterized by low silicon content but enrichment of aluminum, titanium, and alkali, predominantly comprising Tschermakitic hornblende and Magnesio-hornblende with mantle-derived traits; Amp-II, exhibiting elevated silicon content but diminished levels of aluminum, titanium, and alkali, primarily constituted of Magnesio-hornblende; whereas Amp-III manifests as Actinolitic hornblende, indicative of crustal origins. The calculated temperatures of amphiboles ranged between Amp-I (955–880) °C, Amp-II (852–774) °C, and Amp-III (761–760) °C; the pressures ranged between Amp-I (454–274) MPa, Amp-II (194–93) MPa, and Amp-III (101–84) MPa; the oxygen fugacities (△NNO) ranged between Amp-I (0.93–2.17), Amp-II (1.55–2.52), and Amp-III (1.89); and the water contents (H2Omelt) ranged from (6.69–8.67) to (5.90–7.32). The magma experienced multiple stages of crystallization and underwent complex magma evolution at different depths. The high oxygen fugacity and water content could be attributed to the subduction of the oceanic crust. The magma source of the Dalaku’an intrusion was metasomatized by fluids from subducting plates, thereby originating within a post-collision extension.

Hydrolytic-Assisted Fractionation of Textile Waste Containing Cotton and Polyester

Resulting properties of cotton and polyester blends make polycotton the most common fabric in textile industry. Separation technologies are key for the chemical processing of the massive amount of polycotton waste produced worldwide. The very different chemical nature of cellulose and polyethylene terephthalate determines the fractionation strategies to obtain two valuable monomaterial streams. In this work, we propose separation pathways seeking the conversion both polymers. First, polyester was depolymerised into its monomeric units through catalytic alkaline hydrolysis. The combined effect of alkali concentration and the catalyst was analysed to overcome the hydrophobic nature of polyester and optimise its conversion rate minimising the damaged caused to the cellulose chains. Conversion rates up to 80% were reached in a single separation stage with a limited effect of the polymer chain distribution of cellulose which remains a fiber-grade feedstock. Alternatively, cellulose was fully removed by selective dissolution in ionic solvent and subsequent filtration resulting in a spinnable mixture. Finally, enzymatic treatments for the conversion of cellulose into fermentable sugars were studied. Single stage conversions of 65% were achieved after maximizing the enzymatic activity. Structural and spectroscopic analysis showed that crystalline domains of textile-grade cotton limit the enzymatic activity. Optimal fractionation process is, in our view, highly context dependent what conveys to seek a variety of alternatives seeking for chemical processes driven by the ulterior up-cycling of the monomaterial streams

A comprehensive comparative study of ultrasound-alkaline and thermal-alkaline hydrolysis of duck feather

Feathers, as a byproduct of the poultry industry, present a significant source of keratinous waste. Conventional methods have been widely used to extract keratin from feathers; however, they are associated with limitations such as high operational costs and environmental concerns. It is, therefore, crucial to develop cost-effective and time-efficient methods for extracting keratin on a large scale. In recent years, ultrasound-assisted alkaline hydrolysis has emerged as a promising and sustainable approach for efficient keratin recovery. This study compares the hydrolysis time, yield, and chemical properties of keratin extracted from feathers using ultrasound-assisted alkaline hydrolysis and thermal alkaline hydrolysis (hot plate method). The influence of factors such as particle size, alkali concentration, liquid-to-solid ratio, reactor geometry, temperature of keratin colloid upon precipitation, precipitation pH, and precipitating acid was investigated. Favorable conditions for ultrasound-assisted alkaline hydrolysis were found to be 3% NaOH, a 10:100 (w/v) solid-to-liquid ratio, using a cylindrical vessel, and an ultrasonic energy density of 360 kJ/L, with pH adjustment to 4.5 using citric acid after cooling to room temperature. This method outperformed the thermal approach, yielding 70% keratin in 25 min, compared to 23% in 90 min using a hot plate, due to the exothermic effect of cavitation. The results provide valuable insights into the potential of ultrasound-assisted alkaline hydrolysis as an eco-friendly and cost-effective approach to address the management of keratinous waste and enhance the overall recovery of keratin.

Mesozoic crustal growth and recycling along the Southern margin of Eurasia: Magmatic rocks from the Sanandaj-Sirjan Zone of Iran

The Sanandaj-Sirjan Zone of western Iran is characterized by significant Mesozoic magmatic activity (from the early Jurassic to the late Cretaceous), with Cenozoic rocks being less common. Granitoids are prevalent in this zone, displaying A-, I-, and S-type geochemical characteristics. Despite several studies on these granitoids, there are still some questions regarding their sources– especially the S- and A-type granitoids – and the crustal growth and recycling in this zone, which require further studies using isotopes. This study focuses on the Aligoodarz, Kolah-Ghazi, and Golpayegan granitoids from the central SaSZ to better understand crustal growth and recycling in the Sanandaj-Sirjan Zone. The Aligoodarz and Kolah-Ghazi granitoids are identified as S-type granites, showing strong peraluminous signatures. Geochemical evidence suggests a mixture of melts from sub-crustal metasedimentary and meta-igneous sources, with factors such as source diversity and disequilibrium melting contributing to their formation. in contrast, the Golpayegan granitoids exhibit high total alkali (Na2O + K2O) contents and high field strength elements, indicating alkaline magmatic affinity. Their geochemical signatures suggest derivation from an enriched portion of an Indian MORB-like protolith. Golpayegan syenites share similarities with within-plate A1 granites, suggesting they are related to anorogenic silica-oversaturated granitoids. Golpayegan A-type granites probably originated from high-degree fractionation of alkali basic magmas. Golpayegan gabbros may be derived from a MORB or OIB-like mantle source, with characteristics indicating the presence of garnet in the mantle source and potentially deep melting from a mantle plume. Newly compiled zircon UPb data from the Sanandaj-Sirjan Zone show a complex magmatic chronology spanning from approximately 180 million years ago to the Eocene epoch, revealing peaks of magmatic activity at various intervals. Distinct phases of A-, I-, and S-type magmatism are identified, and synthesis of zircon UPb ages and HfO isotope data reveals the simultaneous occurrence of S-type and I-type magmas during specific periods. Furthermore, our study explores the tectonic settings underlying these magmatic processes and proposes scenarios involving subduction, continental rifting, and asthenospheric upwelling to elucidate the geological dynamics of the SaSZ.

Zircon U-Pb Dating, Geochemistry, Lu-Hf Isotope Characteristics, and Geological Significance of Volcanic Rocks in Zhenghe Fozi Mountain National Geopark, Fujian, China

Fozi Mountain National Geopark is located in Zhenghe County in the northern region of Fujian Province, where the volcanic rocks of the Zhaixia Formation of the Shimaoshan Group are exposed. Zircon U-Pb dating and geochemical analysis were carried out to constrain its age and tectonic environment. The results show that three zircon U-Pb dating samples have attained ages of 99.2 ± 1.0 Ma, 99.6 ± 0.8 Ma, and 99.7 ± 2.0 Ma. Volcanic rocks in the core scenic area of Fozi Mountain were formed during the Late Cretaceous period. Elemental analysis showed that these volcanic rocks were dominated by the shoshonite series. They include gray dacite porphyry, grayish-white breccia tuff, volcanic agglomerate, and gray tuffaceous sandstone. These rocks were characterized by high silicon, high alkali content, and rich potassium levels. Lu-Hf isotope analysis of zircons revealed that their εHf(t) values varied from −8.7 to −6.8. The corresponding TDM2 values were primarily distributed in the range of 1.71 Ga to 1.59 Ga. These findings indicated that the magma primarily originated from the partial melting of the Mesoproterozoic crystalline basement, accompanied by a small number of mantle-derived materials. Tectonic environment analysis indicated that these rocks were formed in the post-orogenic intraplate extensional environment, which was associated with the back-arc extension or lithospheric thinning caused by the subduction of the paleo-Pacific plate beneath the Eurasian plate. The formation of these volcanic rocks was attributed to post-orogenic magmatism.

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.