Alkali Ratio Research Articles

Early Strength and Microscopic Mechanisms of Alkali-Metal Hydroxide-Activated Tungsten Tailings

The excellent mechanical properties of alkaline-activated tailings are essential for their increased use in building materials. While numerous studies have been conducted on activated tailings, the strength of alkaline-activated tungsten slag has not been extensively explored due to the low reactivity of silicon and aluminum in these tailings. This research delves into the early unconfined compressive strength of tungsten tailings activated by two alkali solutions (NaOH and KOH) at three different alkali concentrations (mass ratio of alkali to tungsten tailings), cured at 80 °C over periods of one day, three days, and seven days. The study finds significant improvements in the stability of tungsten tailings when forming (C, N)-A-S-H or (C, K)-A-S-H gels with both alkalis. Scanning Electron Microscope (SEM) results show that the morphology of the (C, N)-A-S-H gels transitions from membranous to flocculated and then to a three-dimensional network as the NaOH content and curing time increase. Conversely, the (C, K)-A-S-H gels primarily exhibit thin-film morphology with some three-dimensional network structures. The presence of flocculation and three-dimensional mesh in the gels fosters the formation of a robust skeletal structure, enhancing the strength of the samples. Furthermore, specimens treated with NaOH solution exhibit a higher gel content compared to those treated with KOH solution. These factors contribute to the superior efficacy of sodium hydroxide in enhancing the strength of tungsten tailings compared to potassium hydroxide. X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) results identify the formation of new phases such as pirssonite, buetschliite, potassium bicarbonate, and potassium carbonate. The first new phase results from the carbonization of excess NaOH solution, while the latter phases arise from the carbonization of excess KOH solution. These carbonization processes negatively impact the strength of the materials.

Insights into freeze-cast hierarchical water–glass foams via in situ time-lapse phase-contrast enhanced microcomputed tomography: Correlating composition, microstructure, and compression failure

We demonstrate how continuous freeze-casting without post-treatment sintering may be successfully employed using a pure water–glass (WG) solution to fabricate hierarchically porous foams lacking a morphology gradient along the freeze direction. By adjusting the water content (dilution) and/or the alkali ratio of the solution, we achieved lamellar structures with sub-features or cellular structures, with porosities spanning ∼65% to 83%. The WG foams exhibit astounding mechanical properties; notably, foams with a relatively low density of ∼0.33 g/cm3 demonstrated the highest compressive strength (5 MPa), due to their microstructure and pore morphology. In situ uniaxial compression tests combined with phase-contrast enhanced micro-computed tomography in a synchrotron revealed bending, buckling, fracture and splitting of the lamellar structures as main failure mechanisms. Our newly developed approach of continuous freeze-casting of pure WG solutions with an improved understanding of the relationship between composition, structure, and failure mechanisms provide a basis for a customized design and manufacture of a wide range of freeze-cast WG-based materials for applications ranging from biomedicine to energy generation and storage.

Response surface study on continuous supercritical hydrothermal synthesis of nano-zirconia: Scale-up from laboratory to industrialization

Commercial interest in nanomaterials and their applications lead to the development of many new methods for mass production. Among them, supercritical hydrothermal synthesis (SCHS) is a highly efficient and environmental-friendly technology. In this work, an advanced industrialized device for SCHS was used to verify the synthesis of nano-zirconia particles. The influencing laws and mechanisms of different material parameters (precursor type, precursor concentration, and pH) and process parameters (reaction temperature, reaction pressure, residence time, and Reynolds number) of nano-zirconia synthesis were studied. For the first time, the state changes of zirconium precursors and the precipitation behavior of nano-zirconia particles were in-situ observed by a high-speed camera. Central composite design (CCD) of response surface methodology (RSM) was adopted to investigate interactive effects of reaction temperature (200–420 °C), reactant concentration (0.01–0.6 mol L−1), alkali ratio (0–5) and flow rate (3–15 mL min−1), with particle size (APS), crystal form ratio (k) and reactant conversion rate (α) serving as response values. The influence of key process parameters follows an order of reaction concentration > reaction temperature > system flow > alkali ratio for APS, alkali ratio > system flow > reaction temperature > reaction concentration for k, and reaction temperature > alkali ratio > system flow > reaction concentration for α, respectively. The optimal process parameters were then obtained and further verified at lab and industrial scale. Zirconia powders with particle sizes of 4.98 nm and 8.74 nm were synthesized, respectively, indicating five hundred times magnification of continuous SCHS of nano zirconia from laboratory to industrialization.

NaOH-urea pretreatment enhanced H2 and CH4 yields via optimizing mixed alkali ratio, pretreatment time, and organic loading rate during anaerobic digestion of corn stover

This work studied the impact of NaOH-urea pretreatment on corn stover for H2 and CH4 production through two-stage anaerobic digestion. Results showed that the NaOH-urea pretreatment process improved CH4 production more significantly compared to H2. Optimized by Box-Behnken design (BBD) experiments, the CH4 cumulative yield was increased by 34.2 % at NaOH: urea = 3.2: 26.8, time = 15.7 min, and organic loading rate (OLR) = 23.4 w/v. Microbial community diversity analysis showed that the hydrogen and methane production stages formed communities dominated by Bacteroidales and Methanobacteriales, respectively. In addition, NaOH-urea pretreatment enhanced the metabolite energy recovery efficiency by 28.5–40.9 %. Finally, the return on investment (ROI) of the NaOH-urea pretreatment process reached 26.1 % with significant economic benefits. This research proposed a chemical pretreatment process for anaerobic digestion of corn stover by optimizing the pretreatment conditions of NaOH- urea.

Petrography and Geochemistry of the Baska Piwaza Ore Mineralization, Halgurd Mountain, Iraqi Kurdistan Region: Insights on the Genesis

This paper is the first attempt to study the mineralogical and geochemical features of mineralization hosted within the volcanic rocks of the Baska Piwaza section, at Halgurd Mountain, which is the highest mountain in Kurdistan and the whole of Iraq. The host lithologies in the studied section represent mostly volcanic rocks (basalts to andesites), and secondary sedimentary lithologies, such as radiolarian chert. There are two main stages of oxide and sulfide mineralization that can be recognized under three-time epochs which are early, middle and late stages that caused the formation of oxide and sulfides ore minerals. The most dominant oxide mineral is hematite, with minor contribution of magnetite, goethite, and rutile. In terms of sulfides, pyrite is the predominant mineral phase with secondary contribution of chalcopyrite. The petrographic study and XRD data of the host volcanic rocks reveal that the most abundant minerals are plagioclase, K-feldspar, pyroxene, and amphibole, while the secondary minerals are quartz, calcite, clinochlore, sericite, prehnite, pumpellyite, and muscovite. Additionally, the radiolarian chert is comprised by quartz, hematite, calcite, ankerite, clay minerals, and apatite which is characterized by low silica content and high iron oxide. Low concentration of TiO2 ,and Fe2O3 are suggesting the quartz vein occurred with the volcanic rocks are formed due to low hydrothermal fluid. Field observation, petrographical and geochemical data indicate that the rocks of the Baska Piwaza section are influenced by hydrothermal alteration, due to the high value of Loss On Ignition (LOI) and the high ratio of alkalis (Na2O+K2O). Moreover, evidences of chloritization and sericitization of the mafic minerals, and feldspar minerals respectively support the hydrothermal impact.

High permeance nanofiltration membrane for harsh organic solvent based on spiral-ring polyesters

Currently, many polymeric membranes are poorly tolerated in harsh (strong polar aprotic) solvents like dimethylformamide (DMF) and N-methylpyrrolidone (NMP) and are not applicable to organic solvent nanofiltration (OSN). In this study, we combined the oxidized poly (arylene sulfide sulfone) (OPASS) supports with excellent organic solvent resistance and the spiral-ring polyester interfacial polymerization (IP) layer together to fabricate ultra-resistant and high permeance membranes for OSN. The tetramethyl-1,1′-spirobisindane-6,6′diol (SBI), a contorted diphenol monomer with a spiral-ring structure, was preferentially selected from six types of polyphenols based on molecular simulations and experimental results. It was conducted to react with trimesoyl chloride (TMC) via interfacial polymerization to yield a polyester separation layer of thin film composites (TFC). Investigating the different alkali ratios and types revealed that the alkali added in the aqueous phase to improve the solubility of the SBI could cause hydrolysis of the polyester layer generated by IP, which led to increased membrane permeance and reduced rejection, and the more alkali and the stronger the alkali used, the more severe the hydrolysis. Besides, DMF activation treatment to the TFC membrane improved the ethanol permeance by at least four times while maintaining high congo red rejection. As a result, combining the effects of alkali and DMF activation, the representative TFC membranes fabricated in our work exhibited excellent permeance of 21.5±1.3, 9.0±1.1 L m−2 h−1 bar−1 for DMF and NMP, respectively, and high rejection rates (≥ 93%) for congo red (Mw 696.7 Da), higher than the earlier reports. This research presents a new and straightforward approach to developing TFC membranes with high-efficiency filtration capabilities, suitable for harsh organic solvent separation applications.

Feasibility and reaction process for recovery of Si and Pb from high‐calcium zinc extraction residue by alkali roasting

AbstractTo explore the feasibility of Si and Pb recovery from high‐calcium zinc extraction residues via alkali roasting, NaOH molten roasting is performed and the reaction process is discussed. Under the optimal reaction conditions—residue–alkali ratio of 1:5.0, reaction time of 1.75 h, and reaction temperature of 500°C—the Si and Pb extraction ratios remained stable at 74.00% and 40.00%, respectively. The X‐ray diffraction patterns of the specimens roasted at different temperatures indicated that the main factor affecting the extraction process was the presence of Na2CaSiO4, Ca2PbO4, and quartz. Further, the phase transformations and reaction processes of Si and Pb were determined. In the final phases, the specimen roasted at 550°C included quartz, Na4SiO4, Na2CaSiO4, Ca2PbO4, and Na2SO4. The kinetics data calculated using the unreacted shrinking core model showed that the roasting process followed a mixed control mechanism with an apparent activation energy of 16.99 kJ · mol−1.

Development of Alkali Activated Concrete using flyash for reducing carbon footprint

The consumption of cement is increasing day by day due to the remarkable development in the infrastructure. One tonne of cement produced emits approximately one tonne of carbon dioxide into the atmosphere. To reduce the use of cement, new-generation concretes such as Alkali Activated Concrete, also known as geopolymer concrete (GPC), have been developed. Geopolymer is a novel material with the potential to replace conventional Portland cement. It is an inorganic material with an amorphous to semi-crystalline polymeric structure that is manufactured by alkali activation of amorphous aluminosilicates at ambient or slightly higher temperatures. In this study, geopolymer concrete was made with low-calcium fly ash. The geopolymer was created by combining sodium silicate and sodium hydroxide solutions with fly-ash. Other materials used for GPC include locally obtainable coarse aggregate and fine sand that is surface dried. Mettur Thermal Power Plant's low-calcium, Class F fly ash was used to make geopolymer concrete. Alkaline solution to fly ash ratio was varied from 0.3 to 0.45. The sodium hydroxide solution concentration was kept constant at 12M (Molars). After being cast in moulds; the specimens were placed in a 60°C oven for 24 hours before being allowed to air dry at room temperature. The compressive strength of geopolymer concrete was tested at 7 and 28 days of age. The test results show that compressive strength increases with an increase in alkali ratio and alkali-to-fly-ash ratio. The slump value for GPC is very less compared with conventional concrete.

Purification of Waste Graphite from Crucibles Used in Photovoltaic Crystallization by an Alkali-Acid Method

The photovoltaic industry generates large amounts of waste graphite (WG) that contains useful metals that can be recycled into high-value products. This study elucidated the impurity elements and their existence states in WG, analyzed and verified the source of the main impurity phase SiC, and determined the SiC content to be 4.66%. WG was purified using an alkaline-acid method, whose optimal process parameters were a solid alkali ratio of 3, calcination temperature of 600 °C, calcination time of 120 min, HCl concentration of 1 M, and acid leaching time of 40 min. Under these conditions, a graphite product with a fixed carbon content of 98.45% was obtained. Impurities were determined to migrate via three pathways: (1) Most main elements (Al, K, and Si) in silicates were removed by alkaline roasting, while the remaining elements were dissolved in acid. (2) Impurities containing metal elements such as Fe, Mg, Ca, and Zn were decomposed in NaOH to form hydroxides or oxides that were dissolved in HCl. (3) Silicon carbide impurities were removed by the alkaline-acid method without decomposition and often existed with graphite in the acid-leaching slag.

Reductive soil disinfestation to improve soil properties in long-term tobacco cultivation

ABSTRACT To alleviate soil deterioration caused by tobacco continuous cropping obstacles, the effect of reductive soil disinfestation (RSD) on soil physicochemical and biological characteristics as well as tobacco growth was investigated through a pot experiment, with four treatments including control (CK), moderate nitrogen fertilizer application (NF), RSD, and RSD coupled with NF (RF). Results showed that soil pH, the content of organic matter, available P and available Fe were significantly increased after using RSD technology. Moreover, RSD technology boosted the relative abundance of Gemmatimonadota (9.0–12.0%), Chloroflexi (4.0–11.0%), and Ascomycota (10.0–12.0%) while decreasing the relative abundance of Mucoromycota (2–4%). Therefore, the biomass and quality of tobacco were also improved after the RSD application. Compared with CK, the biomass of tobacco at the mature stage was increased by 233.7–262.8% by RSD technology, and the chemical coordination (sugar difference, sugar alkali ratio and alkali nitrogen ratio) of the plant was also significantly improved. This study verified the feasibility of RSD technology in repairing soil deterioration caused by tobacco continuous cropping obstacles and provided theoretical and technical support for long-term tobacco production.

Combined removal experiment of multiple impurities from W/O emulsions under high frequency pulsed electric field: Study on laws of desalination, decalcification, and deacidification

AbstractElectrocoalescence is widely used to dehydrate crude oil, but impurities in crude oil are extremely complex, which greatly weaken the effect of dehydration. To understand the coupling law of various impurities, a static demulsification experiment was conducted under a high frequency and high voltage pulsed electric field to investigate the effects of electric field parameters (voltage, frequency, pulse width ratio), emulsification strength, electrocoalescence time, water content, acid value, injection alkali ratio, calcium content, decalcification agent concentration and removal process on desalination, decalcification, and deacidification. The results showed that the desalination and decalcification rates varied synchronously with the electric field parameters and water content. Additionally, the desalination and decalcification rates decreased with the emulsification strength, alkali injection ratio, acid value, and calcium content. Further, they increased first and then decreased with decalcifier concentration. The deacidification rate did not vary with the electric field parameters, but it strengthened with the water content and alkali injection ratio. Conversely, it decreased with the acid value, calcium content, and decalcifier concentration. Additionally, it increased first and then decreased with the emulsification intensity. The best removal procedure is deacidification followed by decalcification. These findings are helpful to achieve the combined removal of various impurities in crude oil.

The Effect of Natrium Hydroxide Molarity Variation and Alkali Ratio on the Compressive Strength of Geopolymer Paste and Mortar

Geopolymers have great potential to replace conventional cementitious materials and are classified as green materials. Their main constituents are silica (Si) and aluminum (Al), which can be found in the fly ash material from industrial processes of the PLTU. The parameters that affect the strength of the concrete are influenced by the molarity of natrium hydroxide and the ratio of alkalis (NaOH/Na2SiO3). This study examined the characteristics of the geopolymer paste and mortar specimens. Furthermore, mixture composition was carried out using the weight ratio method. The mortar produced consists of 65% fine aggregate and 35% paste, while the pasta contains 60% fly ash and 40% alkaline solution. The molarities of NaOH used were 8M, 10M, 12M, and 14M with a base ratio of 1.5, 2, and 2.5 Na2SiO3/NaOH. The curing of specimens was carried out with the humid temperature method. The results showed that the highest compressive strength of geopolymer paste and mortar was obtained at 12M NaOH molarity with an alkaline ratio of 2.5, namely 12.59 MPa and 21.75 MPa at 28 days, respectively. NaOH of more than 12M can cause a decrease, while the base ratio of 2.5 has the highest strength. The results also showed that the higher the molarity of NaOH and the greater the alkaline ratios, the longer the setting time.

Characteristic properties of fly ash-based self-compacting geopolymer mortars with synthetic wollastonite microfiber produced from silica and calcite

This study investigated the fresh, physical, and mechanical properties of self-compacting geopolymer mortars (SCGs) with synthetic wollastonite microfiber (SWM). SCGs were designed with Class F fly ash (FA) as a binder by activating it with Na2SiO3 and NaOH solutions. First, SWM was produced in the laboratory. Alkali ratios were determined as 1.5, 2.0, and 2.5, whereas SWM percentages were utilized as 0%, 4%, 8%, and 12% by weight of the binder. After geopolymer mortars were cured at 80 oC and 100 oC for 24 hours, respectively, they were kept at room temperature until testing age. The compressive strength, flexural strength, ultrasonic pulse velocity, dynamic modulus of elasticity, water sorptivity coefficient values, and physical characteristics of SCGs were tested at the end of the 28th day. The highest compressive strength value was obtained as 28.9 MPa for SCG-1.5-8 cured at 100 oC, while 6.5 MPa was measured as the highest flexural strength for SCG-2-12 cured at 80 oC.

Properties and Mechanism of Al<sub>2</sub>O<sub>3</sub>- Al Composite Powder Prepared by Hydrothermal Method

In order to improve the wear resistance of aluminum matrix composites and reduce the cost at the same time, the Al2O3/Al composite powder was prepared by hydrothermal method in this experiment, and the material properties of the Al2O3/Al metal matrix composite powder material were studied. It can be seen from the results that the encapsulation degree of Al2O3/Al-based composite powder material first increases and then decreases with the increase of ammonia concentration, and first increases and then decreases with the increase of PH value. The optimal molar ratio of salt and alkali is 1:1. Through the optimization of process parameters, the ratio of aluminum nitrate and ammonia water is obtained as: 1:1, the slurry stirring speed is 1500r/min, the stirring time is 10min, and the heating temperature is 200°C, the obtained composite powder is relatively uniform, has a larger specific surface area, and has better powder properties.

Effect of Solution Composition on the Morphology of Synthesized β-Ga2O3 Particles

Micro- and nanoparticles of β-Ga2O3 are synthesized as a result of chemical reaction of an aqueous solution of gallium nitrate and various alkalis: ammonia, sodium, potassium, and lithium hydroxides. It is shown that particles morphology depends on the type and concentration of alkali. The use of microwave treatment of ammonia containing solutions made it possible to change the shape of particles from ellipsoidal to parallelepiped while maintaining their size. In contrast to the synthesis with ammonia, for other alkalis dispersed particles were obtained only at a ratio of alkali to gallium nitrate equal to 3, and these particles did not belong to the gallium oxide β-phase.

Identification of phase transformation during conversion of Ca-bentonite into a low silica-based zeolite structure through fusion and hydrothermal processes

The present study signified the phase transformation during the conversion of Ca-bentonite into zeolite LTA, and hydroxysodalite in the presence of boehmite through the fusion technique. Although opal CT, and other impurities could be easily eliminated by alkali fusion, leading to formation of relatively pure powder, the obtained zeolite structure effectively depends on boehmite content. The cation exchange capacity (CEC) of zeolite powders was found to be increased from 71 to 193 ​mg ​g−1 with rise in boehmite ratio from 0.40 to 0.53 due to formation of LTA structure. Moreover, to create a cubic-shaped morphology, the alkali ratio should be fixed at 1.67 otherwise, the precursor is converted to hydroxysodalite or amorphous phase, depending on boehmite ratio. The particles exhibited a mesoporous structure with mean pore size about 6 ​nm, providing a specific surface area ∼27 ​m2 ​g−1.

Preliminary Studies on Conversion of Sugarcane Bagasse into Sustainable Fibers for Apparel Textiles

Owing to increased environmental awareness and the implementation of stringent governmental regulations, the demand for the valorization of natural fibers has increased in recent years. Sugarcane bagasse after juice extraction could be a potential source of natural fibers to be used in textile applications. In this paper, sugarcane bagasse is converted to textile fibers. Sugarcane fibers are extracted through alkali and H2O2 treatment with varying concentrations (6, 10, 14) g/L and (8, 12, 16) g/L, respectively. To soften the fibers for textile use, extracted fibers were post-treated with a constant ratio of silicone softener (50 g/L). Treatment of sugarcane fibers with varying concentrations of alkali–H2O2 significantly influenced the fiber surface morphology. Furthermore, an increase in the crystallinity of extracted fibers was observed, whereas a reduction in fiber linear density from 54.82 tex to 45.13 tex as well as moisture regain (6.1% to 5.1%) was observed as the ratio of alkali–H2O2 treatment was increased. A notable improvement in overall mechanical strength was achieved upon alkali–H2O2 treatment, but at a higher concentration (conc.) there was a loss of mechanical strength, and the torsional and flexural rigidity also increased significantly. Based on the results, sugarcane fibers treated with 10 g/L NaOH, 12 g/L H2O2 and 50 g/L silicone softener showed the most optimum results. These sustainable fibers have the potential to be used in textile applications due to their enhanced softness, optimum moisture regain, and better mechanical properties.

Optimization of Cellulosic Fiber Extraction from Parsley Stalks and Utilization as Filler in Composite Biobased Films

Food waste is an abundant source of cellulose which can be extracted via mild alkali treatment. The extraction conditions of cellulose fibers can be optimized for reduced chemical and energy use and optimal functionality. This study focused on the optimization of alkali extraction of lignocellulosic fiber from parsley stalks by building an experimental design with the response surface method with alkali concentration (2, 6, and 10%, w/v), fiber:alkali ratio (0.02, 0.035, and 0.05; w/v) and extraction temperature (40, 70, and 100 °C) as independent variables, in order to evaluate the effects of extraction conditions on fiber yield and composition of parsley stalks extract (PSE). Following the optimization, PSE and untreated fibers (PF) were incorporated as filler into gum Arabic-sodium alginate-based films, and film properties such as water vapor permeability, optical and thermal properties, Fourier transform infrared spectra and surface morphology of the films were analyzed for evaluating the compatibility of these fillers with the composite film matrix. The optimal extraction conditions were determined as 2% alkali, sample:alkali ratio of 0.0276 and extraction temperature of 40 °C. PSE extracted at optimal conditions was added to the composite films, and water vapor permeability and optical properties were improved by up to 10% PSE compared to films with PF.

Synthesis of NaHS zeolite using microwave assisted alkali activation of coal fly ash: preparation, mechanism, application

ABSTRACT High value-added NaHS zeolite was prepared using the microwave-assisted alkali fusion hydrothermal method from industrial solid waste coal fly ash as raw material without adding silicon and aluminum sources. The effect of mass ratio of alkali to coal fly ash, crystallization temperature, and crystallization time on the preparation of NaHS zeolite was investigated. The NaHS zeolite was characterized using XRD, SEM, BET, and FT-IR. The experimental results showed that the NaHS zeolite with complete crystal structure could be synthesized at m(sodium hydroxide):m(coal fly ash) = 2:1, crystallization temperature of 140°C, and crystallization time of 48 h. The prepared HS zeolite had high purity, complete crystal structure, and uniform grain size (2 μm). The NaHS zeolite was beneficial for CO2 adsorption properties with 110.9 cm3/g at 25°C.

Immobilization of Pb and Zn in Contaminated Soil Using Alumina–Silica Nano-Amendments Synthesized from Coal Fly Ash

To apply coal fly ash to the remediation of heavy-metal-contaminated soil, an alumina-silica nano-amendment (ASNA) was synthesized from coal fly ash and was used for the immobilization of lead and zinc in contaminated soil. The investigation on the synthesis of the ASNA shows that the ASNA can be obtained under a roasting temperature of 700 °C, a ratio of alkali to coal fly ash of 1.2:1, and a molar ratio of silicon to aluminum of 1:1. The ASNA could increase the soil pH and cation exchange capacity (CEC) and decrease the bioavailability of Pb and Zn. When the ASNA addition increased from 0 to 2%, the bioavailability (extracted by CaCl2) of Pb and Zn decreased by 47% and 72%, respectively. Moreover, the addition of the ASNA facilitated the transformation of Pb from a reducible fraction to oxidizable and residual fractions and Zn from an exchangeable fraction to a residual fraction. The correlation analysis and cluster analysis verify that the ASNA modulates the chemical speciation of heavy metals by increasing the soil's CEC and pH, thereby immobilizing heavy metals. It is expected that this study can provide a new method for the remediation of Pb- and Zn-contaminated soil.