Search Results (141)

Efforts have been underway worldwide to reintroduce seawater to many historically diked salt marshes for restoration of tidal flow and associated estuarine habitat. Seawater restoration to a diked Cape Cod marsh was simulated using the computer program PHREEQC based on previously conducted microcosm experiments to better understand the associated timing and sequence of multiple biogeochemical reactions and their implications to aquatic health. Model simulations show that acidic, reducing waters with high concentrations of sorbed ferrous iron (Fe[II]), aluminum (Al), sulfide (S²⁻), ammonia (NH₄⁺ + NH₃), and phosphate (PO₄³⁻) are released through desorption and sediment weathering following salination that can disrupt aquatic habitat. Models were developed for one-dimensional reactive transport of solutes in diked, flooded (DF) marsh sediments and subaerially exposed, diked, drained (DD) sediments by curve matching porewater solute concentrations and adjusting the sedimentary organic matter (SOM) degradation rates based on the timing and magnitude of Fe(II) and S²⁻ concentrations. Simulated salination of the DD sediments, in particular, showed a large release of Al, Fe(II), NH₄⁺, and PO₄³⁻; the redox shift to reductive dissolution provided higher rates of SOM oxidation. The sediment type, iron source, and seasonal timing associated with seawater restoration can affect the chemical speciation and toxicity of constituents to aquatic habitat. The constituents of concern and their associated complex biogeochemical reactions simulated in this study are directly relevant to the increasingly common coastal marsh salination, either through tidal restoration or rising sea level. Full article

Volcanic rock is a natural mineral material which has garnered interest for its potential application in water treatment due to its unique physicochemical properties. In this study, we prepared a polysilicate aluminum chloride (PSAC) coagulant using volcanic rock which exhibited good coagulation–flocculation performance. Further investigation into the influence of synthetic parameters, such as calcination temperature, reaction time, and alkali types, on the structure and performance of a volcanic rock-derived coagulant was conducted. Techniques including Scanning Electron Microscopy, Energy-Dispersive Spectroscopy, Fourier-Transform Infrared Spectroscopy, and X-Ray Diffraction were utilized to characterize it. Also, a ferron-complexation timed spectrophotometric method was used to study the distribution of aluminum species in the coagulant. Results indicated that the volcanic rock that was treated with acidic and alkaline solutions had the potential to form PSAC with Al-OH, Al-O-Si, Fe-OH, and Fe-O-Si bonds, which influenced the coagulation–flocculation efficiency. An acid leaching temperature of 90 °C, 8 mL of 2 mol/L NaOH, a reaction time of 0.5 h, and a reaction temperature of 60 °C were conducive to the preparation. A higher temperature could result in a higher proportion of Alb species, and, at 100 °C, the Ala, Alc, and Alb were 29%, 24%, and 47%, respectively, achieving a residual turbidity lower than 1 NTU at an appropriate dosage, as well as a reduction of over 0.1 to 0.018 in the level of UV₂₅₄. The findings of this study provide a feasible method to prepare a flocculant using volcanic rock. Further application is expected to yield good results in wastewater/water treatment. Full article

The rapid growth in population and industrialization have significantly increased global energy demand, placing immense pressure on finite and environmentally harmful conventional fossil fuel-based energy sources. In this context, the development of hybrid electrocatalysts presents a crucial solution for energy conversion and storage, addressing environmental challenges while meeting rising energy needs. In this study, the fabrication of a novel bifunctional catalyst, copper nickel aluminum spinel (Cu_0.5Ni_0.5Al₂O₄) supported on graphitic carbon nitride (GCN), using a solid-state synthesis process is reported. Because of its effective interface design and spinel cubic structure, the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, as synthesized, performs exceptionally well in electrochemical energy conversion, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and energy storage. In particular, compared to noble metals, Pt/C- and IrO₂-based water-splitting cells require higher voltages (1.70 V), while for the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, a voltage of 1.49 V is sufficient to generate a current density of 10 mA cm⁻² in an alkaline solution. When used as supercapacitor electrode materials, Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposites show a specific capacitance of 1290 F g⁻¹ at a current density of 1 A g⁻¹ and maintain a specific capacitance of 609 F g⁻¹ even at a higher current density of 5 A g⁻¹, suggesting exceptional rate performance and charge storage capacity. The electrode’s exceptional capacitive properties were further confirmed through the determination of the roughness factor (Rf), which represents surface heterogeneity and active area enhancement, with a value of 345.5. These distinctive characteristics render the Cu_0.5Ni_0.5Al₂O₄/GCN composite a compelling alternative to fossil fuels in the ongoing quest for a viable replacement. Undoubtedly, the creation of the Cu_0.5Ni_0.5Al₂O₄/GCN composite represents a significant breakthrough in addressing the energy crisis and environmental concerns. Owing to its unique composition and electrocatalytic characteristics, it is considered a feasible choice in the pursuit of ecologically sustainable alternatives to fossil fuels. Full article

This study focuses on the design and optimization of a monopolar electrode configuration for the hybrid electrochemical treatment of real washing machine wastewater. A combined electrocoagulation (EC) and electro-oxidation (EO) system was optimized to maximize pollutant removal efficiency while minimizing energy consumption. The monopolar setup employed mixed metal oxide (MMO) and aluminum anodes, along with a stainless steel cathode, operating under controlled conditions with sodium chloride as the supporting electrolyte. An applied current density of 15 mA cm⁻² achieved 90% chemical oxygen demand (COD) removal, 98% surfactant degradation, complete turbidity reduction within 120 min, and pH stabilization near 8. Additionally, electrochemical disinfection achieved <2 MPN/100 mL, with no detectable phenols and the presence of organic anions such as oxalate and acetate. These results demonstrate the effectiveness of an optimized monopolar EC–EO system as a cost-efficient and sustainable strategy for wastewater treatment and potential water reuse. Further studies should focus on refining energy consumption and monitoring reaction by-products to enhance large-scale applicability. Full article

Geopolymer foam concrete (GFC) is a green, lightweight material produced by introducing bubbles into the geopolymer slurry. The raw materials for GFC are primarily silicon–aluminum-rich minerals or solid waste. Lead–zinc tailings (LZTs), as an industrial solid waste with high silicon–aluminum content, hold significant potential as raw materials for building materials. This study innovatively utilized LZTs to prepare GFC, incorporating MK, GGBS, and alkali activators as silicon–aluminum-rich supplementary materials and using H₂O₂ as a foaming agent, successfully producing GFC with excellent properties. The effects of different LZT content on the pore structure and various macroscopic properties of GFC were comprehensively evaluated. The results indicate that an appropriate addition of LZT effectively optimizes the pore structure, resulting in uniform pore distribution and pore shapes that are more spherical. Spherical pores exhibit better geometric compactness. The optimal LZT content was determined to be 40%, at which the GFC exhibits the best compressive strength, thermal conductivity, and water resistance. At this content, the dry density of GFC is 641.95 kg/m³, the compressive strength reaches 6.50 MPa after 28 days, and the thermal conductivity is 0.176 (W/(m·K)). XRD and SEM analyses indicate that under the combined effects of geopolymerization and hydration reactions, N–A–S–H gel and C–S–H gel were formed. The preparation of GFC using LZTs shows significant potential and research value. This study also provides a feasible scheme for the recycling and utilization of LZTs. Full article

This study achieved the preparation of budget-friendly stratified Ca-Al adsorbents using a simplified precipitation synthesis route with subsequent pyroprocessing, showing superior defluoridation capabilities in aqueous environments. The structural properties and defluoridation performance of the adsorbents were systematically investigated by optimizing critical synthesis parameters, including calcium-to-aluminum molar ratios, the solution pH during co-precipitation, and calcination temperature. Characterization results revealed that the optimal sample (prepared at a Ca/Al ratio of 2:3, initial pH of 10, and calcination temperature of 600 °C) exhibited a high specific surface area, ordered mesoporous structure, and abundant surface hydroxyl groups, facilitating efficient fluoride adsorption. Batch adsorption experiments demonstrated significant effects of adsorbent mass, solution pH, and initial fluoride concentration on removal efficiency. The isothermal adsorption characteristics conformed to the Langmuir model, complemented by pseudo-second-order kinetic compliance, which jointly confirmed chemisorption-dominated monolayer coverage. Notably, the maximum adsorption capacity reached 263.33 mg g⁻¹, surpassing most comparable adsorbents reported in the literature. The material maintained a superior fluoride removal performance across a wide pH range (4~12) and exhibited superior recyclability. Rapid adsorption kinetics were observed, with equilibrium achieved within 60 min. The material showed a good removal effect in actual fluoride-containing smelting wastewater, which further proved its application potential. In addition, the analysis of the adsorption mechanism showed that the removal of fluoride was mainly achieved through the coordination between fluoride and metal ions and the ion-exchange reaction with surface hydroxyl groups. These findings suggest that the adsorbent has significant prospects for practical water quality fluoride removal applications. Full article

The rapid growth of aluminum and graphite industries has generated substantial stockpiles of red mud and graphite tailings, which pose environmental risks due to their high heavy metal content and potential for soil and water contamination. This study investigated the leaching behavior of heavy metals from these materials post-stabilization using cement and a sulfonated oil-based ion curing agent, thereby evaluating their suitability for safe reuse. Semi-dynamic leaching experiments were employed to measure heavy metal release, supplemented by kinetic modeling to discern key leaching mechanisms. The findings indicated that the heavy metal concentrations in leachates were consistently below regulatory standards, with leaching dynamics influenced by dual mechanisms: the diffusion of ions and surface chemical reactions. A diffusion coefficient-based analysis further suggested low leachability indices for all metals, confirming effective immobilization. These results suggest that cement and curing agent-stabilized red mud–graphite tailing composites reduce environmental risks and possess characteristics favorable for resource recovery, thus supporting their sustainable use in industrial applications. Full article

In this research, the spodumene mining residue was used as siliceous material, completely replacing quartz sand, to prepare aerated concrete. The mechanical properties, pore structure, hydration characteristics of the aerated concrete, and the spodumene mining residue–cement paste interaction mechanism were studied by orthogonal experiment, X-ray diffraction, Fourier-Transform Infrared Spectroscopy, thermogravimetry, and mercury-injection test methods. The result showed that the water–cement ratio significantly affected the mechanical properties and dry density of the aerated concrete. The content of aluminum powder paste, spodumene mining residue, and water-cement ratio significantly affected the pore structure of aerated concrete. The pore size was mainly distributed in the range of less than 100 nm in hardened samples. The main hydration products of the aerated concrete containing spodumene mining residue were xonotlite, tobermolite, and C-S-H gel (or its derivatives). Spodumene mining residue had a small amount of active silicon and aluminum components, which could be motivated by an alkaline environment. In the simulation pore solution, the weak pozzolanic reaction was produced to generate C-S-H and its derivatives, which adhered to the surface of the spodumene mining-residue particle and filled in the interface between spodumene mining residue and cement paste, to improve the density of aerated concrete. Full article

Catalytic alkane hydroxylation activities of the iron complex encapsulated into the micropore of the Y-type zeolite and mesoporous zeolites, the latter of which were obtained by the partial removal of aluminum and alkaline treatment, have been explored by using H₂O₂ as the oxidant. The iron complex with tris(pyridylmethyl)amine (=TPA) encapsulated into the micropore of the genuine Y-type zeolite was a more stable and effective cyclohexane hydroxylating heterogeneous catalyst compared to the corresponding copper analogue as well as the non-encapsulated homogeneous Fe-TPA complex. The chemical modification of the zeolite supports with the organic groups led to changing the catalytic activity depending on the size and the hydrophobic or hydrophilic nature of the added organic groups. When the content of water in the solvent was increased, the activity of the hydrophilic longer chain-modified catalyst was improved compared to that applied on the reaction with the non-aqueous solvent. The hydrophobic fluoroalkyl modifier located near the entrance of the micropore hindered the access of the substrate and aqueous H₂O₂ to the encapsulated iron complex site in the genuine Y-type zeolite. On the other hand, the hydrophobic modification effectively improved the activity of the catalyst with the zeolite support having higher amounts of mesopores. The synergistic effect of the wider bore diameters and the hydrophobic nature derived from the fluoroalkyl chains led to the concentration of the hydrocarbon substrate near the active iron complex. Full article

The international challenges of water directed the scientists to face the environment-related problems because of the high concentrations of industrial pollutants. In this direction, the present study focuses on designing effective photocatalysts by explosive technique to use light as a driving force for removing industrial pollutants from water. These photocatalysts consist of gold, carbon species (nanotubes, nanofibers, and nanoparticles), and aluminum oxides. By controlling the explosive processes, two photocatalysts were prepared; one was based on carbon nanotubes and nanofibers combined with aluminum oxide, and the other contained the nanoparticles of both carbon and aluminum oxides. The Raman spectra, transmission electronic microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and mapping images confirmed the presence of these nanostructures in homogenous nanocomposites. The optical properties of the prepared nanocomposites were evaluated by UV–Vis absorbance, band gap energy, and photoluminescence (PL) measurements. The experimental results indicated that the presence of CNTs and CNFs led to a lowering of the band gap energy of the prepared nanocomposite to 2.3 eV. This band gap energy is suitable for obtaining an effective photocatalyst. This speculation was confirmed through photocatalytic degradation of the green dyes. The prepared photocatalyst caused a complete removal of the dyes from water after 21 min of light radiation. PL measurement indicated that the CNTs and CNFs have important roles in accelerating the photocatalytic degradation of the pollutants. A kinetic study confirmed that carbon nanotubes boosted the efficiency of the photocatalyst to accelerate the reaction rate of the photocatalytic decomposition of the green dyes more than four times faster than the photocatalyst based on the carbon nanoparticles. Finally, this study concluded that CNTs and CNFs are more favorable than carbon nanoparticles for designing effective photocatalysts to meet the special requirements of the markets of pollutant removal and water purification. Full article

The objective of this study is to examine the effectiveness of the electrocoagulation (EC) process in treating real produced water (PW). The impact of the EC process on water quality parameters (pH and conductivity, turbidity, and oil content) was studied using bench-scale 5 L PW for this process. The findings indicate that prolonged EC leads to the release of metal ions and secondary electrode reactions, which resultantly increase the pH of the outlet water. The EC process decreased in several water quality parameters, including Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and oil and grease (O&G). COD decreased by roughly 1300 mg/L, resulting in a 33% removal. In the same manner, TOC dropped from an initial value of 1300 mg/L to approximately 585 mg/L, exhibiting a maximum removal efficacy of nearly 60%. Oil and gas (O&G) decreased to a value below 10 mg/L, accompanied by a remarkable removal efficacy of up to 99.6%. The turbidity, which was initially recorded at an average of 160 NTU, was reduced to approximately 70 NTU, which is a 44% reduction. The application of centrifugation after EC treatment resulted in a turbidity reduction above 99%. EC treatment removed BTEX (benzene, toluene, ethyl benzene, and xylenes) from PW by more than 99%. The inorganic constituents, specifically heavy metals, exhibited minimal changes following the application of EC, emphasizing the necessity for additional treatment methods to effectively address their presence. In summary, EC demonstrates an acceptable level of efficacy in the removal of turbidity and pollutants from PW, with a special emphasis on organic compounds such as BTEX, but it does not address the elimination of inorganic compounds. Subsequent investigations should prioritize the optimization of EC parameters and the integration of supplementary interventions to effectively address the removal of inorganic elements and insoluble metals from treated PW. The study evaluates the pollutant removal efficiency using iron and aluminum electrodes and the effects of the applied current and electrolysis time on the EC process. Full article

In this work, the results of clean hydrogen production from the direct chemical reaction between aluminum–lithium compounds and distilled water under normal conditions, without additives or catalysts, are presented. The material was prepared by mechanical alloying using a high-energy Spex-type mill in an Al20Li ratio. Relatively short milling times were programmed for the preparation of AlLi phases. Through this process, two phases (AlLi and Al8.9Li1.1) were identified, which react efficiently to produce clean hydrogen. The experiments demonstrate fast and self-sustained reactions between AlLi phases and distilled water. In both the phase preparation and hydrogen generation, 100% efficiency was achieved. The hydrolysis reaction occurred quickly, and the hydrogen volume generated was 1700 mL/g of material. Under these conditions, aluminum generates 1390 mL of hydrogen, and lithium generates 310 mL/g from both AlLi phases. A single by-product (LiAl₂(OH)₇·2H₂O) was identified. According to the results and the conditions applied in this research, the hydrogen produced does not require prior purification and can therefore be used directly in fuel cells. The AlLi–water reaction is a promising process for generating hydrogen in a simple and relatively short time compared to other hydrogen production methods. In this process, no greenhouse gas emissions were produced. Full article

A new method is proposed to generate hydrogen in situ at low pressure from powder-pressed recycled aluminum turnings activated with small amounts of NaOH and drops of water. The contribution of this system is that the user can obtain small flows of high-purity hydrogen (>99%) to charge their portable electronic devices in remote places, in a simple, controlled, and safe way, since only water is used. Test tubes that contain tiny amounts of NaOH on their surface can be transported and used without contact. In addition to being a safer system, a smaller amount of NaOH and water is needed compared to other systems, there is no need to preheat the water, and the system can even generate heat. As the feeding is drop by drop, the hydrogen flow can be easily controlled by manual or automatic dosing. The waste obtained is solid and contains mostly aluminum hydroxide with some NaOH and impurities from the waste of origin, which are easy to sell and recycle. A study has been carried out to optimize the type of test tubes and establish critical parameters. The results show that a constant and controllable flow rate of hydrogen can be obtained depending on the drip frequency where the chemical reaction predominates over diffusion, that the optimal amount of NaOH is 20 wt%, that a finer grain size can increase the H₂ yield with respect to the stoichiometric value but reduces the instantaneous flow with respect to that obtained with larger grains, and that it is very important to control the density and the impurities to increase porosity and therefore water diffusion. The estimated cost of the hydrogen produced is 3.15 EUR/kgH₂ and an energy density of 1.12 kWh/kg was achieved with a test tube of 92% aluminum purity and 20 wt% NaOH. Full article

This paper presents a novel low-carbon binder formulated from fly ash (FA), ground granulated blast furnace slag, steel slag, and desulfurization gypsum as a quaternary solid waste-based material. It specifically examines the influence of FA content on the mechanical properties and hydration reactions of the quaternary solid waste-based binder. The mortar test results indicate that the optimal FA content is 10%, which yields a 28-day compressive strength 11.28% higher than that of the control group without FA. The spherical particles of fly ash reduce the overall water demand and provide a “lubricating” effect to the paste due to their continuous gradation, improving the fluidity of the slag-steel slag-gypsum cementitious materials. The micro test results indicate that fly ash has minimal effect on the early hydration products and process of the solid waste-based cementitious materials, but after 7 days, it continuously dissolves silicon-oxygen tetrahedrons or aluminum-oxygen tetrahedrons, consuming Ca²⁺ and OH⁻ in the system. After 28 days, the amount of ettringite and C-(A)-S-H gel generated increases significantly. The pozzolanic activity of fly ash is mainly stimulated by the Ca(OH)₂ from steel slag in the later hydration stage. Additionally, spherical fly ash particles can fill the voids in the hardened paste, reducing the formation of cracks and weak zones, and thereby contributing to a denser overall structure of the hydrated binder. The findings of this paper provide data support for the development of low-carbon cement-free binders using fly ash in conjunction with metallurgical slags, thereby contributing to the low-carbon advancement of the construction materials industry. Full article

Water treatment necessitates the sustainable use of natural resources. This paper focuses on the characterization of three oxidic lithological materials (OLMs) with the aim of utilizing them to prepare calcined adsorbent substrates for ionic adsorption. The three materials have pH levels of 7.66, 4.63, and 6.57, respectively, and organic matter contents less than 0.5%. All of the materials are sandy loam or loamy sand. Their electric conductivities (0.18, 0.07, and 0.23 dS/m) show low levels of salinity and solubility. Their CEC (13.40, 13.77, and 6.76 cmol(+)kg) values are low, similar to those of amphoteric oxides and kaolin clays. Their aluminum contents range from 7% up to 12%, their iron contents range from 3% up to 7%, their titanium contents range from 0.3% to 0.63%, and their manganese contents range from 0.007% up to 0.033%. The amphoteric oxides of these metals are responsible for their ionic adsorption reactions due to their variable charge surfaces. Their zirconium concentrations range from 100 to 600 mg/g, giving these materials the refractory properties necessary for the preparation of calcined adsorbent substrates. Our XRD analysis shows they share a common mineralogical composition, with quartz as the principal component, as well as albite, which leads to their thermal properties and mechanical resistance against abrasion. The TDA and IR spectra show the presence of kaolinite, which is lost during thermal treatments. The results show that the OLMs might have potential as raw materials to prepare calcined adsorbent substrates for further applications and as granular media in the sustainable treatment of both natural water and wastewater. Full article