Search Results (81)

This research focuses on improving the characteristics of recycled concrete and utilizing solid waste resources through the combination of industrial waste pre-impregnation and the carbonation process. A novel pre-impregnation–carbonation aggregate method is proposed to increase the content of carbonatable components in the surface-bonded mortar of recycled coarse aggregate by pre-impregnating it with carbide slag slurry (CSS). This approach enhances the subsequent carbonation effect and thus the properties of recycled aggregates. The experimental results showed that the method significantly improved the water absorption, crushing value, and apparent density of the recycled aggregate. Additionally, it enhanced the compressive strength, split tensile strength, and flexural strength of the recycled concrete produced using the aggregate improved by this method. Microanalysis revealed that CO₂ reacts with calcium hydroxide and hydrated calcium silicate (C-S-H) to produce calcite-type calcium carbonate and amorphous silica gel. These reaction products fill microcracks and pores on the aggregate and densify the aggregate–paste interfacial transition zone (ITZ), thereby improving the properties of recycled concrete. This study presents a practical approach for the high-value utilization of construction waste and the production of low-carbon building materials by enhancing the quality of recycled concrete. Additionally, carbon sequestration demonstrates broad promise for engineering applications. Full article

The construction industry’s escalating environmental footprint, coupled with the underutilization of construction waste streams, necessitates innovative approaches to sustainable material design. This study investigates the dual functionality of recycled clay brick powder (RCBP) as both a supplementary cementitious material (SCM) and an alkali–silica reaction (ASR) inhibitor in hybrid mortar systems incorporating recycled glass (RG) and recycled clay brick (RCB) aggregates. Leveraging the pozzolanic activity of RCBP’s residual aluminosilicate phases, the research quantifies its influence on mortar durability and mechanical performance under varying substitution scenarios. Experimental findings reveal a nonlinear relationship between RCBP dosage and mortar properties. A 30% cement replacement with RCBP yields a 28-day activity index of 96.95%, confirming significant pozzolanic contributions. Critically, RCBP substitution ≥20% effectively mitigates ASRs induced by RG aggregates, with optimal suppression observed at 25% replacement. This threshold aligns with microstructural analyses showing RCBP’s Al³⁺ ions preferentially reacting with alkali hydroxides to form non-expansive gels, reducing pore solution pH and silica dissolution rates. Mechanical characterization reveals trade-offs between workability and strength development. Increasing RCBP substitution decreases mortar consistency and fluidity, which is more pronounced in RG-RCBS blends due to glass aggregates’ smooth texture. Compressively, both SS-RCBS and RG-RCBS mortars exhibit strength reduction with higher RCBP content, yet all specimens show accelerated compressive strength gain relative to flexural strength over curing time. Notably, 28-day water absorption increases with RCBP substitution, correlating with microstructural porosity modifications. These findings position recycled construction wastes and glass as valuable resources in circular economy frameworks, offering municipalities a pathway to meet recycled content mandates without sacrificing structural integrity. The study underscores the importance of waste synergy in advancing sustainable mortar technology, with implications for net-zero building practices and industrial waste valorization. Full article

It has been proven that silica fume (SF), which is a by-product from the manufacturing of single-crystal silicon, is beneficial for enhancing the mechanical properties, durability, and workability of geopolymers, as it can be quickly dissolved and form silicate-based cementitious phases in alkaline environments. However, the reinforcement mechanism of SF on geopolymer remains unclear due to the chemical complexity of geopolymer and the variety of SF types. Additionally, the solubility of calcite in an alkali environment is quite limited, and thus the formation of the amorphous calcium-based gels will be thwarted due to the lack of soluble calcium ions. Most importantly, with the development of the single-crystal industry, the amorphous silica content, crystallinity, and trace elements of SF itself have changed, which blocks the understanding of the activation mechanism of geopolymers combined with SF and insoluble calcite. To unveil the underlying modification mechanisms of SF on geopolymer materials along with insoluble calcite, in this study, two types of SF were used as the fly ash replacement in a fly ash/limestone system to prepare geopolymer materials. The reinforcement effect significantly depends on the SF types even with similar particle size and chemical compositions. The results indicate that the mechanical properties of geopolymer materials modified with SFs are not only governed by the ratio and contents of Si, Ca, Al, and Mg in SFs but also depend on the crystallinity and activity of the SFs. The hydration products could be varied according to the reaction environment. The research results not only contribute to the optimization design and application of geopolymer materials but also pave new pathways for the upcycling use of solid wastes such as SF, low-grade fly ash, or even other aluminosilicate solid wastes to achieve sustainable development. Full article

The Hall–Héroult aluminum production process generates lithium-rich waste barrier materials, which are challenging to process using conventional acid leaching due to the environmental risks posed by hydrofluoric acid (HF) emissions. This research introduces a two-stage water–HCl sequential leaching (WHSL) approach to recover lithium while reducing these environmental impacts. The method evaluates key factors, such as the liquid–solid ratio, temperature, duration, rotation speed, and HCl concentration, and compares its efficacy with traditional HCl leaching using XRD, FTIR, DBP, and SEM techniques. The findings indicate that initial water leaching dissolves NaF salts, creating surface grooves and cracks. Subsequent HCl leaching selectively extracts lithium from aluminum and silicon, forming silica gel while preserving the nepheline phase due to its structural integrity. The process produces a porous residue with smaller particles, reduced surface potential, and promotes colloidal aggregation. This two-step process achieves efficient lithium recovery while reducing acid consumption and minimizing hydrogen fluoride (HF) emissions. Full article

This paper focuses on the alkaline activation of municipal waste incineration (MSWI) bottom ash to create a dense, non-porous composite structure. Normally, high pH solutions are used to activate MSWI bottom ash, but this has the side effect of creating residual effects in the bottom ash. Due to the uniqueness of the incineration process, the bottom ash retains metallic aluminum, which reacts with the alkali to produce hydrogen gas, which forms a porous structure in the sample during the hardening of the composite. This study demonstrates a method of eliminating this effect by lowering the pH of the alkaline activator below 12.5. An alkali-activated binder was prepared from ground MSWI bottom ash as a precursor and a triple alkali activator: NaOH solution, soluble glass (SG) and silica gel waste (SW). The highest compressive strengths of about 20 MPa were achieved for alkali-activated MSWI bottom ash with triple alkali activators such as sodium hydroxide, soluble glass and silica gel waste. Full article

This work investigates the potential of a sorption-based thermal energy storage (TES) system for enhancing the integration of renewable energy and waste heat recovery in key sectors—industry, transport, and buildings. Sorption-based TES systems, which utilize reversible sorbent–sorbate reactions to store and release thermal energy, offer long-term storage capabilities with minimal losses. In particular, the aim of the study is to evaluate the efficiency of an adsorption TES system for various working pairs under different operating conditions, by means of a thermodynamic model (supported by experimental data). Key findings demonstrate that water-based solutions (e.g., zeolite and silica gel composites) perform well for residential and transport applications, while methanol-based solutions, such as LiCl-silica/methanol, maintain higher efficiency in industrial contexts. Short-term storage shows higher energy efficiencies compared to long-term applications, and the choice of working pairs significantly influences performance. Industrial applications face unique challenges due to extreme operating conditions, limiting the viable solutions to water-based working pairs. This research highlights the capability of sorption-based TES systems to reduce greenhouse gas emissions, improve energy efficiency, and facilitate a transition to sustainable energy practices. The findings contribute to developing cost-effective and reliable solutions for energy storage and renewable integration in various applications. Full article

Glycerol is a biogenic waste that is generated in both the biodiesel and oleo-chemical industries. The value addition of surplus glycerol is of utmost importance for making these industries economically profitable. In line with this, glycerol is converted into glycerol carbonate, a potential candidate for the industrial production of polymers and biobased non-isocyanate polyurethanes. In addition, glycerol can also be converted into solketal, which is the protected form of glycerol with a primary hydroxyl functional group. In this contribution, we developed a microwave-assisted solvent and catalyst-free method for converting solketal into solketal carbonate. Under conventional heating conditions, the reaction of solketal with dimethyl carbonate resulted in 70% solketal carbonate in 48 h. However, under microwave heating, 90% solketal carbonate was obtained in just 30 min. From the perspective of sustainability and green chemistry, biomass-derived heterogeneous catalysts are gaining importance. Therefore, in this project, several green catalysts, such as molecular sieves (MS, 4Å), Hβ-Zeolite, Montmorillonite K-10 clay, activated carbon from groundnut shell (Arachis hypogaea), biochar prepared from the pyrolysis of sawdust, and silica gel, were successfully used for the carbonyl transfer reaction. The obtained solketal carbonate was thoroughly characterized by ¹H NMR, ¹³C NMR, IR, and MS. The method presented here is facile, clean, and environmentally benign, as it eliminates the use of complicated procedures, toxic solvents, and toxic catalysts. Full article

The acid neutralization process is widely recognized for its effectiveness in the dealkalization of red mud, and it faces challenges in solid–liquid separation due to the formation of numerous colloidal components. This study investigated the impact of calcium-containing compounds (CaO, CaCl₂, CaCO₃, and CaSO₄) on the solid–liquid separation and the dealkalization efficiency of red mud during the dealkalization process. The sodium leaching efficiency of the red mud reached 95.6% when the red mud was reacted with 8% of sulfuric acid for 10 min with a stirring speed and liquid to solid ratio of 700 r/min and 5:1, respectively. The replacement of sulfuric acid using simulated waste acid reached similar sodium leaching efficiency. However, the filtration rate of red mud becomes exceedingly sluggish using sulfuric acid or simulated waste acid. Adding calcium-containing compounds significantly augments the efficacy of solid–liquid separation in red mud. With a mass content of 2% for CaO or 8% for CaCl₂, the filtration speed experienced a remarkable fivefold and ninefold increase, respectively. Furthermore, a simplification in the composition was observed within the leaching solution derived from red mud, thereby creating favorable conditions for the extraction of sodium. The influence mechanism was investigated with X-ray diffraction, inductively coupled plasma analysis, and scanning electron microscopy. The addition of calcium compounds led to the formation of calcium silicate and iron silicate in the leaching residue, inhibiting the generation of colloidal substances, such as silica gel. Additionally, these compounds increased the size of red mud particles, facilitating the solid–liquid separation process. This study provides valuable technical insights for the dealkalization of red mud. Full article

This study investigates the use of iron mine tailings (ITs) as a fine aggregate and a clinker-free binder composed of ground granulated blast-furnace slag (GBFS), desulfurization gypsum (DG), and basic oxygen furnace slag (BOFS) to produce low-cost ultra-high-performance concrete (UHPC). The research optimizes the UHPC base by evaluating the impact of key parameters, including the BOFS to GBFS ratio, DG content, BOFS fineness, and binder-to-sand ratio on compressive strength. The study also compares the use of iron mine tailings and silica sand as fine aggregates, demonstrating that tailings are a viable substitute. The results show that the optimal mix, consisting of a 1:1 BOFS to GBFS ratio, 15% DG, and 400 m²/kg BOFS fineness, achieves a compressive strength of 113.7 MPa after 28 days when using iron mine tailings as fine aggregate. Microstructural analysis through X-ray diffraction (XRD), thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) reveal that the primary hydration products—C-S-H gel and AFt—contribute to the dense and strong microstructure of the UHPC. This research offers a sustainable approach to producing cost-effective UHPC by utilizing industrial waste materials, providing a promising solution for reducing both environmental impact and production costs in construction. Full article

The main objective of this study is to reduce CO₂ emissions resulting from rapidly increasing cement production and utilization rates worldwide. For this purpose, the effects of NS (nano-silica) and SF (silica fume) materials, which are the post-production wastes of industrial products, the substitute material obtained by grinding SG (silica gel) wastes used for packaging purposes in the preservation of industrial electronic products and many other areas, and MLS (micritic limestone) obtained by grinding limestone, a natural resource, on mortars after cement substitutions were evaluated. MLS and SG contents were sieved through a 0.063 mm sieve and substituted into the mixtures, while specific surface area values for SF and NS were obtained as 23 m²/g and 150 m²/g. Each of these materials was used in mortars by substituting between 0% and 10% cement by weight. The samples were subjected to consistency determination and then evaluated for setting time. Subsequently, flexural tests were carried out on 40 mm × 40 mm × 160 mm specimens placed in molds, and compressive tests were carried out on prism fragments broken after flexural tests. The experimental results showed that substitution of SG substitutes with cement at 3–10 wt% was highly effective against SF, NS and MLS in terms of strength and workability properties. Full article

Tequila vinasses are organic wastes generated during ethanol fermentation at elevated temperatures (≥90 °C) and pH ≤ 4.0, making them hazardous to the environment. This paper describes a new, simplified UV–vis spectroscopy-based procedure for monitoring the adsorption of color compounds in tequila vinasses onto silica-based adsorbents, along with an optimized synthesis method to produce the most efficient sol–gel synthesized thiol-functionalized adsorbent. Under optimized conditions, the uptake capacity of this adsorbent reaches 0.8 g g⁻¹ in 90 min. Experimental results demonstrate that the adsorbent has a specific affinity for melanoidin-type molecules. The adsorbent demonstrates excellent thermal stability (~316 °C). The results of this work indicate that the adsorbent possesses potential in the treatment of tequila vinasses from wastewater discharges. Full article

The utilization of silicomanganese slag (SiMnS) as a precursor for alkali-activated materials (AAMs) is considered as an efficient approach for sustainable and eco-friendly large-scale resource utilization. However, sodium silicate solutions account for more than 50% of the production costs and carbon emissions of AAMs. In this study, AAM activators were prepared by silica-containing waste (acid leaching residue of boron mud, BM-AR) and NaOH as raw materials, and were successfully substituted for commercial sodium silicate-NaOH activators. Results indicated that the NaOH dosage had a great effect on the concentration and modulus of the activator. With the appropriate dosage of NaOH (NaOH: BM-AR = 0.4–0.7), suitable moduli of AAM activators can be produced at a wide range of solid/liquid ratios (L/S = 3–4.5) under mild conditions (80–100 °C). The compressive strength of the SiMnS AAM specimens prepared by this activator can reach 68.58 MPa, and its hydration products were mainly hydrated calcium silicate and amorphous silica–alumina gel, indicating the successful preparation of AAM. Calculation showed that the carbon emission of the AAMs prepared in this study was 12.4% and 37.6% of that of OPC and commercial water glass/NaOH-activated AAMs, and the cost was only 67.14% and 60.78% of them. The process achieves the use of waste materials to replace commercial activators, and is expected to be extended to a variety of AAMs raw materials and silica-containing waste. This makes it a highly promising alternative method for the production of AAMs, particularly the ‘just add water’ AAMs. Full article

Polycarbonate (PC) is a highly versatile plastic material that is extensively utilized across various industries due to its superior properties, including high impact strength and heat resistance. However, its durability presents significant challenges for recycling and waste management. Polycarbonate is a thermoplastic polymer representative of the class of condensation reaction polymers obtained from the reaction of bisphenol A (BPA) and a carbonyl source, such as phosgene or alkyl and aryl carbonate. The recycling processes for PC waste include mechanical recycling, blending with other materials, pyrolysis, and chemical recycling. The latter is based on the cleavage of carbonate units to their corresponding monomers or derivatives through alcoholysis and/or hydrolysis and ammonolysis, normally under basic conditions and without catalysts. This study investigates the efficacy of the use of several heterogeneous catalysts based on silica gel as a robust support, including Sc(III)silicate (thortveitite), which has been previously reported for the preparation of polyesters, core-shell Si-ILs, and core-shell Si-ILs-ZnO, which has never been used before in the depolymerization of polycarbonate, proposing a sustainable and efficient method for recycling this valuable polymer. We chose to explore core-shell catalysts because these catalysts are robust and recyclable, and have been used in very harsh industrial processes. The core-shell silica catalysts used in this study were characterized by XRD; SEM_EDX, FT-IR, and ICP-OES analysis. In our experimental protocol, polycarbonate samples were exposed to the catalyst under controlled conditions (60–150 °C, for 12–24 h) using both oxygen and nitrogen nucleophiles. The depolymerization process was systematically monitored using advanced analytical techniques (GC/MS and GPC chromatography). The experimental results indicated that core-shell silica catalyst exhibits high efficacy, with up to 75% yield for the ammonolysis reaction, producing monomers of high purity. These monomers can be reused for the synthesis of new polycarbonate materials, contributing to a more sustainable approach to polycarbonate recycling. Full article

This study examines the effects of ultrafine recycled powder (URP) obtained from construction and demolition waste on the hydration kinetics, setting behaviour, and chemical shrinkage of Portland cement pastes. The presence of ultrafine particles in the recycled powder provides more sites for nucleation, thereby promoting the hydration process and accelerating the rate of nucleation. As a result, the setting time is reduced while chemical shrinkage is increased. Incorporating URP improves the early-age mechanical properties. When 7.5% URP is added, the highest compressive strength and flexural strength of cement mortar at a curing age of 3 d are 23.0 MPa and 3.7 MPa, respectively. The secondary hydration between the hydration product and reactive silica from URP contributes to gel formation and enhances mechanical property development. This research provides theoretical insights into utilizing recycled powder in cement-based materials and enhances our understanding of its impact on hydration kinetics. Full article

The use of silico-manganese slag as a substitute for cement in the preparation of concrete will not only reduce pollution in the atmosphere and on land due to solid waste but also reduce the cost of concrete. To explore this possibility, silico-manganese slag concrete was prepared by using silico-manganese slag as an auxiliary cementitious material instead of ordinary silicate cement. The mechanical properties of the silico-manganese slag concrete were investigated by means of slump and cubic compressive strength tests. The rates of mass loss and strength loss of silico-manganese slag concrete were tested after 25, 50, and 75 cycles. The effect of the silica–manganese slag admixture on the microfine structure and properties of concrete was also investigated using scanning electron microscopy (SEM). Finally, the damage to the silica–manganese slag concrete after numerous salt freezing cycles was predicted using the Weibull model. The maximum enhancement of slump and compressive strength by silica–manganese slag was 17.64% and 11.85%, respectively. The minimum loss of compressive strength after 75 cycles was 9.954%, which was 34.96% lower than that of the basic group. An analysis of the data showed that the optimal substitution rate of silica–manganese slag is 10%. It was observed by means of electron microscope scanning that the matrix structure was denser and had less connected pores and that the most complete hydration reaction occurred with a 10% replacement of silica–manganese slag, where an increase in the number of bladed tobermorite and flocculated C-S-H gels was observed to form a three-dimensional reticulated skeleton structure. We decided to use strength damage as a variable, and the two-parameter Weibull theory was chosen to model the damage. The final comparison of the fitted data with the measured data revealed that the model has a good fitting effect, with a fitting parameter above 0.916. This model can be applied in real-world projects and provides a favorable basis for the study of damage to silica–manganese slag concrete under the action of salt freezing. Full article