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Three-dimensional concrete printing (3DCP) technology with solid wastes has significant potential for sustainable construction. However, the hardened mechanical properties of components manufactured using 3DCP technology are affected by weak interlayer interfaces, limiting the widespread application of 3DCP technology. To address the inherent limitations of 3DCP technology, conventional improvement strategies, such as external reinforcement and the optimization of material properties, lead to increased production costs, complex fabrication, and decreased automation. This study proposes an innovative spatial path optimization method to enhance the mechanical performance of 3D-printed, cement-based components. The novel S-path design introduces additional printed layers in the weak interlayer regions of the printed samples. This design improves the spatial distribution of fiber-reinforced filaments in continuous weak zones, thus enhancing the functional efficiency of fibers. This approach improves the mechanical performance of the printed samples, achieving compressive strengths close to those of cast samples and only a 20% reduction in average flexural strength. Compared to using a conventional printing path, the average compressive strength and flexural strength are improved by 30% and 55%, respectively, when the S-path layout is employed in 3DCP. Additionally, this method significantly reduces the anisotropy in compressive and flexural strengths to 26% and 28% of samples using conventional printing paths, respectively. Therefore, the proposed method can improve the mechanical properties and stability of the material, reducing the safety risks of printed structures. [ABSTRACT FROM AUTHOR]

Waste slag and rubber particles are commonly used to modify concrete, offering benefits such as reduced cement consumption and lower greenhouse gas emissions during cement production. In this study, these two environmentally friendly, sustainable waste materials were proposed for the preparation of mortar intended for snow-melting pavements. A series of experiments were conducted to evaluate the performance of the material and to determine whether its compressive and flexural strengths meet the requirements of pavement specifications. The mortar's suitability for snow-melting pavements was assessed based on its thermal conductivity, impermeability, and freeze–thaw resistance. The results indicate that slag, when used in different volume fractions, can enhance the compressive and flexural strength of the mortar. Slag also provides excellent thermal conductivity, impermeability, and resistance to freeze–thaw cycles, contributing to the overall performance of snow-melting pavements. When the slag content was 20%, the performance was optimal, with the compressive strength and flexural strength reaching 58.5 MPa and 8.1 MPa, respectively. The strength loss rate under freeze–thaw cycles was 8.03%, the thermal conductivity reached 2.2895 W/(m * K), and the impermeability pressure value reached 0.5 MPa. Conversely, the addition of rubber particles was found to decrease the material's mechanical and thermal properties. However, when used in small amounts, rubber particles improved the mortar's impermeability and resistance to freeze–thaw cycles. When the rubber content was 5% by volume, the impermeability pressure value reached 0.5 MPa, which was 166.7% lower than that of ordinary cement mortar. Under freeze–thaw cycles, the strength loss rate of the test block with a rubber content of 25% volume fraction was 9.83% lower than that of ordinary cement mortar. [ABSTRACT FROM AUTHOR]

The untreated municipal solid wastes (MSWs) dumping and improper management causes major concerns of environmental degradation and human health risks. In this study, we collected soil and vegetable from the MSWs dumpsites of Khulna City Corporation (KCC) in southwestern Bangladesh. Trace metals (Pb, Cd, Co, Cr, Cu, Ni, Zn, Fe, Mn) were measured to explore the health risk of cultivated vegetables from dumpsites. Soil contamination was evaluated by geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (CF), and pollution load index (PLI), while health risk was evaluated by transfer factor (TF), estimated daily intake (EDI), target hazard quotient (THQ). Results exhibited that the average trace metals in soil and vegetables followed in the order of Fe > Pb > Mn > Zn > Cu > Cr > Ni > Cd > Co. The Igeo, EF, CF, and PLI values revealed that the soil contamination was dominated by Pd, Cd, Mn, and Zn. The EDI of metals in vegetables were exceed the maximum daily intake only for Fe, Pb, and Cr. The total THQ was > 1, implying potential health hazards for the local people due to the long-term consumption of the cultivated vegetables. The multivariate analysis reveled that the sources of trace metals in the soils and vegetables of dumpsites were natural and anthropogenic. Overall, the findings suggest that growing vegetables in dumpsite is unsafe for long-term consumption by local inhabitants. Immediate action should be taken to protect the environment and human health from trace metal hazards.

The objective of this paper was to evaluate the impacts of solid wastes on physicochemical characteristics and habitats of fiddler crabs (Uca tangeri) on the intertidal sediments of Part of the Bonny Estuary, in Rivers State, Nigeria using appropriate standard methods. Results obtained show that the physiochemical characteristic in the study are were pH (4.9 - 6.3); conductivity (780.0 - 6290 µS/cm) sulphate (34.4 - 190.0 mg/kg); phosphate (0.6 - 6.8mg/kg); nitrate (1.2 - 4.5mg/kg); sand (32 - 87%); silt (0.2 - 14%) clay (3 - 54%). Solid wastes observed were plastics, wood/plank, bottles, Styrofoam, tyres, nylon/polyethene, clothes and ropes while fiddler crabs holes ranged from 3 - 38 in the study area. Physico-chemical characteristics of sediment varied between intertidal stations however, changes in pH, phosphate, nitrate and silt particles caused significant (p<0.05) changes in the number of fiddler crab holes. The amount of solid wastes observed at the mid intertidal level also impacted significantly on the number of crab holes but the observation was different at the low and the high intertidal zones. In conclusion, the interplay of physicochemical characteristics of the sediment with solid wastes contributed to the fragmentation and loss of fiddler crab habitats but varied from one intertidal coast to another. It is therefore, important to assess each intertidal coast in order to conserve fiddler crabs and their habitats. [ABSTRACT FROM AUTHOR]

This research focuses on the technical and economic assessment of construction and demolition wastes (C&DW) as filling material for gabions executed for lining works of a river in the city of São Paulo, Brazil. Laboratory tests were performed on C&DW and natural rock to determine the durability, compressive strength, and water absorption necessary for gabion designs. In addition, an economic assessment was performed to estimate the costs of using C&DW to substitute rocks for gabion filling. The results showed that the studied C&DW complies with the technical standards and can be used as gabion-filling material, thus promoting a circular economy. However, due to the hydraulic efforts, a layer of shotcrete must be applied on the gabion surface. The economic assessment highlighted the economic advantages and low costs of substituting rocks for C&DW in gabions filling, even considering the need for a shotcrete layer. [ABSTRACT FROM AUTHOR]

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Increases in the human population and economic development have led to a rise in waste production, which poses significant environmental risks and presents a pressing global issue in waste management. Among other countries, this situation affects the United Arab Emirates (UAE). On the other hand, poor waste segregation practices can result in failed waste recycling efforts, leading to the excessive use of resources and worsening issues (such as energy consumption, global warming, and sustainable development). Waste segregation is a crucial step in waste management, which involves dividing waste according to its characteristics and type. By following this procedure, recycling effectiveness is increased, the environmental impact is decreased, and hazardous material disposal is ensured. Beneficial waste segregation reduces contamination, making it possible to recover valuable materials and thus use fewer landfills. Even though the failings in waste segregation are a severe issue, insufficient research has been carried out. This includes research on the knowledge, attitudes, and practices (KAP) of people living in the UAE regarding waste segregation, information which is crucial to developing a successful intervention to address this problem. The current study evaluated the KAP concerning waste segregation among UAE citizens and identified correlations between KAP variables, with the primary aim of filling a research gap, while analyzing the correlations between sociodemographic characteristics and KAP levels, which was the secondary aim. This was accomplished by a cross-sectional study conducted all over the UAE. Data were collected from 391 participants using a five-point Likert scale questionnaire that was developed from previous research and investigated sociodemographic characteristics, waste segregation practices (5), attitudes (5), and knowledge (5). UAE University's ethical committees approved this study (ERSC_2024_4360) for research, and the results were confirmed through statistical analyses and Cronbach's alpha testing. The inclusion criteria targeted residents of the UAE who were 18 years of age or above, and the survey was distributed via an online platform (Google Forms) with non-probability sampling. G*Power statistical power analysis estimated a minimum sample size of 385 participants. To identify correlations in the results, a structural equation model (SEM) and SPSS, such as Chi-square tests and Spearman correlation coefficients, were used to assess the associations between KAP variables. These tests were chosen for their robustness in handling categorical and continuous data, respectively. A notable majority (84.1%) of the participants were female, and 15.9% were male; the gender difference was highly significant, as revealed by the Chi-square test. Most participants (67.0%) fell into the 18–24 age group. The highest level of education reported was a bachelor's degree (47.3%). The parents' educational levels showed a relatively high level of education, with more than half having at least a high school degree or higher: father's education level (67.2%) and mother's education level (73.1%). Most participants were students (58.8%), but a significant portion of the sample was employed (25.1%). Unemployment was reported at 12.3%. The parents' employment statuses showed a higher percentage of unemployed mothers (49.4%) compared to fathers (6.9%). The average scores suggested a favorable inclination toward sustainability (mean ± standard deviation (SD) for knowledge, 3.59 ± 0.78; poor knowledge, 3.6%; and excellent knowledge, 16.9%), attitudes (3.73 ± 0.77; poor attitudes, 2.8%; and excellent attitudes, 22.5%), and practices (3.62 ± 0.76; poor practices, 2.3%; and excellent practices, 16.4%), with all the means surpassing the midpoint. In the correlation test, the current study demonstrated positive correlations between knowledge and attitudes (r = 0.666, p < 0.001) and between knowledge and practices (r = 0.682, p < 0.001). Also, a positive correlation (r = 0.159, p < 0.001) was found between general waste segregation KAP and sociodemographic variables, with a significant correlation (r = 0.110) between attitudes and gender. These findings emphasize the possibility of using focused educational and policy interventions to improve waste segregation behaviors. An additional investigation is advised to delve into the fundamental mechanisms behind these correlations and devise customized approaches to encourage sustainable waste management practices among various demographic groups in the UAE. [ABSTRACT FROM AUTHOR]

The traditional production of silicate cement is associated with substantial carbon emissions and environmental degradation. In contrast, cementless alkali-activated binders, derived from solid waste and industrial byproducts, have garnered significant interest for their reduced material costs, energy efficiency, and environmental benefits. This research investigates the application potential of an advanced mixture of anhydrous sodium silicate and red mud in one-part alkali-activated binders. It is assessed through various analytical techniques, including compressive strength, X-ray diffraction, fourier transform infrared, thermogravimetric analysis, digital image correlation, and scanning electron microscopy with energy dispersive spectroscopy. Findings demonstrate that the synergy between red mud and anhydrous sodium silicate markedly enhances the early strength of one-part alkali-activated binders incorporated with alkali-thermal activation. The increment in sodium silicate content is pivotal for bolstering binder performance. A 40 % red mud admixture results in a compressive strength of 40 MPa, achieving an optimal carbon-to-strength ratio. The inclusion of polypropylene fiber significantly influences the mode of compression failure in alkali-activated binders. Alkali-thermal activation of red mud elevates the levels of active silicon and aluminum, markedly augmenting the reactive silica and aluminum content. This modification fosters the disintegration and reorganization of Si-O and Al-O bonds in silica-aluminum materials, culminating in a denser structure. This structure is characterized by the generation of amorphous ((N, C)-A-S-H) gels, contributing to the material's enhanced properties.

Abstract The utilization of waste or by-products in geopolymers is an effective strategy that contributes to the development of more sustainable ceramics. The present study aimed to evaluate the physico-mechanical properties of compositions prepared by partially replacing aluminosilicate precursors (metakaolin or calcined diatomite) with solid wastes (granite, roof tile chamotte, or glass powder) at contents of 10, 20, and 40 wt%. Geopolymers were synthesized by blending the solid raw materials (precursor+wastes) with an alkaline activating solution comprising NaOH and colloidal silica suspension. The samples were cured at 40 °C for 24 h, and the following analyses were conducted: elastic modulus, compressive strength, porosity, density, X-ray diffraction, and Fourier-transform infrared spectroscopy measurements. The results demonstrated that the formulation containing 10 wt% of chamotte exhibited the best performance, showing a remarkable mechanical strength of 31.7 MPa after one day of curing. Therefore, by incorporating waste materials into geopolymers, not only can the environmental impact be minimized, but it also presents an opportunity to utilize resources that would otherwise go to waste.

Red mud has been used as a supplement substitute material in the fabrication of concrete. However, the influence mechanism of red mud on the film-forming performance of cement paste is still unclear. In this study, red mud with different substitution rates (by cement mass) was added to cement paste to investigate the influence of red mud on the film-forming performance. The addition of red mud increased the cohesiveness and reduced the fluidity of cement paste. It showed that low fluidity reduced the film thickness of cement paste, and the film thickness decreased gradually with the increase of red mud substitution. Moreover, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy results demonstrated that red mud promotes the hydration process of cement by providing hydration nucleation sites, making the interfacial transition zone denser, which is important for improving the mechanical properties of cement paste. It is expected that this study improves the application of red mud in concrete. [ABSTRACT FROM AUTHOR]

Solid waste management system in Mzuzu City is a growing concern due to its inefficiency and the resulting effect of accumulation of solid waste. In light of this environmental challenge, a study was conducted to assess the system's effectiveness. Through a mixed methods approach and random sampling, 400 respondents from 5 different areas of the city of Mzuzu were selected to provide comprehensive and unbiased responses. It was found that both the public and private sectors lack a complete commitment to sustainable waste management, citing reasons such as limited knowledge on recycling benefits, inadequate infrastructure and budgetary constraints. As a solution, the study proposes a government-led campaign to change attitudes towards waste production and promote recycling. Additionally, a Public-Private Partnership (PPP) should be utilised to develop policies and strategies that encourage private sector involvement in eco-friendly waste management. To further enhance recycling practices, support is needed in transitioning to circular economy waste management practices through regular education and training. [ABSTRACT FROM AUTHOR]

Large amounts of solid wastes are produced in manufacturing of leather and leather products. Nearly 80–85% of solid wastes is generated in leather production whereas 20–30% of leather is ended up as wastes from leather goods and footwear industries which poses significant concern regarding environmental pollution. An attempt was made to produce environmentally friendly bio-composite materials with higher mechanical characteristics by utilizing solid wastes released from leather industries. In this study, leather fibers (LF) from shaving dust and leather cutting scrap were used with plant fibers such as banana (Musa acuminata), pineapple (Ananas comosus), betel nut (Areca catechu), and moringa (Moringa oleifera) for making composite sheets reinforced with natural rubber latex (NRL). New composite materials were characterized by using thermogravimetric (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques which confirmed the presence of desired physical and chemical properties in them. FTIR analysis showed characteristics absorption resonances at 3287, 2919, and 2855 cm−1 which were not apparent in starting single fibers. TGA data indicated that banana fiber (BF) composite is thermally more stable than others. The tensile strengths of pineapple fiber (PF) composite and BF sheet were 3.89 and 3.59 Mpa, respectively, which were higher than those observed in control sheet (CS). New composite sheets possess significant properties which make them suitable to be used as valuable raw materials for manufacturing of various footwear and leather goods. This interesting approach will reduce environmental pollution and ensure the sustainability of the respective ecosystem. [ABSTRACT FROM AUTHOR]

There are some limitations in the application of tuff powder as a supplementary cementitious material (SCM). Exploring its feasibility in new fields will consume a large amount of silica-alumina mine solid wastes. This study has investigated the mechanical properties and mechanism in contact-hardening of tuff powder with a method of compression molding. The compressive strength of specimens was tested, and the X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and Mercury intrusion porosimetry (MIP) methods were used to reveal the mechanism of contact-hardening of tuff powder from a micro-perspective. The results indicated that the compressive strength of specimens was higher when activated by sodium hydroxide compared to calcium hydroxide. Compared to calcium hydroxide, the compressive strength of TFS20 and TFF20 activated by sodium hydroxide was improved by 20% and 23%, respectively. The hydration degree of tuff powder was very low, with a water–cement ratio (w/c) of 0.15, while the hydration degree of coal gangue powder was higher. The results of TGA and SEM indicated that the sodium hydroxide had a better activating effect on slag and fly ash. Therefore, more C-S-H gels were generated in those samples activated by sodium hydroxide. Furthermore, the structure of samples was more compacted, and there was a reduction of porosity by 10% and 11% for TFS20 and TFF20, respectively, especially the proportion of harmful pores. [ABSTRACT FROM AUTHOR]

The objective of this paper was to evaluate the impacts of solid wastes on physicochemical characteristics and habitats of fiddler crabs (Uca tangeri) on the intertidal sediments of Part of the Bonny Estuary, in Rivers State, Nigeria using appropriate standard methods. Results obtained show that the physiochemical characteristic in the study are were pH (4.9 - 6.3); conductivity (780.0 – 6290 µS/cm) sulphate (34.4 – 190.0 mg/kg); phosphate (0.6 – 6.8mg/kg); nitrate (1.2 – 4.5mg/kg); sand (32 – 87%); silt (0.2 - 14%) clay (3 - 54%). Solid wastes observed were plastics, wood/plank, bottles, Styrofoam, tyres, nylon/polyethene, clothes and ropes while fiddler crabs holes ranged from 3 -38 .in the study area. Physico-chemical characteristics of sediment varied between intertidal stations however, changes in pH, phosphate, nitrate and silt particles caused significant (p

Waste slag and rubber particles are commonly used to modify concrete, offering benefits such as reduced cement consumption and lower greenhouse gas emissions during cement production. In this study, these two environmentally friendly, sustainable waste materials were proposed for the preparation of mortar intended for snow-melting pavements. A series of experiments were conducted to evaluate the performance of the material and to determine whether its compressive and flexural strengths meet the requirements of pavement specifications. The mortar’s suitability for snow-melting pavements was assessed based on its thermal conductivity, impermeability, and freeze–thaw resistance. The results indicate that slag, when used in different volume fractions, can enhance the compressive and flexural strength of the mortar. Slag also provides excellent thermal conductivity, impermeability, and resistance to freeze–thaw cycles, contributing to the overall performance of snow-melting pavements. When the slag content was 20%, the performance was optimal, with the compressive strength and flexural strength reaching 58.5 MPa and 8.1 MPa, respectively. The strength loss rate under freeze–thaw cycles was 8.03%, the thermal conductivity reached 2.2895 W/(m * K), and the impermeability pressure value reached 0.5 MPa. Conversely, the addition of rubber particles was found to decrease the material’s mechanical and thermal properties. However, when used in small amounts, rubber particles improved the mortar’s impermeability and resistance to freeze–thaw cycles. When the rubber content was 5% by volume, the impermeability pressure value reached 0.5 MPa, which was 166.7% lower than that of ordinary cement mortar. Under freeze–thaw cycles, the strength loss rate of the test block with a rubber content of 25% volume fraction was 9.83% lower than that of ordinary cement mortar.

• Mixed Cu/Mg ferrites were characterized for the first time as oxygen carriers. • Positive impact of Mg doping on mechanical durability was proven. • Highest reaction rate toward fuel was achieved for Cu 0.75 Mg 0.25 Fe 2 O 4 (1.19 wt.%/min). • Mg-rich OCs exhibited increased reactivity toward fuel in 610–730 °C. Waste wood biomass is considered a renewable energy source. Combining biomass combustion with emerging clean combustion technologies such as chemical looping combustion (CLC) can yield effective and affordable carbon capture and, consequently, lead to negative net emissions of greenhouse gases. Oxygen carrier (OC) is a crucial material in CLC technology that must exhibit certain properties, such as high durability, good chemical stability during numerous red-ox cycles and, important for the combustion of solid fuels, the capability of spontaneously releasing oxygen in a process referred to as chemical looping with oxygen uncoupling (CLOU). In this work, a series of nine Cu x Mg 1-x Fe 2 O 4 spinel-based materials were synthetized and evaluated for the first time as potential OCs for a waste biomass combustion. Their properties, such as oxygen transport capacity and reactivity with biomass (wood chips) as a fuel, were evaluated in a function of temperature (900–1000 °C). Tested oxygen carriers were characterized with an excellent oxygen transport capacity in CLOU process (up to 2.78 wt%) and good reaction rates with the fuel (up to 1.19 wt. %/min), and regeneration rates (up to 3.8 wt. %/min). High conversion of the waste biomass was also achieved (98.9 %). Moreover, new findings revealed a strong positive effect of magnesium addition on mechanical strength (crushing strength > 4 N for samples with Mg content above 0.5). [ABSTRACT FROM AUTHOR]

Sewage sludge contains plant nutrients and organic matter in its composition, making it a potential partial substitute for mineral fertilizers if it meets environmental, agronomic, and sanitary standards. The objective was to evaluate the content of nutrients and heavy metals in the sludge generated in four wastewater treatment stations (WWTPs) in Rio de Janeiro state and assess its potential value and usefulness. The samples of 19 batches from the WTTPs Alegria, Barra da Tijuca, Ilha do Governador, and Sarapuí were analyzed. The WWTPs differ in methods and processes used for treating sewage and sludge. The total contents of C, N, P, K, Ca, Mg, Fe, Al, Na, Co, Mn, As, Ba, Cd, Cr, Cu, Ni, Se, Pb, and Zn were evaluated, as well as the ratio C/N, pH, organic matter content, and electrical conductivity. The grouping of sludge samples was assessed using principal components (PCA) and cluster analysis. The economic valuation of sludge was conducted utilizing the substitute goods method, which compared the sludge's N-P-K contents with the prices of consolidated nutrient sources. All the evaluated sludge batches exhibited concentrations of heavy metals below the limits allowed by Brazilian law, along with high levels of nutrients and organic matter. Considering the chemical characteristics, all evaluated materials showed potential for agricultural use, but it is crucial to evaluate the microbiological characteristics of sludge batches before agriculture application. PCA and cluster analysis demonstrated that sludge samples from the same WWTP clustered close to each other, demonstrating higher similarity among themselves than with samples from other WWTPs. The sludge had an average added value of U$ 88.46 per megagram, considering the total contents of N, P, and K in its composition. Land application of sewage sludge can reduce the need to purchase mineral fertilizers, thereby supporting the feasibility of reusing this material in the agricultural sector. [ABSTRACT FROM AUTHOR]

The release of carbon dioxide (CO2) into the earth's atmosphere is a substantial global environmental concern that arises from the processes of industrialization and urbanization. The increase in atmospheric CO2 concentrations has resulted in the phenomenon of global warming and subsequent alterations in climate patterns. Accelerated CO2 sequestration in cementitious materials is currently the subject of extensive research as a highly efficacious approach to mitigating the carbon footprint of the concrete industry. The sequestration procedure entails the transformation of gaseous CO2 into carbonate minerals. The review presented in this paper outlines the most recent carbonation (i.e., CO2 sequestration) techniques, such as mineral carbonation, accelerated CO2 curing (ACC), pre-carbonation, and carbonation mixing, that have been recently explored. The potential of mineral carbonation of industrial wastes and the advantages of their incorporation in the concrete matrix is investigated. Carbonation technologies and their effect on the performance of cementitious composites are reported. Information on life cycle assessment are also included to evaluate the environmental impact associated with the production of carbonated materials. Various commercialized CO2 utilization technologies in construction sector, such as CarbonCure, Solidia, Carbstone, Calera, and Carbon8 are reviewed. Moreover, this review offers a thorough insight into the carbonation technologies, evaluating their advantages, limitations, and the existing gaps in research.

There are some limitations in the application of tuff powder as a supplementary cementitious material (SCM). Exploring its feasibility in new fields will consume a large amount of silica-alumina mine solid wastes. This study has investigated the mechanical properties and mechanism in contact-hardening of tuff powder with a method of compression molding. The compressive strength of specimens was tested, and the X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and Mercury intrusion porosimetry (MIP) methods were used to reveal the mechanism of contact-hardening of tuff powder from a micro-perspective. The results indicated that the compressive strength of specimens was higher when activated by sodium hydroxide compared to calcium hydroxide. Compared to calcium hydroxide, the compressive strength of TFS20 and TFF20 activated by sodium hydroxide was improved by 20% and 23%, respectively. The hydration degree of tuff powder was very low, with a water–cement ratio (w/c) of 0.15, while the hydration degree of coal gangue powder was higher. The results of TGA and SEM indicated that the sodium hydroxide had a better activating effect on slag and fly ash. Therefore, more C-S-H gels were generated in those samples activated by sodium hydroxide. Furthermore, the structure of samples was more compacted, and there was a reduction of porosity by 10% and 11% for TFS20 and TFF20, respectively, especially the proportion of harmful pores.

Rare earth elements (REEs) are critical components of numerous products widely used in many areas, and the demand for REEs is increasing dramatically in recent years. Physical-chemical leaching is commonly adopted for the recovery of REEs from ores and solid wastes, but concerns over the generation of hazards, operation safety, and environmental pollution have urged the transition to greener and more sustainable leaching methods. Bioleaching is considered an excellent alternative for the recovery of REEs. This review provided an overview on the REEs recovery from primary and secondary resources via different bioleaching strategies. The techno-economics of bioleaching for REEs recovery were highlighted, and key factors affecting the economic viability of bioleaching were identified. Finally, strategies including the utilization of low-cost substrates as feedstocks, non-sterile bioleaching, recycling and reutilization of biolixiviants, and development of robust bioleaching strains were proposed to improve the economic competitiveness of bioleaching. It is expected that this review could serve as a useful guideline on the design of more economically competitive bioleaching processes for the recovery REEs from different resources. [Display omitted] • Bioleaching is effective for the recovery of REEs from ores and solid wastes. • Bioleaching processes are not economically competitive at current stage. • Feedstock, energy consumption and bioreactor are major cost contributors. • Strategies are proposed to improve the economic viability of bioleaching. [ABSTRACT FROM AUTHOR]

In this paper, salt sludge (SS), a solid waste from sodium hydroxide production, was activated at high temperature for the first time. It was combined with soda residue (SR), a solid waste from sodium carbonate production, as a solid activator to activate the solid aluminosilicate precursor, blast furnace slag (BFS). This process developed a novel one-part alkali-activated material, termed salt sludge and soda residue co-activated blast furnace slag cementitious material (SRB), which effectively utilizes solid wastes. The effects of ratios of calcined SS (CSS) to SR, fine aggregate types, and curing methods on the physical and mechanical properties of SRB were investigated. The composition of the hydration products was characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and fourier transform infrared spectroscopy (FTIR), while the hydration process during the setting stage was examined with 1H low-field nuclear magnetic resonance (1H LF NMR). The influence of mix ratio, fine aggregate type, and curing method on the microstructure of SRB was analyzed using scanning electron microscopy (SEM). The results showed that the synergistic activation of BFS by CSS and SR was significantly more effective than individual activation. At the optimal mix ratio (CSS:SR:BFS = 15:15:70), the 3/28 days compressive strength of SRB was 14.3/53.7 MPa. The primary hydration products were C-(A)-S-H gels, along with Friedel's salt, ettringite, and hydrotalcite crystals. Using manufactured sand (MS) as a fine aggregate reduced mortar fluidity compared to river sand (RS) but enhanced the interfacial transition zone (ITZ) with the hardened paste, resulting in a denser microstructure. Heat curing promoted hydration product generation, increasing early (3 days) strength by a factor of 2.5. However, the rapid accumulation and insufficient diffusion of hydration products adversely affected the later strength. • SS was applied in the production of building materials for the first time. • A novel one-part AAM was developed without commercial alkalis. • A salt-alkali synergistic activation effect on BFS was constructed using SS and SR. • The optimal heat curing method of this novel one-part AAM was investigated. • A solution is proposed for the disposal of saline-alkaline solid wastes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Activation of the depressed minerals in cyanide tailing by several activators. • Comprehensive consideration to the reasonable flotation condition for the recovery of the valuable metals from some solid wastes. • Recovery of heavy metals from the secondary resources by the combination of flotation and other techniques. • Several challenges and opportunities faced in recycling heavy metals using flotation technology. Due to the stringent environmental regulations requiring proper disposal of the wastes, recycling/removing heavy metals from solid wastes and wastewater has attracted the worldwide attention. Flotation tends to be one of the promising techniques that have enjoyed widespread use because of its high yield, low cost, and ease of operation. This article provided an overview of the present application status of flotation in the recovery/removal of heavy metals from secondary resources such as tailings, waste printed circuit boards, slags, lithium-ion batteries, leach residue and wastewaters. The study was focused on the reagent regimes and physicochemical & electrochemical mechanism of flotation, in particular, the application of single and hybrid process was reviewed. Finally, the paper has pointed out challenges and future perspectives of the flotation application in metal recovery from secondary resources. Hence, this work aims to promote the development of flotation technology to recover heavy metals from secondary resources. [ABSTRACT FROM AUTHOR]

Solid waste-derived belite-rich calcium sulfoaluminate (BRC) clinker was successfully synthesized, which incorporated incineration bottom ash, recycled concrete powder, and phosphogypsum as the feedstock. The mineral components of BRC clinker were predicted by theoretical formula and thermodynamic modelling, which aligned well with experiments. The effect of clinkering temperature on viscosity, Gibbs free energy, phase equilibrium, and real mineralogy was thoroughly investigated by thermodynamic predictions and experimental characterizations. Optimal clinkering at 1200 °C for 3 h yielded BRC clinker predominantly consisting of 46.3 wt% belite, 22.5 wt% ye'elimite, 16.6 wt% fluorellestadite, and 7.1 wt% brownmillerite. Hydrates AFt and amorphous (AH 3 and C–S–H gel) formed the network, playing a crucial role in developing a 60 d paste strength of 42.2 MPa. Utilizing lower temperatures and low-carbon embodied solid wastes for producing this BRC clinker promised to reduce CO 2 emissions and preserve natural resources. [Display omitted] • Waste-derived belite-rich CSA (BRC) clinker with hydraulic behavior was synthesized. • Modified formula and thermodynamic modelling were good in phase component prediction. • This study could promote CO 2 emission reduction and enhance solid waste management. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of various solid waste materials such as fly ash (CFA), steel slag, and kaolinite on the simultaneous stabilization of As, Cd, Cu, Pb, and Zn in the soil of abandoned lead-smelting slag plant. Synchronous stabilization of HMs in highly contaminated soils was achieved using the application of 29 % formulated material Fe/Ca-Si based co-remediation material (FCS) with a ratio of FeSO 4 + CFA + kaolinite of 14 %: 12 %: 3 %, the bioavailable content of HMs As, Cd, Cu, Pb, and Zn was reduced by 71.55 %, 49.62 %, 91.35 %, 61.37 %, and 41.45 %, respectively, and had little effect on the pH of the soil. Leaching toxicity analyses guaranteed the safety of restorative materials. The results of the field validation experiments showed that the FCS was able to effectively reduce the content of HMs in plant rhizomes and stabilized with maintenance time. European Community Bureau of Reference (BCR) and Wenzel sequential extraction procedures showed that FCS promoted the transformation of HMs in soil from unstable to stable phases. The analysis of soil microbial community diversity by FCS showed that it created a favorable soil living environment for microorganisms and was conducive to the stabilization of HMs. SEM, Surface scanning analysis, XRD, and FTIR results showed that FCS reacts with HMs to form a stable phase. Cost analysis showed that it has certain economic benefits. In conclusion, FCS is feasible for soil remediation in lead-smelting slag-polluted areas and also provides a way for high value-added utilization of solid waste. [Display omitted] • Successful preparation of HMs polluted solid waste soil remediation material. • The resource utilization of CFA and kaolinite had been achieved. • The simultaneous reduction rate of bioavailability of HMs in soil is over 88 %. • FCS composite materials prevent the migration of HMs into plants. • As, Cd, Cu, Pb, Zn by chemical precipitation to produce stable phases. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different factors affecting Ca2+ concentration in leachate from ashes were compared. • Enhancing effect of different promotors on Ca2+ leaching out from ashes was compared. • Addition of CH 3 COOH in the LAM process promoted the formation of vaterite CaCO 3. • TEA as both leaching and absorbing solvents was appropriate for LAM cycled process. • Cycled performance of a LAM process to transform CO 2 into pure CaCO 3 was studied. Mineralization process between CO 2 -rich amine solvents and Ca-rich solid wastes would be very potential for obtaining carbon-free and functional CaCO 3 product with high purity. This study aimed to grasp the performance of a new leaching-absorption-mineralization (LAM) cycled process, in which amines acted as both absorbent for gas mixture with low CO 2 concentration and leaching agent of Ca2+ out from Ca-containing solid wastes. Different parameters affecting this LAM cycled process were investigated and the properties of mineralized products were characterized in detail. The results showed that 3 mol/L TEA exhibited an excellent capability in Ca2+ leaching out from Ca-rich purified dust, and Ca2+ concentration in leachate appeared a positive relationship with TEA concentration, solid-to-liquid ratio and leaching time. With the help of 30 % additives (HCl, NH 4 Cl and CH 3 COOH), Ca2+ concentration in 3 mol/L TEA leachate was enhanced by more than double times. The volume ratio of CO 2 -rich solvent to Ca2+-rich leachate played a significant role in product yields and the size of mineralized crystals. The pure CaCO 3 yield was significantly increased at a bigger volume ratio or a higher adding proportion of additive. When 30 % CH 3 COOH was added into 3 mol/L TEA, most of mineralized product existed as vaterite, and its total yield reached up to be the maximum value of 530.96 g/kg. After completing the fifth cycle, in comparison with fresh TEA, Ca2+ leaching efficiency and CO 2 absorption load of recycled 3 mol/L TEA was decreased by about 18.78 % and 12.53 %, respectively. The regulation in size and morphology of CaCO 3 crystal can be achieved by flexibly changing the volume ratio during LAM cycled process. [ABSTRACT FROM AUTHOR]

Solid waste derived clinker design methodology was established based on thermodynamic simulation and experiment validation via the recycling of incinerated sewage sludge ash (ISSA) and recycled concrete fine (RCF). Compared with 1000 °C and 1100 °C, 1200 °C was the optimum temperature for C 2 S-rich clinker synthesis due to the highest simulated belite content after sintering. A utilization rate of 95 % was achieved, accomplishing the maximization of solid waste recycling. Due to the CaCO 3 phase formation by the reaction of high-content belite (46.8 %) with CO 2 , carbonated 1200ARS eco-cement showed higher compressive strength than OPC and other eco-cements. The lowest porosity (18.1 %) with dense microstructure was also obtained by carbonated 1200ARS. Benefiting from the high CO 2 reactivity of belite, 1200ARS displayed the optimum CO 2 sequestration capacity with a higher carbonation degree (30.1 %) than other batches, providing a promising direction for future development of the low-carbon cement industry to achieve environmental sustainability. • A pioneering kind of solid waste derived clinker design methodology was established. • A utilization rate of 95 % was achieved, accomplishing the maximization of solid waste recycling. • Higher mechanical properties than OPC were displayed by eco-cements after carbonation curing. • The prepared eco-cements possessed excellent CO 2 storage capacity. [ABSTRACT FROM AUTHOR]

To reduce environmental impact of sintered lightweight aggregates (LWAs), in this study, novel glass-based LWAs were produced from municipal solid wastes at 900 °C. The mix was designed by thermodynamic modelling to optimize the phase composition, liquid phase properties, and microstructure of the LWAs. Results demonstrated that the inclusion of incinerated sewage sludge ash (ISSA) increased the viscosity of the liquid phase, resulting in a refined pore structure characterized by smaller, more isolated pores, and thicker pore walls. Additionally, ISSA facilitated the formation of various crystalline phases (e.g. wollastonite) to stabilize the pore structure, thereby enhancing densification and matrix strength. Leaching behaviour tests confirmed the suitability of glass-based LWAs for environmentally safe lightweight products. Lightweight mortars incorporating developed LWAs exhibited a high 28-day compressive strength (up to 57.9 MPa) with a low density of 1688 kg/m3 and a low thermal conductivity of 1.0 W/(m·K). The energy simulation revealed substantial reductions in energy consumption when the lightweight mortars were utilized in the building compared with the reference building using normal-weight C30 concrete, underscoring its promising role in conserving energy and reducing carbon emissions. • Glass-based lightweight aggregates were developed using thermodynamic modelling. • The incorporation of incineration sewage sludge ash favoured the crystallization and improved the pore structure. • Simulation results revealed great energy-saving potential across diverse climates. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1507 articles from 2010 to 2022 were analyzed considering journals, authors, and keywords. • Mineral carbonation mainly lies in chemical engineering, environmental science, and environmental engineering. • Ca-based and Mg-based feedstocks were summarized as possible CCS sorbents. • The poor reaction kinetics and carbonation capacity significantly limited industrial application. • Pilot-scale mineral carbonation and continuous production tests are still scarce. Mineral carbonation as a way of carbon storage has received a particular attention in the reduction of carbon dioxide (CO 2) emission. This work gives a comprehensive description of the research trends and hotspots in the field of mineral carbonation for carbon storage based on bibliometric analysis. A total of 1507 articles were collected from the Web of Science database from 2010 to 2022 and analyzed in details, using a Citepace and VOSviewer software. Keyword cluster analysis indicates that research on mineral carbonation mainly involves natural minerals, industrial wastes, and cement-based materials. Research advances on carbon storage via mineral carbonation are summarized from the aspects of magnesium-based feedstocks and calcium-based feedstocks. Direct aqueous carbonation and indirect carbonation are the most promising methods. Mining tailings and industrial wastes are promising feedstocks for mineral carbonation. The slow kinetics and low carbonation capacity of feedstocks are the main obstacles for industrial application. Finally, challenges and prospects in mineral carbonation are put forward, which is conducive to its rapid and balanced development. This work provides the basis for the future development of cheap, efficient, and green large-scale mineral carbonation processes for carbon storage. [ABSTRACT FROM AUTHOR]

Traditional methods for designing concrete materials typically rely on labor-intensive laboratory experiments, resulting in time and cost inefficiencies. Recently, designing concrete using artificial intelligence (AI) methods has shown high efficiency, but existing AI methods often rely solely on data, which can lead to violation with scientific principles and result in models lacking reasoning abilities. To overcome these challenges, this paper presents an interpretable knowledge graph-guided data-driven design approach. By integrating advanced computing techniques with domain knowledge via knowledge graphs, this approach enables the interpretation of data-driven models and uncovers the underlying mechanisms behind predictions. This approach is applied to ultra-high-performance concrete (UHPC) involving complex physicochemical reactions. The domain knowledge about UHPC is imparted using a knowledge graph, and UHPC properties are predicted using a machine learning model considering mixing proportions, processing methods, and physiochemical properties of materials via natural language processing. The results show that the knowledge graph displays crucial design variables and their effects on UHPC properties, aiding in selecting variables for machine learning models and interpreting their results. The prediction accuracy of the machine learning model reached 0.95. The research paves the way for more transparent and scientific AI models for material design and AI-enabled discovery of scientific knowledge. [Display omitted] ● An artificial intelligence (AI) approach is presented to design concrete with solid wastes. ● The AI approach achieves interpretability by combining machine learning and knowledge graph. ● Knowledge about the physicochemical reactions and properties of concrete is learned and used. ● The AI approach is applied to low-carbon cost-effective ultra-high-performance concrete. ● The AI approach can interpret the underlying mechanisms and generate new knowledge. [ABSTRACT FROM AUTHOR]

C-S-H seeds are expected to be a new type of accelerator to cope with the challenges of reduced strength and poor durability of concrete in the later stage caused by high dosage of accelerator. In this study, two solid wastes, rice husk ash and carbide slag, were used as silicon and calcium sources to synthesize C-S-H seeds. By screening the particle size and solid content of C-S-H seeds, the optimum synthesis condition was determined to be stirring at 25 °C for 2 h. The average particle size of synthesized C-S-H seeds approximates this to 320 nm and was mainly composed of C-S-H gel, PCE and sodium nitrate. The effects of C-S-H seeds on the properties of cement paste were studied by experiments such as fluidity, setting time, compressive strength, heat of hydration, XRD, TG and MIP. The results showed that the addition of C-S-H seeds improved the fluidity of cement paste, shortened its setting time, accelerated its early hydration, especially the NG process, and significantly improved its early compressive strength. Meanwhile, it densified the cement paste and improved the compressive strength in the later stage. The C-S-H seeds synthesized in this study not only showed excellent acceleration, but also were based on solid waste as raw material, while the reaction time was short and the equipment requirements were low. • C-S-H seeds were synthesized from RHA and CS by co-precipitation method. • C-S-H seeds was mainly composed of C-S-H gel, PCE and sodium nitrate. • C-S-H seeds significantly accelerated the early hydration of cement paste. • The accelerating mechanism of C-S-H seeds on Portland cement was revealed. [ABSTRACT FROM AUTHOR]

The release of carbon dioxide (CO 2) into the earth's atmosphere is a substantial global environmental concern that arises from the processes of industrialization and urbanization. The increase in atmospheric CO 2 concentrations has resulted in the phenomenon of global warming and subsequent alterations in climate patterns. Accelerated CO 2 sequestration in cementitious materials is currently the subject of extensive research as a highly efficacious approach to mitigating the carbon footprint of the concrete industry. The sequestration procedure entails the transformation of gaseous CO 2 into carbonate minerals. The review presented in this paper outlines the most recent carbonation (i.e., CO 2 sequestration) techniques, such as mineral carbonation, accelerated CO 2 curing (ACC), pre-carbonation, and carbonation mixing, that have been recently explored. The potential of mineral carbonation of industrial wastes and the advantages of their incorporation in the concrete matrix is investigated. Carbonation technologies and their effect on the performance of cementitious composites are reported. Information on life cycle assessment are also included to evaluate the environmental impact associated with the production of carbonated materials. Various commercialized CO 2 utilization technologies in construction sector, such as CarbonCure, Solidia, Carbstone, Calera, and Carbon8 are reviewed. Moreover, this review offers a thorough insight into the carbonation technologies, evaluating their advantages, limitations, and the existing gaps in research. • Various carbonation techniques for CO 2 incorporation in concrete comprehensively reviewed. • Limitations and research gaps of carbonation technologies are discussed. • Potentials uses of CO 2 -mineralized industrial wastes in the concrete discussed. • Commercial CO 2 utilization technologies in the construction sector identified. • LCA of carbonated materials to ensure sustainable production practices presented. [ABSTRACT FROM AUTHOR]

Red mud, fly ash and waste sawdust are bulk solid wastes discharged from the alumina, power and wood processing industries respectively, and their increasing accumulation has brought serious hazards to the ecological environment and huge waste of secondary resources. A novel rapid roasting method was adopted to produce the ultra-lightweight ceramsites (ULC) using red mud, fly ash and waste sawdust in this work, and the various performances, microstructure and formation mechanism of ULC were investigated using FTIR, XRD, BET, SEM-EDS and Micro-CT. The fly ash significantly enhances the compressive strength of ULC by promoting the formation of small pores and FeAl 2 O 4 , and the increase in roasting temperature is beneficial for the expansion of ULC until they are over burning. As the mass ratios of red mud, fly ash, clay and waste sawdust are 46: 10: 36: 8, the ULC with a compressive strength of 2.25 MPa, a bulk density of 465 kg/m3 and a water absorption of 8.8% are prepared when roasted at 1125 ºC for 5 min after preheating at 600 ºC for 5 min. The environmental assessment results indicates that the ULC are environmentally safe due to the effective solidification of hazardous elements. This study provides a promising way to produce ULC by utilizing industrial solid wastes. • ULC was prepared by novel rapid roasting using red mud, fly ash and sawdust. • The performances and formation mechanism of ULC were investigated. • Fly ash promotes formation of small pores and FeAl 2 O 4 to enhance the strength. • The mesopores generated on the surface contribute to the low water absorption. • The relationship between the performances and microstructure was revealed. [ABSTRACT FROM AUTHOR]

Although solid waste is a good raw material for preparing foam ceramics, the mechanisms of the discrepancies in different solid wastes affecting the properties of foam ceramics remain unelucidated. In this study, the properties of tin tailings-based foam ceramics with different proportions of waste glass (WG) or scheelite tailings (ST) were measured. Significant discrepancies in the influence effects were observed, with higher closed porosity for added WG and higher apparent porosity for added ST. To interpret this phenomenon, the effects of the main fluxing agents of the ST and WG were investigated, and the results indicated that their influence effects were controlled by the type and content of the fluxing agent. Furthermore, the structure and crystalline phase of foam ceramics demonstrated that their compressive strength was jointly driven by their microstructure and crystal phases, but other properties depended only on the microstructure. The pore size and type were significantly affected by the change in liquid phase characteristics and aluminosilicate, with the addition of WG dramatically decreasing the number of pore windows and the addition of ST increasing the content of anorthite. Further sintering process analysis results revealed that the chemical reactions in materials change with chemical compositions, which resulted in significant differences in the crystalline compositions of the foam ceramics for WG and ST additions, and the presence of WG obviously reduced the formation temperature of the liquid phase. Overall, our research provides a theoretical basis for better utilizing different solid wastes to prepare foam ceramics. • Significant differences in the influence of WG and ST on properties were observed. • Fluxing agent play a vital role in the influence effects. • Crystalline phase and liquid phase characteristics of TW and TS were different. • Microstructure were driven by liquid phase characteristics and aluminosilicate. [ABSTRACT FROM AUTHOR]

• The activity index of solid waste based composites is higher than 95%. • Solid waste based composites can replace 40% cement in concrete. • The total amount of solid wastes in concrete is up to 83%. Waste rock is stripped from open pit iron mines, which is often used to prepare aggregate in concrete because of its stable performance. However, with the continuous improvement of aggregate performance, a vast amount of stone powder produced in the process of aggregate preparation causes secondary solid waste pollution. In this paper, the feasibility of preparing supplementary cementitious materials (SCMs) by using solid waste based composites was investigated. The results show that the 28-d activity index of iron ore waste powder (IOWP) based admixture is higher than 95%, and when it is used to replace cement in concrete, the admixture can reach 40% and the performance of concrete is stable. When iron ore waste completely replaces aggregates and IOWP based admixture replaces part of cement for concrete, the solid waste content of solid waste aggregate concrete (SWAC) is up to 83% compared to natural aggregate concrete (NAC). This study provides a new idea for high value, high efficiency and scale development of solid wastes. [ABSTRACT FROM AUTHOR]

• The composite cement (CC) is composed of 40 % clinker and 60 % solid wastes; • The increase of 28d strength of CC is very significant; • The carbon emission of CC is much lower than OPC. In search of a low-carbon cement that meets the requirements of engineering applications, the composite cement (CC) was prepared that using 60% solid wastes and 40% clinker (CL) in this research. Based on the optimized design, the particle size distribution of CC is more in line with the Fuller curve than P.O42.5 cement (OPC), with smaller inter-particle voids. The 7d strength of CC and hydration heat are lower than OPC, while the 28d strength increased significantly. The characteristics of CC meet the application requirements of plastering mortar. In terms of unit carbon emission, CC is about 51% of OPC, and the effect of carbon reduction is significant. [ABSTRACT FROM AUTHOR]

Conversion of solid wastes into useful remediation materials is an encouraging strategy in resource recovery. Iron oxide/carboxylate-rich porous carbon composites (IOCRPC) can be synthesized by using vinegar residue (VR) and ferrous sulfate heptahydrate (FeSO 4 ∙7 H 2 O) recovered from a waste acid of a titanium dioxide factory. Characterization of FeSO 4 -impregnated VR exhibited a high proportion of ferricarboxylate complexes [i.e. FeII(R-COO) n 2-n]. Pyrolysis temperature was the most important reaction parameter to define IOCRPC phase composition. Thermal decomposition of FeII(R-COO) n 2-n produced Fe 3 O 4 nanoparticles partly at a relatively lower pyrolysis temperature (350 ºC), while successful carbonization of VR formed the porous structures of carbon. Both Fe 3 O 4 and ferricarboxylate complexes were the components of IOCRPC responsible for its excellent visible light absorption ability. Under visible light, phenanthrene in contaminated soil was efficiently degraded (90.1%) by IOCRPC at circumneutral pH. Phytotoxicity bioassays demonstrated significant removal of toxicity after treatment with IOCRPC, highlighting its application potential in revegetation strategies. [Display omitted] • Vinegar residue and ferrous sulfate were used to synthesize IOCRPC. • IOCRPC was activated by visible light irradiation. • Phenanthrene-contaminated soil was remediated by IOCRPC at circumneutral pH. • Superoxide (O 2 •-) was the dominant reactive oxygen species released by IOCRPC. • Phytotoxicity of contaminated soil was significantly reduced by IOCRPC. [ABSTRACT FROM AUTHOR]

Fully utilizing regional resources such as marine sand, coral, and desert sand, along with a diverse range of solid wastes from industries, agriculture, and urban areas, not only effectively reduces the costs and carbon footprint of construction activities but also contributes to achieving sustainable development in the building sector. Despite earlier studies focusing on the feasibility of solid waste as lightweight aggregates, the comprehensive evaluation of the performance of alternative aggregates in such innovative materials as geopolymers and ultra-high-performance concrete remains significantly limited amid their rapid development. Therefore, this paper concentrates on a thorough exploration of regional sand and gravel resources, as well as efficient and value-added approaches to incorporating solid wastes from industries, agriculture, and urban areas as alternative aggregates in construction. It provides a comprehensive review of the physical properties of alternative aggregates and their impacts on the workability, mechanical properties, and durability of concrete. Additionally, the paper offers a detailed assessment of the production processes and performance of sintered and cold-bonded artificial aggregates. This research provides valuable insights for researchers and practitioners in the fields of construction, sustainable waste management, resource conservation, and recycling. • Regional resources, industrial and agricultural and urban solid wastes are used as clean aggregates. • Potential legal challenges to the use of clean aggregates are revealed. • Reviewed the modification methods of granular solid waste. • Reviewed artificial agglomeration techniques and potential challenges for powdered solid waste. [ABSTRACT FROM AUTHOR]

Geopolymers are novel aluminosilicate inorganic polymers. The preparation of geopolymers has the potential to minimize the environmental impacts of solid wastes through a reduction in both resource depletion and pollution. Owing to their high mechanical performance, resource/energy conservation, and low-carbon emission, waste-based geopolymer materials (WGM) have attracted increasing attention in recent years. This paper reviews the research and application of WGM in solid waste disposal, wastewater treatment, and greenhouse gas emission reduction. The potential raw materials for producing WGM from available solid wastes are classified into three categories, highlighting significant differences among these wastes. Moreover, this paper comprehensively reviews the current status of WGM with different forms and functions used in the wastewater treatment field, along with their effect mechanisms. Additionally, this paper extensively elucidates the significant contributions of WGM in reducing greenhouse gas emissions. The wide range of raw materials, multifunctionality for water treatment, and low greenhouse gas emission characteristics of WGM ensure its practical and economically feasible application as an environmentally functional material. Owing to these characteristics, this paper outlines the future development prospects of WGM, further highlighting its advantages in preparation and practical application. This review provides references for addressing future challenges and promoting the development of WGM, contributing to its accelerated application in sustainable development and environmental protection. • WGM has great potential for the disposal and high value-added utilization of solid waste from different fields. • Based on the functional diversity, WGM has shown significant advantages in wastewater treatment. • GHG emission characteristics of WGM in application determine it is a low carbon material. [ABSTRACT FROM AUTHOR]

Geopolymer is considered the most promising alternative to Portland cement due to its excellent performance and low cost. In this study, the hydration mechanism of red mud-fly ash based geopolymer (RFG) was analyzed using low-field nuclear magnetic resonance (LNMR), rheological tests, Fourier transform infrared spectrometry (FT-IR), isothermal calorimetry, and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS). The compressive strength of RFG falls with increasing dosages of red mud, and initially increased and subsequently decreased with the increment of SiO 2 /Na 2 O ratio. According to the results of LNMR and rheological tests, the geopolymerical hydration process of RFG is divided into three phases: an induction phase, an acceleration phase, and a stabilization phase. When the SiO 2 /Na 2 O ratio of the activator is lower than 2.4, it has an activation effect on the cementitious material, and the optimal value is 2.1. The hydration rate of the cementitious material decreases as the dosage of red mud is increased. The slurry transitions from the Herschel-Barkley model to the Bingham fluid model as the hydration reaction advances. The hydration products is verified with different red mud dosage and SiO 2 /Na 2 O ratio by SEM-EDS. The findings of this study enrich our understanding of RFG, promote its engineering applications, and improve the utilization efficiency of red mud. • The utilization of solid wastes such as coal gangue are solved. • The preparation process system of coal gangue based geopolymer was improved. • The effects of particle size on coal gangue based geopolymer were analyzed. • The effects of thermal activation on coal gangue based geopolymer were analyzed. [ABSTRACT FROM AUTHOR]

Facing the challenges of natural aggregate sustainability and carbon neutrality, a novel low-carbon and high-strength core-shell aggregate (CSA) was developed in this study by cold-bonding with solid wastes. The developed CSA was characterized by crushing strength (CS), loose bulk density (LBD), water absorption (WA), and analyzed by hydration heat, pore properties, and then evaluated by carbon footprint assessment for comparing with the common artificial lightweight aggregates. The results showed that a water/binder ratio of 0.21 for the CSA production restricted the cement hydration, which provided a chance to reduce the cement usage by replacing it with GGBS and FA for low carbon purposes. Compared with FA, GGBS was more suitable for replacing cement in producing CSA because of its better micro-aggregate effect and secondary volcanic ash reaction for promoting hydration and optimizing pore structure. The pelletization CO 2 emission (COE) for the CSA production only ranged from 4.2% to 11.9% of the total COE, which proved the green feature of cold-bonding in producing CSA. Replacing cement with 0–80% GGBS decreased the COE from 578.9 kg to 188.1 kg for 1 ton of CSA production. The CSA with 80% GGBS developed in this study attained CS of 7.68 MPa, LBD of 843 kg/m3, and WA of 17.8%, which showed much higher strength efficiency of 9110 Pa·m3/kg and much lower COE of 188.1 kgCO2 eq/t than the common artificial lightweight aggregates. • A low-carbon high-strength aggregate was developed by cold-bonding waste with LCA analysis. • A core-shell structure of the aggregate was designed for lightweight and high strength. • GGBS and FA was utilized to replace OPC for low carbon and keep performance. • Hydration heat and pore features were analyzed to explain the physical properties. [ABSTRACT FROM AUTHOR]

In the context of contaminated soils and industrial solid waste utilizations, a low-carbon curing agent (RAS) was synthesized in this study using red mud (RM), blast furnace slag (GGBS), calcium carbide residue (CCR), and phosphogypsum (PG) for solidification/stabilization (S/S) of cadmium (Cd)-contaminated soils. The effects of Cd contents, RAS dosages, and curing times on the strength and leaching properties of the solidified/stabilized soil were investigated in this study. In addition, the main mechanisms governing the RAS-based S/S of the Cd-contaminated soil were revealed using an improved four-step extraction method (BCR), mercury intrusion porosimetry (MIP), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results showed that the RAS binder significantly enhanced the compressive strength and Cd chemical stability of the Cd-contaminated soil, thereby reducing Cd2+ leaching amounts and soil porosity. The soil strength and Cd2+ leaching amounts from the solidified/stabilized soil met their corresponding standards after 14 days of curing. The main products of the solidified/stabilized soil consisted of Cd precipitates, ettringite (AFt), and calcium silicate hydrate (C–S–H). Their contents were related to the initial soil Cd content, RAS dosage, and curing time. The Cd precipitate, C–S–H, and AFt products can not only fill inter-particle voids of the soil but also exhibit physical encapsulation, surface complexation, co-precipitation, electrostatic adsorption, and ion exchange effects on Cd. The results of this study can provide a novel approach for treating and utilizing solid wastes and an environmentally friendly, economical, and efficient curing agent for the remediation of Cd-contaminated soils. • RAS, a sustainable by-product-based curing agent is developed. • RAS improves the strength but reduces the leachability of contaminated soil. • The solidification/stabilization mechanism of RAS was investigated. • Cadmium content, curing time, and RAS dosage are investigated for soil stabilization/solidification. [ABSTRACT FROM AUTHOR]

Designing easy and sustainable strategies for the synthesis of metal-organic frameworks (MOFs) from organic and inorganic wastes with the efficient removal of phosphate from water remains a challenge. The majority of the reported works have utilized costly precursors and nonsoluble ligands for the synthesis of MOFs. Herein, we have developed a low-cost, simple, and sustainable alternative approach using the coprecipitation method in water at room temperature for the synthesis of a new adsorbent-based trimetallic MOF. Poly(ethylene terephthalate) and stainless steel wastes were used as sources of water-soluble disodium terephthalate ligand and three metallic species (chromium, nickel, and iron salts) for the fabrication of trimetallic MOF (CrNiFe-MOF), respectively. The newly developed MOF demonstrates a superior space-time yield of 5760 g m -3 day -1 , reaching a level allowing the industrialization production of this sustainable MOF. The scanning electron microscopy and adsorption studies revealed that the developed trimetallic MOF consists of aggregated nanoparticles and the presence of defective as well as mesoporous structures. This MOF showed an enhanced adsorption capacity of phosphate from real eutrophic water samples and higher stability in a range of pHs. The density functional theory calculations evidenced that the phosphate ions preferentially adsorb over H 2 O toward the metal oxo-trimers, with the adsorption energies increasing from H 3 PO 4 to PO 4 3- species in line with an improvement of the adsorption performance of CrNiFe-MOF when the pH increases, i.e., when HPO 4 2- and PO 4 3- become more predominant. These calculations also supported that the incorporation of Cr metal sites in the oxo-trimer is expected to boost the phosphate affinity of the MOF. Finally, our work provides an easy and eco-friendly approach for MOF designing to enhance phosphate removal from water.