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This study developed a novel geopolymer (RM-SGP) using industrial solid wastes red mud and slag activated by sodium silicate, aiming to remediate composite heavy metal contaminated soil. The effects of aluminosilicate component dosage, alkali equivalent, and heavy metal concentration on the unconfined compressive strength (UCS), toxicity leaching characteristics, resistivity, pH, and electrical conductivity (EC) of RM-SGP solidified composite heavy metal contaminated soil were systematically investigated. Additionally, the chemical composition and microstructural characteristics of solidified soil were analyzed using XRD, FTIR, SEM, and NMR tests to elucidate the solidification mechanisms. The results demonstrated that RM-SGP exhibited excellent solidification efficacy for composite heavy metal contaminated soil. Optimal performance occurred at 15 % aluminosilicate component dosage and 16 % alkali equivalent, achieving UCS >350 kPa and compliant heavy metal leaching (excluding Cd in high-concentration groups). Acid/alkaline leaching tests revealed distinct metal behaviors: Cu/Cd decreased progressively, while Pb initially declined then rebounded. Microstructural analysis indicated that RM-SGP generated abundant hydration products (e.g., C-A-S-H, N-A-S-H gels), which acted as cementitious substances wrapping soil particles and filling and connecting pores, thereby increasing the soil's compactness and improving the solidification effect. Furthermore, heavy metal ions were solidified through adsorption, encapsulation, precipitation, ion exchange, and covalent bond et al., transforming their active states into less bioavailable forms, proving novel insights into the remediation of composite heavy metal contaminated soils and the resource utilization of industrial solid wastes.

期刊论文 2025-08-08 DOI: 10.1016/j.conbuildmat.2025.141996 ISSN: 0950-0618

The remediation and management of old municipal solid waste (MSW) landfills are pivotal for advancing urban ecological sustainability. This study aims to systematically assess the mechanical properties, environmental behaviors, and synergistic mechanisms of remediated landfill-mined soil-like material (SLM) through advanced oxidation and stabilization processes. The results indicate that synergistic remediation with advanced oxidation and stabilization processes significantly increased the mechanical strength of stabilized SLM to over 0.6 MPa, and reduced the organic content by about 20 %, making it suitable for reuse in geotechnical engineering. The choice of oxidizing agents markedly affected the mechanical properties of stabilized SLM; for example, the application of sodium percarbonate in conjunction with stabilized materials further enhances the strength by simultaneously promoting the pozzolanic reaction. Furthermore, the heavy metal leaching behaviors of the stabilized SLM were found to be environmentally safe. The enhanced performance of stabilized SLM is primarily attributed to the synergistic effects of oxidation and pozzolanic reactions. The advanced oxidation process decreases organic matter content and increases its stability by reducing the proportion of readily decomposable O-alkyl C. Concurrently, pozzolanic reactions produce ettringite crystals and C-(A)-S-H gels, which not only fill micropores and improve particle bonding but also aid in heavy metal immobilization through surface adsorption, complexation, and physical encapsulation. These insights provide a comprehensive understanding of the remediation processes and resource recovery potential of SLM from old MSW landfills.

期刊论文 2025-06-01 DOI: 10.1016/j.psep.2025.107162 ISSN: 0957-5820

The solidification effect of contaminated soil degrades under wet-dry (W-D) cycles and acid rain. Acidic dry-wet cycle tests for Cr-contaminated soil solidified by alkali-activated granulated blast furnace slag (GGBS) are carried out. Toxic leaching test and accelerated leaching test are performed to study the leaching characteristic and mechanism. Scanning electron microscopy and energy spectrum analysis are used to investigate the microscopic mechanism. The long-term stability is evaluated through the apparent diffusion coefficient. The results show that a few W-D cycles at pH=7 will cause additional hydraulic reaction of GGBS and thus reduce the leaching concentration of total Cr and Cr(VI). Along with W-D cycles more AFt is generated. The expansion of AFt results in micro-fracture and thus more Cr leaching. In acidic W-D cycles, AFt dissolves first, releasing Cr immobilized by ion exchange. With the increasing acidity, C-S-H gels dissolve and more gypsum is generated, resulting in more micro-fractures. Consequently, the encapsulation effect weakens, resulting in more Cr leaching. However, the C-A-S-H gels remain stable. The slopes of the logarithmic curves of cumulative leached fraction versus time range from 0.373 to 0.675. The errors of fitting by a pure-diffusion analytical solution are mainly below 0.5%, indicating that diffusion is the dominant leaching mechanism. However, after 18 W-D cycles at pH=3, the effect of dissolution increases and the diffusion-dominated criteria are not satisfied. The mobility of Cr under neutral, weak acidic, and strong acidic W-D cycles is low, moderate, and high, respectively. It is necessary to take measures to reduce acid rain infiltration and W-D cycles when utilizing solidified soil. This research provides a reference for evaluating the long-term stability of solidified contaminated soil.

期刊论文 2025-04-01 DOI: 10.16285/j.rsm.2024.0861 ISSN: 1000-7598

The preparation of geopolymer for solidification/stabilization of heavy metal contaminated soils using industrial solid waste was a sustainable method. In this study, a binary geopolymer curing agent was synthesized from red mud and fly ash for the treatment of copper- and cadmium- contaminated soils. The changes in the properties of the cured soil were investigated by analyzing compressive strength, permeability coefficient, pH value, toxicity leaching, and the chemical forms of heavy metals. These parameters were examined under varying amounts of curing agent and curing time. The solidification mechanism of contaminated soil was revealed by microscopic experiments such as X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that geopolymer could significantly improved the mechanical properties and environmental safety of contaminated soil. Compressive strengths of Cu and Cd contaminated soils after 28d of curing with 30 % geopolymer were 1.27 and 1.44 MPa, the permeability coefficients were 4.2 and 3.8-6cm/s, and toxic leaching amounts of Cu2+ and Cd2+ were 4.8 and 0.21 mg/L, and pH values were 10.9 and 10.6, respectively. Geopolymer gel structures not only filled the voids between soil particles but also physically encapsulated, chemically bonded, precipitated and ion-exchanged to achieve solidification/stabilization of contaminated soils. This research provided a new technology for the management of heavy metal contaminated soil and promoted the sustainable use of industrial solid waste.

期刊论文 2025-03-28 DOI: 10.1016/j.conbuildmat.2025.140515 ISSN: 0950-0618

Featured Application Incorporating phosphogypsum and sediment into subgrade material for pavement construction offers a promising solution for waste management and resource conservation while potentially enhancing the performance and cost-effectiveness of pavement systems.Abstract (1) Background: The construction industry continuously seeks sustainable alternatives to traditional materials for subgrade material in pavement construction, aiming to mitigate environmental impact while maintaining performance standards. This study investigates the feasibility of incorporating phosphogypsum (PG) and contaminated sediment into subgrade materials, focusing on their physico-chemical and physico-mechanical properties. (2) Methods: The physico-chemical and physico-mechanical properties, performance, and mechanisms of solidified sediment with phosphogypsum (3% and 5% of phosphogypsum in mixture) were studied using long-term leaching tests (ANS 16.1), uniaxial compressive strength (UCS), California Bearing Ratio (CBR), X-ray fluorescence (XRF), and thermogravimetric analysis (TGA). (3) Results: Based on the pseudo-total metal content (Cr, Ni, Cu, Zn, As, Cd, Pb), the sediment is classified as third- and fourth-class, indicating it is polluted and requires treatment before disposal in the environment. To assess the long-term behavior of the sediment treated with phosphogypsum (S/S), a semi-dynamic ANS 16.1 leaching test was performed. The results showed that the metals exhibit moderate mobility, with average diffusion coefficients (De) ranging from 10-8 cm2/s for Zn (in both mixtures) to 10-12 cm2/s for Cr (in mixture F-3). The leaching index (LX) values for both mixtures were above 9 for most metals, confirming their suitability for controlled use. Granulometric analysis indicated a predominance of fine particles, which enhances the material's plasticity and mechanical properties. Atterberg consistency tests showed that increasing phosphogypsum content improved both the Liquid Limit and Plastic Index. However, UCS tests indicated that neither the 3% nor 5% phosphogypsum mixtures met the minimum strength requirements for subgrade material. On the other hand, CBR values demonstrated promising performance, with 12.5% for the 3% phosphogypsum mixture and 22.9% for the 5% phosphogypsum mixture. Overall, phosphogypsum positively influenced the strength development of the sediment-PG mixtures, as confirmed by XRF and TGA analyses. (4) Conclusions: Environmental considerations, such as leachability of contaminants, were investigated to ensure the sustainability of the proposed subgrade materials. Leaching tests indicated minimal pollutant release, suggesting the potential for safe utilization of PG and sediment in subgrade material. This study provides valuable insights into the physico-chemical and physico-mechanical properties of pavement mixes incorporating PG and sediment, supporting the feasibility of using these alternative materials in sustainable subgrade material for pavement construction and offering a viable solution to mitigate waste generation while enhancing pavement performance.

期刊论文 2025-01-01 DOI: 10.3390/app15010347

To prevent the transmission of airborne infectious diseases (SARS, H1N1, COVID-19, and influenza), the use of disposable surgical face masks has increased dramatically in the past few years. To mitigate the environmental consequences associated with mask waste, implementing circular economy strategies with the reuse of mask waste is a sustainable method. This study explores an innovative way to reuse mask fiber (MF) with dredged sediment waste together as road construction materials. First, the MF was introduced into cement-treated/ untreated dredged marine sediment mixtures with different content and lengths. Then, a variety of laboratory tests were carried out to explore the basic physical and chemical characterization of raw materials and the development of mechanical properties of mixtures. In addition, the intrinsic mechanism of MF inclusion on cement-treated sediments was analyzed by scanning electron microscope (SEM) test. The results show that the inclusion of MF significantly improves the unconfined compression strength (UCS) and splitting tensile strength (STS) of both treated and untreated specimens. The highest UCS and STS values are at the condition with an MF content of 0.25%, a length of MF of 2 cm, and a curing time of 28 days. The combined strength increase caused by cement-MF together inclusion is much greater than the strength increase caused by either of them separately. It was also found that the elastic modulus (E50) decreased with the inclusion of MF. Furthermore, the addition of MF changes the brittle behavior of the specimens, which also improves the ductility and residual strength of the specimens. The SEM analysis demonstrates the microstructure of MF and MF-reinforced specimens. The creation of a stable and interconnected microstructure is largely attributed to the bridging impact of MF and the binding effect of hydration products, which significantly improves the mechanical behavior of specimens. The MFreinforced cement-treated sediment could be an innovative, environmentally friendly, and economical material for road construction.

期刊论文 2024-10-25 DOI: 10.1016/j.conbuildmat.2024.138450 ISSN: 0950-0618

Lead (Pb2+) and cadmium (Cd2+) are common heavy metal pollution, which is harmful to humans and animals. However, the diffusion rate of heavy metal ions moves faster in acidic environment, there are a large number of acidic heavy metal polluted soil in China, but the conventional binders are not effective to deal with them. Phosphate-based geopolymers (PGEOs) are acidic materials, and have excellence mechanical properties in acidic environment and solidification/stabilization (S/S) effect on Pb2+, but the applicability of PGEOs to Cd, Pb and Cd composite pollution is not clear. Therefore, this study discusses the applicability of PGEOs fabricated from fly ash (FA) and aluminum dihydrogen phosphate (ADP) as activator for S/S treatment of Cd, Pb-Cd composite pollution. Results show that the influence of Cd2+ and Pb2+ on the compressive strength of PGEOs was inconsistent, as the Cd2+ content raised, the compressive strength reduced slightly at 7 and 14 days, but it did not change basically at 28 days. However, the compressive strength rose firstly and then declined with an increase in Pb-Cd content when partial Pb2+ was used to replace Cd2+. The compressive strength of PGEOs with a Pb-Cd content of 0.6 % reached maximum (11.45 MPa), exceeding the compressive strength of PGEOs containing Cd2+. Moreover, the PGEOs presents an excellent stabilization effect on Pb2+, but poor effect on Cd2+. The Pb2+ leaching concentration meet the hazardous solid waste identification criteria (<5 mg/L), but the Cd2+ leaching is high and is more than 1 mg/L. Furthermore, the compressive strength of PGEOs had a good correlation with pH and EC. The S/S mechanism of PGEOs for Pb2+, Cd2+ includes physical adsorption, encapsulation, and chemical precipitation. However, Pb2+ involved in the geopolymerization process, while Cd2+ can not participate in the structure formation, so the PGEOs have a poor S/S effect. Therefore, it needs to be further improved when using PGEOs to stabilize acidic Cd2+ contaminated soil.

期刊论文 2024-10-01 DOI: 10.1016/j.jece.2024.113846 ISSN: 2213-2929

Mudflat sediments can pose dual challenges of engineering diseases and pollution risks due to unfavourable mechanical performances and potential heavy metal enrichment, impacting coastal engineering construction, ecological environments, and human health. Commonly used Portland cement has significant restrictions in ensuring mechanical stability and environmental sustainability during the remediation of heavy metalcontaminated mudflats. This study investigates a novel approach using chitosan-enhance alkali-activated geopolymer (CS-AGP), composed of slag, fly ash, and desulphurised gypsum, for solidifying/stabilizing highly toxic and concentrated Cu-/Cr(VI)-polluted sediments. The unconfined compressive strength, durability, and leaching toxicity of these sediments are assessed across varying binder incorporations, contamination concentrations, curing periods, and dry-wet cycles. The results demonstrate that the CS-AGP remarkedly increases both early and long-term strength as well as environmental stability of Cu-/Cr(VI)-polluted sediments, even after suffering serious dry-wet alternations and pollutant accumulation, far surpassing the USEPA strength criterion (0.35 MPa) for safe landfill and suiting for in-situ engineering applications. Moreover, the CS-AGP solidified/stabilized contaminated sediments exhibit excellent acid resistance and minimal environmental risk and leaching concentrations meet Cu <= 1.5 mg/L and Cr(VI) <= 0.1 mg/L, as these metals primarily redistribute to the residual fraction. Microstructure evolution reveals CS-AGP generates significant amounts of calcium silicate hydrate, calcium aluminium silicate hydrate, and ettringite to compact sediment skeleton structures, which is the improvement source of mechanical performance. Simultaneously, the comprehensive physical encapsulation, chemical bonding, and coordination effects promote the transformation of Cu/Cr(VI) into a low availability state. The study offers new insights for efficient remediation and safe development of coastal mudflats.

期刊论文 2024-10-01 DOI: 10.1016/j.jece.2024.113408 ISSN: 2213-2929

The existing binders are difficult to be compatible with the acidic environment of acidic heavy metal contaminated soil, it is hard to repair acidic heavy metal contaminated soil. In this study, a modified acid phosphorusbased geopolymer (MAPG) binder suitable for the solidification/stabilization (S/S) treatment of acidic heavy metal Pb2+ contaminated soil was fabricated using aluminum dihydrogen phosphate (ADP) as activator, fly ash and metakaolin (MK) as raw materials. The influences of liquid-solid ratio (L/S), MK content, ADP concentration, curing age and leaching environment on the compressive strength, toxic leaching, resistivity, pH and EC of MAPG stabilized acidic Pb2+ contaminated soil were studied. Meantime, the X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, and mercury intrusion (MIP) experiments were used to study the chemical properties and microscopic performance of MAPG treated acidic Pb2+ contaminated soil. The results showed that the MAPG binder prepared from MK had an excellent S/S effect on the acidic Pb2+ contaminated soil, and the MAPG binders had good compatibility with the acidic environment. The compressive strength of each group of MAPG stabilized soil could meet the strength standard (>350 kPa) for solid waste landfill and Pb2+ leaching concentration is < 5 mg/L for toxicity identification criteria after 7 days of curing. With an increase in curing age, the strength of stabilized acidic contaminated soil decreased slightly, but the strength still met the requirements of landfill strength standard after 28 days of curing. In three different leaching environments, the Pb2+ leaching decreased with an increase in curing age. Microscopic analysis showed that the main crystalline compounds in stabilized contaminated soil were potassium feldspar, Berlinite and lead phosphate compounds, and their contents were related to L/S, MK content, ADP concentration, and curing time. Potassium feldspar, berlinite, and lead phosphate compounds could not only fill pores, but also had physisorption, encapsulation and chemical precipitation effects on Pb2+. The study could provide an economical, environmental friendly and efficient binder for the remediation of acidic Pb(2+ )contaminated soil, but the further investigation into the long-term effectiveness of the MAPG binder or its applicability to other types of contaminated soil is also needed.

期刊论文 2024-09-15 DOI: 10.1016/j.cej.2024.154336 ISSN: 1385-8947

Among different types of heavy metal-contaminated soil, copper (Cu)-contaminated soil is very serious, and the Cu concentration in it is usually very high. It is common to solidify/stabilize Cu-contaminated soil using alkaline cementitious material. However, the remediated Cu-contaminated soil fails to meet the requirements of environmental safety and load-bearing capacity. This dilemma in the remediation of Cu-contaminated soil hinders the effective utilization of land resources. In this study, epoxy resin (EP) was utilized to solidify/stabilize Cu contaminated soil due to its stable and rapid curing performance and excellent resistance to acid, alkali, and salt erosion. The mechanical properties, environmental effects, and curing mechanism of EP-cured Cu -contaminated soil were investigated. The results showed that the application of EP significantly enhanced the unconfined compressive strength (UCS), cohesion and internal friction angle of Cu-contaminated soil. All specimens met the UCS criterion specified by the United States Environmental Protection Agency (USPEA), namely no less than 0.35 MPa, which indicated that those EP-cured Cu-contaminated soil were qualified for practical engineering applications. According to the toxicity characteristic leaching procedure (TCLP), the application of EP enhanced the stability of Cu in Cu-contaminated soil. The leaching index of Cu ranged from 11 to 14. A high leaching index showed that the S/S treatment was safe and effective and the remediated Cu-contaminated soil satisfied the environmental requirement for heavy metals. This study confirmed the feasibility of utilizing EP in the solidification/stabilization (S/S) technology to convert high-concentration Cu-contaminated soil into secure and stable engineering materials. The remediation of Cu-contaminated soil by EP lays a solid foundation for the safe treatment and reuse of heavy metal-contaminated land resources.

期刊论文 2024-01-01 DOI: 10.1016/j.envres.2023.117512 ISSN: 0013-9351
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