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Tang P, Javadi AA, Vinai R. Sustainable utilisation of calcium-rich industrial wastes in soil stabilisation: Potential use of calcium carbide residue. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2024; 357:120800. [PMID: 38579471 DOI: 10.1016/j.jenvman.2024.120800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 03/27/2024] [Accepted: 03/28/2024] [Indexed: 04/07/2024]
Abstract
Calcium carbide residue (CCR), a by-product of the acetylene industry, is generated at a rate of 136 million tonnes per year, posing significant environmental risks. This review examines the potential utilisation of CCR in soil stabilisation, focusing on its stabilisation mechanism, performance in improving mechanical properties, environmental safety, and sustainability. The aim is to identify future research directions for CCR-based stabilisation to promote its broader application, and to provide references for managing similar Ca-rich wastes. CCR-based materials demonstrate promising benefits in enhancing various soil properties, such as uniaxial strength, swelling properties, triaxial shear behaviour, compressibility, and dynamic responses, while also reducing the mobility of contaminants. Compared to conventional stabilisers, CCR-based materials exhibit comparable performance in soil improvement, environmental impact and safety, and economic feasibility. However, further research is required to delve deeper into stabilisation mechanisms, mechanical properties, and stability of contaminants for the soil treated with CCR-based materials under diverse conditions.
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Affiliation(s)
- Panpan Tang
- Department of Engineering, University of Exeter, Exeter, United Kingdom.
| | - Akbar A Javadi
- Department of Engineering, University of Exeter, Exeter, United Kingdom
| | - Raffaele Vinai
- Department of Engineering, University of Exeter, Exeter, United Kingdom
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2
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Deng T, Fisonga M, Ke H, Li L, Wang J, Deng Y. Mixing uniformity effect on leaching behaviour of cement-based solidified contaminated clay. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 908:167957. [PMID: 37866593 DOI: 10.1016/j.scitotenv.2023.167957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/18/2023] [Accepted: 10/18/2023] [Indexed: 10/24/2023]
Abstract
Mixing uniformity is essential for the quality control of the contaminated clay's solidification. To investigate the effect of the mixing uniformity on the leaching behaviour of the cement-based solidified contaminated clay, this study proposed a quantitative method to characterize the mixing uniformity and investigated the leaching behaviour by the leaching toxicity tests and semi-dynamic leaching tests. X-ray computed tomography (X-CT) was employed to reveal the internal mesoscopic structure. In this case, Pb2+ was selected as a tagged pollutant because of the widespread attention at heavy metal-contaminated sites. The leaching toxicity indicates the significant Pb2+ concentration deviation among the parallel specimens and non-association with the mixing uniformity. However, the Pb2+ cumulative leaching mass and observed diffusion coefficient by the semi-dynamic leaching tests both decrease with the mixing uniformity. X-CT image analysis reveals that the high cement zones wrap the low cement zones with different dimensions in the heterogeneous solidified matrix. Moreover, the specimen pretreatment method in the existing leaching toxicity standards may be inadequate because of the overall encapsulation destruction by the crushing process and representativeness uncertainty when sampling. However, for semi-dynamic leaching, the Pb2+ migration depends on the uniformity, reflecting the continuous distribution of high cement zones.
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Affiliation(s)
- Tingting Deng
- Institute of Geotechnical Engineering, School of Transportation, Southeast University, Nanjing 211189, China
| | - Marsheal Fisonga
- Institute of Geotechnical Engineering, School of Transportation, Southeast University, Nanjing 211189, China
| | - Han Ke
- School of Civil Engineering, Zhejiang University, Hangzhou 310058, China
| | - Ling Li
- CECEP DADI Environmental Remediation Co., Ltd., Beijing 100085, China
| | - Jianwei Wang
- CECEP DADI Environmental Remediation Co., Ltd., Beijing 100085, China
| | - Yongfeng Deng
- Institute of Geotechnical Engineering, School of Transportation, Southeast University, Nanjing 211189, China.
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Yang Z, Zhang K, Li X, Ren S, Li P. The effects of long-term freezing-thawing on the strength properties and the chemical stability of compound solidified/stabilized lead-contaminated soil. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:38185-38201. [PMID: 36576635 DOI: 10.1007/s11356-022-24881-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 12/16/2022] [Indexed: 06/17/2023]
Abstract
Solidification/stabilization (S/S) is the prevalent remediation technology for the treatment of heavy metal contaminated soils (HMCS). However, under the stress of complex surrounding environments, S/S effectiveness tends to deteriorate and freezing-thawing is one of the most influential natural forcings. The different proportions of cement, lime, and fly ash were used as the compound curing agents to treat solidified/stabilized HMCS with varying levels of lead contamination. The resulting samples were subjected to up to 180 freeze-thaw cycles (F-T) (1 day per cycle). Unconfined compressive strength (UCS) tests and semi-dynamic leaching tests were performed after F-T to explore the strength evolution of compound solidified/stabilized lead-contaminated soils (Pb-CSCS) and the chemical stability of the lead within. The results show that the F-T duration changes the strength deterioration mechanism of Pb-CSCS under F-T. There has been a shift in the main influencing factor from the promoted curing agent hydration by short-term F-T to the structural damage of the specimen induced by prolonged F-T. The variations in leachate pH, lead leachability, and diffusion ability with progressing F-T revealed a degradation effect of the changes in the physical states of water and crack propagation brought by F-T. These unfavorable changes in soil structure and chemistry reduce the acid resistance of Pb-CSCS. Notably, fly ash and cement facilitate the strength maintenance of Pb-CSCS under long-term F-T conditions. Curing formulations that included both cement and fly ash significantly increased the UCS of treated soils by up to 80.5% (3 F-T) under short-term F-T. In contrast, the curing formulation without fly ash lost 51.8% of its strength after 180 F-T conditions. For lead stabilization, cement and especially lime are favored. The results showed a 25% increase in the total proportion of lime and cement in the curing agent formulation, leading to a 41.4% reduction of lead leaching risk.
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Affiliation(s)
- Zhongping Yang
- School of Civil Engineering, Chongqing University, Chongqing, 400045, China
- Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China
- National Joint Engineering Research Centre for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing, 400045, China
| | - Keshan Zhang
- School of Civil Engineering, Chongqing University, Chongqing, 400045, China
- Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China
- National Joint Engineering Research Centre for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing, 400045, China
| | - Xuyong Li
- School of Civil Engineering, Chongqing University, Chongqing, 400045, China.
- Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China.
- National Joint Engineering Research Centre for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing, 400045, China.
| | - Shupei Ren
- School of Civil Engineering, Chongqing University, Chongqing, 400045, China
- Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China
- National Joint Engineering Research Centre for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing, 400045, China
| | - Peng Li
- School of Civil Engineering, Chongqing University, Chongqing, 400045, China
- Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China
- National Joint Engineering Research Centre for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing, 400045, China
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Rozbahani M, Goodarzi AR, Lajevardi SH. Coupling effect of superfine zeolite and fiber on enhancing the long-term performance of stabilized/solidified Pb-contaminated clayey soils. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:4203-4218. [PMID: 35965302 DOI: 10.1007/s11356-022-22453-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 08/05/2022] [Indexed: 06/15/2023]
Abstract
The focus of the present study was on the applicability of superfine zeolite (SZ) and polypropylene fibers in improving the geo-environmental parameters as well as the durability of cement-based stabilized/solidified low plasticity clay containing different dosages of Pb. The leaching data revealed that while adding a low range (≤ 7.5%) of sole cement even in the severely polluted soils could fully eliminate the Pb bioavailability, the metal retention capacity might portray a marked sensitivity to the acid-washing process. A major reduction was also observed in the mechanical/leaching performance of those samples after undergoing the wetting-drying (w-d) cycle, especially at a high proportion of Pb, which could weaken the cementation bonding dramatically; hence, much more cement was needed to pass the required stabilization/solidification (S/S) standards. Besides, the micro level tests indicated that the application of SZ (with 25% cement replacement) would alleviate the Pb declining impact on the S/S reactions and modify the porous network of soil. As a result, the specimens amended by cement-SZ (CSZ) were more functional (~ 1.4 times) in immobilizing the toxic ions than the cement alone was. However, the CSZ admixture might not perfectly restrain the w-d forces/deteriorations. Such a potential drawback was found to be solvable by the insertion of fiber, in which case, an enhancement in the ductility and the metal capsulation could be also manifested. In fact, the CSZ/fiber treatment could form a well-intertwined matrix, showing high success rates in stabilizing/solidifying the contaminated soils alongside a significant decrease (~ 2-folds) in the quantity of needed amount of cement to give the S/S satisfactory operation under the harsh environmental conditions.
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Affiliation(s)
- Mazaher Rozbahani
- Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran
| | - Amir Reza Goodarzi
- Faculty of Engineering, Hamedan Branch, Islamic Azad University, Hamedan, Iran.
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Effects of Temperature on the Leaching Behavior of Pb from Cement Stabilization/Solidification-Treated Contaminated Soil. SEPARATIONS 2022. [DOI: 10.3390/separations9120402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Solidification/stabilization (S/S) is one of the most widely used techniques in the disposal of heavy-metal-contaminated soil, though the long-term effectiveness of S/S technology remains implicit. Temperature is an important factor affecting the leaching behavior of heavy metals and the long-term effectiveness of S/S treatment. This study systematically explored the influence of temperature on the leaching behavior of lead in an S/S monolith through semi-dynamic leaching test at different temperatures. The results showed that an increase in temperature could accelerate the leaching concentration and cumulative leaching amount of lead ions in the S/S monolith. The cumulative leaching amount of lead ions in the S/S monolith after 11 days at 55 °C was about 5.8 times that at 25 °C. The leaching rate of lead ions in the S/S monolith increased with the increase in temperature. The leaching index of lead ions was larger than 9, which met the requirements for “controlled utilization” in the environment. The leaching mechanism of lead ions was diffusion control and did not change in the temperature range of 25–55 °C. These findings indicate that temperature affects the leaching behavior and the long-term effectiveness of S/S treatment, and temperature variation should be considered in the effectiveness evaluation of S/S treatment.
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Xu B, Yi Y. Immobilization of lead (Pb) using ladle furnace slag and carbon dioxide. CHEMOSPHERE 2022; 308:136387. [PMID: 36088964 DOI: 10.1016/j.chemosphere.2022.136387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 09/03/2022] [Accepted: 09/05/2022] [Indexed: 06/15/2023]
Abstract
Global sustainable development faces challenges in greenhouse gas emissions, consumption of energy and non-renewable resources, environmental pollution, and waste landfilling. Current technologies for immobilization of heavy metals face similar challenges; for example, the use of cement, magnesia, lime, and other binders for immobilization of heavy metals is associated with carbon dioxide emission and consumption of limestone/magnesite and energy. In these contexts, this study introduced a novel and sustainable method for immobilization of lead (Pb) by using an industrial solid waste (ladle furnace slag, LFS) and a greenhouse gas (carbon dioxide). In this laboratory investigation, LFS was first mixed with the lead nitrate and then treated by conventional curing (without carbon dioxide) and carbonation curing (with carbon dioxide) for different periods. The treated LFS were then analyzed by various chemical analyses and microanalysis. The results showed that LFS with conventional curing is not effective in immobilization of lead, while LFS with carbonation curing can effectively immobilize lead. The leaching concentrations of Pb from carbonated LFS were four orders of magnitude lower than those with conventional curing. LFS can achieve carbon dioxide uptake of up to 8% of LFS mass. During the carbonation process, carbonates were produced and wrapped LFS particles to prevent the release of lead, lead nitrate was also carbonated into lead carbonate, and the pH of LFS was reduced to 9.36-9.58, close to the minimum solubility of lead carbonate; these are the main reasons for lead immobilization. In summary, the use of LFS with carbon dioxide for immobilization of lead can not only sequester carbon dioxide, but also reduce the cost of binders, non-renewable resource consumption, energy use, and LFS landfilling.
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Affiliation(s)
- Bo Xu
- School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
| | - Yaolin Yi
- School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
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Li W, Qin J, Yi Y. Treating Pb-contaminated clay slurry by three curing agents. CHEMOSPHERE 2022; 303:135011. [PMID: 35609664 DOI: 10.1016/j.chemosphere.2022.135011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 05/03/2022] [Accepted: 05/16/2022] [Indexed: 06/15/2023]
Abstract
Each year, extensive dredged clay slurries containing heavy metals need to be treated before being reused; in such contaminated slurries, lead (Pb) is frequently identified. Quicklime (CaO)-activated ground granulated blast-furnace slag (GGBS), magnesium (MgO)-activated GGBS, and ordinary Portland cement (OPC) are usually used to remediate the lead (Pb)-contaminated soil; nevertheless, using these curing agents (or binders), particularly CaO-GGBS and MgO-GGBS, to treat Pb-contaminated slurry with high water content is rarely reported. Moreover, inconsistent results were obtained from previous studies in terms of the mechanical and leaching performance of Pb-contaminated soils with the three binders. Based on the above-mentioned reasons, this study used CaO-GGBS, MgO-GGBS, and OPC to treat the Pb-contaminated clay slurry, and compared the effectiveness of the three binders in improving the mechanical and leaching properties of the slurry. Laboratory tests were performed to examine the leaching, strength, mineralogical, and micro-structural performance of treated clay slurries. The results showed that GGBS-based binders were more effective than OPC in improving the strength and Pb leachability of contaminated slurries. When suitable ratios between activators (CaO and MgO) and GGBS were used, a similar or even higher UCS was produced by CaO-GGBS than MgO-GGBS. Similar leachate pH and Pb leachability could be achieved between CaO-GGBS- and MgO-GGBS-treated contaminated clay slurries. Therefore, it is not rigorous to state that MgO-GGBS is better in improving the strength and leachability of Pb-contaminated soils than CaO-GGBS only by comparing the two GGBS-binders based on the same activator/GGBS ratio, as reported in some previous studies. The leachability of Pb was affected by the pH, but the addition of GGBS facilitated the decrease of Pb leachability in slurries. The XRD result showed the formation of CSH and Pb(OH)2, which facilitated the reduction of Pb leachability.
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Affiliation(s)
- Wentao Li
- School of Civil Engineering, Architecture and Environment, Hubei University of Technology, 430068, China; School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore; Innovation Demonstration Base of Ecological Environment Geotechnical and Ecological Restoration of Rivers and Lakes, Hubei University of Technology, 430068, China
| | - Junde Qin
- School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore; Nanyang Environment & Water Research Institute, Nanyang Technological University, 639798, Singapore
| | - Yaolin Yi
- School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore.
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Zhang Y, Ong YJ, Yi Y. Comparison between CaO- and MgO-activated ground granulated blast-furnace slag (GGBS) for stabilization/solidification of Zn-contaminated clay slurry. CHEMOSPHERE 2022; 286:131860. [PMID: 34391116 DOI: 10.1016/j.chemosphere.2021.131860] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Revised: 08/02/2021] [Accepted: 08/08/2021] [Indexed: 06/13/2023]
Abstract
Stabilization/solidification (S/S) is a low-cost and effective remedial technique for dredged contaminated sediments. Quick lime (CaO)-activated and reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS) are effective and low-carbon S/S binders. However, the existence of metals, especially Zn, in contaminated sediments, may hinder the hydration of GGBS. This study compared the performance and mechanisms of CaO-GGBS, MgO-GGBS and ordinary Portland cement (OPC) for the treatment of Zn-contaminated clay slurry using unconfined compressive strength (UCS) test, one-stage batch leaching test, and mineralogical and thermal analyses. The results showed that the application of the MgO-GGBS (GGBS dosage of 10 % and MgO of 0 %-3 % (of dry clay by mass)) had positive effects on the mechanical strength and Zn immobilization of the contaminated clay slurry while the CaO-GGBS affected negatively and the situation became even worse at a higher CaO dosage (0 %-1.5 % of dry clay by mass). In comparison with OPC, the application of MgO-GGBS produced higher mechanical strength and that for CaO-GGBS was the lowest. The Zn leaching difference depends on initial Zn concentrations. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results showed that a retarder, calcium zinc hydroxide, formed in the immobilization process when adding the CaO-GGBS binder, hindering the GGBS hydration and further leading to inferior strength and higher Zn leachability. The clay slurry treated by the MgO-GGBS binder was found to have a higher calcium silicate hydrate content which explained its high strength and low leachability.
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Affiliation(s)
- Yunhui Zhang
- Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore
| | - Yi Jie Ong
- School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore
| | - Yaolin Yi
- School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore.
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Li X, Yu X, Liu L, Yang J. Cyclic drying and wetting tests on combined remediation of chromium-contaminated soil by calcium polysulfide, synthetic zeolite and cement. Sci Rep 2021; 11:11643. [PMID: 34079041 PMCID: PMC8172870 DOI: 10.1038/s41598-021-91282-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 05/24/2021] [Indexed: 11/09/2022] Open
Abstract
Using calcium polysulfide as the reducing agent, synthetic zeolite as the adsorbent, and cement as the curing agent, the dual-index orthogonal test method was used to determine the best remediation dosage of chromium-contaminated soil. On this basis, through the dry-wet cycle test, the durability of the chromium-contaminated soil after repair is analyzed from the perspectives of unconfined compressive strength, toxic leaching concentration, quality loss, and microscopic characterization. Test results showed that the optimal ratio for the joint repair of chromium-contaminated soil was 3 times the amount of CaS5, 15% synthetic zeolite, and 20% cement. With the increase in the number of wet-dry cycles, the unconfined compressive strength of the composite preparation combined to repair chromium-contaminated soil was first increased and then reduced, and the concentration of Cr(VI) and total chromium in the leachate was first decreased and then increased. The higher the chromium content of the contaminated soil was, the lower the unconfined compressive strength, and the higher the leaching concentration of Cr(VI) and total chromium were. With the increase in cycle times, the cumulative mass-loss rate of composite preparations for repairing chromium-contaminated soil gradually increased, and the higher the chromium content was, the higher the cumulative mass-loss rate, which was less than 2%, reflecting the combination of composite preparations for repairing chromium-contaminated soil to have good durability. Microscopic and macroscopic results are consistent with each other.
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Affiliation(s)
- Xilin Li
- School of Civil Engineering, Liaoning Technical University, Fuxin, 123000, Liaoning Province, China.
| | - Xiaowan Yu
- School of Civil Engineering, Liaoning Technical University, Fuxin, 123000, Liaoning Province, China
| | - Ling Liu
- School of Civil Engineering, Liaoning Technical University, Fuxin, 123000, Liaoning Province, China
| | - Jianlin Yang
- College of Materials Science and Engineering, Liaoning Technical University, Fuxin, 123000, Liaoning Province, China
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Yang Z, Li X, Wang Y, Chang J, Liu X. Trace element contamination in urban topsoil in China during 2000-2009 and 2010-2019: Pollution assessment and spatiotemporal analysis. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 758:143647. [PMID: 33280869 DOI: 10.1016/j.scitotenv.2020.143647] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 10/28/2020] [Accepted: 11/03/2020] [Indexed: 06/12/2023]
Abstract
The Chinese government has launched a critical battle against soil pollution in recent years to establish an effective pollution prevention and control framework. This study sought to investigate the long-term pollution status of potentially toxic trace elements in urban topsoil nationwide, and to further investigate the effectiveness of pollution control over the past decade. The concentrations of 8 elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in urban topsoil in China between 2000-2009 and 2010-2019 were separately collected for comparative analysis. Individual and comprehensive pollution levels of the elements were evaluated at the city, provincial, regional, and national scales, and further spatially mapped using GIS. Combined with PCA, the main factors influencing these elements in soil nationwide were identified. The results revealed a severe situation in terms of potentially toxic trace element accumulation in urban topsoil, where the NNIPIs surpassed 3 in both periods. The elements As, Cd, and Hg were closely associated with industrial activity and coal burning. Hg and, in particular, Cd pollution (NPI > 3) were found to be severe in most of the cities studied. For the elements As, Cu, Pb, and Zn, pollution ranged from slight to moderate (1.0 < NPI ≤ 3.0), and Cu, Pb, and Zn were related to a significant degree with vehicle use. Soil Cr and Ni were mainly controlled by parent materials of lithogenic origin, and slight pollution was identified (1.0 < NPI ≤ 2.0). Pollution patterns showed different characteristics across the regions, and those of the same region and the nation hardly changed over time. Mercury pollution was dominant in the northern regions (NW, MYeR, NE, and NC), while Cd pollution was more severe for the south (EC, MYaR, SC, and SW). Notably, the country's comprehensive pollution level was stable across the two periods, with momentum towards improvement observed over the past decade.
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Affiliation(s)
- Zhongping Yang
- School of Civil Engineering, Chongqing University, Chongqing 400045, China; Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China; National Joint Engineering Research Center for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing 400045, China.
| | - Xuyong Li
- School of Civil Engineering, Chongqing University, Chongqing 400045, China; Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China; National Joint Engineering Research Center for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing 400045, China
| | - Yao Wang
- School of Civil Engineering, Chongqing University, Chongqing 400045, China; Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China; National Joint Engineering Research Center for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing 400045, China
| | - Jiazhuo Chang
- School of Civil Engineering, Chongqing University, Chongqing 400045, China; Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China; National Joint Engineering Research Center for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing 400045, China
| | - Xinrong Liu
- School of Civil Engineering, Chongqing University, Chongqing 400045, China; Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China; National Joint Engineering Research Center for Prevention and Control of Environmental Geological Hazards in the TGR Area Chongqing University, Chongqing 400045, China
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11
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Effects of Long-Term Repeated Freeze-Thaw Cycles on the Engineering Properties of Compound Solidified/Stabilized Pb-Contaminated Soil: Deterioration Characteristics and Mechanisms. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2020; 17:ijerph17051798. [PMID: 32164256 PMCID: PMC7084238 DOI: 10.3390/ijerph17051798] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 03/06/2020] [Accepted: 03/06/2020] [Indexed: 01/20/2023]
Abstract
The effects of long-term repeated freeze-thaw cycles and pollution levels on the engineering properties (qu, E50, φ, c, and k) of Pb-contaminated soils were investigated in various laboratory tests. These soils were solidified/stabilized (S/S) with three types of cement-based combined binders (C2.5S5F5, C5S2.5F2.5, and C5S5, cement, lime, and fly ash, mixed in different proportions; these materials are widely used in S/S technology). The strength and permeability coefficient of compound solidified/stabilized Pb-contaminated soils (Pb-CSCSs) were determined based on measurements of unconfined compressive strength (UCS), direct shear, and permeability. CT scanning, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests were employed to analyse the deterioration mechanisms under various repetitions of freeze-thaw cycles. The results showed that, under repeated freeze-thaw cycles, the engineering properties of Pb-CSCSs all degraded to varying degrees, though degradation tended to stabilise after 30 days of freeze-thaw cycles. The study also found that the pollutants obstruct hydration and other favourable reactions within the soil structure (such as ion exchanges and agglomerations and pozzolanic reactions). The activation of hydration reactions and the rearrangement of soil particles by freeze-thaw cycles thus caused the engineering properties to fluctuate, and soils exhibited different deterioration characteristics with changes in Pb2+ content.
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