Cement-stabilized contaminated soil: Understanding Pb retention with XANES and Raman spectroscopy

Industrial by-products-derived binders for in-situ remediation of high Pb content pyrite ash: Synergistic use of ground granulated blast furnace slag and steel slag to achieve efficient Pb retention and CO2 mitigation

Ordinary Portland cement (OPC) is a cost-effective and conventional binder that is widely adopted in brownfield site remediation and redevelopment. However, the substantial carbon dioxide emission during OPC production and the concerns about its undesirable retention capacity for potentially toxic elements strain this strategy. To tackle this objective, we herein tailored four alternative binders (calcium aluminate cement, OPC-activated ground-granulated blast-furnace slag (GGBFS), white-steel-slag activated GGBFS, and alkaline-activated GGBFS) for facilitating immobilization of high Pb content pyrite ash, with the perspectives of enhancing Pb retention and mitigating anthropogenic carbon dioxide emissions. The characterizations revealed that the incorporation of white steel slag efficiently benefits the activity of GGBFS, herein facilitating the hydration products (mainly ettringite and calcium silicate hydrates) precipitation and Pb immobilization. Further, we quantified the cradle-to-gate carbon footprint and cost analysis attributed to each binder-Pb contaminants system, finding that the application of these alternative binders could be pivotal in the envisaged carbon-neutral world if the growth of the OPC-free roadmap continues. The findings suggest that the synergistic use of recycled white steel slag and GGBFS can be proposed as a profitable and sustainable OPC-free candidate to facilitate the management of lead-contaminated brownfield sites. The overall results underscore the potential immobilization mechanisms of Pb in multiple OPC-free/substitution binder systems and highlight the urgent need to bridge the zero-emission insights to sustainable in-situ solidification/stabilization technologies.

Application of X-ray based modern instrumental techniques to determine the heavy metals in soils, minerals and organic media

To evaluate the environmental concerns associated with heavy metals (HMs) during their translocations in food chains, it is crucial to gather data on the types of HMs present in soils in order to ascertain their toxicity and potential to migrate. An overview of the findings from several physical techniques used to determine and identify the HMs, sediments, individual minerals, and organic components in contaminated agricultural and industrial soils, is provided in this review article. These studies cover a variety of X-ray-based analytical techniques, including most widely used ones like X-ray absorption near edge structure, extended X-ray absorption fine structure, X-ray diffraction, and less popular ones X-ray fluorescence, etc. When compared to techniques that rely on laboratory radiation sources, synchrotron radiation offers more precision and efficiency. These methods could pinpoint the primary mechanisms influencing the soil's ability to transport contaminants and track their subsequent migration up the food chain.

Enhancing road performance of lead-contaminated soil through biochar-cement solidification: An experimental study

The effectiveness of cement-based solidification for remediating heavy metal-contaminated soil diminishes at high levels of contamination. To overcome this limitation, the potential of a biochar-cement composite curing agent to enhance the properties of Pb 2+ contaminated soil was investigated in this study. The permeability, unconfined compressive strength (UCS), and leaching characteristics of the biochar-cement composite material were assessed under varying biochar contents. The results revealed that the addition of 1-5 wt% biochar in cement significantly improved the UCS of the solidified soil. However, excessive biochar contents had a detrimental effect on the strength of samples. Additionally, the incorporation of 3.0% biochar reduced the hydraulic conductivity and porosity to 7.75 × 10-9 cm/s and 43.12%, respectively. Moreover, the biochar-cement composite material exhibited remarkable efficiency in treating highly concentrated Pb2+ contaminated soil, with leaching concentration decreasing significantly with increasing biochar content, falling below the Chinese hazardous waste identification standard. Overall, the utilization of a biochar-cement composite curing agent in the solidification of heavy metal-contaminated soil could be considered a promising subgrade filler technique.

Biotechnology to reduce logistics burden and promote environmental stewardship for Air Force civil engineering requirements

This review provides discussion of advances in biotechnology with specific application to civil engineering requirements for airfield and airbase operations. The broad objectives are soil stabilization, waste management, and environmental protection. The biotechnology focal areas address (1) treatment of soil and sand by biomineralization and biopolymer addition, (2) reduction of solid organic waste by anaerobic digestion, (3) application of microbes and higher plants for biological processing of contaminated wastewater, and (4) use of indigenous materials for airbase construction and repair. The consideration of these methods in military operating scenarios, including austere environments, involves comparison with conventional techniques. All four focal areas potentially reduce logistics burden, increase environmental sustainability, and may provide energy source, or energy-neutral practices that benefit military operations.

Review of the Interactions between Conventional Cementitious Materials and Heavy Metal Ions in Stabilization/Solidification Processing

In the past few decades, solidification/stabilization (S/S) technology has been put forward for the purpose of improving soil strength and inhibiting contaminant migration in the remediation of heavy metal-contaminated sites. Cement, lime, and fly ash are among the most common and effective binders to treat contaminated soils. During S/S processing, the main interactions that are responsible for improving the soil's behaviors can be summarized as gelification, self-hardening, and aggregation. Currently, precipitation, incorporation, and substitution have been commonly accepted as the predominant immobilization mechanisms for heavy metal ions and have been directly verified by some micro-testing techniques. While replacement of Ca²⁺/Si⁴⁺ in the cementitious products and physical encapsulation remain controversial, which is proposed dependent on the indirect results. Lead and zinc can retard both the initial and final setting times of cement hydration, while chromium can accelerate the initial cement hydration. Though cadmium can shorten the initial setting time, further cement hydration will be inhibited. While for mercury, the interference impact is closely associated with its adapted anion. It should be pointed out that obtaining a better understanding of the remediation mechanism involved in S/S processing will contribute to facilitating technical improvement, further extension, and application.

Recent advances toward structural incorporation for stabilizing heavy metal contaminants: A critical review

Heavy metal pollution has resulted in serious environmental damage and raised significant public health concerns. One potential solution in terminal waste treatment is to structurally incorporate and immobilize heavy metals in some robust frameworks. Yet extant research offers a limited perspective on how metal incorporation behavior and stabilization mechanisms can effectively manage heavy metal-laden waste. This review sets forth detailed research on the feasibility of treatment strategies to incorporate heavy metals into structural frameworks; this paper also compares common methods and advanced characterization techniques for identifying metal stabilization mechanisms. Furthermore, this review analyses the typical hosting structures for heavy metal contaminants and metal incorporation behavior, highlighting the importance of structural features on metal speciation and immobilization efficiency. Lastly, this paper systematically summarizes key factors (i.e., intrinsic properties and external conditions) affecting metal incorporation behavior. Drawing on these impactful findings, the paper discusses future directions in the design of waste forms that efficiently, effectively treat heavy metal contaminants. By examining tailored composition-structure-property relationships in metal immobilization strategies, this review reveals possible solutions for crucial challenges in waste treatment and enhances the development of structural incorporation strategies for heavy metal immobilization in environmental applications.

Incorporation and solidification mechanism of manganese doped cement clinker

Using municipal and industrial solid waste as a substitute raw material and fuel in cement rotary kiln co-processing is considered an economic and environmentally friendly alternative to the use of traditional fuels. However, the presence of heavy metals in solid waste is a growing concern in the cement rotary kiln co-processing technique. The solidification mechanism of heavy metals in cement clinker is directly related to their stabilization. Cement clinkers doped with manganese oxide (MnO2: 0.0%–5.0% wt%) were prepared in a laboratory to investigate the impacts of extrinsic Mn on cement clinker calcination. The insignificant changes in X-ray diffractometer patterns indicated that the fixed Mn had little influence on the mineral lattice structure. Raman spectra and X-ray photoelectron spectroscopy revealed the transformation of the silicate phase when the Mn dose was increased. Moreover, the satisfactory solidification ratio confirmed the incorporation of Mn in the cement clinker. These results provided evidence of the influence rule of Mn in the cement clinker calcination process. Furthermore, Raman spectroscopy showed great potential for the qualitative and semi-quantitative analysis of the cementitious materials derived from cement rotary kiln co-processing. These results will be important for the further development of green cement manufacturing technology.

Converting industrial waste into a value-added cement material through ambient pressure carbonation

Converting industrial wastes into value-added building products in an environmental management strategy is a challenging yet vital component of the industrial process. Steel slag (SS), an industrial waste by-product from the steel-making process, is typically disposed of in landfill which consumes land resources and pollutes the environment. This paper explores the possibility of a closed-loop system to convert steel slag into a cement material through carbonation activation, thereby significantly reducing the amount of steel slag waste sent to landfills across Canada. The production of this cementing material can occur next to the steel mill, utilizing steel slag and carbon dioxide collected on-site to fabricate carbon-negative products. To save energy and allow production to be feasible on an industrial scale, ambient pressure (AP) carbonation is developed to reduce carbon emissions while improving their performance. High pressure (HP) carbonation curing and normal hydration (NH) references were also implemented at the same time to justify the application of AP carbonation in reducing CO₂ emission. The results of this study found AP carbonation-activated SS compacts have comparable CO₂ uptake (about 7.5 tons CO₂/100 tons slag) and mechanically compressive strength values as those subjected to HP carbonation, suggesting that AP could be used to replace HP in carbonation curing to ensure a lower energy input. Additionally, AP seemed to possess as effective carbonation as HP. The studies investigated by multiple techniques including X-ray diffractometer (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopic analysis, and scanning electron microscopy (SEM) aim to identify the microstructure development of carbonated SS paste to assess carbonation results. Developed with life cycle assessment (LCA), environmental impact evaluation shows that AP presents a smaller global warming potential (GWP) value than HP. The comparable CO₂ sequestration, satisfactory engineering properties, enhanced microstructure and lesser environmental impact in AP carbonation confirm the feasibility of replacing high pressure with extremely low pressure to cure concrete products. The use of AP carbonation for cement material created using steel slag reduces carbon emissions, energy usage, and natural resource consumption.

Does Current Knowledge Give a Variety of Possibilities for the Stabilization/Solidification of Soil Contaminated with Heavy Metals?-A Review

Stabilization/solidification of contaminated soil is a process that allows simultaneous strengthening of the soil structure, disposal of contamination and recycling of industrial waste, implemented as substitutes for Portland cement or additives to improve the properties of the final product obtained. Extremely intensive development of studies pertaining to the S/S process prompted the authors to systematize the binders used and the corresponding methods of binding the contamination, and to perform an analysis of the effectiveness expressed in geomechanical properties and leachability. The study pays close attention to the types of additives and binders of waste origin, as well as the ecological and economic benefits of their use. The methods of preparing and caring for the specimens were reviewed, in addition to the methods of testing the effectiveness of the S/S process, including the influence of aging factors on long-term properties. The results of the analyses carried out are presented in the form of diagrams and charts, facilitating individual evaluation of the various solutions for the stabilization/solidification of soils contaminated with heavy metals.

The validation of converting pyrite ash-contaminated soil into End-of-Waste by the High-Performance Solidification/Stabilization process application

One of the major challenges to establishing more sustainable management strategies than landfill disposal of metals-contaminated soils is the lack of End-of-Waste (EoW) criteria defined at the European and national levels. Another limitation stems from the scarcity of information on industrial-scale applications of treatment technologies able to obtain safe and reusable materials from such contaminated waste. In this context, the High-Performance Solidification/Stabilization process was applied for the full-scale remediation of pyrite ash-contaminated soil (ca. 24 000 m³ ), and a dedicated sampling and analytical protocol was developed and implemented to verify if the treated material obtained complied with the general EoW criteria established by article 6 of the Waste Framework Directive 2008/98/EC. The results of the leaching, ecotoxicological, and mechanical tests carried out on representative samples of the treated soil showed that this material (ca. 19 000 m³ ) could be classified as EoW and thus was deemed reusable both in-situ as filler for the excavation and ex-situ as road construction material. These results improve the knowledge of the performance of a state-of-the-art technique for the treatment of metals-contaminated soil. Furthermore, the developed monitoring plan can support future assessments on the compliance of materials obtained from contaminated soil with the general EoW criteria. Integr Environ Assess Manag 2022;00:1-9. © 2022 SETAC.

Mechanical Properties, Durability and Leaching Toxicity of Cement-Stabilized Macadam Incorporating Reclaimed Clay Bricks as Fine Aggregate

The utilization of reclaimed clay brick (RCB) from construction and demolition (C&D) waste is an extremely troublesome problem, which is beneficial and necessary for environmental protection and resource conservation. The objective of this study is to evaluate the mechanical properties, durability and environmental impact of cement-stabilized macadam (CSM) incorporating RCB. The physical and chemical properties of RCB were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) technologies. RCB exhibited a porous surface micro-morphology, high water absorption and pozzolanic activity. The higher RCB substitution ratio resulted in a lower unconfined compressive strength of CSM. Meanwhile, the higher the RCB substitution ratio was, the larger the 90 d indirect tensile strength of CSM at the late curing period. The RCB substitution ratio within 50% was beneficial for the freeze-thaw resistance of CSM. Additionally, RCB had a smaller aggregate size, causing a negative influence on the anti-scouring property of CSM. CSM incorporating RCB had an overall increasing accumulative water loss rate, and average coefficients of dry shrinkage and temperature shrinkage, except that 20% RCB substitution ratio resulted in an excellent dry shrinkage property. Based on the chemical analysis of EDTA-2Na, the pozzolanic RCB reacted mainly at later curing to form the crystal structure, enhancing the interfacial transition zone. Additionally, the leaching solutions could meet the identification requirements for extraction toxicity, surface water and groundwater referring to Chinese standards. Utilizing RCB in road engineering as the substitute for natural aggregate would be a promising step forward to sustainable development and green construction.

Study on Properties of Copper-Contaminated Soil Solidified by Solid Waste System Combined with Cement

Three industrial solid wastes including red mud, carbide slag, and phosphogypsum combined with ordinary Portland cement were used as curing agents to solidify/stabilize loess polluted by a high concentration of copper ions. The unconfined compressive strength, resistivity, permeability coefficient, copper ion leaching concentration, pH value, and other engineering application evaluation indexes were analyzed to preliminarily assess the applicability of the curing agent in the remediation of soil contaminated with a high concentration of copper ions. The mineral phases and functional groups of solidified soil were detected using XRD and FTIR, showing that the strength, electrical resistivity, and pH value of solidified soil decrease following the addition of copper ions. Moreover, the strength and resistivity of solidified soil increase with the curing age, and the pH value decreases with age. For solidified contaminated soil, when the total content of curing agent increases from 10 to 20%, the maximum 28 d strength increases from 1.35 to 5.43 MPa, and in this study, its permeability coefficient, copper ion leaching concentration, and pH value were found to be within the limits set by relevant national standards. In conclusion, red mud-carbide slag-phosphogypsum combined with cement has a good stabilizing effect on sites polluted with a high concentration of copper ions.

Technologies for the cobalt-contaminated soil remediation: A review

The cobalt-contaminated soil has exposed potential toxicity to humans, plants, and animals. Industrial activities like ore smelting, alloy manufacture, and electric and electronic devices production have induced the increased cobalt content in soil resulting in higher ecosystem risk in diverse environmental media. However, knowledge gaps in cobalt transfer in soil and the limited understanding of remediation techniques make it challenging to estimate their potential application scenarios. Thus, keeping in view the above facts, this paper summarizes the natural and anthropogenic sources arousing the increase of cobalt in soil and reviews the cobalt species in soil and factors that influence the mobilization of cobalt. Moreover, the status of the remediation technologies is critically evaluated, including phytoremediation, immobilization, and separation technologies (soil washing and electroremediation) with a focus on the application and mechanism of phytoremediation and immobilization. Based on the actual application, further improvements and prospects of all techniques are proposed. This comprehensive review might serve to guide technique selection and inspire more scientific exploration on the remediation of cobalt-contaminated soil.

Impact of diatomite addition on lead immobilization in air pollution control residues from a municipal solid waste incinerator

Air pollution control (APC) residues, which are known to be the byproducts of incineration treatment, exhibit a high leaching potential of toxic metals. Calcium silicate hydrate (C-S-H), which is a major hydration product of hardened cement and immobilizes toxic metal, can be formed by the reaction of Ca with pozzolanic Si in a highly alkaline environment. Toxic metals might be immobilized by the addition of pozzolanic material to APC residues (instead of using cement), which is a Ca source and provides an alkaline condition. In this study, diatomite, which mainly comprises amorphous silica (SiO₂·nH₂O), was investigated as a pozzolanic material for Pb immobilization in APC residues obtained from a municipal solid waste incinerator. APC residues were cured with and without the addition of diatomite at different temperatures. When diatomite was added to APC residues, pozzolanic phases such as C-S-H gel were formed via the consumption of Ca(OH)₂ and CaClOH. Compared to APC residues cured without diatomite, the leaching of Pb decreased by 99% for APC residues cured for 14 days with 10% diatomite at 70 °C. The results of sequential chemical extraction showed that water-soluble Pb in APC residues was reduced from 10.3% to nearly zero by the pozzolanic reaction. Consequently, the leaching amount of Pb dropped below 0.3 mg/L (Japanese criteria for landfill disposal). Overall, these experiments provide promising results regarding the possibility of using diatomite for pretreating APC residues.

Fluorescence "off-on" probe for lead (II) detection based on Atractylodes III CQDs and bioimaging

In this work, a type of carbon quantum dots (CQDs) with bright blue emission were readily fabricated through one-step hydrothermal treatment from Atractylodes III. We explored the surface morphology and optical properties of CQDs by Transmission electron microscope (TEM), X-ray diffraction patterns (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectrophotometer. The obtained CQDs possessed good photoluminescence properties, water solubility and biocompatibility. The fluorescence quantum yield of them was 3.72%. It was found that the fluorescence intensity of CQDs will be quenched by picric acid (PA). After adding lead (II), the fluorescence can be effectively recovered. Hence, an "off-on" fluorescence probe was designed to detect lead (II) in the range of 0-580 μM and the limit of detection (LOD) was 0.068 μM. In the meanwhile, the experiments showed that the CQDs can be successfully used in bioimaging and as a hidden fluorescent ink.

Efficiency and comprehensive risk assessment of soil Pb and Cd by washing technique with three biodegradable eluents

Soil washing with environmentally friendly eluents is a rapid remediation technique for farmland polluted by heavy metals. In this study, polyepoxysuccinic acid (PESA), ethylenediamine tetra (methylene phosphonic acid) sodium (EDTMPS), and phosphonyl carboxylic acid copolymer (POCA) were applied to remedy paddy and arid soils polluted by Pb and Cd. At the same time, ethylenediaminetetraacetic acid (EDTA) was used as a control eluent. PESA showed comparable removal of soil Pb and Cd (over 80.0%) with EDTA, and EDTMPS and POCA removed two heavy metals by 35.2-50.3%. For labile fractions, PESA significantly removed Pb by 93.5-96.7% and Cd by 84.9-90.3% in two soils. EDTMPS and POCA removed Pb by 75.5-85.8% in two soils, while they only removed Cd by 11.7-42.2% in paddy soil, and 76.3-81.7% in arid soil. The risks of total heavy metal concentrations were reduced from the high risk to low risk in paddy soil, and to considerable risk in arid soil, while only dropped to considerable or even had no change by EDTMPS and POCA leaching. The risks of the two soils reduced from high to low or considerable level after PESA washing based on labile fraction change, and to considerable or high level after EDTMPS and POCA leaching, respectively. Therefore, PESA is an ecological benefit eluent for remediating the farmland polluted by heavy metals, and the risk assessment based on labile fraction more easily identifies the dynamic change of heavy metal during the washing process.

Effects of Long-Term Freeze-Thaw Cycles on the Properties of Stabilized/Solidified Lead-Zinc-Cadmium Composite-Contaminated Soil

Lead, zinc, and cadmium were used to prepare a composite-contaminated soil to replicate common situations, in which soil is usually simultaneously contaminated by multiple metals. To examine the long-term durability of stabilized/solidified (S/S) contaminated soil, specimens were subjected to a series of freeze–thaw (F-T) cycles, up to ninety times (one day per cycle), prior to testing. Triaxial compression tests, soil column leaching tests, and X-ray diffraction analysis were then employed to study the mechanical properties, environmental influences, and micro-mechanisms of the S/S lead-zinc-cadmium composite-contaminated soils after long-term F-T. The results showed that triaxial compressive strength increases within three F-T cycles, then decreases before slightly increasing or stabilizing after thirty F-T cycles. The stage of decreased cohesion thus occurs between three and fourteen F-T cycles, with variation in other factors similar to that of the triaxial compressive strength. The cohesion mainly increases between three and seven cycles. The soil column leaching test showed that the permeability of soil is more than four times higher than that of soil not subject to freeze–thaw cycles after ninety F-T cycles. XRD tests further revealed that the chemical composition of S/S contaminated soil and the occurrence of each heavy metal (HM) remained unchanged under F-T treatment.

Use of thermally modified waste concrete powder for removal of Pb (II) from wastewater: Effects and mechanism

Exploring effective uses of waste concrete powder (WCP), produced from recycling of construction & demolition waste is beneficial to the environment and sustainable development. In this study, WCP was first treated thermally to enhance the ability to remove Pb (II) from aqueous solutions. The experimental results revealed that the thermal treatment could enhance adsorption capacity due to modification of calcium bonding and pore structure of WCP. Preparation parameters such as temperature, particle size, and water-cement ratio were investigated to obtain the optimal operational conditions. Batch adsorption experiments were performed to explore influence factors of pH (1.00-6.00), ionic strength (0.05-2 mol/L), dosage (2-50 g/L), and temperature (25-45 °C). The pseudo-second-order kinetics model could adequately describe the adsorption process, and the Langmuir model was capable to predict the isotherm data well in the low concentration region (C₀ < 500 mg/L). The maximum uptake capacity for Pb (II) calculated by Langmuir model at 25, 35 and 45 °C were 46.02, 38.58 and 30.01 mg/g respectively, and the removal rate of Pb (II) was 92.96% at a dosage of 50 g/L (C₀ = 1000 mg/L). Precipitation, ion exchange, and surface complexation were identified to be the main mechanisms of Pb (II) adsorption through microscopic investigation by SEM-EDX, XRD, FTIR, XPS, and BET inspections. The study confirms that the WCP after thermal modification, can be selected as a promising adsorbent for the high performance and eco-friendliness.

Derivation of empirical model to predict the accumulation of Pb in rice grain

Lead contamination in soil has become a worldwide threat on food security and human health. To assess the Pb bioavailability and evaluate the safe use of low Pb polluted soil for food production, the speciation of Pb in 19 types of paddy soil were investigated by chemical extraction and X-ray absorption near-edge structure (XANES), and the uptake and accumulation characteristics of Pb in different soil-rice systems were investigated. Moreover, an empirical model was established to predict the content of Pb in rice grain, and field validation was conduct to evaluate model performance. Results showed that the proportion of available Pb in different soil satisfied normal distribution N (0.47, 0.23). Pb(CH₃COO)₂, GSH-Pb, PbO, PbHPO₄ and Pb₃(PO₄)₂ performed well in characterizing the speciation of Pb in different rhizosphere soils, and PbHPO₄ accounted for more than 70%. The exceedance of Pb in grain in CK, 0.5X and 1X treatment were 10.5%, 36.1% and 42.1%, respectively, and the accumulation of Pb in grain was significantly related with Pb content in root. Carbonate and organic bound Pb in rhizosphere soil were two major Pb species that influenced the accumulation of Pb in rice. Moreover, content of total Pb, clay and SOM performed well in predicting the Pb content in grain, both for pot and field samples. Above all, our predicting model worked well in evaluating Pb accumulation in rice grain among low polluted paddy farmland (Total Pb < 300 mg/kg).