Leaching Toxicity Research Articles

Tire wear particle leachate exhibits trophic and multi-generational amplification: Potential threat to population viability

The toxic additives leached from tire wear particles (TWPs) in road runoff can directly poison aquatic organism through high-dose exposure in sporadic hotspots. Given the ubiquity of road runoff carrying TWPs, it is necessary to assess whether there are lagging effects from low-dose exposure, as the toxicity of TWPs leachate can be transferred and amplified across multi-generations and different trophic levels: microalgae, zooplankton and larval fish. In this study, Chlorella pyrenoidesa exposed to different concentrations of TWPs leachate were fed to rotifer Brachionus calyciflorus, which were subsequently used as the initial feeding for fry of Cyprinus carpio. Below 1000mg/L, the growth of microalgae was not influenced by TWPs leachate. Rotifer fed with contaminated microalgae for a single generation exhibited hormesis in their reproduction. After multigenerational feeding, the microalgae from 500mg/L treatment were sufficient to suppress reproduction of rotifer since the third generation. For the secondary consumer carp fry, survival, growth, and feeding rate were significantly inhibited at first generation when consuming the rotifers fed with microalgae exposed to 250mg/L TWPs leachate. So, evidence was presented for the generational and trophic amplification of toxicity in TWPs leachate within the food chain. A seemingly innocuous low dose can exhibit evident ecotoxicity after trophic and generational transfer, which could decline population viability of the aquatic organisms in the future.

The Toxicity Leaching and the Cement Admixtures Properties with Incineration Fly Ash of Different Furnace Types.

Incineration of fly ash is a hazardous solid waste, and there are two types of furnaces used for production. The impact of furnace types on the properties and toxicity of incineration fly ash was studied. The resource utilization of incineration fly ash has been tested. The results showed that circulated fluidized bed (CFB) ash and grate (GF) ash were alkaline materials, dioxin content ranged between 98 and 359 ng-TEQ/kg, and heavy metals exceeded 7700 ppm. The leaching of Zn in CFB ash was 110.474 ppm, and that in the GF ash was 5.985 ppm. The chlorine content in GF ash was 27.07%, 2.7 times that of CFB ash. When the content was 5%, GF ash promoted cement grinding and improved the 3-day compressive strength of cement, which was 35.55% higher than the control sample. CFB ash generates hydrogen gas during the hydration process, causing volume cracking. When 20% GF ash was added, the hydration heat release peak appeared 10.5 h ahead of time. According to the Chinese standard GB 175-2023, the maximum dosages of CFB ash and GF ash in cement were 0.22 and 0.57%. There was no risk of excessive leaching of heavy metals. During cement production with CFB and GF ash, attention should be paid to the issues of chlorine and dioxins.

Effect of inorganic salt composition on strength, microstructure and leaching toxicity of coal-based solid waste backfill materials

This study explores the potential of coal-fired slag, desulfurized gypsum and modified magnesium slag as cementing agents for coal-based solid waste backfill materials. Inorganic salts like CaCl2, Na2SO4 and Na2SiO3 were used as excitants to investigate their combined impact on the mechanical properties, microstructure and leaching risk of hazardous elements from the coal-based solid waste backfill materials. The findings show that the addition of inorganic salt boosts the alkalinity within the liquid-phase reaction system. This disrupted the hydration-blocking membrane, accelerating the dissolution and reaction rate of the silica-alumina mineral components within the cementitious material. Concurrently, the inorganic salt ions consumed the early alkaline hydration products, destroying the hydration reaction equilibrium and facilitating the formation of hydration products like AFt, C-S-H gel, C-A-S-H gel, and Friedel's salt. This increase in the solid-phase volume content and microscopic densities in the reaction system improved the early mechanical properties of the coal-based solid waste backfill materials. Additionally, after a 28-day curing period, the leaching concentration of deleterious elements in the coal-based solid waste backfill material containing inorganic salt components was below the permissible concentration limit of the Class III groundwater quality standard. This eco-friendly backfill material is promising for mine backfilling, a potential substitute for traditional cement-based backfill material.

Adsorption and Immobilization of Cadmium by an Iron-Coated Montmorillonite Composite

In this study, an iron-coated montmorillonite composite (FMC) was prepared, and the adsorption and immobilization of cadmium (Cd) was investigated. The composite was coated with spherical amorphous iron (Fe), which can promote the adsorption of Cd. At the fifth minute of adsorption, the rate of Cd adsorption by the FMC reached 97.8%. With temperature, the adsorption of Cd by FMCs first increases and then decreases. High pH can promote Cd adsorption; under the same ionic strength, the adsorption of Cd was greater by montmorillonite (Mont) than that by the FMC at pH < 4, but greater by FMC than that by Mont at pH > 4. High ionic strength had negative effects on Cd(II) adsorption by FMC and Mont, and ionic strength had less of an influence on the FMC than on Mont. Soil microorganisms promoted the dissolution of Fe and the release of Cd in the FMC. High temperature can promote the dissolution of Fe, but its effect on Cd release is not significant. At 32 °C, the Fe dissolution can promote Cd release in the FMC. Both the FMC and Mont reduced the bioavailability and leaching toxicity of Cd, reduced the exchangeable Cd, and increased the Fe-Mn bound and residual Cd. Overall, the FMC was more effective than Mont at immobilizing Cd.

Performance and hydration mechanism of MSWI FA-barium slag-based all-solid waste binder

Barium slag (BS) and municipal solid waste incineration fly ash (MSWI FA) are hazardous wastes produced in large quantities, with heavy metals such as Ba, Pb, and Cr significantly exceeding acceptable levels, posing a threat to the ecological environment and living organisms. The development of technologies for the harmless disposal and resource utilization of hazardous waste is a current research focus. This study used BS, blast furnace slag (BFS), MSWI FA, and flue gas desulphurized (FGD) gypsum to replace cement in the preparation of solid waste-based binder. The results indicated that the optimal mass ratio was BS: BFS: FGD gypsum: MSWI FA = 14 %:56 %:20 %:10 %. The compressive strengths of the binder at 3, 7,and 28 days were 23.7 MPa, 30.76 MPa, and 38.65 MPa, respectively. Chinese standard HJ557–2010 was adopted to carry out heavy metal leaching experiment on raw materials, the immobilization efficiency of heavy metals Ba, Pb, and Cr were 99 %, 99 %, and 96 %, respectively, and the leachate toxicity was below the Class III groundwater limit. XRD, FT-IR, TG-DSC, XPS, SEM-EDS and other experimental methods were used to study the effect of BS content on the properties of cementable materials. An appropriate amount of BS hydrolyzes during hydration, releasing Ba²⁺ and OH⁻ ions, which activated the BFS, producing AFt and C–(A)–S–H gel. These products interweaved with material particles to fill the pore spaces, enhancing the binder’s mechanical strength and heavy metal immobilization capability. However, when excessive BS was added, the hydration products favored the formation of FS, leading to a decline in binder performance.

Research on the Preparation of Dry Mixed Mortar Using Waste Incineration Fly Ash

This study investigated the effect of water-washed municipal solid waste incineration fly ash (MSWI FA) as an admixture on the performance of dry mixed mortar and used X-ray diffraction (XRD) and scanning electron microscope (SEM) detection methods to conduct microscopic analysis. The experiment investigated the effects of the amount and water content of washed municipal solid waste incineration fly ash, cement, additives, sand and gravel, and curing time on the compressive flexural strength of dry mixed mortar at 28 days. The results show that when the content of water-washed MSWI FA is 9.80%, the content of sand and gravel is 73.50%, the content of ordinary Portland cement (PO42.5) is 16.66%, the content of water-reducing agent is 1.47‰, the content of cellulose is 0.03‰, the content of the expansion agent is 0.49‰, the addition of water is 130–160 mL/kg, the consistency of the sample can reach 91.8 mm, and the water retention rate can reach 93.6%. The flexural strength of the sample at 28 days can reach 7.5 MPa, and the compressive strength at 28 days can reach 28.30 MPa. Metal ions, such as Pb2+ and Gd2+ in MSWI FA, under the combined action of silicate cement in dry mixed mortar and fibers in cellulose, crisscross and form a solidified material, which will not be leached out. This quality meets the requirements of dry mixed mortar for ordinary plastering and masonry mortar (GB-T 25181-2019), and the leaching toxicity of the sample meets the “Identification Standard for Hazardous Waste” (GB5085.3-2007). This work provides a meaningful exploration of the resource utilization of water-washed MSWI FA.

Synergistic organic manure treatment with Al/Fe/Ca-based fluoride-fixing agents promote soil formation and utilization of phosphate flotation tailings

Soil utilization of phosphate ore flotation tailings (PTs) was achieved using F-fixing agents combined with organic manure treatment to address issues related to inefficient stabilization of P-F, heavy metal solidification/stabilization, poor physicochemical properties, and ecological disruption. The formulation for PTs soil utilization included 1.75 % polyaluminum sulfate (PAS), 1.75 % FeSO4, and 0.25 % CaO, with PTs content at ≥86.75 %. This approach enhanced water retention and improved nutrient and biochemical conditions. Various nutrient indexes met general planting soil requirements: organic matter 24.93 g/kg, available K 252.26 mg/kg, available Ca 2048.67 mg/kg, available Mg 246.13 mg/kg, and ammonia-nitrogen 42.47 mg/kg. The water-soluble P content of PTs-based soil decreased to 6.96 mg/kg, while available P increased to 677.99 mg/kg. Mn leaching toxicity was less than 0.016 mg/L, with a stabilization efficiency of 96.86 %. Water-soluble F in PTs-based soil was reduced to 11.133 mg/kg. This study maximized phosphorus resource utilization and prevented the migration of water-soluble P, F, and Mn to the surrounding environment. Potting experiments showed PTs-based soil was more effective than red soil and PTs-based raw materials in cabbage plantation, achieving a maximum seedling emergence rate of 98.33 %. Microbial diversity increased, and community structure improved in 40-day soil formation experiments, with PTs-based soils developing microbial communities involved in carbon and nitrogen cycling, enhancing resistance to external environmental disturbances, and promoting ecological utilization. These findings offer practical insights into the ecological utilization of large quantities of PTs and present a cost-effective approach for producing planting soils or ecological mulches from similar solid wastes.

High temperature co-processing of stainless-steel slag and red mud: Towards a selective Cr immobilization and harmless treatment

Stainless-steel slag and red mud are bulk metallurgical wastes, which are difficult to reuse due to the complex composition and high environmental risk. To realize their harmless and resource utilization, a collaborative treatment of the stainless-steel slag (AOD slag) and red mud at high temperature was proposed in this study. The influence of the stainless-steel slag to red mud ratio on spinel phase precipitation and crystallization, Cr enrichment and immobilization in the mixed slags were systematically investigated. The results demonstrated that when the stainless-steel slag to red mud ratio was 6:4, the enrichment degree of Cr in spinel phase was 94.12 wt%, and the precipitation amount of spinel reached the highest, 20.98 wt%. In this case, only small amounts of other mineral phases existed, the crystal particle size of spinel phase was larger, and the self-wrapped spinel phases were formed in the stage of cooling. The outer Cr-poor spinel could avoid the abrasion and erosion of the inner Cr-rich spinel in the subsequent physical separation process, thus reducing the risk of Cr6+ dissolution. In the toxic leaching test, the total Cr concentration leached from the mixed slag (stainless-steel slag to red mud ratio was 6:4) was far lower than the national leaching concentration limit of Cr-related ions. The Cr and Fe-rich spinel phases separated from the mixed slag of stainless-steel slag and red mud can be used as the raw material for the production of stainless steel, while the residual Cr-poor slag rich in Ca, Si and Al can be applied in the field of construction.

Stabilization of compound lead and arsenic contaminated soils by using two iron-based materials: Long-term efficacy

Long time scale tests are a key step in verifying the effectiveness and practicability of remediation materials in treating soil contaminated by heavy metal(oids)s (HMs). In this study, two materials, compound calcium oxide and ferrous sulfate (inorganic-inorganic combined material, denoted as IIM), and goethite nanoparticles modified biochar (organic-inorganic combined material, denoted as OIM), were tested for stabilization of arsenic (As) and lead (Pb) co-contaminated soil. Monitoring occurred at several fixed intervals up to 180 days, which includes leaching toxicity assessment, microstructure, and mechanical strength testing. The results indicate that IIM exhibited superior remediation effect within the initial 7 days but was less effective than OIM from 30 to 180 days. After 180 days, stabilization rates of IIM and OIM were 65.53% and 93.58% for As, and 99.27% and 99.71% for Pb, respectively. The cohesion of IIM-treated soils increased by 24.80% to improve the shear strength, while OIM-treated soil mainly rose the internal friction angle by 14.94%. This can be attributed to fact that IIM has a mean weight diameter (MWD) of 0.69 mm with better stability and a richer macropore structure, while OIM aggregates are slightly less stable at 0.64 mm of MWD, with mesoporous content at 49.79%. These findings provide valuable data and guidance on the long-term efficacy of remediation materials in HMs contaminated soils.

High-temperature anaerobic calcination for stabilizing environmentally stressful elements in phosphoric acid production by-products

Phosphorus tailings (P) refer to the waste materials left over after the extraction of phosphorus from phosphate rock during mining and processing. phosphogypsum (PG) is typical by-products of phosphoric acid production (PPB), containing numerous environmentally hazardous elements (EHE) that pose significant risks to ecological safety. In this study, we examined the impact of high-temperature anaerobic calcination on the migration and immobilization of EHE in PPB. The results indicated that higher temperature ranges favorably controlled the leaching toxicity of PPB. In the calcination products of P and PG, the inhibition efficiency of Pb leaching toxicity reached 84.93% and 89.33%, respectively. Under higher temperature conditions (P at 700 °C, PG at 600 °C), the inhibition of Cr leaching toxicity reached 100%. The inhibitory effects of high-temperature environments on EHE in PPB were ranked as fluorine > phosphorus > heavy metals. The mechanisms of migration and transformation of EHE in PPB under high-temperature anaerobic calcination were elucidated in three aspects, ranked from strongest to weakest. Firstly, the encapsulation of EHE by a shell-like structure, attributed to the “melt-wrap” phenomenon. Secondly, the decomposition-gasification phenomenon induced by high-temperature conditions. Thirdly, the effect of high temperature on the transformation of the storage forms of EHE. This study fills a research gap in the field of thermal treatment of PPB, enhancing the understanding of the specific effects of thermal treatment on the transformation of EHE in PPB, and provides theoretical and data support for the high-temperature thermal treatment of solid wastes.

Pollution Characteristics, Risk Assessment, and Source Analysis of Heavy Metals in Soil from a Typical Abandoned Antimony Smelting Factory

Considering the surface soil （0-20 cm） from a typical abandoned antimony smelting factory area in Dachang Town, Qinglong County, Guizhou Province, as a case study, a total of 14 soil samples were systematically collected from both within and outside the smelting factory area. The analysis focused on the pollution status, distribution characteristics, and potential ecological risks of heavy metals such as Sb, As, Cd, Cr, Pb, Cu, Zn, Ni, and V in the soil. Additionally, an evaluation and analysis of pollution sources were conducted. The results showed that the mean concentrations of heavy metals including ω（Sb）, ω（As）, ω（Cd）, ω（Cr）, ω（Pb）, ω（Cu）, ω（Zn）, ω（Ni）, and ω（V） in the surface soil of the abandoned antimony smelting factory ranged from 4.58 to 15 049.33 mg·kg-1. With the exception of Cr and Ni, all values exceeded the background values of soils in Guizhou province. The single factor pollution indices of Sb and As were 83.61 and 7.01, respectively, indicating severe contamination. In contrast, Pb fell within the non-polluted to slightly polluted range. The comprehensive potential ecological risk of soil heavy metals was characterized by severe potential ecological risk levels for Sb, As, and Cd, while the remaining heavy metals fell within a range of moderate to substantial potential ecological risk levels. The assessment of the geoaccumulation index revealed that the soil in the study area was primarily contaminated by Sb and As, predominantly exhibiting contamination levels ranging from moderate to severe. The results from the RAC method suggested that Sb was the dominant focus for remediation in this abandoned smelting factory. The two primary pollutants, Sb and As, exhibited elevated levels in leachate toxicity, acid-soluble fraction, available fraction, gastric phase, and intestinal phase in terms of bioavailable content, indicating a certain potential hazard. Further, correlation analysis indicated a certain correlation between the total amount of heavy metals and leachate toxicity, available fraction, acid-soluble fraction, reducible fraction, oxidizable fraction, gastric phase extractable fraction, and intestinal phase extractable fraction. The APCS-MLR model indicated that the sources of Sb, As, Zn, Cu, and Cd were primarily industrial, while the sources of Cr and V were mainly natural, and Pb originated mainly from mixed sources.

Ozone Plasma Nanobubble (OPN) Reactor Combined with Coagulation-Flocculation Process: A Promising Technology for Leachate Treatment

According to World Bank data, approximately 2.01 billion tons of urban waste is produced annually, with approximately 33% of waste being improperly managed, leading to concentrated and toxic leachate. This poses a global challenge due to its varied characteristics influenced by climate, landfill age, and waste composition, resulting in groundwater and surface water pollution with severe impacts on human health, ecosystems, and biodiversity, necessitating stringent treatment measures. To address this, a study integrated coagulation-flocculation and advanced oxidation processes (AOPs) using a dielectric barrier discharge (DBD) ozone plasma nanobubble (OPN) reactor to degrade leachate. Gas flow rate, plasma voltage, and gas sources are variated. This research uses O2 or air as a gas source that produces plasma. The leachate is fed into the DBD reactor, so the bubble will burst and produce further ROS. Optimal results were observed after 60 min, with oxygen gas feed reducing total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD) by 100, 93.93, and 74.12%, respectively, alongside a decrease in pH. This study indicates the promising potential of this technology for leachate treatment and demonstrates the potential for nitrate production using both types of gas feed.

Feasibility analysis of 3D printed concrete with sludge incineration slag: Mechanical properties and environmental impacts

This study substituted sludge incineration slag for natural sand in the application of 3D printed concrete technology (3DCP). It analyzed the influence of the sludge incineration slag incorporation on the workability, printability, mechanical properties, and the solidifying effect of heavy metals in 3DCP. Furthermore, the environmental and economic benefits were also examined. The results indicated that the incorporation of sludge incineration slag accelerated the loss of workability factors such as flowability and consistency in 3DCP. However, it significantly enhanced the early strength of 3DCP and improved its buildability. Additionally, the addition of sludge incineration slag diminished the mechanical properties of 3DCP. When the substitution rate reached 50 % of natural sand with sludge incineration slag, the strength of the 3D printed specimens decreased by 22.1 %. Experimental investigations at a micro-scale indicated that the porosity of interlayer interfaces was a crucial factor causing strength reduction and could be ameliorated by appropriately increasing the extrusion amount to address excessive pore sizes. Toxicity leaching tests for heavy metals demonstrated that the maximum heavy metal leaching concentration in 3DCP specimens with sludge incineration slag incorporation was 0.14 mg/L, meeting the specified requirements. The 3DCP with sludge incineration slag incorporation not only addressed the difficulty in handling incineration bottom slag but also conserved natural sand resources, presenting outstanding environmental and economic benefits. For instance, by substituting 100 % natural sand with sludge incineration slag, there were 5 % reduction in carbon emissions and 30 % increase in economic benefits.

Methodological Review of Methods and Technology for Utilization of Spent Carbon Cathode in Aluminum Electrolysis

Spent carbon cathode (SCC) is one of the major hazardous solid wastes generated during the overhaul of electrolysis cells in the aluminum production process. SCC is not only rich in carbon resources but also contains soluble fluoride and cyanide, which gives it both recycling value and significant leaching toxicity. In this study, we explore the properties, emissions, and disposal strategies for SCC. Pyrometallurgy involves processes such as vacuum distillation, molten salt roasting, and high-temperature roasting. Hydrometallurgy describes various methods used to separate valuable components from leachate and prepare products. Collaborative disposal plays a positive role in treating SCC alongside other solid wastes. High-value utilization provides an approach to make full use of high-purity carbon-based materials. Finally, we analyze and summarize future prospects for the disposal of SCC. This study aims to contribute to the large-scale treatment and resource utilization of SCC while promoting circular economy principles and green development initiatives.

Enhanced self-cementation of arsenic-contaminated soil via activation of non-thermal plasma-irradiated ferromanganese: A mechanistic investigation

The self-cementation characteristics of arsenic (As)-contaminated soil were comprehensively investigated in this study. Different non-thermal plasma-irradiated binary (hydro)oxides of polyvalent ferromanganese (poly-Fe-Mn) were synthesized and exploratorily dispersed to soil samples to activate solidification and stabilization during the self-cemented process. The maximum compressive strength of 56.35 MPa and the lowest leaching toxicity of 0.004 mg/L were obtained in the proof test under optimal conditions (i.e., the mass ratio of the poly-Fe-Mn to the soil sample of 0.05; the mass ratio of the composite alkali activator (NaOH + CaO) to the soil sample of 0.25; the mass ratio of CaO to NaOH of 1.5; the mass ratio of the DI water to the binder of 0.515). The composite alkaline activator primarily contributed to the strength formation of the self-cemented matrix while the poly-Fe-Mn significantly influenced the reduction of the As-leaching toxicities. The poly-Fe-Mn maintained diffusion-controlled polycondensation and strengthened the nucleation process during self-cementation. The amount of water and the dosage of poly-Fe-Mn caused an interactive influence on the self-cemented solidification of contaminated soils. The solidified samples with poly-Fe-Mn exhibited better thermal decomposition than their counterparts, reflecting the enhancement of poly-Fe-Mn to the matrix. Some minerals including C-S-H, kaolinite, gehlenite, diopside sodian, augite, and albite were matched in the samples, directly demonstrating the geopolymerization-steered self-cementation of the As soil. The employment of poly-Fe-Mn not only reinforced the immobilization of As pollutants in the matrix but also induced the self-cementation of soils by intensifying the composite alkaline-activated geopolymerization kinetics.

Evaluation of a novel attapulgite loaded sulfidized nanoscale zero-valent iron for immobilization of Pb in sediment: Performance, microenvironmental response, and mechanisms

In recent years, industrial activities involving electroplating and mining have caused Pb to enter rivers and become over-enriched in sediments, posing a potential risk to aquatic organisms. Given this, in this study, attapulgite loaded sulfidized nZVI (S-nZVI@ATP) was prepared by sulfidized modification and ATP loading and applied for the first time to the remediation of Pb contaminated sediments. The immobilization effect and mechanism of S-nZVI@ATP on Pb contaminated sediments were comprehensively investigated, as well as the changes in the microenvironment during the remediation process were assessed. Characterization analysis revealed that S-nZVI was uniformly loaded on the surface of ATP, and the characteristic functional groups of ATP, such as Al/Mg-OH and Si-O, were successfully loaded. Incubation experiments demonstrated that S-nZVI@ATP significantly reduced the availability and leaching toxicity of sediment Pb with immobilization efficiencies as high as 94.08% and 73.15%, respectively (P < 0.05), meanwhile, it facilitated the conversion of acid soluble Pb to the residue state. This phenomenon suggested that S-nZVI@ATP displayed excellent performance in immobilizing Pb. The increase of sediment pH and the decrease of Eh were beneficial to the immobilization of Pb. The addition of S-nZVI@ATP changed the structure and composition of the sediment bacterial community, with Proteobacteria, Firmicutes, and Bacteroidota being the dominant phyla. Except for sucrase, urease and catalase activities were increased by 1.23 and 2.48 times, respectively. Correlation analysis highlighted the importance of pH, Eh, Proteobacteria phylum, and Firmicutes phylum in sediment Pb immobilization. Post-reaction material characterization indicated that the main mechanisms of S-nZVI@ATP for sediment Pb immobilization were adsorption, complexation, ion exchange, electrostatic attraction, reduction and precipitation.

High-volume utilization of circulating fluidized bed fly ash for the production of autoclaved aerated concrete: Performance optimization and hydration characteristics

Circulating fluidized bed fly ash (CFA) is a waste emitted from coal combustion process in circulating fluidized bed boilers. The high SO3 and f-CaO content severely limits its application in building materials. The purpose of this study is to explore the possibility of large-scale application of CFA in autoclaved aerated concrete (AAC). The preparation parameters of AAC were discussed and the performance was optimized. Moreover, the workability and environmental properties of AAC were explored. The results indicated that AAC was well adapted to high CFA content, although a high CFA content caused a higher water demand as well as a reduction in the silicon content. The introduction of quartz sand and blast furnace slag effectively addressed the problems of insufficient active silica and high specific gravity. When the CFA doping was 50 %, H4 sample showed the best mechanical properties (3.82 MPa and 641 kg/m3), which meet the requests of A3.5, B06 in the Chinese national standard GB/T 11968–2020. Moreover, the toxicity leaching results showed that H4 sample was green and harmless. During the performance optimization process, more well-crystallized tobermorite was produced, whose crystal form changed from acicular to slat. Massive C-S-H gels and better crystallinity of tobermorite were observed, where were bonded and intercalated with each other, thus enhancing the properties. The paper may provide guidance for high dosing of CFA in AAC.

A synergistic method using ferrous sulfate and cementitious materials to solidify landfilled municipal sludge

The filling of landfilled municipal sludge (LMS), which is typical of high water content and low strength, poses great challenges for the landfill expansion and its mechanical stability. This study proposed a synergistic method to treat the LMS using ferrous sulfate (FS)-conditioning and cementitious materials (e.g., lime, fly ash, and cement) solidification. A series of water content, unconfined compressive strength (UCS), pH, and toxicity leaching tests were conducted to evaluate the dewatering/solidification performance of this synergistic method. The results showed that this synergistic method was effective in LMS dewatering and solidification. For the LMS tested, the proposed optimum dosage was 7 % FS, 4 % lime, 5 % fly ash, and 10 % cement, which is a much lower usage than similar studies in the literature. At this dosage, the treated LMS after 28 days of curing exhibited water content of 57.8 %, UCS of 279.1 kPa, pH value below 10.0, and no leaching toxicity, which satisfied the landfill disposal requirement by Chinese standard GB/T 23485–2009. Microscopic analyses (e.g., optical microscope, bound water measurement, scanning electron microscopy, and X-ray diffraction) revealed that FS-conditioning destroyed the colloidal agglomerate in the sludge and released the bound water to become free water; then, the cementitious materials reacted with the free water and generated cementation products (e.g., ettringite, and calcium silicate/aluminate hydrate), which significantly improved the sludge strength. The novelty of this work is that the proposed synergistic use of FS and cementitious materials, relative to the traditional method, is more effective in sludge dewatering and solidification and yet has a lower cost.

Novel chitosan-enhanced alkali-activated material for remediation of zinc-contaminated coastal mudflat sediment

Sustainable utilization and development for contaminated mudflat sites face dual challenges associated with contaminant enrichment and engineering diseases, impacting ecological quality and coastal construction. Commonly used cement has limitations in ensuring geo-environmental engineering performances for polluted sediments. This study investigates a solidification/stabilization approach using novel chitosan-enhanced alkali-activated material (CTS-AAM) to remediate highly concentrated zinc-contaminated sediments. Results exhibit that the compressive strength and water stability of sediments are remarkably improved by CTS-AAM, satisfying engineering service even under long-term immersion and zinc accumulation. Significant improvements dependent on curing period and CTS-AAM dosage also reflect in the resistance to deformation of remediated sediments, maintaining low-compressibility states due to the enhancement of structural yield stress. The leaching toxicity of remediated sediments meets Zn ≤ 5.0 mg/L, as zinc primarily distributes to the residual fraction associated with low mobility. The bidirectional enhancement of toxic sediment is attributed to the generation of hydrates with cementitious and pore-filling effects through hydration reactions. Simultaneously, chitosan with hydrated gels and ettringite collectively form gel networks and compact skeleton structures within sediments, as well as immobilize Zn through comprehensive physical encapsulation, chemical binding, and chelation. This study provides a feasible strategy for future projects involving remediation and utilization of mudflats.

Mineralogical and leaching characteristics of sulfur concentrate and hot filter residue from zinc–oxygen-pressure leaching

The mineralogical properties and environmental impact of sulfur concentrate and hot filter residue produced from the zinc–oxygen-pressure leaching were studied through a series of characterization, including X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP–OES), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDS), particle size distribution (PSD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and thermogravimetry and differential thermal analysis (TG–DTA). Furthermore, short-term environmental activity was assessed using the toxic leaching procedure (TCLP). The results indicated that the sulfur concentrate exhibited a coarser particle size compared with the hot filter residue, primarily appearing as spindle-shaped element sulfur (S0). The hot filter residue contained spindle-shaped S0 and rod gypsum, alongside phases of sphalerite, pyrite, and copper–silver-containing phases encapsulated by S0, recovering valuable metals first requires the removal of S0. The surfaces of both sulfur concentrate and hot filter residue were composed of S, ZnS, Al-O, PbSO4, and SiO2. They exhibited thermal instability and some degree of water absorption, with vigorous burning observed at temperatures ranging from 200 °C to 380 °C. The leachates from these materials exhibited increased concentrations of elements such as zinc, lead, and cadmium surpassing permissible limits, highlighting the importance of their safe disposal for the stable production of zinc–oxygen-pressure systems.