The volume of tailings discharged worldwide from iron ore smelting processes (i.e., iron ore tailings) has increased dramatically in recent years, and the disposal of this waste poses a substantial ...ecological threat to soil, and surface and sub-surface water. This threat can be alleviated to a large extent by employing iron ore tailings to fabricate brick building materials, while also effectively meeting the large demand for construction materials. The present paper discusses the preparation of eco-friendly bricks using fine-grained low-silica iron ore tailings and a non-cement curing agent system as the primary raw materials, and a triethanolamine hardening accelerator and a stearic acid emulsion waterproofing agent are also employed as minor components. We first evaluate the effect of the waterproofing agent content on the compressive strength and water resistance of the resulting products. In addition, the phase composition, chemical structure, and microstructure of the products are analyzed via X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy to explore the formation mechanism of the brick products. The analyses demonstrate that hydrated calcium silicate gel and ettringite formed in the curing process are strong binders. The water resistance and compressive strength of the product was optimal when the waterproofing agent and curing agent were 0.3 wt% with an initial curing temperature of 60 °C. The compressive strength and saturated compressive strength of the optimally formed brick products after curing for 28 d were 27.2 MPa and 24.3 MPa, respectively. The other physical properties and durability conform to the Chinese JC/T422-2007 standard for unfired bricks made of tailings.
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•One-part geopolymer was synthesized by using Bayer red mud as main raw material.•Long-term strength of binder was significantly improved with addition of 20–30wt% SF.•Lower ...water/solid ratio contributed to increasing the strength.•The compressive strength of geopolymer cured for 28d reached 31.5MPa.•Geopolymerization of dissolved aluminosilicate and silica formed dense matrices.
One-part geopolymer was synthesized from alkali–thermal activated Bayer red mud (RM) with addition of silica to optimize its composition. The RM was pretreated through alkali–thermal activation and turned to geopolymer precursor, which could be used by only adding water in blending process. However the long-term strength of the binder with only RM was poor because of the unstable polymerization due to the low SiO2/Al2O3 molar ratio (1.41). Silica fume (SF) was chosen to increase the SiO2/Al2O3 molar ratio of the geopolymer formulation. By adding 25wt% of SF, the 28d compressive strength of the geopolymer with a SiO2/Al2O3 molar ratio of 3.45 could reach 31.5MPa at a water/solid ratio of 0.45. Sodium aluminosilicate in the activated RM dissolved in water and formed an alkaline environment to dissolve SF. The dissolved silica participated in geopolymerization, leading to a satisfactory geopolymer composition. Typical amorphous geopolymer matrices were formed in the binder completely cured.
Metal-organic frameworks (MOFs) have garnered multidisciplinary attention due to their structural tailorability, controlled pore size, and physicochemical functions, and their inherent properties can ...be exploited by applying them as precursors and/or templates for fabricating derived hollow porous nanomaterials. The fascinating, functional properties and applications of MOF-derived hollow porous materials primarily lie in their chemical composition, hollow character, and unique porous structure. Herein, a comprehensive overview of the synthetic strategies and emerging applications of hollow porous materials derived from MOF-based templates and/or precursors is given. Based on the role of MOFs in the preparation of hollow porous materials, the synthetic strategies are described in detail, including (1) MOFs as removable templates, (2) MOF nanocrystals as both self-sacrificing templates and precursors, (3) MOF@secondary-component core-shell composites as precursors, and (4) hollow MOF nanocrystals and their composites as precursors. Subsequently, the applications of these hollow porous materials for chemical catalysis, electrocatalysis, energy storage and conversion, and environmental management are presented. Finally, a perspective on the research challenges and future opportunities and prospects for MOF-derived hollow materials is provided.
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•MOFs have garnered multi-disciplinary attention due to their unique inherent properties•Various synthetic strategies of MOFs-derived hollow porous materials are summarized•Emerging applications of MOFs-derived hollow porous materials are reviewed
We collected street dust from Huainan, a typical coal-mining city in China, to investigate the contamination features and health risks of heavy metals. Concentrations of Co, Cr, Cu, Pb, As, and Sb ...were generally low to moderate, while pollution levels of Cd and Hg were moderate to high. Concentrations of Cd and Hg were associated with considerable health risks at 64.3% and 58.6% of sites, respectively. In particular, about a fifth of samples had associated high risks as a result of Hg contamination levels. Relative to other urban areas, the street dust from the mining area had no more severe metal pollution, which might be partly attributed to the deposition of coal dust onto street dusts. A source assessment indicated that metals in dust form Huainan were mainly derived from vehicular-related activities, industrial emissions, weathering of coal dust and natural soils, and coal combustion. Although the health risk levels from exposure to individual metals in dusts were low, the non-carcinogenic risks from multiple metals to local children exceeded the acceptable level (1.0), suggesting that the overall risk from exposure to multiple metals in dust is concerning.
•Metal concentrations in street dusts from a coal-mining city were investigated.•Pollution levels of Cd and Hg were moderate to high.•Metal pollution in dust from the mining area was no more severe than urban areas.•The overall risk from multiple metals in dusts to local children is unacceptable.
•A method to investigate leachate’ long-term leakage and its impact on groundwater was constructed.•Production and leakage of leachate increase due to performance degradation of landfill.•The ...currently safe landfill may pollute the groundwater around it due to performance degradation.•The decline in landfill performance magnifies the uncertainty of its environment risk.
The long-term dynamics of leachate leakage from hazardous waste landfills (HWLs) and its influence on the surrounding groundwater and human health urgently requires decision-making processes for long-term HWL management and risk control. This study, based on the DMFU model, which is described in the literature as simulating the performance degradation of a landfill's main functional units, constructs a comprehensive model by coupling the HELP, EPACMTP, and Dose-Effect modules to investigate the long-term emissions of leachate from HWLs and their potential influence on groundwater quality and human health. Our results showed that the leakage rate over a long time period (50–1000 years) is 10 times higher than that of either a short (0–10 years) or medium (10–50 years) period. Due to the substantial increase in leakage rate, the negative influence on regional groundwater quality and human health changes from “insignificant” in the short term to “slight but acceptable” in the medium term, and finally to “substantial and unacceptable” in the long term. Studies also reveal that the uncertainty of risk increases over time. The information gained from this research provides useful insights into the long-term dynamics of leachate leakage, its risk consequences, and associated uncertainty, which can help landfill owners or risk managers make better decisions regarding the after-closure management of landfills.
Rapid, accurate detection of heavy-metal content is extremely important for precise risk control and targeted remediation. Herein, a general modeling method and process based on the relationship ...between Pxrf measured values and site parameters are explored to construct a Pxrf correction model suitable to improve each site's measurement accuracy. Results show a significant correlation between Pb, Mn, and Zn Pxrf measured values and actual concentrations, with correlation coefficients between 0.8 and 0.93. Through the correlation analysis, the correlation coefficient between the water content and the measured value of pxrf is in the range of 0.2-0.5. Pxrf measurement of all heavy metals was weakly affected by soil organic matter content, with correlation coefficients all lower than 0.5. Model transformation effectively improved the correlation between measured Pxrf value and actual concentration, and transformation increased the correlations of Sr, Mn, and Cu by around 0.11. Model verification results showed that the Pb, Zn, Fe, and Mn models can be used to improve Pxrf method detection accuracy.
Heavy metals and polycyclic aromatic hydrocarbons (PAHs) are the important contaminants in used mineral oil (UMO) and likely pose environmental risks in the processes of disposal and regeneration. ...However, little information on the concentrations and associated with the risk of heavy metals and PAHs in various types of UMO from different industries is available. In this study, the occurrence of heavy metals and PAHs in the UMOs from typical industries in China was investigated. The median concentrations of 12 metals were 0.1–28 mg/kg. PAHs were mainly composed of 2- and 3-ring compounds and the median concentrations of 16 PAHs were 0.03–7.6 mg/kg in different UMO. The cluster analysis showed that samples with high heavy metal and PAH concentrations mainly originated from machine manufacturing and vehicle industries. The random forest model suggested that the species and phase of UMO were the main influencing factors associated with heavy metal concentrations, and the relative importance was 71.1–19.9%, 100–30.7%, 42.3–20.7%, 38.0–11.8%, and 100–24.1% for Cu, Zn, Ni, Cr, and Pb models, respectively, while industry was the main influencing factor associated with PAHs in UMO, and the relative importance was 81.5–51.5%, 27.7–16.5%, 83.4–25.3%, 94.8–21.4%, and 53.3–16.1% for 2- to 6-ring models, respectively.
A large amount of waste salts (WS) produced during the production of pesticides has posed a great threat to enterprise production and human health. In the study, the regularity and efficiency of ...low-medium temperature pretreatment of pesticide WS were studied to provide help for the subsequent treatment and recycling of the WS. Eight kinds of WS originating from herbicides, insecticides, and bactericides were studied by thermogravimetric (TG) analyses and tubular furnace simulation experiments. The TG and kinetic results showed that the pretreatment temperatures ranged from 350 °C to 700 °C. The optimal disposal temperature varied for different WS, and oxygen could facilitate the pretreatment of WS. Tubular furnace simulation experiments indicated that the effect of pretreatment depends on the organic toxic pollutants (OTPs) components of the samples rather than the type of pesticide. Dicamba WS had the lowest removal rate of OTPs (58.23%), while triadimefon WS had the highest rate (99.74%). The mean rate of OTPs removal from WS was 80%. The results confirmed that low-medium temperature pretreatment can effectively eliminate most of OTPs in WS and reduce the burden of subsequent management and disposal. This technique can be useful for large-scale waste management in the pesticide industry.
•Different pesticide waste salts can be pretreated at low-medium temperatures.•Atmosphere and temperature have an impact on the effectiveness of pretreatment.•Pretreatment can remove about 80% of the organic pollutants from the waste salts.•Low-medium temperature pretreatment is a clean, simple, and efficient method.•Pretreatment can effectively reduce the subsequent disposal pressure of waste salts.
During a three-day industrial trial, municipal solid waste incineration fly ash (FA) was co-processed in a cement kiln after water-washing pretreatment for waste-to-resource conversion. All inputs ...and outputs were sampled to obtain the dioxin fingerprints. During washing, the relative contents of polychlorinated dibenzo-p-dioxins and dibenzofurans in FA, washed FA and sludge were basically the same and only a simple physical migration resulted. During drying, only physical processes resulted, which included volatilization and migration. Minimal dioxins residue remained in the clinker, cement kiln dust and flue gas, and the dioxins degraded completely. Through co-processing, the dioxins degraded obviously. The main compounds synthesized include 1,2,3,4,7,8-hepta-chlorodibenzo-p-dioxin, 2,3,7,8-tetra- chlorodibenzofuran and octa-chlorodibenzofuran. A comparison of dioxins fingerprints in the clinker, cement kiln dust and flue gas under baseline and co-processing conditions showed that co-processing had no effect on the cement kiln production. The baseline sample also contained a certain amount of dioxins, possibly because of the ‘memory effect’ and heterogeneous formations. The dioxins concentrations in the clinker and FA were far lower than the national standards. Thus, no environmental risk results during co-processing.
•Dioxin fingerprints studied in washing and cement kiln co-processing MSWI fly ash.•Stack emissions of PCDD/Fs were below the national limits for cement kilns.•1,2,3,4,7,8-Hepta-CDD, 2,3,7,8-tetra-CDF and octa-CDF are major forms in the kiln.•Only simple physical migration resulted during washing pretreatment and drying.•No environmental risk of PCDD/Fs release during pretreatment and co-processing.
A considerable amount of secondary aluminum dross is generated in the aluminum refining process. Secondary aluminum dross (SAD) is hazardous waste because of its constituent pollutants, such as AlN, ...fluoride, chloride, and heavy metal pollutants. SAD treatment can be categorized into thermal and wet methods. The thermal process has attracted considerable research attention because of its simplicity and ability to prepare Al–Mg spinels, refractory materials, and ceramics and recover alumina during the treatment. However, at this stage, SAD pyrolysis processes are typically focused on the removal of single pollutants. Limited studies have explored the simultaneous removal of various pollutants and their interactions. This study focused on the pyroprocess in the SAD treatment process and investigated the SAD mechanism in the preparation of Al–Mg spinel, refractories, ceramics, and recycled alumina. Furthermore, the conversion of AlN, fluoride, chloride salts, and heavy metals, which are the main pollutants generated in the thermal reaction of SAD, and their control mechanisms were analyzed. The synergistic mechanism of SAD denitrification∖chlorine salt and fluoride fixation∖heavy metal was studied through the reaction mechanism of similar component minerals in the pyroprocess for improving the high-value utilization of SAD and scientific prevention and control of secondary pollution. Finally, the feasibility of preparing ceramic pellets from aluminum dross (AD) was evaluated. The results of the study can provide crucial development directions for SAD utilization.
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