Abstract Under high-temperature conditions, the fluidity retention properties of polycarboxylate superplasticizers remain a challenge. This study improved the molecular structure of traditional slow-release polycarboxylate superplasticizers (also known as slump-retention agents) by introducing hydroxypropyl acrylate, successfully synthesizing a novel slump-retention agent that maintains concrete slump for an extended period at high temperatures. Comparing its performance with two other conventionally synthesized slump-retention agents, the superior performance of the new agent was verified. We then delved into the behavior of this novel slump-retention agent under different temperature conditions.

Red mud is an industrial solid waste rarely utilized and often disposed of in landfills, resulting in resource waste and environmental pollution. However, due to its high pH and abundance of iron and aluminum oxides and hydroxides, red mud has excellent adsorption properties which can effectively remove heavy metals through ion exchange, adsorption, and precipitation. Therefore, red mud is a valuable resource rather than a waste byproduct. In recent years, red mud has been increasingly studied for its potential in wastewater treatment and soil improvement. Red mud can effectively reduce the migration and impact of heavy metals in soils and water bodies. This paper reviews the research results from using red mud to mitigate cadmium pollution in water bodies and soils, discusses the environmental risks of red mud, and proposes key research directions for the future management of red mud in cadmium-contaminated environments.

The photocatalytic degradation technique is considered to be one of the most promising approaches for solving the problem of environmental pollution. In this study, novel binary Bi2Ti2O7/g-C3N4 Z-scheme heterojunctions were prepared using a calcination method. The prepared composite materials were used to degrade bisphenol A under visible-light irradiation. The degradation experiments proved that the composite material with 50 wt.% Bi2Ti2O7 (denoted as BTC-50) showed excellent photocatalytic performance, which was consistent with the characterization results. The composite material displayed no significant decrease in photocatalytic activity after five recycles, and the degradation process was proven to follow pseudo-first-order kinetics. Besides, it was found that center dot O-2(-) played the main role in the photocatalytic reaction process. This work significantly deepens the understanding of Z-scheme heterojunction material for organic degradation and provides ideas for the design of high-performance catalysts.

The leachate sludge (LS) and fly ash (FA) are the foci of hazardous wastes which generated from the municipal solid waste incineration (MSWI). The current work developed a new way to use energy from MSWI process for the on-site sintering of LS and FA at a relatively low temperature . With the assistance of CaF2, granule of LS and MSWI FA was co-sintered. The temperature, influence of the mass of CaF2, and the mass ratio of LS/MSWI FA were investigated. As a result, heavy metals volatilization and leaching in the form of chlorinated salts were controlled. In addition, CaF2 improved the compressive strength of the granule under low-temperature sintering. The lower sintering temperature facilitates the formation of calcium chloroaluminate, which then brings certain benefits to the system, such as changes to particle properties and heavy metal stabilization. The deduction of the heavy metal escaping was characterized by the toxicity characteristic leaching procedure test. Moreover, the scaled-up co-sintering was achieved in an MSWI chamber. The results show that the optimum condition was sintering at 700 ℃ for 1 h. The compressive strength of sintered product reached 6.25Mpa. Moreover, with the addition of CaF2, the volatilization of Pb, Zn, and Cd decreased by 4%, 4%, and 3%, respectively. This method can be a promising technique for the utilization of solid waste for construction materials instead of landfill.

Gaseous mercury pollution control is pressing to both human health and environment protection. Achieving high demercuration performance with the lowest possible amount of active species is critical for developing demercuration adsorbent. Herein, motivated by waste plastic recycling and flue gas demercuration, we report a cost-effective and mild method to reclaim waste polystyrene into highly porous hyper-cross-linked polymers for flue gas demercuration. The waste derived hyper-cross-linked polymer exhibits superior porosity and strong hydrophobic property. Further chemical modification at ultralow concentration (similar to 0.001 mmol/g) over pristine HCPs could promote the chemically Hg-0 bonding ability thus obtaining remarkable demercuration ability (>90% in 15 mins for FeBr3-HCPs) under complicated flue gas conditions along with the interference of 1200 ppm SO2 and 10% H2O. Such HCP-based demercuration adsorbents could greatly surpass state-of-the-art adsorbents. Comprehensive characterizations and density functional theory calculations are performed to illustrate the interaction between HCPs substrate and different active species as well as the Hg-0 removal process over metal and halogen sites. The activity of Fe sites can be optimized by surrounding Cl and Br sites thus promoting the Hg-0 bonding and oxidation. This work could broaden the reutilization methods for waste polystyrene and contribute to the development of gaseous Hg-0 control technology.

The development of sustainable cementitious materials is essential and urgent for the construction industry. Benefiting from excellent engineering properties and a reduced greenhouse gas footprint, alkali-activated materials (AAM) are among the robust alternatives to Portland cement for civil infrastructure. Meanwhile, concrete production also accounts for around 20% of all industrial water consumption, and the global freshwater shortage is increasing. This review discusses recent investigations on seawater-mixed AAMs, including the effects of seawater on workability, reaction mechanism, shrinkage, short and long-term strength, binding of chloride and corrosion of steel reinforcement. Attention is also paid to the utilization of sea sand as aggregate, as well as discussions on the challenges and further research perspectives on the field application of AAMs with seawater and sea sand.

Currently, there is an urgent need to remediate heavy metals (HMs) and high alkalinity in the washing solution of fly ash (FA). This study investigated the remediation with simulated exhaust gases of two CO2 partial pressure and revealed the removal efficiency of target pollutants, mainly including Pb ions. The results verify that under the preferred conditions of 25 °C and 15 mL/min flow rate, bubbling two kinds of simulated flue gases could efficiently remove 97.9–99.2% of Pb ions. Moreover, the initial 40 min removal of Pb ions fits in a way with a pseudo-first-order equation. Based on the thermodynamic parameters, we infer that the removal of Pb ions was a spontaneous, exothermic, and entropy-decreasing process. Furthermore, residual HMs and terminal pH after remediation of the FA washing solution basically met the regulatory threshold values of the integrated wastewater discharge standard in China (GB 8978−1996). Additionally, the particles obtained from the washing solution of FA were identified as CaCO3, which was mainly composed of vaterite and calcite crystalline. This study provides a fundamental guide for remediating multiple pollutants in the washing solution of FA and simultaneously sequestrating carbon emissions from power plants and industries.

The leachate sludge (LS) and fly ash (FA) are the foci of hazardous wastes which generated from the municipal solid waste incineration (MSWI). The current work developed a new way to use energy from MSWI process for the on-site sintering of LS and FA at a relatively low temperature. With the assistance of CaF2, granule of LS and MSWI FA were co-sintered. The influence of temperature, the mass of CaF2, and the mass ratio of LS/MSWI FA were investigated. As a result, heavy metals volatilization and leaching in the form of chlorinated salts were controlled. In addition, CaF2 improved the compressive strength of the granule under low-temperature sintering. Moreover, the scale-up co-sintering test was achieved in an MSWI chamber. The results showed that the optimum condition was sintering at 973K for 1 h. The compressive strength of sintered product reached 4.25 MPa, which met the standard of ceramic granule. Moreover, with the addition of CaF2, the volatilization rate of Pb, Zn, and Cd decreased by 6%, 7%, and 6%, respectively. This method can be a promising technique for the utilization of solid wastes.

As a resource treatment method, pyrolysis realizes the recovery of oil and immobilization of heavy metals in oily sludge (OS). The results showed that the composition of OS had little effect on the trend of the whole pyrolysis process, but it had different effects on the mass loss and maximum weight loss rate at each pyrolysis stage. SEM-EDS results showed that the pyrolysis residue had a porous internal structure, which was similar to that of activated carbon. The elements S, Ca, O, Fe, Al, and Si were embedded in the carbon skeleton. After OS pyrolysis, the oil content of the solid residue was far less than 2%, which met the pollution control requirements for comprehensive utilization specified in China's oil and gas industry standard. At the same time, the ratio of exchangeable fraction decreased and the ratio of residual fraction increased after OS pyrolysis. The potential ecological hazard coefficient (Er) of Cd in OS2, OS2-500, and OS2-600 was greater than 40, which were strong and medium hazards. The Er values of OS2-700 and other metals were far lower than 40, which were low hazards. With the increase of pyrolysis temperature, the comprehensive ecological hazard index (RI) of heavy metals in the residue gradually decreased and the RI value of OS2-700 decreased to 28.01. Therefore, the pyrolysis residue had an internal porous structure and controllable environmental risk. It could be used as an adsorption material for heavy metals to realize the comprehensive utilization of OS.

In this paper, AgBiO3 and g-C3N4 materials were prepared by the ion-exchange method and calcination method, respectively. Their composite materials with different compositions were prepared by changing the dosage of raw materials during the synthetic process. The prepared nano-composite materials were utilized to degrade bisphenol A (BPA) under visible light irradiation. By comparison, 50 wt.% AgBiO3 in AgBiO3/g-C3N4 (ABC-50) owns the supreme photocatalytic activity with 95.75% degradation efficiency of BPA and the degradation process was proven to follow the pseudo-first-order kinetics. In addition, the oxidative species of O-center dot(2)- and h(+) and OH were found to play equal roles in the photocatalytic reaction process.

Investigations concerning the release of potentially harmful substances are carried out on hardened concrete only and just in a few countries (e. g. Netherlands and Germany). However, in some applications, cementitious material can be exposed to water in a fresh state during the construction phase. Therefore, a tank test for fresh concrete has been developed. In contrast to common leaching tests, e. g. the European dynamic surface leaching test (DSLT, CEN/TS 16637-2), water is applied on the fresh concrete surface rather than on a hardened, monolithic specimen. This paper summarizes the results of several research projects on this topic conducted during the last 20 years. For the parameters Ba, Cr, Cu, Pb and V, the leaching of fresh cementitious materials (concrete and cement grouts) including the subsequent leaching of the hardening materials are compared with DSLT results. For Ba, Cr, Cu, V, the release of fresh materials is significantly higher than that of hardened materials, which can be explained by the decreasing diffusion coefficient with progressing hydration. However, for Pb, the leaching of hardened materials is higher. (C) 2020 Elsevier Ltd. All rights reserved.

Different percolation tests were developed worldwide to characterize the leaching and to evaluate the environmental compatibility of granular materials. The German standard up-flow percolation test has a short testing time and can be used for both coarse and fine-grain materials. Some very fine-grain materials are difficult to percolate. According to the standard, admixture of 80% quartz sand (20% material) can be used for cohesive materials. It is assumed that equilibrium concentrations are reached and therefore the sand does not cause any interfering processes. However, the 80% sand admixture cannot be used for coarse materials due to dilution. A standardized sand admixture for both coarse and fine-grain materials is beneficial for the routine of laboratories. The sand admixture has the further advantage that it reduces the testing time. The experimental and the analysis procedures of the German standard were checked, specified, and optimized. An admixture of 50% sand is a good compromise for cohesive and coarse materials. The statistical variations of heavy metal and polycyclic aromatic hydrocarbons from the optimized test with and without sand admixture were determined with an 8-fold intralaboratory and an interlaboratory test. Then the sand admixture was validated for 16 materials (soils, demolition wastes, ashes and other industrial wastes).

A novel alkali activated slag-asphalt emulsion composite was creatively synthesized in this work. Four mixing proportions were developed with the asphalt emulsion/alkali activated slag ratio ranging from 0.25 to 1. Attention is paid to the mixing stability of asphalt emulsion, for which two mixing procedures were compared. The evolution of density, mechanical strength and microstructure of synthesized composites were well characterized. Results show that both the density and mechanical behaviors of obtained composites decrease with the increase of asphalt content. The composites exhibit decent microstructure with interpenetrating network of alkali activated slag binder, asphalt film and aggregate. Compared with cement-asphalt emulsion composite, the alkali activated slag-asphalt emulsion composite possess comparable or even better mechanical performance, suggesting its great potential as sustainable alternative of cement-asphalt emulsion composite. (C) 2020 Elsevier Ltd. All rights reserved.

The sustainable development of the building sector is an important concern of the public, industry and governments. One way to reduce the ecological footprint is to use building materials with less energy consumption and lower CO2 emissions. In this study, a clinker-free cementitious binder was synthesized through an alkali activation of ground granulated blast furnace slag. Flexural and compressive strength of the resulting alkali activated slag (AAS) were measured and compared with ordinary Portland cement (OPC). The Aachen Polishing Machine (APM) equipped with real vehicle tires and a British pendulum tester was applied to assess the skid resistance of AAS and OPC after polishing. Reaction products were documented using the X-ray Diffraction (XRD) technique to explore the reaction mechanism. In addition, the equivalent CO2 emission of AAS production was calculated to evaluate its environmental impact. Results show that the AAS possesses comparable after polishing skid resistance to OPC, but higher flexural strength and lower equivalent CO2 emission. All these demonstrate that AAS can be used as an environmentally friendly alternative binder for concrete pavement construction.

In this paper, clinker-free cementitious binders were synthesized to produce ambient temperature cured pervious concrete of high aggregate-to-binder ratio. The binders are alkali activated slag, metakaolin geopolymer and metakaolin-slag geopolymer. Effects of aggregate size and binder type on the physical properties of resultant pervious concrete were studied in terms of compressive strength, density, total porosity and water permeability. Reaction products of binding materials were measured using X-ray diffraction (XRD) to study the reaction mechanisms. The pervious concretes produced in this work are not only environmentally friendly, but also achieved better mechanical properties and water permeability than cement pervious concretes. (C) 2018 Elsevier Ltd. All rights reserved.