Advances on resource utilization of semi-dry desulfurization ash by thermal decomposition: a high-efficiency and low-temperature method for large-scale processing.

The semi-dry flue gas desulfurization ash (SFGDA) is an industrial waste generated by the semi-dry desulfurization process, and its resources have been continuously attracted attention. Through the method of heat decomposition, the SFGDA decomposed into CaO and SO2 has emerged as a prominent research topic. This paper summarizes various of research workers, who revealed that the decomposition temperature of CaSO4 in SFGDA is greater than 1678 K and 1603 K in the air atmosphere and N2 atmosphere, respectively, presenting challenges such as high energy consumption and limited economic feasibility. On the one hand, the effects of CO and C regulating the pyrolysis atmosphere on reducing the pyrolysis temperature were reviewed. On the other hand, the impact of additives such as Fe2O3 and FeS2 was considered. Ultimately, the joint effects of regulating atmosphere and additives were discussed, and an efficient and low-temperature decomposition route was obtained; adding solid C source and Fe2O3 for pyrolysis reaction, the decomposition temperature of CaSO4 can be reduced by at least 230 K and desulfurization efficiency exceeds 95% under the condition of micro-oxidizing atmosphere. Moreover, the CaO resulting from SFGDA decomposition can be further synthesized into calcium ferrite, while the enriched SO2 can be utilized for the production of industrial sulfuric acid, which holds promising prospects for large-scale industrial applications.

Oily cold rolling mill sludge conditioned by quicklime to improve dewatering performance: optimization and mechanism study.

Dewatering is critical to oily cold rolling mill (CRM) sludge treatment. Therefore, finding an efficient, energy-saving, and applicable dewatering technology for oily CRM sludge is still urgent. This study investigated the performance of quicklime as a conditioning agent for oily CRM sludge conditioning and dewatering. The interactive effects of quicklime dosage, temperature, and time on filter cake's specific resistance to filtration (SRF) and the dewatering rate of oily CRM sludge were studied by response surface methodology (RSM). The optimal parameters for conditioning oily CRM sludge were quicklime dosage of 18.7%, temperature of 54 °C, and time of 43.3 min, which resulted in filter cake SRF of 0.50 × 1010 m/kg and dewatering rate of 61.2%. The viscosity of oily CRM sludge could be reduced by 90% after conditioned with quicklime, which caused by the neutralization or hydrolysis of high viscosity organic matter in the oil phase with quicklime to produce low viscosity organic matter. The study indicated the excellent performance of quicklime as a conditioning agent for oily CRM sludge treatment and provided an effective route for the recycling of the oily CRM sludge for steel production.

Efficient Co-Valorization of Phosphogypsum and Red Mud for Synthesis of Alkali-Activated Materials.

Phosphogypsum and red mud are bulk industrial solid wastes that trigger local environmental problems. In the present investigation, an efficient valorization process was developed through which phosphogypsum and red mud can be transformed into a precursor for the synthesis of high-strength, alkali-activated materials with a seawater-bearing sodium silicate solution as the alkaline activator. The effects of the activator modulus and liquid-to-solid ratio on the strength evolution of the synthesized AAMs as well as the microstructure and chemistry of the reaction products were investigated. The results showed that mineral reconstruction between PG and RM took place during calcination at 950 °C, forming ye'elimite, anhydrite and gehlenite, which then took part in the alkali-activation process and generated thenardite and C-A-S-H gel. The mechanical properties of the synthesized AAMs, ranging from 12.9 MPa to 40.6 MPa, were determined with the activator modulus and liquid-to-solid ratio. Results from the present investigation contributed to the facile and efficient valorization of phosphogypsum and red mud into cementitious construction materials.

Recent Advances in Alkali-Activated Materials with Seawater and Sea Sand.

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.

Co-treatment of municipal solid waste incineration fly ash (MSWI FA) and municipal sludge: A innovative method to improve sludge dewatering with fly ash dechlorination.

The complexity of municipal sludge dewatering is a bottleneck problem limiting resource utilization. In this paper, adding municipal solid waste incineration fly ash (MSWI FA) to municipal sludge for enhanced dewatering was applied, while the chlorine salt in MSWI FA was simultaneously removed using water in municipal sludge. The effects of different dosages and chemical components of MSWI FA on municipal sludge dewatering, and the removal effect of municipal sludge washing on Cl element were investigated. The results showed that the municipal sludge's specific resistance to filtration after co-treatment was significantly reduced, and more hydrophobic channels were formed in the vacuum suction filtration of the treated municipal sludge, conducive to efficient water removal. The moisture content of municipal sludge was reduced from 96.0% to 48.3%, and the moisture reduction rate increased from 17.7% to 32.1%. The chemical composition of MSWI FA could effectively promote the dewatering of municipal sludge, among which CaO was the best, followed by CaCl2 and NaCl, and KCl was the worst. Simultaneously, the municipal sludge showed a good effect on removing Cl from MSWI FA. The minimum Cl content in the mixture after Co-treatment is 1.5%. These results could provide a new way to dispose of MSWI FA and municipal sludge.

Subcritical hydrothermal treatment of municipal solid waste incineration fly ash: A review.

Municipal solid waste incineration fly ash (MSWI-FA) is a hazardous waste generated from the incineration process, and the harmless treatment of MSWI-FA has attracted widespread attention. Subcritical hydrothermal treatment is competitive in achieving the harmless treatment and resource recycling of MSWI-FA. It exhibits excellent performance in degrading dioxins, stabilizing heavy metals, and converting MSWI-FA into zeolite or tobermorite at low temperatures. This paper clearly introduces the characteristics of MSWI-FA, roundly summarizes the current research status of treating MSWI-FA by subcritical hydrothermal methods, and deeply clarifies the mechanisms of dioxins degradation, zeolite/tobermorite synthesis, and heavy metals stabilization. Considering the research status of handling MSWI-FA by subcritical hydrothermal methods, future research directions are proposed. Owing to the advantages of high efficiency, energy-saving, and environmental sustainability, subcritical hydrothermal treatment of MSWI-FA exhibits promising prospects for industrialization.

Long-term intermittent hypoxia induces anxiety-like behavior and affects expression of orexin and its receptors differently in the mouse brain.

Studies have revealed a possible connection between orexin, narcolepsy, and obstructive sleep apnea (OSA). Orexin has an important role in the maintenance of arousal and wakefulness/sleeping states. To better understand the pathophysiological mechanism of OSA, we used a chronic intermittent hypoxia (CIH) model in mice to mimic OSA. In this way, we explored the effect of CIH on the locomotor activity and orexin system in the hypothalamus, cerebral cortex, and brainstem of mice. Male C57BL/6 J mice (8 weeks) in the CIH group were exposed in a hypoxia chamber for 8 h/day for 28 weeks. The re-oxygenation groups comprised the W2 group and W4 group, which were exposed to 28 weeks of CIH followed by 2 weeks and 4 weeks of re-oxygenation, respectively. The open field test was undertaken to observe locomotor activity. mRNA expression of orexin, orexin receptor type 1 (OX1R), and OX2R mRNA was evaluated by real-time reverse transcription-quantitative polymerase chain reaction. Mice subjected to long-term CIH exhibited significant anxiety-like behavior during the light period, and this behavior lasted until 4 weeks of re-oxygenation. mRNA expression of orexin was upregulated in the hypothalamus. mRNA expression of OX1R mRNA in the cerebral cortex and brainstem was downregulated by CIH. Two weeks and 4 weeks of re-oxygenation could not reverse these alternations. Long-term CIH may induce anxiety-like behavior and re-oxygenation cannot reverse these behavior. Moreover, OX1R has a significant role in the anxiety-related symptoms observed in long-term CIH.

Basic Research on Co-treatment of Municipal Solid Waste Incineration Fly Ash and Municipal Sludge for Energy-Saving Melting.

MSWI fly ash and municipal sludge are solid wastes. Melting vitrification treatment was a resource utilization method. However, the flow temperature of grate furnace MSWI fly ash and municipal sludge was high (>1325 °C), which increased the energy consumption in the melting process. MSWI fly ash contained a large amount of CaO, and municipal sludge contained a large amount of SiO2, Al2O3, and Fe2O3. The temperature of melting vitrification can be reduced using these two kinds of CITY garbage as raw materials to change the proportion of ingredients. The eutectic characteristics of MSWI fly ash and municipal sludge and the phase diagrams of CaO-SiO2-Al2O3 (C-S-A) and CaO-SiO2-Al2O3-Fe2O3 (C-S-A-F) were analyzed in this paper. It established a low melting point mixing system. The results showed that when the amount of municipal sludge was 50-70%, the flow temperature of the mixtures was <1215 °C, which was significantly lower than that of MSWI fly ash (1490 °C) and municipal sludge (1325 °C). The optimal range of low melting point components was 14.1-36.3% CaO, 21.6-40.4% SiO2, 6.7-12.6% Al2O3, and 6.3-11.4% Fe2O3. At 400-1400 °C, the minerals in the mixtures mainly changed as follows: CaCO3 + SiO2 + Al2O3 → Ca2SiO4 + Ca3SiO5 + Ca2Al2SiO7 + Ca3Al2O6 + Ca12Al14O33 → CaAl2Si2O8. In the melting experiment, with the increase in temperature, most of the phases in the mixtures might become amorphous. Therefore, the low melting point phase anorthite (CaAl2Si2O8) only accounted for a small part of the final molten product.

Enhancing the Dewaterability of Oily Cold Rolling Mill Sludge Using Quicklime as a Conditioning Agent.

The high moisture and viscosity characteristics of oily cold rolling mill (CRM) sludge led to limitations in its recycling. In this paper, the results of using quicklime as a conditioning agent to improve the dewaterability of the oily CRM sludge cake were reported. Quicklime was selected as the best conditioning agent through conditioning-dewatering experiments because it could effectively reduce the viscosity of oily CRM sludge and improve the dewaterability of the oil sludge filter cake. The optimal conditioning effect was obtained when the quicklime dosage was 10%, the temperature was 60 °C, the liquid/solid ratio was 1.5:1, and the time was 30 min. The reduction of specific resistance to filtration was 95.9%, and the coefficient of compressibility of the filter cake decreased from 1.11 to 0.89. The dewatering rate increased from 9.0 to 52.6%. The oily CRM sludge cake formed an incompressible rigid porous structure because of conditioning with quicklime. In addition, after conditioning with quicklime, the oil content, chemical oxygen demand, and turbidity of the filtrate decreased, and the composition of the dried filter cake met the requirements of ironmaking raw materials. Using quicklime to condition the oily CRM sludge provided a green approach to waste recovery and sustainable management.

Investigation on the application of by-product steam in iron ore sintering: performance and function mechanism.

The combustion-supporting effect of steam to coke breeze in sintering has the potential to improve sinter quality and reduce pollutants emissions. The results show that increasing the by-product steam injection concentration (0.32-0.47vol%) and prolonging the injection time (5 min) within a proper range (10-15 min) can improve sinter quality. 2.13kgce/t-sinter of the fuel consumption was decreased by reducing coke breeze usage from 5.60 to 5.45% under the recommended parameters, with 15.16% decrease of CO in sintering waste gas. By comparing experimental data with thermodynamic calculations, although the reaction between CO and steam can reduce CO emission and generate H2, steam tends to react with coke breeze to generate H2 and CO (react at 674℃), and OH radical produced by H2 which can reduce the activation energy of CO oxidation reaction is the key to reducing pollutant emissions. The potential economic benefit of steam injection technology was calculated based on a 360m2 sintering machine (the annual sinter output is 3.2million tons), excluding the equipment modification and steam injection cost of $300,000; a profit of $737491.2 per year or 0.23 dollars per ton sinter can be achieved. Therefore, low-carbon and cleaner iron ore sintering production can be realized through applying by-product steam.

Dioxins control as co-processing water-washed municipal solid waste incineration fly ash in iron ore sintering process.

Co-processing water-washed municipal solid waste incineration fly ash (WM-FA) in iron ore sintering process is of great prospect. In this paper, the emission characteristics of dioxins during sintering process combined with WM-FA were studied, and the control method for dioxins was proposed. The results showed that adding WM-FA in the form of pellets with diameter 5-8 mm slightly influenced sinter quality. Increasing the diameter of WM-FA from 5-8 mm to 10-12 mm helped to reduce the concentration of PCDD/Fs from 1.0425 ng I-TEQ/N m3 to 0.7720 ng I-TEQ/N m3. However, compared with no WM-FA adding case, adding WM-FA pellets caused the increase of PCDD/Fs concentration in the sintering flue gas. A novel method for dioxin control was proposed through preparing WM-FA into 5-8 mm pellets and coated with CaO-containing additive with its function to adsorb and fix HCl and Cl2, which were the key components to synthesize dioxin. Due to the inhibiting effect of CaO to the chlorination reaction, the emission concentration of PCDD/Fs was decreased to 0.6240 ng I-TEQ/N m3, which was lower than that of no WM-FA adding case. The research findings lay a foundation for the resource utilization of WM-FA and the harmonious development of city and steel plant.

Self-Compacting Alkali-Activated Materials: Progress and Perspectives.

Alkali-activated materials (AAMs) are considered to be alternative cementitious materials for civil infrastructures. Nowadays, efforts have been made in developing AAMs with self-compacting ability. The obtained self-compacting AAMs (SCAAMs) accomplish superior passing and filling properties as well as excellent mechanical and environmental advantages. This work critically revisits recent progresses in SCAAMs including mixture proportions, fresh properties, mechanical strength, microstructure, acid and sulfate resistance, high temperature behaviors, impact resistance and interface shear strength. To facilitate direct comparison and interpretation of data from different publications, mixture proportions were normalized in terms of the content of key reactive components from precursors and activators, and correlation with mechanical behaviors was made. Moreover, special attention was paid to current research challenges and perspectives to promote further investigation and field application of SCAAMs as advanced construction material.

Co-disposal of municipal solid waste incineration fly ash and bottom slag: A novel method of low temperature melting treatment.

Conventional melting for disposing municipal solid waste incineration (MSWI) fly ash or bottom slag needed high temperature and consumed high energy. High calcium content in fly ash and high silicon content in bottom slag brought them high melting point, respectively. Based on the analysis of chemical composition and phase diagram, suitable contents, namely 30%-40% CaO, 45%-60% SiO2 and 10%-15% Al2O3, were proposed to obtain a lower-melting-point mixture system. When the mass ratio of fly ash to bottom slag was 1:5, lowest melting point can be obtained. It was 1,190 â„ƒ, lower than that of fly ash (1,448 â„ƒ) and bottom slag (1,310 â„ƒ). The toxicity characteristic leaching procedure of slags obtained from low melting treatment met the leaching toxicity of Chinese standard GB 5085.3-2007, and the slags containing about 25 wt% CaO, 10 wt% Al2O3 and 45 wt% SiO2 can be used for preparing CaO-Al2O3-SiO2 glass ceramics. The co-process of fly ash and bottom slag realized the low temperature melting treatment with low energy consumption.

Influences of fine-grained NaCl particles on performance and denitration efficiency of activated carbon during sintering flue gas purification process.

Alkali metal chlorides emitted from sintering flue gas are easily adsorbed on the surface of activated carbon (AC) in the purification process. In this paper, NaCl particles adsorbing onto AC were simulated by impregnation method, and the size and morphology of NaCl particles were similar to those of NaCl-PM10 emitted from sintering flue gas. With the adsorption of NaCl particles, 2-10-µm pores of AC were filled, and the specific surface area of AC decreased. But NaCl led to the increase of acidic functional groups on the surface of AC. When 0.75 wt% NaCl was adsorbed, it was beneficial for AC catalytic denitration (de-NOx), because the chemical reaction was strengthened by acidic functional groups, so it showed a certain promotion of de-NOx efficiency. As 1.5 wt% NaCl and 3 wt% NaCl were adsorbed, NaCl had an inhibitory effect on AC de-NOx, which was because the specific surface area of AC decreased, and the prevention of physical adsorption played a major role. As a result, the de-NOx efficiency of AC adsorbed with 3 wt% NaCl decreased from 40.59 to 23.02% at 150 °C. Therefore, the absorption of NaCl fine particles on AC should not exceed 0.75 wt%.

Clean recycle and utilization of hazardous iron-bearing waste in iron ore sintering process.

Applying recycled iron-bearing waste materials (RIM) into iron ore sintering process is the general disposal approach worldwide, while its use is still a thorny problem. Results showed that adding RIM increased contents of hazardous elements (K, Na, Pb, Zn, and Cl) in sinter product, and also enhanced emission concentration of PM2.5 in flue gas; increasing reaction temperature, and contents of CaO & coke breeze in raw mixtures improved hazardous elements removal. Based on these features, a novel method through granulating natural iron ores and RIM separately and distributing granulated RIM in bottom sintering layers was proposed for clean RIM cycle. When recycling 5% RIM, granulating RIM separately with higher contents of CaO and coke breeze removed hazardous elements effectively, the contents of which in sinter were reduced to comparable level of the case without RIM. Moreover, distributing RIM in bottom sintering layer reached intensive release of hazardous elements and PM2.5 during sintering, which reduced the flue gas volume needing purification by about 2/3. Through activated carbon purification, about 60% of PM2.5 comprised high contents of hazardous elements was removed. Novel technique eliminated the negative impact of RIM and has the prospect to reach clean recycle in sinter-making plants.

Influence of sulfur dioxide-related interactions on PM2.5 formation in iron ore sintering.

The formation of PM2.5 (aerosol particulate matter less than 2.5 µm in aerodynamic diameter) in association with SO2 emission during sintering process has been studied by dividing the whole sintering process into six typical sampling stages. A low-pressure cascade impactor was used to collect PM2.5 by automatically segregating particulates into six sizes. It was found that strong correlation existed between the emission properties of PM2.5 and SO2. Wet mixture layer (overwetted layer and raw mixture layer) had the function to simultaneously capture SO2 and PM2.5 during the early sintering stages, and released them back into flue gas mainly in the flue gas temperature-rising period. CaSO4 crystals constituted the main SO2-related PM2.5 during the disappearing process of overwetted layer, which was able to form perfect individual crystals or to form particles with complex chemical compositions. Besides the existence of individual CaSO4 crystals, mixed crystals of K2SO4-CaSO4 in PM2.5 were also found during the first half of the temperature-rising period of flue gas. The interaction between fine-grained Ca-based fluxes, potassium vapors, and SO2 was the potential source of SO2-related PM2.5. IMPLICATIONS: The emission property of PM2.5 and SO2 throughout the sintering process exhibited well similarity. This phenomenon tightened the relationship between the formation of PM2.5 and the emission of SO2. Through revealing the properties of SO2-related PM2.5 during sintering process, the potential interaction between fine-grained Ca-based fluxes, potassium vapors, and SO2 was found to be the source of SO2-related PM2.5. This information can serve as the guidance to develop efficient techniques to control the formation and emission of PM2.5 in practical sintering plants.