Flue Gas Desulphurization Gypsum Research Articles

Mechanical properties of solid waste-based composite cementitious system enhanced by CO2 modification

Utilizing CO2 to modify solid waste and produce high-performance cementitious material is a promising strategy. In this study, circulating fluidized bed fly ash (CFBFA), calcium carbide slag (CS) and flue gas desulphurization gypsum (FGDG) were prepared by mixing CO2 to produce cementitious materials. The impacts of CO2 on mechanical properties and carbonation reaction mechanism of composite materials were investigated. The results shown that the microstructure and mechanical properties of the gelling materials were improved by CO2 modification. When the CO2 mass transfer conditions as followed: CO2 flow rate was 1.5 L/min, stirring rate at 600 r/min, and stirring time at 20 min, compressive strength of modified material was 22 % higher than that of the non-CO2 modified material. Additionally, the density increased by 3.2 %, and porosity was reduced by 34.1 %. Among them, TG/DTG analysis found that the highest effective fixed CO2 rate was 11.1 %. The ultrasonic nondestructive testing also shown that the structure of the CO2-modified cementitious material was significantly better than that of the CFBFA-CS-FGDG composite cementitious system, and the ultrasonic loss rate was reduced by 9.4 %. Therefore, the use of CO2 to modify the composite system was of great significance for the realization of CO2 storage and the improvement of the properties of composite materials. One interesting future possibility is solid waste-based grouting materials production at energy plants: CFBFA, CS and FGDG can be used to capture CO2 from flue gases, thus improving the strength of produced grouting materials.

The Hydration Mechanisms of Co-Stabilization Saline Soils by Using Multiple Solid Wastes

In this paper, an approach was employed to fabricate a curing agent using multiple solid wastes. To determine the optimal mixing ratio, orthogonal and compaction tests were initially conducted, followed by a comparative analysis of the excitation effects elicited by sodium silicate and NaOH. Remarkably, sodium silicate demonstrated superior suitability as an activator. The final composition was established as follows: 4% sodium silicate, 26% carbide slag, 25% granulated blast furnace (GBF) slag, 35% coal fly ash, and 10% flue gas desulphurization (FGD) gypsum. Under controlled conditions of 20% of curing agent content, the unconfined compressive strength of the solidified soil at 7 d attained 1.54 MPa, thereby satisfying the rigorous construction requirements for highways across all levels. XRD and SEM-EDS analyses revealed that the principal hydration products in the system consisted of ettringite, Friedel’s salt, and C-S-H gel. These products enveloped the soil particles, with ettringite and Friedel’s salt intermingling and occupying the intricate framework formed by the gel. The synergistic interplay among the components ultimately fostered the development of a coherent soil structure and enhanced overall densification.

Study on the influence mechanism of flue gas desulphurisation gypsum on solid waste-based geopolymer grouting materials

Solid waste-based geopolymer grouting materials were prepared using fly ash, calcium carbide slag, and flue gas desulphurisation gypsum as the main raw materials. The effect of desulphurisation gypsum dried at different temperatures on the performance of the solid waste-based geopolymer grouting materials was explored. The mechanical properties, phase composition, and microstructure of the grouting materials were determined using a universal testing machine, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The results show that flue gas desulphurisation gypsum dried at 120 °C generated more whiskers. The mechanical properties of the solid waste-based geopolymer grouting materials prepared by drying flue gas desulphurisation gypsum at 120 °C were significantly improved, and the compressive strength was increased by more than 11%, thereby promoting the hydration reaction of the system and generating over 3% of the hydration products.

Preparing new supplementary cementitious materials with co-calcined waste glass-dolomite and environmental assessment

Recycling waste glass (WG) for supplementary cementitious materials is one of the most viable methods to address the environmental issues of waste generation. In this study, homogenised WG–dolomite with different mass ratios was first calcined at 800 °C and 1000 °C. Then non-cement clinker cementitious materials (NCCMs) were prepared by mixing calcined WG–dolomite, superfine slag (SS) and flue gas desulphurisation gypsum. Finally, coupled with silica tailings, NCCMs were used to prepare cemented paste backfill (CPB) samples. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Isothermal calorimeter, Thermogravimetry (TG) and scanning electron microscopy (SEM) were employed to study the thermal transformation of calcined WG–dolomite and microstruction evolution of NCCMs hydration. The experimental results show that the main products of calcined WG–dolomite have high contents of MgO, calcite and CaO at 800 °C, whereas they have large proportions of C2S and CA at 1,000 °C. As the calcination temperature increases, the chemical shift of 29Si moves steadily towards higher frequencies, indicating the dominance of Q0/Q1 sites from silicate. In addition, the high contents of MgO and CaO in calcined WG–dolomite accelerate NCCM paste hydration, which is conducive to the formation of C–A–S–H and M−S−H. Moreover, due to SS hydration being more dependent on alkaline environments, co-calcined WG-dolomite at 800 °C enables the CPB sample to have better mechanical performance.

Properties of Flue Gas Desulphurization Gypsum–Activated Steel Slag Fine Aggregate Red Mud–Based Concrete

The large amount of discharge and accumulation of red mud and steel slag has led to the waste of land resources and serious environmental pollution problems. Therefore, the utilization of a large amount of red mud and steel slag in reasonable fields is an urgent problem. At present, the main practical methods include using red mud as a substitute for cement or raw material in cement clinker production and grinding steel slag as a mineral admixture or directly replacing fine aggregates. However, experimental studies on the simultaneous use of large amounts of red mud and steel slag in concrete are extremely limited. In this paper, red mud was used to replace cement (40%–60%) and steel slag to replace fine aggregate (50%–100%) to prepare steel slag fine aggregate red mud–based concrete (SFA-RM concrete). In addition, flue gas desulphurization gypsum (FGDG) was added as a sulfate activator in the concrete to stimulate the potential cementitious activity of red mud and steel slag to prepare the FGDG-activated SFA-RM concrete with improved strength. A total of 18 concrete mixes with different proportions of red mud, steel slag, and gypsum were designed and the mechanical properties, workability, hydration products, and microstructure of these concretes were studied. The results showed that the mechanical properties of FGDG-activated SFA-RM concretes were excellent, the 60 day compressive strength of the SFA-RM concrete reached 43.8 MPa, and the compressive strength of FGDG-activated SFA-RM with 15% gypsum and 100% replacement rate of steel slag improved to 47.1 MPa, which were both better than ordinary concrete. Moreover, the results of X-ray diffraction (XRD) and scanning electron microscope (SEM) tests indicated that the hydration products of concrete mainly included Ca(OH)2, C-S-H gel, ettringite, and zeolite, with small and few micropores as well as dense microstructure.

Properties and hydration characteristics of an iron-rich sulfoaluminate cementitious material under cold temperatures

In this study, an iron-rich steel-slag-based sulfoaluminate cementitious material (SSCM) was prepared using steel slag, flue gas desulphurisation gypsum, aluminium ash, and limestone tailings. The basic and cold-temperature characteristics of SSCM were studied. The results show that Fe2O3 introduced by steel slag promotes the transformation of C4A3S¯-o to C4A3S¯-c, making SSCM more resistant to freezing injuries than Portland cement. As the curing temperature decreases, the formation rate of ettringite in the early stage slows down obviously. With the hydration progressing, the ettringite content in pastes cured at low temperatures (0–5 °C) becomes similar to that cured at 20 °C, and the proportion of harmful pores is decreased. Although the pastes cured at negative temperatures still contain a large amount of unhydrated phase and a significantly increased proportion of harmful pores, the hydration reaction can still be maintained. The performance of SSCM shows a promising application prospect for construction in cold regions.

Enrichment of keystone fungal taxa after flue gas desulphurization gypsum application drives reclamation of the saline‐sodic soil

AbstractSoil salinization is a major threat to sustainable agriculture in the western part of Songnen Plain, Northeast China. Flue gas desulphurization gypsum (FGDG) is commonly used for reclaiming of saline soils due to its high efficiency and cost‐effectiveness. However, the responses of soil and root‐associated fungi after FGDG amendment and the keystone fungal taxa in determining soil reclamation effect remain elusive. In this study, a long‐term field experiment was conducted to explore the effect of different levels of one‐time FGDG application on the soil reclamation and the herbage (Leymus chinensis) growth. Our results showed that the FGDG application greatly reduced soil salinity level, increased soil fertility and fungal diversity, and promoted aboveground biomass of L. chinensis, whereas reduced FGDG dose to 60% of gypsum requirement (GR) exhibited non‐significant difference on these characters compared with 100% GR treatment. We further discovered that both soil and root fungal communities were greatly changed after FGDG application, with root fungal community more sensitive than soil fungi. Through applying the Random Forest model, the arbuscular mycorrhizal fungi Glomeromycota was identified as the keystone taxa in predicting the soil salinity, soil fertility, and plant growth trait. Intriguingly, some Glomeromycota‐affiliated ZOTUs were consistently enriched in the FGDG application treatments, and acted as keystone hubs in the co‐occurrence network of fungal communities. Together, our study provides new insights that the enrichment of keystone Glomeromycota after FGDG application determines the reclamation of the saline‐sodic soil, which would guide the microbial‐based strategy for the development of degraded ecosystems.

Evaluation of flue gas desulfurization gypsum as a low-cost precipitant for phosphorus removal from anaerobic digestion effluent filtrate

Land application of anaerobic digestion (AD) effluent as a fertilizer is desirable for nutrient recycle, but often supplies excess phosphorus (P), which contributes to surface water eutrophication. Reducing the P content in AD effluent using calcium treatment prior to land application is a potential strategy for improving effluent disposability. In order to solve the problems of low phosphorus removal efficiency and high operating cost in wastewaters, this study took flue gas desulphurization (FGD) gypsum, a by-product of coal-fired power plants, as a low-cost calcium source, and combined with traditional phosphorus removal agents to achieve high phosphorus removal efficiency with less chemical inputs. As the results showed, FGD gypsum dosages of 20 mM Ca (3.44 g/L) and 40 mM Ca (6.89 g/L) removed up to 97.1% of soluble P (initially 102.8 mg/L) within 60-90 minutes. Combining FGD gypsum treatment with traditional chemical treatments using Ca(OH)2 or FeCl3 could achieve >99% P removal with reduced chemical costs. This study demonstrated that FGD gypsum is an effective calcium precipitant for phosphorus removal.

Leaching of arsenic from flue gas desulphurisation gypsum using ultrasound-enhanced sulfuric acid

The flue gas desulphurisation gypsum (FGDG) produced in nonferrous metal metallurgy industry is defined as hazardous waste because of its arsenic content. In this study, a new process for arsenic removal by ultrasound-enhanced sulfuric acid leaching was developed. The leaching characteristics of arsenic under ultrasound-enhanced leaching and conventional leaching conditions were compared. Furthermore, the results indicated that under the optimal experimental conditions, the leaching efficiency of arsenic in ultrasound-enhanced leaching was 97.07%, while that in conventional leaching was only 79.67%. The leaching kinetic data further proved that the leaching rate of arsenic is controlled by the diffusion process in the ultrasound-enhanced sulfuric acid leaching system, and the activation energy of the reaction is 13.38 kJ mol−1. On the basis of optimization of leaching process parameters, the reaction mechanism of the leaching process was studied by X-ray diffraction, X-ray photoelectron spectroscopy, Electron probe X-ray microanalyser, and scanning electron microscopy. The results of the toxicity assessment indicated that FGDG treated with ultrasound-enhanced sulfuric acid was no longer a solid hazardous waste, which is of great significance for its efficient utilization.

Experimental Study and Mechanism Analysis of Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum with Dynamic Method.

Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum and crystal modifiers was approximately 18%, and the pH value was approximately 6.0. The mixture did not need to be pressed into bricks or made into slurry, and it was directly sent into the autoclave reactor for reaction. It was successfully applied to the practical production and application of FGD gypsum, citric acid gypsum and phosphogypsum. In this work, the compositions and morphology of the product at different stages of the reaction were examined and compared. In particular, single-crystal diffraction was used to produce the crystal structure of CaSO4·0.5H2O, and the results were as follows: a = 13.550(3); b = 13.855(3); c = 12.658(3); β = 117.79(3)°; space group C2. The preferential growth along the c-axis and the interaction mechanism between the carboxylate groups and the crystal were discussed throughout the analysis of the crystal structure.

Research Summary on the Processing, Mechanical and Tribological Properties of Aluminium Matrix Composites as Effected by Fly Ash Reinforcement

Fly ash is the main waste as a result of combustion in coal fired power plants. It represents about 40% of the wastes of coal combustion products (fly ash, boiler ash, flue gas desulphurization gypsum and bottom ash). Currently, coal waste is not fully utilized and waste disposal remains a serious concern despite tremendous global efforts in reducing fossil fuel dependency and shifting to sustainable energy sources. Owing to that, employment of fly ash as reinforcement particles in metallic matrix composites are gaining momentum as part of recycling effort and also as a means to improve the specifications of the materials that are added to it to form composite materials. Many studies have been done on fly ash to study composite materials wear characteristics including the effects of fly ash content, applied load, and sliding velocity. Here, particular attention is given to studies carried out on the influence FA content on physical, mechanical, and the thermal behavior of Aluminium-FA composites. Considerable changes in these properties are seen by fly ash refinement with limited size and weight fraction. The advantage of fly ash addition results in low density of composites materials, improvement of strength, and hardness. It further reduces the thermal expansion coefficient and improve wear resistance.

Efflorescence during the drying of a technical gypsum body: Application of thermodynamic principles

The drying process of a technical flue gas desulphurization (FGD) gypsum body was studied. At low surface-to-volume ratios, it showed a significant efflorescence of hexahydrite (MgSO4·6H2O) after less than one day. A countermeasure against this phenomenon is the addition of small amounts of Ordinary Portland Cement (OPC) (0.2 wt%). Prisms of pure FGD and FGD-OPC mixtures were synthesized and investigated with a combination of 1H-TD-NMR and ICPMS measurements to monitor both the physical water content during the drying process and the chemical pore water composition within the first 48 h. The experiments showed no differences in the drying rate and pore water distribution and only small differences in the pore water composition. In combination with thermodynamic calculations, the prevention of efflorescence could be attributed to chemical processes in the pore water. Mg-sulfates potentially can form on both samples with the same chance. Therefore, it was concluded that OPC can only hinder efflorescence indirectly by decreasing the Mg concentration in the pore water. An increase in pH can cause Mg-phases to precipitate, thereby binding the Mg before Mg-sulfates can form on the surface of the body. Further calculations revealed, that the two phases hydrotalcite and M−S−H can potentially form inside the FGD-OPC prism, probably due to an increase of the pH.

Experimental Study on Mechanical Properties of Paste Backfill with Flue-Gas Desulphurisation Gypsum under Combined Action of Dry–Wet Cycles and Chloride Erosion

Flue-gas desulphurisation gypsum—a solid waste from power plants—can be used to prepare paste backfill for reducing costs. Most paste backfills are exposed to dry–wet cycles and chloride salt-rich water in mines. Therefore, the mechanical properties and damage mechanisms of paste backfill with desulphurised gypsum under the coupling action of erosion due to chloride with different concentrations and dry–wet cycles were investigated using methods such as visual observation, mass measurement, uniaxial compression, acoustic emission, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and field-emission scanning electron microscopy. With an increasing number of dry–wet cycles, the mass, elastic modulus, and strength of the paste backfill exhibited the trend of increasing first and then decreasing. The failure mechanism changed from mainly vertical fractures to the alternating development of vertical and horizontal fractures. The surface denudation effect of the specimens in a solution with a higher concentration was more severe under the same number of dry–wet cycles. In this study, the laws governing the mass change, strength change, degree of surface denudation, and failure pattern of desulphurised gypsum-filled specimens under different concentrations of chloride salt and different numbers of dry–wet cycles were derived.

Limestone Sorbents Market for Flue Gas Desulphurisation in Coal-Fired Power Plants in the Context of the Transformation of the Power Industry—A Case of Poland

Since the beginning of the 1990s, due to international regulations on air quality, a large number of flue gas desulphurisation (FGD) installations have been constructed in the Polish coal-fired power industry. Thanks to that, SO2 capture in this industry increased to ca. 90%. Since wet lime or fluidized bed boilers were mostly used for FGD purposes, a significant increase in the domestic demand for lime sorbents has been reported. Between 1994 and 2019, it has increased from virtually zero before 1994 to about 3.3–3.4 million tpy (tonnes per year) today. On the basis of official governmental data and completed surveys of the Polish power companies, the paper analyses the process of the implementation of FGD in Poland along with limestone sorbents consumption and FGD gypsum production in the Polish coal-fired power plants. It also presents the current and potential limestone resource base for production of limestone sorbents applied in FGD. Electric energy mix in Poland is expected to be changed radically in the coming 30 years. Share of coal-based electricity is still very high—ca. 80%—and it will remain dominant for at least next decade. With the next coming FGD installations, further moderate increase of limestone sorbents consumption is expected, up to 3.7 million tpy in 2030. After 2030, a significant, quick decrease of share of coal-fired electricity is expected in Poland, down to max. 30% just before 2050. This will result in a gradual decrease in limestone sorbent demand, to max. 1.3 million tpy before 2050 and virtually zero after 2050, which will be followed by collapse of FGD gypsum production.

Soil salinity and sodicity changes after a one‐time application of flue gas desulphurization gypsum to paddy fields

AbstractSodic soil is more likely to deteriorate in paddy fields than in other fields. Flue gas desulfurization (FGD) gypsum can reclaim sodic soils, but how long a one‐time application of FGD gypsum provides benefits in paddy fields is poorly understood. In this study, soil salinity, sodicity, and soluble and exchangeable cation concentrations were evaluated over a 7‐year period to investigate the reclamation of sodic soil in a paddy field by FGD gypsum. After 7 years, compared with those in the initial soil, the pH, sodium adsorption ratio, and exchangeable sodium percentage of the topsoil (0–20 cm) decreased by at least 2 units, 72.2% and 80.9%, respectively. In the process of FGD gypsum reclamation, substantial changes in topsoil salinity and sodicity occurred mainly between the 4th and 5th years of reclamation, representing the boundary of the FGD gypsum dissolution stage, which was followed by the soil reclamation maintenance stage. In the FGD gypsum dissolution stage, soil salinity was dominated by Ca2+ that accumulated in the 0–10 cm soil layer. Over time, the exchangeable Ca2+ concentration decreased with soil depth to 40 cm. In the reclamation maintenance stage, FGD gypsum was basically depleted, but the sodicity still showed a significant decrease compared with that in the initial soil. These results indicate that FGD gypsum can significantly and effectively reclaim sodic soil in paddy fields for at least 7 years. Though the FGD gypsum was exhausted 5 years after its application, reclamation continued to be maintained due to the presence of exchangeable Ca2+.

Properties and hydration characteristics of mine cemented paste backfill material containing secondary smelting water-granulated nickel slag

In order to improve the level of solid waste comprehensive utilization and reduce the cost of filling raw materials for mining, a study is carried out on the preparation of cementing agents (CA) for underground mine filling using secondary smelting water-granulated nickel slag (SWNS) as the main raw material. The mechanical properties test, X-ray diffraction (XRD), flourier transform-infrared spectroscopy (FT-IR), thermogravimetric/differential scanning calorimeter (DSC-TG), scanning electron microscope (SEM) and other test methods were used to study the working performance and mechanical properties of the cemented paste backfill (CPB) material, and the types of hydration products, micro-morphology and hydration characteristics of CA of SWNS for CPB material were analyzed. The results show that when the ratio of CA used for CPB material is SWNS:cement clink (CC):Na2SO4:flue gas desulphurization gypsum (FGDG):carbide slag (CS) = 85:2:3:5:5, the binder content on dry basis of tailings (CA/iron ore tailings (IOT)) 1:4, the slurry concentration 82%, and the addition of 0.156% PC water-reducer, the static compressive strength of CPB material 28 days is 7.94 MPa, which is 57% higher under dynamic loading conditions than that under static loading, the tensile strength is increased by 72%, and the shear strength is increased by 127%, which meets the strength requirements of CPB materials used in underground mines. CA of SWNS is a CPB material containing glass phase and crystalline materials. Under the action of various activators, it can participate in the hydration reaction, and the main hydration products are ettringite (AFt) and hydrated aluminosilicate gel material (C–M–S–H) containing Ca2+ and Mg2+; (C–M–S–H) is the main source of strength in the later stage of CPB material.

Soil bacterial microbiota predetermines rice yield in reclaiming saline-sodic soils leached with brackish ice.

Saline-sodic lands threaten the food supply and ecological security in the western Songnen Plain of northeast China, and the gypsum is commonly adopted for restoration. However, the dynamics of soil bacterial community and the correlation with crop yield during restoring processes remain poorly understood. Here, we elucidated the soil chemical properties and bacterial communities and their associations with rice yield under different flue gas desulphurization gypsum (FGDG) application rates combined with brackish ice leaching. The increased application rate of FGDG generally improved soil reclamation effects, as indicated by soil chemical properties, bacterial diversity, and rice yield. Compared with fresh ice irrigation, the rice yield in brackish ice treatment increased by 15.84%, and the soil alkalinity and sodium adsorption ratio (SAR) decreased by 35.19% and 10.30%, respectively. The bacterial alpha diversity significantly correlated and predicted rice yield as early as brackish ice melt, suggesting the bacterial diversity was a sensitive indicator in predicting rice yield. Meanwhile, the bacterial communities in the control possessed a high abundance of oligotrophic Firmicutes, while eutrophic bacterial taxa (e.g. Proteobacteria) were enriched after brackish water irrigation and FGDG application. Moreover, we also established a Random Forest model and identified a bacterial consortium that explained an 80.0% variance of rice yield. Together, our results highlight the reclaiming effect of brackish ice in the saline-sodic field and demonstrate the sensitivity and importance of the soil bacterial community in predicting crop yield, which would provide essential knowledge on the soil quality indication and bio-fertilizer development for soil reclamation. © 2021 Society of Chemical Industry.

Evaluation of hydroxyapatite derived from flue gas desulphurization gypsum on simultaneous immobilization of lead and cadmium in contaminated soil

Flue gas desulphurization gypsum (FGD) is a major solid waste in coal-fired energy plants, and the appropriate reuse of this resources is still a major challenge. In this study, the feasibility of FGD as a calcium source to produce hydroxyapatite (FGD-HAP) for the immobilization of lead (Pb) and cadmium (Cd) in spiked soil was investigated. The effects of FGD and FGD-HAP on soil properties and redistribution, bioaccessibility and plant uptake of Pb and Cd were examined. Results showed that application of FGD and FGD-HAP could significantly improve the enzymes activities of contaminated soils, but the effectiveness was more pronounced with FGD-HAP. Addition of only 1% FGD-HAP could effectively reduce bioavailable Pb and Cd concentration in soil as measured by CaCl2 extraction by 60.6% and 65.4%, respectively. On the other hand, plant available Pb and Cd could significantly decrease by 93.8% and 73.2% after amendment of 5% FGD-HAP. Significant changes in the micro-scale distribution of heavy metals before and after FGD-HAP treatment demonstrated that while heavy metals were predominantly associated with iron/manganese oxides in untreated soil, high correlation between heavy metals and phosphorus/sulfur was observed in FGD-HAP treated soil. In addition, results of the leaching tests showed that incorporation of FGD-HAP enhanced the retention capacity of heavy metals in soil, indicating that application of FGD-HAP could diminish the environmental risk of leachable heavy metals to groundwater. Overall, this study highlighted the potential value of FGD-HAP as a low-cost and high-efficient amendment for remediation of Pb and Cd contaminated soils.

Valorization of FGD and Bauxite Residue in Sulfobelite Cement Production

Cement, the most used building material amounts to an annual world production of 3.5 Gt. Sulfobelite cements, SB, require lower kiln temperature and emit less CO2, compared to Ordinary Portland cement, OPC. The main difference of SB from OPC is the reduction of alite (CaO)3SiO2, the increase of belite (CaO)2SiO2 and the formation of yeelimite (CaO)4(Al2O3)3SO3, also called “Klein’s salt”. Industrial byproducts, such as Flue Gas Desulphurization gypsum, FGD and dry Red Mud, the so–called bauxite residue, BR can also be used as raw materials, decreasing the CO2 footprint. In the present study, SB cements were prepared in laboratory scale from FGD and BR, as well as, conventional raw materials. All compositions were characterized by XRD, Q–XRD, optical microscopy, SEM and were tested for their compressive strength, soundness, coagulation, etc. The main result of this work is that the studied industrial byproducts, FGD and BR, can be used as alternative raw materials for the raw meals of SB cements, accomplishing low–temperature clinkering at 1330 °C and lower quantities of conventional raw materials. Conclusions suggest that SB cements can be a promising eco–friendly building material and can be used in other applications such as 3-D printed building, rapid-setting mortars, rapid sealants, etc. Moreover, this is an attempt to apply circular economy in cement production utilizing the established production route of cement industries.

The characteristics of arsenic in Chinese coal-fired power plant flue gas desulphurisation gypsum

Flue gas desulphurization (FGD) gypsum had broad application prospects in soil, but the trace heavy metals in FGD gypsum directly determine the severity of secondary pollution. In this work, we focused on arsenic in FGD gypsum for 70 samples from Chinese 20 provinces, investigating the characteristics of distribution and leaching by total contents, fractions, leaching tests, and species, and identifying arsenic mode of occurrence and possible risk for FGD gypsum applications. The result showed arsenic was generally approximately 15 mg/kg in Chinese FGD gypsum, and had an obvious geographical distribution by samples from different areas. Leaching tests showed a lower ability of arsenic release in short-term leaching as well as a large potential leaching risk by the sustained release of arsenic in long-term leaching for high-level arsenic FGD gypsum. X-ray photoelectron spectroscopy showed arsenic in FGD gypsum was mainly present as As(III), which has a higher toxicity. Based on our results, with regard of arsenic, most FGD gypsum is a safe material for soil application, but we did notice the potential risk of arsenic release due to long-term leaching and the content of arsenite.