Addition Of CaO Research Articles

In-situ Synchrotron Radiation XRD Crystal Structure and Microstructure Analysis of CaO-ZrO2 solid-solution at 1100°C with Prolonged Heating

Abstract The structural analysis of the CaO-ZrO2 solid-solutions was carried out using in-situ synchrotron radiation X-ray diffraction (SR-XRD). CaO-ZrO2 solid-solutions with 0, 2.5, and 5 at.% CaO contents were synthesized via a solid-solid ball milling technique. The amorphous ZrO2 powder was synthesized via co-precipitation using ZrCl4 and NH4OH as precursors, while the CaO powder was purified from a local limestone. In-situ SR-XRD measurements were conducted on the CaO-ZrO2 mixtures by independently heating them to 1100°C for different holding times of 0, 12, 24, and 36 minutes using a DHS furnace. Qualitative analysis of all SR-XRD patterns showed that only tetragonal zirconia (t-ZrO2) was present. The crystallite size of tetragonal zirconia ranged from 17 to 22 nm, depending on calcination holding time and CaO addition. Further analysis showed that the tetragonality (c/a) parameter remained relatively constant over the 36-minute holding time. However, the introduction of CaO led to an insignificant reduction in tetragonality, averaging 0.292%.

A novel approach to heavy metal immobilization in municipal solid waste incineration fly ash: Investigating the use of chicken eggshell waste and CaO addition

Municipal solid waste incineration (MSWI) fly ash is a significant byproduct of waste-to-energy processes, and poses substantial environmental and health hazards if not treated properly. The process of Stabilization/Solidification (S/S) efficiently immobilizes hazardous elements present in the fly ash through a combination of physical and chemical mechanisms. The objective of this research is to thoroughly examine the feasibility of using chicken eggshell waste powder as a stabilizing agent for heavy metals, specifically targeting Pb, in MSWI fly ash. Experimental analysis involved varying eggshell waste to fly ash weight proportions, extending from 0.0 (control group), 7:3 up to 9.5:0.5 ratio, with designated curing durations of 2 and 72 hours, and maintaining a liquid-to-solid (L/S) ratio at 1.0 mL/g. In the two-hour curing period, the immobilization efficiency of Pb reached 100% with the addition of only 1.5% eggshell waste. Optimal ratios for Pb stabilization in MSWI fly ash were identified: maximum 2% eggshell waste for 2-hour curing and 1.5% for 72 hours due to elevated Pb and Cd levels of 7:3 ratio. Adding CaO mitigated these levels, enhancing stabilization and compliance with landfill criteria. The results demonstrated that the addition of CaO led to efficient immobilization of Pb, achieving approximately 99%. In addition, the observed enhancement in compressive strength resulting from the incorporation of CaO highlights its effectiveness in enhancing the stabilizing process of MSWI fly ash. By demonstrating the effectiveness of eggshell waste and CaO in stabilizing hazardous elements, this study advocates for scalable solutions and further research on long-term stability and environmental impacts.

Aspen Simulation Study of Dual-Fluidized Bed Biomass Gasification

This article establishes a thermodynamic model of a dual-fluidized bed biomass gasification process based on the Aspen Plus software platform and studies the operational control characteristics of the dual-fluidized bed. Firstly, the reliability of the model is verified by comparing it with the existing experimental data, and then the influence of different process parameters on the operation and gasification characteristics of the dual-fluidized bed system is investigated. The main parameters studied in the operational process include the fuel feed rate, steam/biomass ratio (S/B), air equivalent ratio (ER), and circulating bed material amount, etc. Their influence on the gasification product composition, reactor temperature, gas heat value (QV), gas production rate (GV), carbon conversion rate (ηc), and gasification efficiency (η) is investigated. The study finds that fuel feed rate and circulating bed material amount are positively correlated with QV, ηc, and η; ER is positively correlated with GV and ηc but negatively correlated with QV and η; S/B is positively correlated with GV, ηc, and η but negatively correlated with QV. The addition of CaO is beneficial for increasing QV. In actual operation, a lower reaction temperature in the gasification bed can be achieved by reducing the circulating bed material amount, and a larger temperature difference between the combustion furnace and the gasification furnace helps to further improve the quality of the gas. At the same time, GV, ηc, and η need to be considered to find the most optimized operating conditions for maximizing the benefits. The model simulation results agree well with the experimental data, providing a reference for the operation and design of dual-fluidized beds and chemical looping technology based on dual-fluidized beds.

Effects of CaO addition into CuO/ZnO/Al2O3 catalyst on hydrogen production through water gas shift reaction

Effects of CaO addition into CuO/ZnO/Al2O3 catalyst on hydrogen production through water gas shift reaction

Development of a low carbon binder system based on metakaolin: Focus on corrosion inhibitor-intercalated layered double hydroxides

In this work, MgO-CaO activated blends were produced by using metakaolin (MK). Roles of sodium nitrite (NaNO2) corrosion inhibitor on phase assemblance, micro-structure, and chloride binding of layered double hydroxides (LDH) in the systems were systematically studied. The results showed that the compressive strength in the middle and late stages were increased for 32.78% and 73.74% with the addition of CaO, and pore structure of the MgO-CaO-MK blends was optimized. After the addition of 5% NaNO2, NO2− anions were preferably intercalated into the layers of self-formed MgAl LDH and CaAl LDH. The chloride binding capacity of the samples was stronger than that of cement paste, which was attributed to the generation of more LDH by accelerating hydration of the system.

Formation behavior of PCDD/Fs during waste pyrolysis and incineration: Effect of temperature, calcium oxide addition, and redox atmosphere

The clean and efficient utilization of municipal solid waste (MSW) has attracted increasing concerns in recent years. Pyrolysis of MSW is one of the promising options due to the production of high-value intermediates and the inhibition of pollutants at reducing atmosphere. Herein, the formation behavior of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during MSW pyrolysis and incineration was experimentally investigated and compared. The influence of reaction temperature, CaO addition, and redox atmosphere on PCDD/Fs formation were compared and discussed. The results showed as the pyrolysis temperature increased, the mass concentration and international toxicity equivalence quantity of PCDD/Fs initially peaked at ∼750 °C before declining. Most of the generated PCDD/Fs were concentrated in the liquid and gaseous products, accounting for ∼90% of the total. Among liquid products, octachlorodibenzo-p-dioxin (O8CDD), 2,3,4,7,8-pentachlorodibenzofuran and 1,2,3,4,6,7,8-heptachlorodibenzofuran (H7CDF) were the most crucial mass concentration contributors, while in gas products, high-chlorinated PCDD/Fs, such as O8CDD, octachlorodibenzofuran (O8CDF) and 1,2,3,4,6,7,8-H7CDF were predominant. Compared to incineration, the formation of PCDD/Fs was 7–20 times greater than that from pyrolysis. This discrepancy can be attributed to the hydrogen-rich and oxygen-deficient atmosphere during pyrolysis, which effectively inhibited the Deacon reaction and the formation of C–Cl bonds, thereby reducing the active chlorine in the system. The addition of in-situ CaO additives also decreased the active chlorine content in the system, bolstering the inhibiting of PCDD/Fs formation during MSW pyrolysis.

Revealing the intrinsic sintering mechanism of high-strength ceramsite from CFB fly ash: Focus on the role of CaO

The preparation of high-strength ceramsite from circulating fluidized bed (CFB) fly ash is an effective approach for commercial utilization. The role of CaO plays a key factor in the performance of ceramsite. The impact of CaO on the sintering mechanism was studied at the sintering temperature from 1200 °C to 1300 °C and the CaO addition ratio from 2 wt% to 8 wt%. The in-situ visual furnace equipped with a high-resolution microscope, incorporated with TG-DSC-FTIR, SEM, XRD, and the semi-quantitative analysis method of XRD, was conducted to investigate the sintering process of ceramsite. The results verified that during the high-temperature sintering, CaO reacted with SiO2 and Al2O3 in CFB fly ash to constitute low-melting minerals like anorthite, and the elevation of sintering temperature expedited the conversion of anorthite and eutectics into the molten liquid phase. The expansion gas was wrapped by the molten liquid phase and reached equilibrium, which contributed to the closure of the pores and the elevation of the shrinkage rate of ceramsite. In addition, the rise in sintering temperature dropped the amorphous phase content and increased the mullite content, further enhancing the compressive strength. When the sintering temperature was in the range of 1250 °C–1300 °C and the CaO content was in the range of 2 wt%-4 wt%, the high-strength ceramsite with excellent physicochemical properties could be obtained. It suggested that the synergistic impacts of sintering temperature and CaO improved the performance of ceramsite.

Extraction of natural dyes from tarum leaves (Indigofera Tinctoria L.) using the Ultrasound-Assisted Extraction (UAE) method

The rapid development of the textile industry has led to increased use of synthetic dyes. Although synthetic dyes are more practical and economical, their use can have adverse effects on health and the environment. Natural dyes are utilized as alternatives with indigo leaves (Indigofera tinctoria L.) being one source known for producing a blue color. However, the commonly used extraction methods require long extraction times and significant solvent consumption. Given the limitations of current methods, innovation is needed for an efficient extraction method that produces safe and environmentally friendly natural dyes, one of which is ultrasound-assisted extraction (UAE). Therefore, this study aims to determine the extraction process of indigo leaves using UAE method, then identify the parameters influencing the extraction process using the UAE, determine the extraction yield using UAE, assess the dyeing results of the extracted dye from indigo leaves on cotton fabric, and compare the extraction results of indigo dye through the UAE method with the addition of CaO and NaOH solutions. The results of this study indicate that the natural dye from Indigofera tinctoria obtained the best conditions at extraction time of 90 min, feed-to-solvent ratio of 0.05 g/ml, and CaO-to-solvent ratio of 0.005 g/ml. Furthermore, the addition of CaO solution obtained the highest yield at 4.25 %, while the addition of NaOH solution resulted in 4.8 %. Additionally, the analysis and test results of the application of natural dye from Indigofera tinctoria on cotton fabric revealed a darker color with the addition of NaOH solution compared to the addition of CaO solution.

Thermodynamic Analysis of the Oxidation Behavior of Cerium in High‐Speed Steel during Electroslag Remelting

Cerium loss is difficult to be avoided during the electroslag remelting (ESR) process. To reduce the cerium loss in high‐speed steel during the ESR process, the present study investigates the thermodynamics of cerium oxidation in cerium‐containing high‐speed steel based on the thermodynamic calculation and laboratory‐scale steel–slag reaction experiments. The results show that the reactions between [Ce] and (Al2O3), as well as [Ce] and (MgO) contribute to the cerium loss in the steel. Increasing the contents of CaF2 and MgO in the slag, the activities of Al2O3 and Ce2O3 show a slightly decreasing trend. The addition of CaO and Ce2O3 significantly reduces the Al2O3 activity but enhances the Ce2O3 activity. MgO activity shows an insignificant change with the contents of CaO and Ce2O3, while it decreases with adding Al2O3 and CaF2. Reducing Al2O3 content and enhancing Ce2O3 content in the slag are feasible to increase the cerium yield in the steel. With increasing Al2O3 content from 16.93 to 26.92 wt%, the cerium yield decreases from 8.4% to 6.0%. Increasing Ce2O3 content from 3.98 to 11.01 wt% enhances the cerium yield from 6.0% to 16.9%. The actual soluble Ce content in equilibrium with slag is almost less than 0.001 wt%.

Observations and simulations for separation mechanism of vanadium and chromium: Progressive study based on oxides, spinels and vanadium-chromium slag

In this study, V2O3-CaO-Cr2O3 oxides system, Fe2VO4-CaO-FeCr2O4 spinels system and V-Cr slag-CaO system were established progressively to investigate the separation effect of vanadium and chromium components in vanadium-chromium slag (V-Cr slag). Then, the separation mechanism was proposed by XRD, SEM and leaching experiments. The results show that the reaction ability of vanadium with calcium is far stronger than that of chromium. In oxides and spinels systems, as CaO increases, CaV2O6, Ca2V2O7, and Ca3V2O8 are generated sequentially. In V-Cr slag-CaO system, additive CaO, along with manganese, magnesium and iron components in V-Cr slag reacts with vanadium, resulting in the complex composition of vanadate. As to chromium component, Cr2O3 in oxides system will be converted into CaCrO4 as n(CaO)/n(V2O3) is higher than 2. Iron in the spinels system reacts with chromium and form solid solution (FexCr1-x)2O3, resulting in less chromium reacting with calcium to produce CaCrO4. In V-Cr slag-CaO system, SiO2 generated by the decomposition of silicate phase combines with part of calcium expected to react with chromium, making CaCrO4 generation more difficult, promoting the separation of vanadium and chromium further. Consequently, during H2SO4 leaching, chromium leaching ratios are 98.75%, 45.77% and 5.91%, respectively, in oxides, spinels and V-Cr slag system when n(CaO)/n(V2O3) is 5. And when n(CaO)/n(V2O3) is 2, more than 90% of vanadium can be leached, however, the leaching ratios of chromium are 0.22%, 0.17% and 0.094% in these three systems. Furthermore, the variation regularities of chromium leaching ratios with CaO amount are described by regression equations. These findings would provide the theoretical support for the calcification roasting process with V-Cr slag.

Ash melting and slagging and residual K ion content in biomass pellet combustion

ABSTRACT Combustion of biomass pellets is an effective way to reduce greenhouse gas emissions and achieve carbon neutrality. However, the alkali metal content (represented by K) in ash directly affects its slagging behavior, which can corrode the reactor and shorten its service life. In this study, the ash fusion slag and residual K ion contents were investigated at different combustion times (2, 5, 10, 20, 30 and 60 min) and temperatures (600, 700, 800, 900 and 1000°C). At the same combustion temperature, the residual content of K ions in ash decreases as the combustion time increases; at the same combustion time, the residual content of K ions decreases as the combustion temperature increases. The addition of 5% CaO promotes K precipitation, but at 10% CaO addition, the K precipitation rate is less than that at 5% CaO addition, indicating that the addition of CaO is beneficial to K ion precipitation only within a certain range. Adding CaO also generates high-melting-substances, such as CaSiO3 and calcite, which improve the overall slag resistance of the fuel.

Effect of CaO on the shrinkage and microstructure of alkali-activated slag/fly ash microsphere

Alkali-activated materials (AAMs) are regarded as promising alternatives to Portland cement. However, the significant high shrinkage of AAMs, particularly in alkali-activated slag system, is a critical issue that hinders their wide application. This study investigated the effect of expansive admixture, i.e. CaO on the autogenous shrinkage and drying shrinkage of alkali-activated slag/ fly ash microsphere (AASFAM). The effect of CaO content on heat evolution, reaction products, microstructure development and compressive strength was systematically investigated. The results revealed that the addition of CaO can effectively reduce both the autogenous and drying shrinkage of AASFAM. Mixture with 3% and 5% CaO exhibited expansion within the first 24 hours after casting, while the drying shrinkage was reduced by 72% and 82%, respectively. The addition of CaO promoted the formation of crystalline phases including Ca(OH)2, hydrotalcite and calcite, leading to a lower free water content and coarser pore structure, which in turn reduced the capillary stress during the drying process. The results demonstrated the promising potential of CaO in effectively mitigating the high autogenous shrinkage and drying shrinkage of AAMs without compromising its mechanical properties.

Catalytic pyrolysis of brewer's spent grain in spouted bed reactor using calcium oxide for upgrading oil

This study investigates the potential of brewer's spent grain as a fuel source through fast pyrolysis in a spouted bed reactor, aiming to contribute to sustainable fuel alternatives and the mitigation of the environmental consequences of fossil fuel consumption. Both non-catalytic and catalytic tests evaluated the effects of temperature, biomass feed rate, and catalyst concentration on yields and hydrocarbon composition. The intermediate temperature (550 °C) and biomass feed rate (960 g/h) were optimal for non-catalytic tests, favoring oil production. Additionally, the oil yield was enhanced with the use of CaO as a catalyst during the pyrolysis process. An optimization study identified conditions maximizing both liquid yield and hydrocarbon content. While catalytic tests showed a modest increase in oil yield compared to non-catalytic tests, the addition of CaO significantly improved oil quality by increasing hydrocarbon concentration and facilitating deoxygenation. Under optimal conditions, non-catalytic pyrolysis achieved a 41% liquid yield with 15% hydrocarbon content. For catalytic pyrolysis, optimal conditions yielded 43% oil with a hydrocarbon content of 33% and low water content. Moreover, the resulting oil exhibited a higher heating value (HHV) of 25.7 MJ/kg compared to the spent grain's 19.8 MJ/kg. Utilizing the CaO catalyst further increased the HHV value to 28.2 MJ/kg, highlighting its efficiency in enhancing liquid product quality. The solid products resembled mineral coals with higher energy density compared to the feedstock. This study highlights the potential of brewer's spent grain for fuel production in a spouted bed reactor and the CaO catalyst's effectiveness in improving liquid product quality.

Hydrogen-rich syngas production via steam reforming of acetic acid as bio-oil model compound: Effect of CaO addition to NiAl2O4 catalyst

Bio-oil by-products are inevitable with biomass gasification. It is considered a potential resource for hydrogen production via steam reforming. This study investigated acetic acid as a bio-model compound using a NiAl2O4 catalyst. The effect of reaction conditions on hydrogen-rich production has also been discussed, including reaction time (1 h, 3 h, 5 h and 7 h), steam/carbon ratio (S/C = 1–4) and the blend of NiAl2O4 and CaO (1:0, 3:1, 1:1, 1:3 and 0:1). The fresh and spent samples were characterized by XRD, XPS, SEM, BET, etc. The result showed that the CaO addition has several advantages: 1) it increases hydrogen gas purification; 2) it prevents Ni separation from NiAl2O4; 3) it decreases the sintering of NiAl2O4. However, Ca5Al6O14 formation decreases the activity of hydrogen production. In reaction conditions, steam is an essential factor for hydrogen gas production. The S/C ratio = 3 shows the optimum result for hydrogen gas production. Although the higher S/C ratio = 4 can maintain the adsorption activity of CaO, it causes Ni separation from NiAl2O4. The blend of NiAl2O4 and CaO is another essential factor for hydrogen gas production. Adding CaO has increased hydrogen gas production significantly. However, a little CaO in a blend ratio 3:1 does not maintain the stability of the NiAl2O4 structure. In the end, the optimum conditions are S/C ratio = 3 and blend = 1:1 at 650 °C, which produces hydrogen gas yield (2.1 mol/mol) and H2/CO (5.83).

Effect of calcium and potassium oxide addition on the viscosity and fragility of a calcium aluminosilicate melt

AbstractFragility is commonly quantified as the magnitude of change in viscosity at a temperature close to the glass transition temperature (Tg). It is a critical characteristic of melts used in scientific and industrial applications. The fragility of silicate melts generally increases with the depolymerization of silicate anions upon the addition of alkali or alkaline earth oxides. However, the effects of oxide additives on the fragility of aluminosilicate melts remain unclear. In this study, the effect of CaO or K2O addition on the viscosity of the 36CaO–51SiO2–13Al2O3 (mol.%) melt for the wide viscosity range of 10−1–1012 Pa s was studied. The relationship between the logarithmic viscosity and Tg‐scaled temperature indicated that the melt fragility increased with the addition of CaO, whereas the addition of K2O reduced the fragility when the additive content of CaO or K2O was less than 10.8 mol.%. The effect of the addition of K2O on fragility cannot be explained by the depolymerization of silicate anions alone. Raman and 27Al nuclear magnetic resonance spectroscopies of the glasses indicated that a decrease in the level of distortion of the AlO4 tetrahedra decreased the fragility of the aluminosilicate melt.

Electrical properties, microstructure, and thermal conductivity of hot-pressed CaO-doped AlN ceramics

AlN ceramics exhibit good physical and chemical properties and are ideal materials for the dielectric layer of electrostatic chucks. However, they cannot generate a strong J−R-type electrostatic adsorption force because of their high resistivity. Therefore, adding other substances is necessary to regulate the electrical properties and enable their application. In this study, AlN ceramics were prepared using hot-pressed sintering with 0.2 wt% CaO as an additive at a sintering temperature range of 1700–1900 °C. The effects of CaO doping on the phase composition, microstructure, electrical properties, and thermal conductivity of the AlN ceramics were systematically investigated. The addition of CaO not only enhanced the sintering process of the AlN ceramics, but also significantly reduced the electrical resistivity and increased the thermal conductivity. The relative density of CaO-doped AlN ceramics reached 98.88 % at 1700 °C, with a thermal conductivity of 81.51 W m−1•K−1. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and AC impedance spectroscopy were used to analyse the impurities and defects in the AlN ceramics. The lattice parameters and fitting grain resistance indicated that the CaO-doped AlN presented a higher lattice oxygen concentration, increasing the concentration of Al vacancies and electrons. Moreover, the level of dissolved oxygen could be controlled by altering the sintering temperature, resulting in AlN ceramics with electrical resistivity ranging from 8.1 × 106 to 1.7 × 1012 Ω cm. Further research was conducted to investigate the effect of the electrical resistivity of AlN ceramics on the J−R-type electrostatic adsorption force, and it was found that AlN ceramics with a specific resistivity of 109 Ω cm exhibited the highest electrostatic adsorption of 351.7 g/cm2.

The Direct Alloying of Steel through Silicothermic Self-Reduction of Chromite Ore Utilizing Si-Containing Solid Waste

Organosilicon materials generate copious amounts of Si-containing solid waste during production, leading to severe environmental pollution and substantial resource squandering. In pursuit of the resource utilization of Si-containing solid waste, this study conducted experimental research on the direct alloying of molten steel through the silicothermic self-reduction of chromite ore using Si-containing solid waste as a reducing agent. Additionally, thermodynamic analysis was performed, employing the thermodynamic calculation software FactSage 8.2 (Thermfact Ltd., Montreal, QC, Canada and GTT-Technologies, Aachen, Germany), to examine the equilibrium reactions of the silicothermic reduction of chromite ore and the variations in the thermodynamic equilibrium compositions of slag and metal phases. The results indicate a reduction sequence for the reducible components in chromite ore as Fe2O3 → Cr2O3. The introduction of CaO and Al2O3 into the silicothermic self-reduction compacts altered the forms of Fe and Cr oxides in equilibrium, significantly reducing the standard Gibbs free energy (ΔG0) of the silicothermic reduction reaction. The initial slag melting point decreased from 1700 °C without the addition of CaO and Al2O3 to 1500 °C with the addition of CaO and Al2O3. Correspondingly, the slag viscosity at 1600 °C decreased from 134.1 Pa·s without CaO and Al2O3 addition to 1.81 Pa·s with CaO and Al2O3 addition. The addition of CaO and Al2O3 accelerated the reduction of Cr oxide in chromite ore and enhanced the recovery of Cr, consistent with the thermodynamic calculation results. In the process of steelmaking through the direct alloying of chromite ore silicothermic self-reduction compacts, the final recovery rate of Cr increased from 86.4% without CaO and Al2O3 addition to 95.4% with CaO and Al2O3 addition.

Ammonia removal and simultaneous immobilization of manganese and magnesium from electrolytic manganese residue by a low-temperature CaO roasting process.

A large amount of open-dumped electrolytic manganese residue (EMR) has posed a severe threat to the ecosystem and public health due to the leaching of ammonia (NH4+) and manganese (Mn). In this study, CaO addition coupled with low-temperature roasting was applied for the treatment of EMR. The effects of roasting temperature, roasting time, CaO-EMR mass ratio and solid-liquid ratio were investigated. The most cost-effective and practically viable condition was explored through response surface methodology. At a CaO: EMR ratio of 1:16.7, after roasting at 187°C for 60 min, the leaching concentrations of NH4+ and Mn dropped to 10.18 mg/L and 1.05 mg/L, respectively, below their discharge standards. In addition, the magnesium hazard (MH) of EMR, which was often neglected, was studied. After treatment, the MH of the EMR leachate was reduced from 60 to 37. Mechanism analysis reveals that roasting can promote NH4+ to escape as NH3 and convert dihydrate gypsum to hemihydrate gypsum. Mn2+ and Mg2+ were mainly solidified as MnO2 and Mg(OH)2, respectively. This study proposes an efficient and low-cost approach for the treatment of EMR and provides valuable information for its practical application.

Effect of calcium-based additives on NO release of coals under different combustion modes

The nitrogen oxides and sulfur oxides released from coal combustion pose serious environmental hazards, but there exists a contradiction between low-nitrogen combustion and efficient desulfurization, necessitating a deeper understanding of the impact of calcium-based desulfurization agents on NOx release. Based on one-stage and two-stage horizontal furnaces, the effects of temperature, coal types and CaO on the release of NO were explored under the coupled combustion and the separated combustion. The experimental results indicate that: under both conditions, the NO emissions of coals decrease with the increase of temperature. The reaction time of separated combustion is shorter than that of coupled combustion. Under the coupled combustion, the order of NO emissions is: anthracite (AC) > bituminous coal (BC) > lignite (LC) > high chlorine coal (HC), and the order are mainly affected by the content of N in coal. At 800 °C, the fuel-N conversion rates of BC, AC, LC, and HC are all the highest, and the rates are 20.52 %, 25.93 %, 14.90 %, and 15.34 %, respectively. As the temperature rises, both volatile-N and char-N emissions show a downward trend. The NO emissions in the separated combustion are greater and the fuel-N conversion rates of BC, AC, LC, and HC are 44.11 %, 47.31 %, 40.44 % and 32.21 %, respectively. The reduction reaction between char and NO plays a crucial role. After the addition of CaO, there is a significant increase in NO release, indicating that CaO has a catalytic effect on the release of volatile-N and char-N. Under the separated combustion, the impact of CaO on NO emissions is relatively minor, and sometimes it leads to a reduction in NO emission. The role of CaO on the NO release is multifaceted.

Evaluation and mechanistic analysis of the effect of the addition of alkaline earth metal CaO on Cd solidification enhancement in lightweight aggregate preparation.

The volatilization of Cd during the preparation of lightweight aggregates (LWAs) can cause serious damage to the environment, so a method to harmlessly transform Cd during this process is required. In this regard, the alkaline earth metal CaO was added to Cd-containing aggregate raw materials for treatment, and the effect of CaO addition on the properties of LWAs in the presence of chlorine and sulfate was investigated. Kinetic models of the Cd volatilization were established by using the Arrhenius equation to predict the volatilization of Cd at different sintering stages. The results showed that 0.8% wt of CaO under the influence of chlorine can reduce the Cd volatilization rate from 84.9% to 12.64%, corresponding to an increase in the reaction activation energy (E a) from 22.62 to 49.55 kJ mol-1. Additionally, the Cd volatilization rate under the influence of sulfate was reduced from 30% to 8%, with an increase in the E a from 33.25 to 42.62 kJ mol-1. The activation energy increase suggests that the addition of CaO is beneficial because it increases the energy required for Cd volatilization. According to the Cd leaching experiments conducted on the LWAs, it was found that the solidification ratio of Cd was higher than 99.9% for all samples after the addition of CaO. The addition of CaO promotes the formation of CdFe2O4 and anorthite for effective solidification of Cd, thus optimizing the structures of the LWAs. This work may provide a new idea for Cd waste recycling.