Presence Of CaO Research Articles

CaO assisted mechanochemical remediation of lindane-contaminated soil

In this study, the planetary ball milling with CaO addition was used to remediate lindane-contaminated soil. Based on Hertzian theory, a mathematical model was proposed to simulate the trajectory of grinding ball and the local energy transfer during a planetary operation at the disk rotation velocities of 150–250 rpm. Besides, the influence of different parameters on lindane removal in soil was investigated, whose results showed that disk rotation velocity and reagent-to-soil ratio had a positive effect, while soil moisture, initial concentration of lindane, and mass of polluted soil demonstrated a negative influence. The mechanochemical method exhibited a higher degradation performance at 3 wt% CaO addition, and a disk rotation velocity of 250 rpm. Active species generated by ball collisions in the presence of CaO, especially superoxide (·O2−) demonstrated a significant role in participating in the lindane conversion. In combination with GCMS and XPS analysis, the proposed model provides insight into mechanochemical remediation process from physical and chemical perspectives, which mainly includes four main steps: mixing, inducing, chemical reaction, and structure destruction.

Co-pyrolysis of phenolic printed circuit boards with CaO and Ca(OH)2 mixture in a fluidized bed reactor: Optimization of the operating conditions and the kinetic analysis

In a previous study (Haghi et al., 2023), we demonstrated that co-pyrolysis of paper-laminated phenolic PCB (FR2-PCB) with a mixture of CaO and Ca(OH)2 in a fluidized bed reactor results in the simultaneous enhancement of the production of the pyrolysis oil and a significant decrease in its halide content. To advance the utilization of a blend of CaO and Ca(OH)2 for scaling up the pyrolysis of FR2-PCB beyond laboratory-scale pyrolyzers, especially in fluidized bed reactors renowned for their effectiveness in large-scale pyrolysis of polymeric materials, the optimal operating conditions, as well as the kinetic parameters in the presence of CaO and Ca(OH)2 should be explored. To this end, this study focuses on optimizing the temperature (T), retention time (t), and PCB-to-additive ratio (FR2/A) as the parameters controlling the co-pyrolysis of paper-laminated phenolic PCB (FR2-PCB) with a 50:50 mixture of CaO and Ca(OH)2 in a fluidized bed reactor. According to the results of the experiments designed based on the response surface methodology, the maximum recovery of pyrolysis oil (40.6 %) was obtained at T = 620 °C, t = 22 min, and FR2/A= 5.4 g/g. Additional tests were carried out to explore the impact of CaO+Ca(OH)2 concentration on the halogen content of the pyrolysis products. Furthermore, the thermogravimetric analysis (TGA) was performed to investigate the influence of the tested additives on the pyrolysis behavior and the kinetic characteristics of FR2-PCB. By employing three iso-conversional model-free approaches, i.e., the Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink integral methods, it was found that adding CaO+Ca(OH)2 to FR2-PCB can reduce the activation energy of the pyrolysis reactions by 20 %.

Co-combustion behavior and catalytic mechanism of high CaO/SiO2 biomass mixed with anthracite for blast furnace injection: Experiment, modeling and DFT investigation

The physical and chemical properties of apricot tree (AT), corncob (CC), and anthracite (CC) were systematically analyzed. Their combustion behaviors and blends were examined using a non-isothermal thermogravimetric method, which revealed the catalytic mechanism of biomass mineral composition in the combustion process. The presence of high CaO content resulted in better combustibility, particularly with an addition ratio of more than 50 % AT, which enhanced anthracite combustion. Kinetic analysis indicated that the random pore model had a better fit than the volume reaction model. At 75 % addition of AT and CC, the lowest apparent activation energies were observed, with values of 100.5 kJ/mol and 110.23 kJ/mol, respectively. Density functional theory calculations demonstrated that the presence of CaO caused reconfiguration in the coal's molecular structure, making it easier for aliphatic chains attached to six-membered rings to detach. The co-combustion process and catalytic combustion mechanism of biomass and coal were discussed, highlighting CaO's ability to remove oxygen-containing functional groups and aliphatic chains, while facilitating O2 diffusion within the molecular structure. Conversely, SiO2 tended to generate silicates, leading to the deactivation of CaO's catalytic effect.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

Evaluation of Presence of Quicklime (CaO) in Ohafia-Arochukwu Areas of Nsukka Formation, Afikpo Basin, Southeastern Nigeria

The co-ordinates of the area studied are within latitudes 5o29ˈ to 5o51ˈN and longitudes 7o29ˈ to 8o00ˈE. The Nsukka Formation in the studied area consists of two facies associations; limestone-shale and cross bedded sandstone. The Limestone-shale facies association consists of the following lithofacies; rippled clayey sandstone, carbonaceous shale, heterolithic sandstone-shale, laminated grey shale, fossiliferous limestone, Fine grained sandstone, Silty shale, Medium grained sandstone and carbonaceous sandstone. The cross bedded sandstone facies association consists of only cross bedded sandstone. Representative samples of these rocks from Ohafia area were collected and stored in a polythene bag for further investigations. XRF analyses were carried out on these rock samples. The XRF oxide content of elements in sample OHA 1 of original rock was found to be CaO (76.00), Fe₂O₃ (8.35), SiO₂ (7.13), Al₂O₃ (2.46), SO₃ (2.29) and MgO (1.81) with other oxides in minor quantities. The shale-limestone lithofacies of OHA 2 of the same rock showed CaO (85.90), SiO₂ (5.13), MgO (2.56), Al₂O₃ (1.80), SO₃ (1.71), Fe₂O₃ (1.20) and P₂O₅ (1.02) with other oxides in minor quantities. OHA 3 of cross-bedded sandstone lithofacies contains SiO₂ (52.70), Fe₂O₃ (14.10), Al₂O₃ (14.50), MgO (3.74), CaO (9.00), TiO₂ (2.54), K₂O (1.41) and Cl (0.12) with other oxides in minor quantities. For OHA 4 through the XRF indicates Chloride (Cl), CaO and SiO2 contains 79.60%, 0.58% and 3.52%. The samples showed that major component were SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO and TiO₂. The presence of CaO was determined to be deposited on the surface of debris of rocks in the area. It was observed that the occurrence of CaO is amorphous in nature and not crystalline.

Characterization of different samples of the gypsum mineral from the Araripe gypsum Pole: from macro to micro with Rietveld refinement

The gypsum mineral is composed of calcium sulfate dihydrate and has as its main application the production of gypsum plaster. In the deposits of the Araripe gypsum pole there are, in natura, different varieties, identified by the names: "Johnson", alabaster, "estrelinha", "cocadinha", "rapadura" and "boró". The characterization of the varieties of gypsum in fracture was performed by SEM and the characterization of the powder was performed by FRX and DRX. By FRX, the presence of CaO was detected with a weight range of 42.5% to 47.1%, and SO3 with a weight range of 48.1% to 53.2%. By XRD analysis, the majority gypsum phase was identified, with the presence of the crystalline planes characteristic of the mineral. From the refinement by the Rietveld method a X2 result between 0.86 and 1.11 was obtained, and it was possible to obtain information about the microstructure of the gypsum varieties and their unit cell.

Stabilizing Cr3+ in a mixture of solid solution phases for high-temperature applications

The major drawback of Cr-containing materials is the generation of toxic Cr6+ compounds, especially at high temperatures in contact with oxygen, alkali or alkaline earth elements/oxides/salts. In this work, we compared the oxidation of two different Cr3+ species, (a) Cr2O3 and (b) a solid-solution mixture of Ca(Al,Cr)12O19 and (Al,Cr)2O3, upon reheating (500–1500 °C) in the presence of CaO, Al2O3, and SiO2 under air atmosphere. The mixture of Ca(Al,Cr)12O19 and (Al,Cr)2O3 was found to be more stable (7.5 mg/kg Cr6+) than Cr2O3 (5646 mg/kg Cr6+). Prolonged reheating (up to 24 h) of Cr3+ solid-solution phases at 900 °C reveals a slight increase in Cr6+ (3.0 to 4.8 mg/kg and 7.5 to 9.1 mg/kg for sample M2 and M2-S (with SiO2), respectively). However, the Cr3+ solid-solution phases in the presence of SiO2 reveal higher Cr-evaporation than undoped counterparts. Nonetheless, the mixture of (Al,Cr)2O3 and Ca(Al,Cr)12O19 hardly showed reoxidation and was more inert.

Co-pyrolysis of paper-laminated phenolic printed circuit boards and calcium-based additives in fixed and fluidized bed reactors

This study compares the impact of the calcium-based additives and the pyrolyzer on the recovery and the halide content of the oil produced from the pyrolysis of paper-laminated phenolic resin printed circuit boards (FR2-PCB). The preliminary experiments showed that the maximum liquid recovery (40.6%) was achieved in a fluidized bed pyrolyzer containing a 50:50 mixture of CaO and Ca(OH)2 operating at T = 620 °C and PCB-to-additive ratio (FR2/A) = 5.4 g/g for 22 min. Extra tests were then carried out under these conditions in fixed and fluidized bed pyrolyzers to separately explore the impact of CaO, Ca(OH)2, and CaO + Ca(OH)2 on the liquid recovery (LR) and the halogen content of the non-solid products. In the fluidized bed, LR in the presence of CaO, Ca(OH)2, and CaO + Ca(OH)2 was 34.5%, 41.2%, and 38.9 wt%, respectively. The fraction of phenolic compounds in the pyrolysis oil ranged from 86% to 93%, about 1–3% higher than the corresponding values in the fixed bed. Using additives led to lower halide content in the pyrolysis oil of the fluidized bed than that of the fixed bed. However, the opposite trend was observed in the absence of additives. Regardless of the type of pyrolyzer, Ca(OH)2 was more successful than CaO in increasing LR, whereas CaO was more effective than Ca(OH)2 in pyrolysis oil dechlorination. Co-pyrolysis of FR2-PCB and CaO + Ca(OH)2 in a fluidized bed reactor was identified as a practical approach to enhance the recovery of pyrolysis oil comprising only 5% of the original halogen content of the feedstock.

High-Strength Building Material Based on a Glass Concrete Binder Obtained by Mechanical Activation

As part of the work, the chemical interaction of finely ground glass (~1 μm), calcium oxide, and water was studied. It is shown that an increase in the fineness of grinding makes it possible to abandon autoclave hardening in the production of products on a hydrosilicate binder. The study of chemical interaction was carried out by calculating the thermodynamic equilibrium and was also confirmed by XRD analysis. DTA analysis showed that an increase in the treatment temperature leads to an increase in the proportion of the reacted phase at the first stage. Subsequently, phase formation is associated with the presence of CaO. The carrier of strength characteristics is the CaO×2SiO2×2H2O phase. The selection and optimization of the composition make it possible to obtain a high-strength glass concrete material with a strength of about 110 MPa. The micrographs of the obtained samples correspond to classical hydrosilicate systems.

Pyrolytic mechanisms of typical organic components of sewage sludge in the presence of CaO: Polysaccharides, proteins, and lipids

The addition of CaO could facilitate the conversion of sewage sludge (SS) from waste to high-purity syngas. The pyrolytic characteristics of SS are a comprehensive manifestation of polysaccharides, proteins, and lipids, while the influence of CaO on their pyrolytic characteristics is rarely reported. This study conducted a thorough investigation into the pyrolytic mechanism of starch, protein, and lipid in the presence of CaO by analysing their thermal behavior, gaseous products, liquid tar, and residual char. The findings from TGA, GC, GC–MS, and FT-IR analysis indicate that the addition of CaO catalytically lowers the pyrolysis temperature of starch, protein, and lipid components and promotes their conversion into small molecules, resulting in increased syngas production. Moreover, the combination of char with the carbonation and calcination cycle of CaO leads to a significant boost in syngas (H2 and CO) yield, with up to 3 and 10 times increase from starch and protein, respectively, and a higher syngas selectivity of up to 65 %. The study also identifies those polysaccharides and proteins are the primary sources of syngas. This study can provide further insight into SS pyrolysis for syngas production in the presence of CaO and the necessary parameters to predict the pyrolysis behavior of SS in industrial applications.

Co-gasification of rice husk and plastic in the presence of CaO using a novel ANN model-incorporated Aspen plus simulation

This study presents a novel model for the simulation of co-gasification of rice husk and plastic using Aspen Plus. The new approach involved using an artificial neural network (ANN) to predict pyrolysis process involved in the gasification, purposely with the aim of providing a more realistic model. Three ANN models were developed with inputs as ultimate analysis (C, H and O), higher heating value (HHV) and pyrolysis temperature. In the gasification section, effects of temperature (600–850 °C), steam-to-feed ratio and CaO to feed ratio were examined. The developed ANN models proved to have good agreement with the actual data with a correlation coefficient (R) > 0.979. The performances of the models were also assessed by absolute mean error (MAE), root mean square error (RMSE) and mean bias error (MBE). A maximum of 69.42 vol% H2 content was obtained at 750 °C from the Aspen Plus gasification model, which was validated with experimental data and a least RMSE of 2.62 was obtained.

Synthesis and Characterization of Physically Mixed V2O5.CaO as Bifunctional Catalyst for Methyl Ester Production from Waste Cooking Oil

Synthesis of the solid bifunctional vanadium-calcium mixed oxides catalyst was accomplished by application of a simple physical mixing approach. In this work, we compared the catalytic activity of CaO and 2%V2O5.CaO catalyst. Various characterization methods, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), BET surface area, and temperature-programmed desorption (TPD) of CO2 and NH3, were involved in studying the newly synthesized catalysts. The presence of CaO, CaCO3, and Ca(OH)2 compounds in the synthesized catalyst were detected by XRD and FTIR analysis. The existence of 2% V2O5 on the CaO catalyst surface was demonstrated by XRF analysis. From TPD-NH3, TPD-CO2, and BET surface area analysis, it was known that the 2% V2O5-CaO catalyst had a higher total number of acid-base sites and surface area than the CaO catalyst. In the fatty acid methyl esters (FAME) production from waste cooking oil (WCO) with higher free fatty acid (FFA), CaO could only catalyze the transesterification reaction. In contrast, 2%V2O5-CaO could successfully catalyze both the esterification of FFA and the transesterification of triglyceride (TG) simultaneously in a one-step reaction process. Thus, these results prove that 2%V2O5.CaO can act as a bifunctional catalyst in the production of biodiesel from WCO. Moreover, the synthesized 2%V2O5.CaO catalyst could achieve a maximum FAME yield of 51.30% under mild reaction conditions, including a 20:1 methanol to oil molar ratio, 60 °C reaction temperature, 1 wt% of catalyst loading, and 3 hours of reaction time.

Simulation of a sorption-enhanced methanation process with CaO in a dual interconnected fluidized bed system

In the framework of carbon capture and utilization technologies and bio-energy transition, catalytic methanation seems to be an interesting pathway for production of synthetic methane for energy storage. This fuel has the main advantage to be already largely used in the current society, with the existence of an extensive transportation and storage infrastructure and a good social acceptance. The production of synthetic methane is under scrutiny by the scientific community. Innovative concepts such as sorption-enhanced methanation have been recently proposed, to improve the performance of catalytic methanation in terms of CH4 yield and cost-effectiveness of the process.In this work, the simulation of a sorption-enhanced methanation process in a dual interconnected fluidized bed system was carried out in ASPEN plus using the ‘fluid bed’ block and using low-cost CaO (derived from limestone) as the sorbent for steam capture. The model consists of two bubbling fluidized beds operated, respectively, as methanator and regenerator under chemical looping conditions with the support of a Ni-based catalyst. The feeding gas, characterized by different concentrations of H2, CO2 and CO, enters the methanator where the catalytic hydrogenation reactions take place with the presence of CaO coming from the regenerator for the exploitation of sorption- enhanced methanation conditions. In the regenerator, the de-hydration reaction of the hydrated sorbent occurs. The optimal operating conditions were investigated in terms of gas feeding composition and recirculation of CaO between the methanator and the regenerator, to produce methane streams that are suitable for injection into the natural gas grid. Also, the effect on the system performance induced by methanation temperature was scrutinized.The results showed that the (unwanted) carbonation reaction of the CaO sorbent had a negative impact on methanation when a stoichiometric gas feeding was fed into the methanator. Conversely, with hydrogen-lean gas feeding, it was possible to find conditions suitable for direct injection of the outlet gas in the grid since the limited amount of H2 was properly balanced by CO2 capture by the sorbent. Moreover, a specific thermodynamic analysis highlighted the possibility of carbon formation induced by H2 sub-stoichiometric feeding and sorption-enhanced methanation conditions.

The impact of heating rate on the decomposition kinetics and product distribution of algal waste pyrolysis with in-situ weight measurement

Converting algal biomass to clean energy via a thermochemical pathway is an emerging technique for tackling environment and energy issues. Traditional kinetic studies on biomass pyrolysis employ a thermogravimetric analyzer (TGA) which heats the biomass sample at a rate of 0 ∼ 2 K s−1, so TGA could only replicate the thermal behavior of the biomass sample in a fixed bed reactor. However, biomass samples can be heated at a rate over ∼102 K s−1 in industrial reactors, including fluidized beds, spouted beds, or rotary kilns due to the direct contact between biomass samples and the solid heat carriers, thus TGA is incapable to reproduce these thermal behaviors. In view of the limitation of TGA in fast heating cases, this study has developed a fast-heating thermo-balance consisting of wire-mesh and wireless power supply technique to investigate the kinetics of fast pyrolysis. Seaweed is fast-growing and can be considered a promising feedstock for biofuel production. Therefore, this study selected seaweed as representative biomass waste and compared the pyrolysis behaviors under both slow and fast pyrolysis conditions. A key finding was the TGA-derived kinetic parameters were unable to describe the pyrolysis rate under fast pyrolysis conditions with significant overestimation. When compared to slow pyrolysis, fast pyrolysis can increase bio-oil yield by about 3–17%, but the N- and S-containing compounds in the bio-oil increase by about 1.1% and 0.15% respectively at a final temperature of 700 °C. Fast pyrolysis produced about 16–53% more CO2 than slow pyrolysis above a final temperature of 500 °C. The polarity of compounds in biochar was reduced with increasing temperature and the presence of CaO was only found in biochar at a high temperature of 700 °C. The specific surface area of biochar was higher under fast heating pyrolysis (5.534–7.469 m2 g−1) than that under slow heating pyrolysis (4.076–6.414 m2 g−1).

APPLICATION OF HETEROGENEOUS CATALYST OF Meti SHELLS (Batissa violecea L. von Lamark 1818) IN THE PRODUCTION OF BIODIESEL BASED ON MORINGA SEED OIL

Meti shell contains calcium carbonate which can be calcined into CaO and used as a heterogeneous catalyst in biodiesel synthesis. This study evaluated the ability of CaO catalyst from Meti shell with concentrations of 1, 2, 3, 4, and 5% for the synthesis of biodiesel from Moringa seed oil at various transesterification times (1, 2, 3, and 4 hours). The presence of CaO in the Meti shell was indicated by diffraction at 2θ angles of 32.47o , 37.74o , 54.22o , 64.65o , and 67.67oC. Utilizing CaO 3% and a transesterification reaction time of 3 hours resulted in an Rf value corresponding to the standard biodiesel Rf ranges, i.e. 0.69 and 0.66, respectively. The synthesized biodiesel has the highest methyl oleate content of 59.16% with characteristics that have met Indonesian National Standard (SNI 04-7182-2006), including water content of 0.004%, an acid number of 0.06 mg KOH/g, saponification number 273.6 mgKOH/g, iodine number 78.678 g iodine/100 g, the cloud point is 10oC, the pour point is 21oC, however, the cetane number is still below the minimum number of 51.

Phase transformation mechanism of oxidation roasting of low-grade polymetallic chalcopyrite ore in the presence of CaO

Low-grade polymetallic chalcopyrite ore has a high lead and iron content and a low softening point, which is difficult to treat using conventional pyrometallurgical and hydrometallurgical processes. In order to investigate the suitable methodology for efficient utilization, it was pelletized with CaO for oxidation roasting in the present work. By controlling the Po2 and Pso2 in the gas phase, the metal sulfide in the ore was converted into easily soluble metal oxide, the thermal analysis of the roasting process was carried out and the acid leaching of the extracted calcine at atmospheric pressure was investigated. The results show that by pelletizing with CaO and then roasting at 800 ? for 1 h, chalcopyrite is converted into CuO, which can be easily dissolved, galena and pyrite are converted into PbO2 and Fe2O3, respectively, and sulfur reacts with CaO and turns into CaSO4, which can fix the sulfur in the calcine. The copper leaching rate of calcine can reach 98.60 wt.% under atmospheric pressure in the H2SO4-H2O system. CaO can increase the softening point of raw materials, improve the roasting effect, promote the phase transformation of chalcopyrite in the oxidation process, and convert sulfur into CaSO4 to fix sulfur, effectively avoiding SO2 pollution to the environment.

Crystallization behavior and structural evaluation of cordierite base glass-ceramic in the presence of CaO and B2O3 additives

The purpose of the present work is to highlight the role of CaO and B2O3 additives on the crystallization behavior and microstructural properties of stoichiometric cordierite glass-ceramics using differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Vickers micro-hardness and scanning electron microscopy (SEM). The results show that the presence of B2O3 and CaO in the initial glass led to the precipitation of only one exothermic peak (α-cordierite: Mg2Al4Si5O18). During the heat treatment process, the presence of calcium oxide favors crystallization of anorthite (CaAl2Si2O8) besides α-cordierite phase. It is worth mentioning that, CaO and B2O3 additives strongly encourage the formation of α-cordierite and have the opposite effect on the crystallization of μ-cordierite. In order to determine the effect of crystallization and B2O3 and CaO additives on the hardness of specimens, the micro-hardness measurement of glasses and glass-ceramics shows that the glass-ceramic containing CaO (MAS5C) exhibits the highest micro-hardness value, which depends on the high crystallinity value in this specimen.

Interaction investigation of three forest waste biochars and CaO in the process of Ca-L/CARBONOx

Ca-L/CARBONOx technology has realized the simultaneous removal of CO2 and NO in the flue gas from coal-fired power plants. Forest wastes are characterized by wide sources, low cost, high lignin content, and high chemical activity. In this study, three forest waste biochars including elm biochar (YB), fir biochar (SB) and bamboo biochar (ZB) were blended with CaO, and their simultaneous CO2/NO removal characteristics were compared. The interaction mechanism between CaO and biochar (BC) in the Ca-L/CARBONOx process was also discussed. Results show that the addition of biochar inhibits the pore structure collapse of CaO at higher cyclic numbers. CaO can also improves the NO removal efficiency for three biochars by catalyzing and providing active adsorption sites. The removal efficiency of NO by three biochars added with CaO are greater than 97% at 650 ℃ in the chemical control stage of CO2 adsorption. SB showed the best NO removal performance and reaction selectivity among the three biochars. Under the presence of CaO, CaO/YB and CaO/ZB have similar CO2 capture performance, while CaO/SB and CaO/ZB have the highest NO removal performance and the best NO reaction selectivity, respectively.

Photo-reduction of nitrate to nitrite in aqueous solution in presence of CaO: Selectivity, mechanism and application

Nitrate (NO3−) photolysis leads to various nitrogenous products, which depends on the reaction conditions and solution properties. How to regulate the composition of products is an important issue. Herein, we found that the involvement of CaO in the NO3− photolysis could selectively reduce NO3− to nitrite (NO2−). Almost 100 % NO2− selectivity was achieved in CaO/UV/NO3− system at initial pH (3–10), initial NO3− concentration (5–45 mg N/L) and CaO dosage (1–6 g/L). The high NO2− selectivity in CaO/UV/NO3− system was attributed to the rich basic sites and paramagnetic surface species of CaO, which captured nitrogen oxides (NOX) and promoted the conversion of NOX to NO2−, respectively. The two-step reduction strategy of CaO/UV coupled with H2NSO3H was used to remove NO3− in wastewater, in which NO3− was firstly reduced to NO2−, then the produced NO2− was further reduced to N2 by H2NSO3H. As for secondary effluent of municipal wastewater with initial NO3− concentration of 30 mg N/L, 93 % removal of NO3− and 100 % of N2 selectivity were achieved at CaO dosage of 2 g/L and H2NSO3H dosage of 0.4 g/L.

Structural, Microstructural and Magnetic Properties of SmCo5/20wt%Fe Magnetic Nanocomposites Produced by Mechanical Milling in the Presence of CaO

In this work, we demonstrate the possibility of using a soluble ceramic material, 5 wt% CaO, as an additive for an SmCo5/20wt%Fe exchange-coupled nanocomposite obtained by mechanical milling in order to inhibit the grain growth of the soft magnetic phase during annealing, which results in a more stable microstructure and an implicit improvement in the hard–soft interphase exchange coupling. Moreover, we show that the additive improves the phase stability of the composite material, reducing the amount of Sm2Co17-type phases formed during the synthesis process, an important aspect because Sm2Co17 is detrimental to the magnetic performance of the SmCo5/20%Fe nanocomposite. These effects are reflected in a nearly 13% increase in the coercive field (Hc) and a 20% increase in the energy product, (BH)max, for the powders produced using CaO as compared to pure SmCo5/20%Fe nanocomposites processed in the same manner.