Calcium Sulfide Research Articles

Simulation of a bubbling fluidized bed reactor for phosphogypsum decomposition with carbon monoxide

AbstractPhosphogypsum (PG), a by‐product of the phosphoric acid industry and rich in calcium sulphate (CaSO4), has an unfavourable environmental impact, making its management one of the crucial issues of phosphoric acid production. As a result, PG production is integrated with or without treatment in many industries, such as agriculture, building materials, and sulphuric acid. In the latter application, carbon monoxide (CO) is used to decompose PG to extract the sulphur according to a two‐parallel reaction producing calcium sulphide (CaS) and calcium monoxide (CaO) in the solid phase. To depict the effect of the solid temperature (T), CO partial pressure (PCO), inlet gas velocity (U0), residence time (), particle size (PS), and solid exchange coefficient () on the overall fluidized bed reactor performance, a simulation study was performed according to the dynamic two‐phase model. The results show that CO partial pressure, solid residence time, particle size, and inlet gas velocity have the most significant effect on the PG conversion. On the other hand, the temperature and partial pressure of CO have the most critical effect on product selectivity. The concentration profiles of both reactants CaSO4 and CO reveal that the reaction in the emulsion phase is faster than in the bubble phase due to the good mixing in this phase.

In Situ Slow-Release Hydrogen Sulfide Therapeutics for Advanced Disease Treatments.

Hydrogen sulfide (H2S) gas therapygarners significant attention for its potential to improve outcomes in various disease treatments. The quantitative control of H2S release is crucial for effective the rapeutic interventions; however, traditional researchon H2S therapy frequently utilizes static release models and neglects the dynamic nature of blood flow. In this study, we propose a novel slow-release in-situ H2S release model that leverages the dynamic hydrolysis of H2S donorswithin the bloodstream. Calcium sulfide nanoparticles (CaS NPs) withmicrosolubility characteristics exhibit continuous H2S release, surpassing 24 h at normal blood flow velocities. The extended-release profile demonstrates superior potential in aligning with the bell-shapedpharmacological effect of H2S, compared to NaHS. Moreover, we synthesisedrare earth-doped CaS NPs (CaS: Eu2+, Sm3+ NPs) tha texhibit persistent luminescence, enabling visualisation of the continuous H2S release in trials. Our results demonstrate that lowdose CaS: Eu2+, Sm3+ NPs significantly reduces seizureduration to 1.2±0.7 minutes, while high dose effectively suppresses colontumor growth with a tumor inhibition rate of 54%. Remarkably, these findings closely resemble endogenous H2S levels in treating epilepsy and tumors. This innovative slow-release, in-situ H2S the rapeutic approach via hydrolysis rejuvenates the development of H2S-basedtherapeutics.

Influence of feedstock composition on the pressure drop buildup in gas oil hydrotreater

In this work two samples of solid particulates obtained from the intergranular space of the guard beds catalyst of industrial gas oil hydrotreating reactors were investigated. The hydrotreating reactors were operated on feedstock of different composition. One of the samples of solid particulates was obtained during hydrotreating of feedstock containing a large amount of sodium and calcium. The compositions of the samples of solid particulates were determined. Quantitative elemental and structural analyses were carried out. As a result, the formed solid particulates contained a large amount of sodium chloride, sulfate and calcium sulfide. The qualitative calculations show that the pressure drop in the guard bed of five-segment rings with a diameter of 16.0 mm, due to the deposition of solid particulates in the intergranular space, increases by 108% more than the pressure drop during hydrotreating of feedstock not containing calcium and sodium compounds (under the same operating modes of the hydrotreating reactors and operating time). The obtained results on the effect of the feedstock composition on the pressure drop buildup can be used in optimizing the loading of reactors and in other oil refining processes.

Study of the Process of Calcium Sulfide-Based Luminophore Formation from Phosphogypsum.

One of the priority goals of sustainable socio-economic development for the period up to 2030 is providing food for the planet's population. This entails an increase in the output of mineral fertilizers and, consequently, an increase in the quantities of solid industrial waste. Phosphogypsum, a by-product of phosphate fertilizer production from apatite ore, is one example of such waste. The problem of solid industrial waste recycling is urgent. The present study examines the process of converting calcium sulfate, in the form of a reagent, and phosphogypsum into a composite material of calcium sulfate/sulfide. An environmentally friendly material, sucrose, is used as a reducing agent. Reduced phosphogypsum (as well as calcium sulfate) luminescence is suggested to be associated with the formation of a CaS/CaSO4 composite material. The synthesized materials are characterized by X-ray phase analysis, X-ray photoelectron spectroscopy, elemental analysis, and calcium sulfide qualitative and quantitative content in the samples. It is shown that in the reduction process at the phase contact point, crystal grids are formed with a significant number of defects, which contributes to the convergence of some of the energy levels of the calcium cation and sulfide anion, facilitating the transitions of electrons from the valence zone to the core zone and the formation of luminescence centers (cross-luminescence). Both samples of reduced phosphogypsum and alkaline earth metal sulfates are found to exhibit luminescence properties under ultraviolet radiation. The data obtained open up broad prospects for the use of solid industrial waste for the synthesis of new materials.

Calcium Sulfide Based Nanophosphors-A Review on Synthesis Techniques, Characterization and Applications.

Calcium sulfide (CaS) is a widely investigated alkaline earth sulfide nanophosphor with promising applications in optoelectronics and biomedical fields due to its excellent photoluminescence properties. The selection of the synthesis method is a crucial factor in determining the efficacy of nanophosphors for various applications. This review provides a comprehensive overview of the various synthesis techniques employed to develop CaS nanophosphors, including solvothermal, alkoxide, sol-gel, microwave, wet chemical co-precipitation, solid-state diffusion, and single-source precursor methods. The structural and optical properties of CaS nanophosphors are discussed in detail, highlighting the influence of different dopants on the emission color, which can be tuned from blue to red. The review also explores the potential applications of CaS nanophosphors in optoelectronics and biomedicine. This review serves as a valuable resource for researchers interested in developing CaS nanophosphors for various optoelectronic and biomedical applications, providing insights into the latest advancements and future prospects in this field.

Near-infrared-II photocharging nanozyme for enhanced tumor immunotherapy

In tumor therapy, copper (Cu)-based nanozymes with peroxidase-like activity play a crucial role in converting hydrogen peroxide into hydroxyl radicals (OH). This process induces immunogenic cell death, which in turn activates the body’s immune response, enhancing the efficacy of tumor immunotherapy. Nonetheless, the efficiency of this reaction is curtailed due to the oxidation of Cu(I) to Cu(II), leading to the self-depletion of the nanozyme’s activity and an insufficient yield of OH for effective immunotherapeutic activation. To surmount this challenge, our research introduces a photocharging self-doped semiconductor nanozyme, copper sulfide (Cu9S8). The photocharging effect enables the nanozyme to convert internal Cu(II) back to Cu(I) through charge transfer induced by near-infrared (NIR)-II photothermal energy, thereby effectively maintaining the enzyme-like activity of the nanozyme. Additionally, Cu9S8 is enhanced with a calcium sulfide (CaS) coating. This coating reacts in the acidic microenvironment of tumors to generate hydrogen sulfide (H2S) gas, which in turn suppresses the catalase activity inherent in tumor cells, ensuring a plentiful supply of H2O2 for the nanozyme’s operation. This dual strategy of amplifying enzyme-like activity and substrate availability culminates in the generation of ample OH within tumor cells, leading to significant immunogenic cell death and thereby realizing potent immunotherapy.

Industrial grade calcium sulfide modified by selenium for elemental mercury removal from flue gas

Metallic sulfides (MS) adsorption is considered as an effective method to remove Hg0 from coal-fire flue gas. Se modification can significantly improve Hg0 removal process on MS due to the high affinity constant between Se and Hg0. CaS as a production from wet flue gas desulfurization has potential Hg0 removal ability. Therefore, in the present work, Se modified industrial grade CaS was prepared to remove Hg0 and the effect of the ratio of CaS to Se on Hg0 removal process was studied. Characterization results show that Ca1-Se1.7 had the richest porous structure and largest surface area resulting in more available surface active sites. In addition, Ca1-Se1.7 has the highest content of Se−, who can remove Hg0 via Hg0(ad)+Se22-→HgSe+Se2-. As a result, Ca1-Se1.7 has the highest Hg0 removal efficiency of nearly 100 % from 60 ℃ to 100 ℃, and it reaches 85 % even in the presence of 500 ppm SO2. The Hg0 adsorption kinetic was well defined by the pseudo-first-order kinetic model and internal diffusion model, so that Hg0 diffusion especially internal diffusion is the primary controlling step.

Gas-Amplified Metalloimmunotherapy with Dual Activation of Pyroptosis and the STING Pathway for Remodeling the Immunosuppressive Cervical Cancer Microenvironment.

The immunosuppressive microenvironment of cervical cancer significantly hampers the effectiveness of immunotherapy. Herein, PEGylated manganese-doped calcium sulfide nanoparticles (MCSP) were developed to effectively enhance the antitumor immune response of the cervical cancer through gas-amplified metalloimmunotherapy with dual activation of pyroptosis and STING pathway. The bioactive MCSP exhibited the ability to rapidly release Ca2+, Mn2+, and H2S in response to the tumor microenvironment. H2S disrupted the calcium buffer system of cancer cells by interfering with the oxidative phosphorylation pathway, leading to calcium overload-triggered pyroptosis. On the other hand, H2S-mediated mitochondrial dysfunction further promoted the release of mitochondrial DNA (mtDNA), enhancing the activation effect of Mn2+ on the cGAS-STING signaling axis and thereby activating immunosuppressed dendritic cells. The released H2S acted as an important synergist between Mn2+ and Ca2+ by modulating dual signaling mechanisms to bridge innate and adaptive immune responses. The combination of MCSP NPs and PD-1 immunotherapy achieved synergistic antitumor effects and effectively inhibited tumor growth. This study reveals the potential collaboration between H2S gas therapy and metalloimmunotherapy and provides an idea for the design of nanoimmunomodulators for rational regulation of the immunosuppressive tumor microenvironment.

Ultrafast and highly efficient Cd(II) and Pb(II) removal by magnetic adsorbents derived from gypsum and corncob: Performances and mechanisms

The utilization of gypsum and biomass in environmental remediation has become a novel approach to promote waste recycling. Generally, raw waste materials exhibit limited adsorption capacity for heavy metal ions (HMIs) and often result in poor solid–liquid separation. In this study, through co-pyrolysis with corncob waste, titanium gypsum (TiG) was transformed into magnetic adsorbents (GCx, where x denotes the proportion of corncob in the gypsum–corncob mixture) for the removal of Cd(II) and Pb(II). GC10, the optimal adsorbent, which was composed primarily of anhydrite, calcium sulfide, and magnetic Fe3O4, exhibited significantly faster adsorption kinetics (rate constant k1 was 218 times and 9 times of raw TiG for Cd(II) and Pb(II)) and higher adsorption capacity (Qe exceeded 200 mg/g for Cd(II) and 400 mg/g for Pb(II)) than raw TiG and previous adsorbents. Cd(II) removal was more profoundly inhibited in a Cd(II) + Pb(II) binary system, suggesting that GC10 showed better selectivity for Pb(II). Moreover, GC10 could be easily separated from purified water for further recovery, due to its high saturation magnetization value (6.3 emu/g). The superior removal capabilities of GC10 were due to adsorption and surface precipitation of metal sulfides and metal sulfates on the adsorbent surface. Overall, these waste-derived magnetic adsorbents provide a novel and sustainable approach to waste recycling and the deep purification of multiple HMIs.

Redox condition changes caused by impacts: Insights from Chang’e-5 lunar glass beads

Lunar materials are overall more reducing compared with their terrestrial counterparts, but the mechanism remains to be elucidated. In this study, we present a possible explanation for the changes in redox state of the lunar regolith caused by impact events, based on our investigations of the impact glass beads from Chang’e-5 mission. These glass beads contain iron metal grains and show concentration gradients of FeO and K2O (with or without Na2O) from their rims to centers. The compositional profiles exhibit error-function-like shapes, which indicates a diffusion-limited mechanism. Our numerical modeling results suggest that the iron metal grains on the surface of the glass beads were generated through the reduction of FeO by elemental K and (or) Na produced during the impact events. Meanwhile, the iron metal grains inside the bead may have formed due to oxygen diffusion driven by redox potential gradients. Furthermore, our study suggests that impact processes intensify the local reducing conditions, as evidenced by the presence of calcium sulfide particles within troilite grains that coexist with iron metal grains on the surface of the glass beads. This study provides insights into the oxygen diffusion kinetics during the formation of iron metal spherules and sheds light on the changes in redox conditions of lunar materials caused by impact events.

FISIOLOGÍA DE LA MADURACIÓN Y MANEJO EN POSTCOSECHA DE FRUTILLA CHILENA (Fragaria chiloensis)

The Chilean strawberry (Fragaria chiloensis) is a native species to Chile. Consumers value this fruit for its organoleptic properties, but it is highly perishable. Since it is a non-climacteric fruit, harvesting at the optimum ripening stage is essential to ensure its quality during commercialization. In this fruit, quality is determined by appearance, flavor, aroma, nutritional value, and firmness, which changes during ripening. The species presents a high rate of firmness loss or softening, associated with the elevated enzymatic activity of cell wall-modifying enzymes of the pectin and hemicellulose fractions, such as polygalacturonase, α-arabinofuranosidase, β-galactosidase, endo-glucanase, β-xylosidase, xyloglucan endotransglycosilase/hydrolase and rhamnogalacturonan lyase at different ripening stages. Firmness is a key trait for commercialization and organoleptic quality; hence, its management during storage is necessary. Different studies have investigated the effects of pre or postharvest treatments, such as modified atmosphere packaging and exogenous applications of calcium, auxin, methyl jasmonate, chitosan, and hydrogen sulfide, which maintain fruit firmness by reducing pectin solubilization and improve other attributes responsible for organoleptic and nutritional quality during storage. This literature review focuses on the ripening biology of Fragaria chiloensis and recent findings regarding softening and its biochemical and molecular basis, as well as interventions oriented to maintain the quality and extend the shelf-life of this fruit.

Homeopathic Medicines in Third (Omicron) Wave of COVID-19: Prognostic Factor Research.

With the emergence of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, such as the Omicron variant, during the third wave of the coronavirus disease 2019 (COVID-19) pandemic, there was a need to identify useful homeopathic medicines. This study aimed to identify such medicines and their indications using prognostic factor research (PFR). This was an open-label, multi-centred observational study conducted in January 2022, on confirmed COVID-19 cases. The data were collected from integrated COVID Care Centres in Delhi, India, where homeopathic medicines were prescribed along with conventional treatment. Only those cases that met a set of selection criteria were considered for analysis. The likelihood ratio (LR) was calculated for the frequently occurring symptoms of the frequently prescribed medicines. An LR of 1.3 or greater was considered meaningful. Out of the 362 COVID-19 cases, 263 cases were selected for analysis after applying selection criteria. Common symptoms included fatigue, cough, sore throat, myalgia and headache. Twenty-one medicines were prescribed, of which nine medicines - Gelsemium sempervirens, Bryonia alba, Hepar sulphuris, Rhus toxicodendron, Pulsatilla nigricans, Arsenicum album, Belladonna, Nux vomica and Phosphorus - were frequently used. By calculating LRs, the study identified meaningful indications for these medicines. Homeopathic medicines have shown promising results in the third wave of COVID-19 as an adjunct therapy. The medicines that were used in the first and second waves were found useful in the third wave also, and their indications were analogous to those found in the earlier waves. Certain new indications of some medicines were elicited in this wave, which warrant further research. However, it is important not to restrict to these medicines only and to continue data collection on COVID-19 in future waves for the improvement of the COVID-19 mini-repertory.

Utilization of inherent minerals in coal for high-performance activated carbon production: The mechanism of deSO2 and/or deNOx enhanced by in situ transformed calcium sulfide (CaS)

Calcium sulfide (CaS) is transformed from the interaction between inherent pyrite and calcite in coal during activated carbon (AC) preparation by vapor activation, which could impact AC's textural and performance. For elucidating the contribution of in situ transformed CaS on the AC structure and SO2/NO removal, as-obtained AC-XCaS (X is the CaS content) were produced by Taixi coal and calcium sulfide (0–4 wt.%) through steam activation. The textural evolution and denitrification and/or desulfurization were also investigated. The results indicated that: (1) Calcium sulfide declined the burn-off linearly. The graphitization degree of ACs presents first enhancing and then decreasing trend with the CaS content increased. Calcium sulfide promotes the AC's micropore porosity development by catalyzing the corrosion of steam on the carbon surface. The specific surface area including total BET and micropore from 954 m2/g and 894 m2/g (AC) first raised to 1017 m2/g and 962 m2/g (AC-1CaS) and then decreased to 808 m2/g and 768 m2/g (AC-4CaS), respectively. Meanwhile, calcium sulfide improves the AC's amounts of C–O and C=O. (2) Calcium sulfide strengthens AC's removal ability of NO and SO2 evidently. The maximum desulfurization capacity is up to 67.1 mg/g of AC-4CaS, which is higher by 50.8% than 44.5 mg/g of AC. Calcium sulfide enhances AC's surface chemical feature and finally favors the adsorption of SO2/O2/H2O. Meanwhile, calcium sulfide catalyzes the desulfurization reaction. The AC-3CaS's NO conversion is up to 22.7%, which is higher 39.3% than 16.3% of AC. Calcium sulfide favors oxygen dissociation to form intermediate C(O), which could strengthen the adsorption of NH3 and NO. (3) During simultaneous removal of SO2 and NO, calcium sulfide shows that anti-SO2 poisoning ability is promising. The results of this research could complement the reference by utilizing coal with high-inorganic-iron/calcium/sulfur for high-performance AC preparations.

Crystallization and activator reduction simultaneously for calcium sulfide nanophosphors and evaluation of red-light compensation - Environmental reliability

Calcium sulfide nanophosphors (CaS:Eu2+) with red emissions were synthesized by hydrothermal-derived 250 nm carbon-sphere templates to induce a reduction atmosphere to activate an activator valence transition and crystallize (Ca,Eu)S simultaneously at 800 °C without extra sulfur atmosphere. The cationic concentration z = [Ca2++Eu2+] and ionic ratio y = [S2−]/[Ca2++Eu2+] were controlled in an innovative chemical solution reflux process to synthesize a sulfide nanophosphor precursor on carbon-sphere template. The particle size and crystallinity of the prepared nanophosphors increased with the “y” value increase. The photoluminescence (PL) intensity of the 652 nm emission excited by 450 nm increased to y = 1 and kept nearly constant to y = 20. High PL intensity was achieved by 0.025CaS-1 and 0.025CaS-10 samples with individually sphere-like nanoparticles, enough crystallinity and homogeneous Eu doping as well as fully reduced Eu2+ in the nanophosphors. The CaS:Eu2+ nanoparticles prepared by carbon-sphere templates showed thermal quenching with temperature. The Eu2+-doped CaS emitted 652 nm red light by 450 nm but not by 380 nm excitation that was only for CaS host at 555 nm emission. The prepared 0.025CaS-10 paste of only 7 wt% was individually coated on a blue-light LED and commercially available YAG-LED. The red emission intensity was enhanced and broadened by the prepared sulfide nanophosphor compared to a commercially available red LED. The CRI value for R9 increased to higher than 90, and the measured Ra was higher than 95 for the prepared sulfide nanophosphor-coated commercial WLED. The prepared sulfide nanophosphors could keep the red-light brightness over six months' exposure at rainy marina to show the environmental reliability.

Calcium sulfide based nanoreservoirs elicit dual pyroptosis pathways for enhanced anti-tumor immunity

The therapeutic efficacy of immunotherapy for most solid tumors is unsatisfactory due to the “immune-cold” nature. As a form of lytic pro-inflammatory programmed cell death, pyroptosis can release abundant immunogenic damage-associated molecular patterns to extracellular milieu, exhibiting self-cascade amplifying capacity for cancer immunotherapy. However, the activation of the caspase-3-mediated pyroptosis is difficult because mRNA hypermethylation induces the down-regulated GSDME expression. Herein, an integrated strategy to elicit dual pyroptosis pathways is introduced based on calcium sulfide-based nanoreservoirs (denoted as CSSG). CSSG are degraded in the aggravated acidic tumor microenvironment (TME) triggered by the surface GOx participating oxidation and result in the avalanching generation of H2S and Ca2+, which elevate oxidative pressure and induce mitochondrial respiration inhibition. Moreover, the sudden surge in H2S evokes GSDMD mediated pyroptosis through “DUSP6/ERK/NLRP3/caspase-1” signaling pathway, which synergistically reinforces the performance of the Ca2+ overloading initiating GSDME-mediated pyroptosis. CSSG elicit robust pyroptotic cell death to effectively stimulate tumor immunogenicity, and promote an impressive antitumor immunity with effective elimination of primary and distant tumors. Collectively, this work establishes TME-associated degradable nanomaterials to introduce dual pyroptosis pathways simultaneously and has a promising prospect in optimizing cancer immunotherapy.

Reduction of phosphogypsum for SO2 production: Insights into the release characteristics of SO2 following the solid–solid reaction of CaS and CaSO4 under different atmospheres

AbstractPhosphogypsum (PG) severely pollutes the environment and is difficult to recycle. PG is primarily composed of CaSO4 · 2H2O. In this study, the characteristics of SO2 released from the solid–solid reaction between calcium sulphide (CaS) and CaSO4 were thoroughly investigated using thermodynamic calculations. Experiments were performed by tuning the molar ratio of CaS to CaSO4, reaction atmosphere (S, CH4, N2, and air), and the heating rate. As shown by the phase diagram, high reaction temperatures favour CaO stability, and the corresponding maximum SO2 equilibrium partial pressure increases. The total SO2 production significantly increased with increasing molar ratio and slightly increased when the ratio exceeded 1:3. The SO2 productions were ranked from highest to lowest as follows: S, CH4, N2, CO, and air. The total SO2 production decreased with increasing heating rate. For the reaction between CaS and CaSO4, a higher molar ratio of CaS to CaSO4 no less than 1:3, both S and CH4 reductive atmospheres, and a lower heating rate (2°C/min) favour the total SO2 emission.

Recycling of pyrite and gypsum mining residues through thermochemical conversion into valuable products

Pyrite-containing tailings pose an environmental challenge due to the risk of Acid Mine Drainage (AMD) upon storing if not properly managed. AMD can, however, be neutralized with alkali materials like lime which leads to the generation of gypsum that also ends up in the landfill. Instead of landfilling this residue, it can be recycled into potentially useful products. A proposed process involves decomposing pyrite, reduction of pyrrhotite, and finally conversion of gypsum to lime. This study evaluates the recycling/thermochemical conversion process of pyrite tailings and gypsum residues from the Boliden Aitik mine using thermodynamic modeling, simultaneous thermal analyses coupled with mass spectroscopy, and mineralogical composition identification. It was observed that pyrite can undergo complete decomposition into pyrrhotite and release elemental sulfur below 750 °C in an inert atmosphere. Furthermore, successful reduction of pyrrhotite was achieved through the application of biochar in the presence of lime at 950 °C in an inert atmosphere. The study also reveals that gypsum can be effectively converted to lime at 1200 °C in an inert atmosphere when accompanied by calcium sulfide (CaS). Moreover, the energy and material balance of the process was analyzed, considering the conversion of 1 ton of pyrite tailings. The products include 0.4 tons of iron powder, 2.7 tons of SO2 gas, 0.4 tons of CO2 gas, and 1.21 tons of excess active lime. The calculated energy consumption for this process was determined to be 2893 kWh.

Reaction mechanism of thermal decomposition of Phosphogypsum

Phosphogypsum (PG) is a co-product of the phosphoric acid industry. To reduce the environmental impact and land occupation caused by PG disposal, researchers are trying to integrate it into building materials, agriculture, etc. Herein, PG decomposition with carbon monoxide (CO) was studied with i) thermogravimetric analysis (TGA), ii) induction heated fluidized bed reactor (IHFBR), and iii) thermodynamically using FactSageTM. Experimentally, PG starts decomposing around 600 °C and produces mainly calcium sulfide (CaS) at high CO partial pressure, above 50 %, and mainly to calcium oxide (CaO) at lower CO partial pressure (<20 %). At 1000 °C and above, CaSO4 was completely converted to CaS, CaO, and minor co-products due to the presence of impurities in PG. Elemental and XRD analyses were adopted to understand the reaction mechanisms of PG decomposition. Thermodynamic simulations confirmed the full conversion of calcium sulfate (CaSO4) above 600 °C for a CO/CaSO4 ratio above 6.81 (mol/mol), whereas only 60 % conversion would be achieved at 1500 °C and lower ratio (<0.49 (mol/mol)). As a result, CaS and CaO may be produced, depending on the temperature and CO partial pressure.

Sulfurization- Desulfurization of Iron-Calcium Oxygen Carriers during Chemical Looping Combustion of Syngas

Chemical looping combustion of SO2-containing syngas with various fabricated iron-calcium oxygen carriers was studied to comprehend the sulfurization and desulfurization of oxygen carriers during combustion. Experimental results indicated calcium-iron oxygen carriers fabricated with CaO:Fe2O3 weight ratio of 3:7 and calcined at 800°C (CaFe-378) was suitable for chemical looping combustion of syngas. CaFe2O4 was noticed to be the dominant crystalline phase in CaFe-378 even after 10 redox operations. Reduction kinetics for chemical looping combustion of both H2 or CO in syngas with CaFe-378 were adequately described by the 2-dimension diffusion model. The activation energies of H2 and CO with CaFe-378 were determined to be 35.4 kJ mol−1 and 46.0 kJ mol−1, respectively. Calcium sulfide (CaS) was generated during the chemical looping combustion of SO2-containing syngas with CaFe-378. CaS was further oxidized to CaSO4 on the surface of CaFe-378 during air regeneration, which might inhibit the complete regeneration of iron oxides. Satisfactory regeneration of sulfurized oxygen carriers was accomplished by introducing hydrogen after the air-regeneration because of the reduction of calcium sulfate to calcium oxide.

Using calcium-containing injection wire filled with electrolytic calcium in steel ladle treatment

Aluminum is one of the most common deoxidizers; when it is used in the melt, refractory inclusions of alumina are formed. The presence of these non-metallic inclusions negatively affects the purity of liquid steel, mechanical properties, makes casting difficult due to tightening of the steel-pouring fittings. The modification of alumina inclusions with calcium promotes the formation of liquid calcium aluminates, which leads to an acceleration of their removal from the metal due to a higher ascent rate. Having a high affinity for sulfur, calcium reduces its harmful effect by binding it with the formation of calcium sulfides, reducing the anisotropy of steel properties during further rolling. For steel treatment with calcium, injection wires with a calcium-containing filler are used. As a filler can be used: electrolytic calcium, silicocalcium, aluminum-tremic calcium, or ferrocalcium. The paper describes results of the tests carried out on a calcium-containing wire filled with electrolytic calcium and silicocalcium. It is shown that the consumption of calcium when using silicocalcium wire is on average 35 % higher in comparison with calcium injection wire filled with electrolytic calcium. The calcium recovery rate for different steel grades was evaluated using calcium-containing wires of different designs and filler. In this work, the steel pourability was analyzed. As a determining parameter, dependence of change in position of the tundish stopper rod on calcium content in the metal was considered in the sample from CCM. It was established that a wire filled with electrolytic calcium shows a more effective result in comparison with a silicocalcium wire.