High Hydration Activity Research Articles

Understanding synergistic effects between MgO expansive agents and hydrophilic nano-silica in UHPC

Ultra-high performance concrete (UHPC) incorporating MgO expansive agents (MEAs) demonstrates reduced early shrinkage but can potentially compromise mechanical strength, which may lead to serious quality incidents during early construction. Nanomaterials, with small particles, large specific surface area, and high hydration activity, have proven effective in enhancing the mechanical properties of cementitious materials. Nonetheless, limited research exists on the impact of nanomaterials on the performance of MEA-containing UHPC. This study aims to enhance the mechanical strength of the hybrid system by incorporating nanomaterials, specifically hydrophilic nano-SiO2 (HNS). The effect of HNS and/or MEA on UHPC performance was systematically investigated through various tests, including heat of hydration, MIP, XRD, TG-DTG, FTIR, and SEM-EDS. The results show that HNS improves the hydration process of cement, and effectively increases the compressive strength of MEA-containing UHPC by up to 30.87 % at 3 days. The improvement of the mechanical properties of MEA-UHPC was attributed to the filling effect of the unreacted HNS, which effectively enhanced the densification of the matrix. Additionally, the crystallization and nucleation effect of hydrated HNS produced more C–S–H gels with high stiffness, which resisted the stresses generated by the micro-expansion of MEA. Importantly, in terms of less shrinkage, HNS exhibits a synergistic effect with MEA, wherein MEA provides the necessary weakly alkaline environment for the dissolution of reactive silica, while HNS appropriately increases the initial hydration degree of MEA. These combined effects further reduce the early shrinkage of UHPC, consequently lowering the risk of cracking. The collective improvement of all the aforementioned results suggests that HNS holds significant potential for application in MEA-containing UHPC.

Preparation and property studies of ferric sulfoaluminate cement based on Bayer red mud and phosphogypsum.

The Bayer red mud (RM) and phosphogypsum (PG) accumulation have caused significant environmental contamination. However, practical and effective resource utilization technologies are still lacking currently. This work aims to develop ferric sulfoaluminate cement (FSAC) employing low-cost materials including Bayer red mud, phosphogypsum, and other materials. This method effectively improves the utilization rate of Bayer red mud and phosphogypsum. Under the premise of ensuring the performance of FSAC, the utilization rate of solid waste can reach up to 48.56%. The effects of different red mud dosages on cement mineral formation, workability, and mechanical properties are investigated. Then, untreated phosphogypsum is adopted as a retarder for FSAC, and the hydration process, working properties, mechanical properties, types of hydration products, and morphology of FSAC are explored. The results suggest that the crystal transformation of Ye'elemite is promoted with the increase of Bayer red mud content. Cubic crystal system Ye'elemite with higher hydration activity is generated, which increases the early strength of cement but greatly reduces the setting time, hindering the later strength growth. Untreated phosphogypsum can effectively delay the early hydration process of FSAC, prolong the setting time of cement, and increase the strength of FSAC in the later stage. When the dosage of Bayer red mud and phosphogypsum is 17.64% and 9.21%, respectively, with phosphogypsum dosage of 20%, the prepared FSAC has satisfactory mechanical properties, and the 3-day and 90-day compressive strengths are 34.6 MPa and 57.1 MPa, respectively. In addition, the study of heavy metal leaching indicates that the FSAC prepared by Bayer red mud, phosphogypsum, and other raw materials will generate no environment pollution, and the solidification of heavy metal elements in the cement slurry is superior.

Identification and evolution of non-traditional nitrilase from Spirosoma linguale DSM 74 with high hydration activity

Hydration, a secondary activity mediated by nitrilase, is a promising new pathway for amide production. However, low hydration activity of nitrilase or trade-off between hydration and catalytic activity hinders its application in the production of amides. Here, natural C-terminal-truncated wild-type nitrilase, mined from a public database, obtained a high-hydration activity nitrilase as a novel evolutionary starting point for further protein engineering. The nitrilase Nit-74 from Spirosoma linguale DSM 74 was successfully obtained and exhibited the highest hydration activity level, performing 50.7 % nicotinamide formation and 87.6 % conversion to 2 mM substrate 3-cyanopyridine. Steric hindrance of the catalytic activity center and the N-terminus of the catalytic cysteine residue helped us identify three key residues: I166, W168, and T191. Saturation mutations resulted in three single mutants that further improved the hydration activity of N-heterocyclic nitriles. Among them, the mutant T191S performed 72.7 % nicotinamide formation, which was much higher than the previously reported highest level of 18.7 %. Additionally, mutants I166N and W168Y exhibited a 97.5 % 2-picolinamide ratio and 97.7 % isonicotinamide ratio without any loss of catalytic activity, which did not indicate a trade-off effect. Our results expand the screening and evolution library of promiscuous nitrilases with high hydration activity for amide formation.

The role of P2O5 on the stability of β-C2S in AOD slag based on the improvement of hydration activity

The original AOD slag in the cold state contained more than 50 wt% low-hydration activity γ-C2S, which significantly affects the hydration activity. Therefore, the effect of the typical crystal stabilizer P2O5 on the formation of a new phase and the enhancement in the mass fraction of high hydration activity β-C2S in AOD slag were studied, and the internal factors that controlled the doping preference and influenced the hydration activity of the crystal stabilizer P2O5 were revealed. When the addition of P2O5 was 0.6 wt%, the mass fraction of β-C2S in AOD slag was increased by 50.8 wt%. The P5+ and its oxide P2O5 entered the lattice of C2S in solid solution, causing lattice distortion. After P doping, the charge energies of the Ca, Si and O atoms shifted toward the low energy direction by approximately 5 eV, which increased the stability of the electronic structure. In addition, P doping changed the delocalization of the CBM in the pure phase, partially located the LDOS of the VBM and CBM, and increased the numbers of nucleophilic and electrophilic attack sites, thus improving the hydration activity of β-C2S.

Study on the source of activity and differences between modified and unmodified magnesium slag as a filling cementitious materials

The best alternative for producing magnesium metal cleanly has emerged as the realization of magnesium slag resource usage. Magnesium slag is simple to pulverize, low activity, and difficult to utilize. For this, our team proposed adding an optimization agent before reducing metal magnesium to obtain modified magnesium slag (MMS). This study aims to contrast the differences between MMS and unmodified magnesium slag' (UMS) cementitious characteristics. First, it was determined how MMS and UMS differed in terms of cementation activity. Then, the performance variations of the filled cementitious materials (MF-A, MF-B, and UMF), which were made by combining fly ash (FA) with MMS and UMS, respectively, were compared. The findings indicate that, the main mineral compositions of MMS and UMS are β-C2S and γ-C2S, respectively, MMS exhibits non-swelling and non-powdering properties compared with UMS. The 28 d activity indices for MMSA and MMSB were respectively 90.78% and 88.48%, higher than those for UMS by 23.02% and 20.72%. The early hydration reactions of MF-A and MF-B were more rapid, per the hydration heat data. Additionally, microscopic analysis revealed that the unconfined compressive strength of MF-A at 28 d (8.39 MPa) was much higher than that of UMF (4.99 MPa), which was mostly caused by the difference in the concentration of hydration products. In conclusion, MMS has higher hydration activity and stable properties, which can be combined with FA and other applications in the field of mine filling to achieve resource utilization.

Rehydration Activity of High-Temperature Calcined Recycled Sand Autoclaved Aerated Concrete

Autoclaved aerated concrete is an excellent thermal insulation wall material, but with a large amount of waste. This paper describes the high-temperature activation and rehydration activity of waste cement–lime–sand autoclaved aerated concrete (SAAC) and discusses the high-temperature phase transition of SAAC. SAAC calcined at 750 °C was confirmed to be a metastable and amorphous state, which could hydrolyze Ca2+ ions with reactivity in water. The conductivity curve demonstrates that the concentration of ions in the suspension decreases rapidly at 150–250 min, and the hydration reaction turns dominant at this time. The hydration heat curve also displays a hydration exothermic peak at 2.5 h. In addition, the conductivity measurement of suspension and the exothermic measurement of hydration reaction proves that SAAC calcined at 750 °C has a hydration activity and can rehydrate with SiO2 in the system. The rehydration activity was verified by replacing 30% cement in the standard test block with calcined SAAC because the calcined SAAC at 750 °C has high hydration activity, and its activity index reached 89.58%. Fly ash is a commonly used cement admixture at present. Hence, the SAAC calcined at 750 °C and the fly ash were used to replace 30% of the cement in the cement test block, respectively. The results of this comparative experiment vividly showed that the reaction activity of SAAC calcined at 750 °C was higher than that of fly ash. Therefore, according to this research, SAAC has activity after calcination at 750 °C and can be hydrated again.

Hydration activity and expansibility of different divalent metal oxide solution compositions in steel slag

Steel slag (SS) accounts for 15–20% of steelmaking output; its application in cement concrete has been limited because of poor stability. In this study, the divalent metal oxide solid solution (RO phase) in SS was analogue synthesised to study its hydration activity and expansibility. The results showed that the hydration activity and expansibility of magnesium oxide (MgO) in the analogue-RO phase is affected by the content of ferrous oxide (FeO); with the increase of molar ratio (x) of iron oxide to magnesium oxide in the analogue-RO phase, the autoclave expansion rate and hydration activity of the cement paste decreased. When x ≤ 0.5, the RO phase had high hydration activity and could cause poor soundness of SS. When x = 1, the RO phase had low hydration activity and could cause slight expansion of SS. When x ≥ 2, the RO phase had no hydration activity and could not cause any expansion of SS. The control of different analogue-RO phase compositions induced different hydration and expansibility, which provided a theoretical basis for the influence of the RO phase on the soundness of SS and enabled measures to be proposed to reduce the expansion of SS, thereby promoting high-volume utilisation of SS in cement and concrete.

Effect of High Temperature Reconstruction and Modification on Phase Composition and Structure of Steel Slag

This study investigates the pattern of influence of blast furnace slag tempering on the composition and structure of steel slag. The chemical composition, equilibrium phase composition, microscopic morphological characteristics and elemental composition of microscopic regions of steel slag and blast furnace slag modified by high temperature reconstruction were analyzed using X-ray diffractometer (XRD), FactSage7.1 thermodynamic analysis software, mineral phase microscopy and field emission scanning electron microscopy. The results show that blast furnace slag blending can promote the generation of a low melting point phase in the slag, as well as reducing its melting temperature and improving its high temperature kinetic conditions. On the one hand, the incorporation of blast furnace slag was found to promote the generation of C2S in the steel slag and improve its gelling activity. Notably, at 1400 °C, the C2S content (mass fraction) of steel slag modified with 15% high temperature reconstruction reached 39.04%, while that of unmodified steel slag at this temperature was only 16.92%, i.e., only 1/4 of the C2S content in the modified slag. On the other hand, the incorporation of blast furnace slag inhibited the generation of a-C2S-C3P and calcium ferrate minerals, refined the grains of calcium–aluminum yellow feldspar, reduced the alkalinity and promoted the generation of silicate phases with high hydration activity in steel slag.

Investigation on the crystallization properties of BaO-bearing blast furnace slag through a confocal laser scanning microscope

• The crystallization ability of blast furnace slag is weakened with an increase in BaO content. • One-dimension growth of crystals at low temperature is identified. • A high BaO content induces a phase transformation from melilite to merwinite. Investigating the crystallization behavior of BaO-bearing blast furnace slag (BFs) is of great significance for the dry granulation technology to guide the production of glassy slag with high hydration activity, and simultaneously collect the waste heat of hot slag. In this study, the influence of BaO content on the crystallization behavior was investigated through in-situ observation using a confocal laser scanning microscope (CLSM). The theoretical calculations by FactSage 8.0 and X-ray diffraction (XRD) analysis of the quenched slag were carried out for the crystalline phases characterization. The results showed that the incubation time increased in the isothermal crystallization process and the initial crystallization temperature decreased in the continuous cooling process with the increasing BaO concentration, indicating that the crystallization ability of the slag was weakened. BaO existence had little effect on the crystal morphology during the isothermal crystallization process at 1200℃. Furthermore, the crystallization kinetics analysis of the JMA model showed the Avrami index n close to 1.5, indicating the one-dimension growth of crystals at low temperature. The akermanite (Ca 2 MgSi 2 O 7 ) and gehlenite (Ca 2 AlSi 2 O 7 ) were the main crystalline phases, and their precipitation was restrained to a certain extent as the BaO content increased.

Preparation of Sludge Ash–Desulfurization Gypsum-Based Backfill Materials Using Microwave Calcination

Paper mill sludge ash (PMSA), sewage sludge ash (SSA), and desulfurization gypsum (DG) were mixed and calcined by microwave radiation to acquire a product with higher hydration activity. The resulting mixture was used as a supplementary cementitious material to prepare backfill materials for mining. The influence of the mixing ratio of raw materials, microwave parameters, and sample size on the properties and microstructure of the microwave-sintered sludge ash (MSSA) and MSSA-cement pastes was determined. Both the MSSA and the prepared pastes were characterized using X-ray diffraction (XRD), Fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). Results indicated that the minerals in the MSSA were rankinite, mayenite, and belite, which all exhibited relatively high hydration activity and significantly improved the degree of hydration of the MSSA–cement system. As the microwave power and irradiation time increased, the water demand of the MSSA–cement pastes decreased, the setting time decreased, and the compressive strength increased. The MSSA prepared with a small length-to-diameter ratio produced more crystals and gels compared with that prepared with a larger length-to-diameter ratio. The gels mutually fused to form a dense structure, and this further enhanced the strength of the MSSA–cement pastes.

Humidity Sensitivity of Hydration of Expansive Agent and Its Expansive Efficiency in Ultra-High Performance Concrete

Ultra-high performance concrete (UHPC) has a potential cracking risk due to its large autogenous shrinkage. The use of an expansive agent is an effective approach to reduce autogenous shrinkage of UHPC. However, different kinds of expansive agents show different expansive efficiency in UHPC. To study the cause for the difference in expansive efficiency, this study selected three expansive agents, namely highly reactive MgO-based, medium reactive MgO-based, and CaO-based expansive agents, and carried out the following experiments: autogenous shrinkage, hydration heat, hydration process of expansive agent under different relative humidity (RH), and micrographs. The results showed that the CaO-based expansive agent has high hydration activity at RH of more than 44.0%, while the hydration activity of two kinds of MgO-based expansive agents, especially a medium reactive MgO-based expansive agent, decreases significantly when RH drops below 80%. Meanwhile, the CaO-based expansive agent had higher expansive efficiency in UHPC than the MgO-based expansive agent. This study suggested that the CaO-based expansive agent is more suitable for compensating autogenous shrinkage of UHPC due to its low humidity sensitivity compared to the MgO-based expansive agent.

Rational Regulation of Reaction Specificity of Nitrilase for Efficient Biosynthesis of 2-Chloronicotinic Acid through a Single Site Mutation.

Nitrilase-catalyzed hydrolysis of 2-chloronicotinonitrile (2-CN) is a promising approach for the efficient synthesis of 2-chloronicotinic acid (2-CA). The development of nitrilase with ideal catalytic properties is crucial for the biosynthetic route with industrial potential. Herein, a nitrilase from Rhodococcus zopfii (RzNIT), which showed much higher hydration activity than hydrolysis activity, was designed for efficient hydrolysis of 2-CN. Two residues (N165 and W167) significantly affecting the reaction specificity were precisely identified. By tuning these two residues, a single mutation of W167G with abolished hydration activity and 20-fold improved hydrolysis activity was obtained. Molecular dynamics simulation and molecular docking revealed that the mutation generated a larger binding pocket, causing the substrate 2-CN to bind more deeply in the pocket and form a delocalized π bond between the residues W190 and Y196, which reduced the negative influence of steric hindrance and electron effect caused by chlorine substituent. With mutant W167G as biocatalyst, 100 mM 2-CN was exclusively converted into 2-CA within 16 h. The study provides useful guidance in nitrilase engineering for simultaneous improvement of reaction specificity and catalytic activity, which are highly desirable in value-added carboxylic acids production from nitriles hydrolysis. IMPORTANCE 2-CA is an important building block for agrochemicals and pharmaceuticals with a rapid increase in demand in recent years. It is currently manufactured from 3-cyanopyridine by chemical methods. However, during the final step of 2-CN hydrolysis under high temperature and strong alkaline conditions, the byproduct 2-CM was generated except for the target product, leading to low yield and tedious separation steps. Nitrilase-mediated hydrolysis is regarded as a promising alternative for 2-CA production, which proceeded under mild conditions. Nevertheless, nitrilase capable of efficient hydrolysis of 2-CN has not been reported because the enzymes showed either extremely low activity or surprisingly high hydration activity toward 2-CN. Herein, the reaction specificity of RzNIT was precisely tuned through a single site mutation. The mutant exhibited remarkably enhanced hydrolysis activity without the formation of byproducts, providing a robust biocatalyst for 2-CA biosynthesis with industrial potential.

Study on the phase composition and structure of hardened cement paste during heat treatment

To utilize the fine powder produced in the process of preparing recycled concrete or recycled aggregate, the phase composition and structure of hardened cement paste during calcination at low temperature are investigated in this paper. Results show that as the temperature increases, both ettringite and AFm decompose to form C12A7, CaSO4 and CaCO3. Hydrated calcium silicate is dehydrated to form highly active α'-C2S at 600 °C. α'-C2S has higher hydration activity than C2S formed at high temperatures. When the temperature continues to increase to 800 °C, α'-C2S begins to transform into β-C2S. The dehydration phase at 700–800 °C has the best activity. At the same time, cement paste will inevitably produce more CaO during the heat treatment process. and the Ca(OH)2 generated when it meets with water can be used to stimulate the pozzolanic activity of the calcined coal gangue. To prepare recycled cementitious materials with high strength and excellent performance.

Preparation of nano cement particles by wet-grinding and its effect on hydration of cementitious system

In this study, nano cement particles (Nano-C) were prepared via wet grinding cement. Nano-C was characterized by laser particle size distribution, X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Scanning electron microscope (SEM), Transmission electron microscope (TEM) and 29Si magic-angle spinning nuclear magnetic resonance (29Si MAS NMR). The particle size of Nano-C was D50 = 53.1 nm. In order to disperse the nano particles, polycarboxylate superplasticizer was used in the process of grinding. The results show that 0.5%, 1.0%, 2.0%, and 4.0% Nano-C could increase the 12-h compressive strength by 49%, 109%, 194% and 197%, in comparison with the reference. The influence of Nano-C on the hydration, hydration products, microstructure was tested by means of hydration heat, chemical shrinkage, XRD, Thermogravimetric analysis (TGA), SEM, 29Si MAS NMR, and Mercury injection porosimetry (MIP). The results revealed that Nano-C not only used as distinguished nucleus seed to enhance the PC system hydration but also exhibited high hydration activity to produce C-S-H gel to further raise the PC hydration up. These findings provided a novel way to prepare nanomaterials, which was expected to provide a way to improve the early strength of precast concrete.

Fabrication, microstructure, and hydration of nano β-Ca2SiO4 powder by co-precipitation method

As the main component of belite cement, nanosizing (decreasing the average particle sizes) of β-C2S is one of the important methods to improve its activity. In this paper, nano β-Ca2SiO4 (β-C2S) powders were synthesized by co-precipitation method which was a facile and easy route. Ca(NO3)2, Tetraethyl orthosilicate (TEOS), and NaOH were used as calcium source, silicon source, and precipitant respectively to make the precursor, which was then sintered into β-C2S phase at 700-1100 °C. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer Emmett-Teller (BET), transmission electron microscopy (TEM), and isothermal calorimetry. The results indicated that the sintering temperature had a great influence on the properties of synthesized powders. β-C2S prepared at lower sintering temperature exhibited smaller crystal and particle size, lower crystallinity, higher specific surface area, lower purity (higher f-CaO content) and higher hydration activity. High purity nano-sized β-C2S particles were prepared at sintering temperatures of 900 °C with low relative crystallinity (41.6%), high specific surface area (8.67 m2/g), low f-CaO content (0.66%), nanoparticle size(around 65 nm). Compared with ordinary β-C2S, the hydration activity of nano β-C2S has been greatly improved, which also provides a large imagination space for its future application.

Preparation of Paste Backfill Material from Mix-Calcined Sludge Ash

Paper mill sludge ash (PMSA) and sewage sludge ash (SSA) were mixed and calcined at high temperatures to improve the hydration activity of the sludge ash. The resulting mixture was utilized as an auxiliary cementing material to prepare backfill material for mining. Factors, including sludge ash mixing ratio and calcination temperature, affecting the properties and microstructure of the mixed calcinated sludge ash (MCSA) and cement paste were analyzed. Both raw materials and prepared cement pastes were characterized by different techniques, including XRD, FTIR, TG–DSC, SEM, and EDS. Results show that the major reaction products of PMSA and SSA mixture calcined at high temperature are gehlenite and belite, which exhibit high hydration activity in the pozzolanic reaction and significantly improve the degree of hydration of the MCSA–cement system. Compared with trials involving separate calcination of the two sludge ashes, pastes prepared by mixing calcination had a lower water demand, shorter setting time, and higher compressive strength. The amounts of Ca(OH)2 and C–A(F)–S–H gel produced by the MCSA–cement hydration reaction increased, and the degree of polymerization of the gel phase improved with the increase in calcination temperature as well as the decrease in PMSA mixing ratio, which resulted in the formation of a dense microstructure at the later stage of hydration. This research also suggested that the best modulus range values of MCSA should be controlled to within 1.42 ≤ HM ≤ 1.48 and SM = 0.72, the optimal calcination temperature was 1200 ℃, and the appropriate replacement rate of MCSA for cement should be equal to or smaller than 40% in laboratory conditions.

Study on hydration characteristics of circulating fluidized bed combustion fly ash (CFBCA)

Circulating fluidized bed combustion fly ash (CFBCA) is a by-product of the coal-fired process in power plants. In this paper, the hydration characteristics of CFBCA are studied. The pozzolanic activity of CFBCA and pulverized coal combustion fly ash (PCA) at different ages was tested, the hydration products, microstructure of CFBCA-cement paste and PCA-cement paste and the elements distribution of Si, Al and Ca on the surface of fly ash particles were studied. Then the effects of pH value and SO3 content on the dissolution of active SiO2 and active Al2O3 from CFBCA and PCA were further discussed. The experimental results show that the pozzolanic activity of CFBCA is higher than that of PCA, and the surface of CFBCA is more easily corroded and the active SiO2 and active Al2O3 are easy to dissolve in the hydration process. CaO and anhydrite (CaSO4•II) contained in CFBCA play an important role in promoting the dissolution of active SiO2 and active Al2O3. In addition, the loose structure of CFBCA and the low degree of polymerization of [SiO4] and [AlO6] are also one of the reasons for its higher hydration activity than PCA. Relevant research revealed the hydration mechanism of CFBCA, and provided a theoretical basis for its application in cement and concrete.

Contributions of Burtron H. Davis to Fischer–Tropsch Refining Catalysis: Dehydration as Applied to Processes for 1-Octene Production

The contributions of Burtron H. Davis to the understanding and description of alcohol dehydration over metal oxide catalysts, is discussed and applied to process improvement and process synthesis. Some of the key findings from his work are that the dehydration mechanism over metal oxides involves a concerted removal of OH and adjacent H, that weakly basic metal oxides are sensitive to the acidity of the H abstracted during dehydration, and that anti-Saytzeff elimination is possible with >80 % selectivity over weakly basic metal oxides (In2O3, Y2O3, ZrO2, Eu2O3 and ThO2). These findings were applied to show how the dehydration step of the industrial Fischer–Tropsch based process for 1-heptene to 1-octene conversion can be improved through the use of a weakly basic metal oxide catalyst with low hydration activity. New processes were also suggested for the production of 1-octene from more commonly available feed materials, such as the C8 fraction of natural gas condensate and petroleum naphtha. These processes employed weakly basic metal oxide catalysts with high hydration activity.

Effects of MgO Containing Additive on Low-Temperature Metallurgical Properties of Oxidized Pellet

As a main charging form of BF (blast furnace), pellets play an important role in blast furnace process. However, comparing with sinters, pellets have many disadvantages, such as reduction swelling, low softening and melting temperature and so on. Therefore, the flux pellets have been applied in blast furnace widely, especially MgO containing pellets. The light burned magnesite is applied as MgO containing additive in pellet production. The characters of light burned magnesite are explored. Meanwhile, the effects of it on low-temperature metallurgical properties are investigated such as low-temperature reduction degradation index (RDI), compressive strength (CS) and the reduction swelling index (RSI). The light burned magnesite calcined at 850 °C manifests better grindability, larger specific surface area, and higher hydration activity. It is found that the addition of light burned magnesite can improve low-temperature metallurgical properties (RDI, RSI) of the pellets. With the increase of light burned magnesite in pellets, the RSI and RDI decrease gradually; when the proportion of light burned magnesite does not exceed 2.0% in pellets, the CS decreases slightly, but it still surpasses 2 689 N, which can still meet the demand of BF.

Experimental Studies and Technology Process on Phosphor-Gypsum Decomposition for Producing Sulfuric Acid and Lime

Using phosphor-gypsum (PG) to produce sulfuric acid is one of the most effective ways of recycling sulfur resources. This paper studied the melting and decomposition behavior of PG with High Temperature Microscope and Infrared Sulfur Analyzer. Moreover, a new process of PG decomposition for producing sulfuric acid and lime is proposed and discussed. The result shows that the minimum communion point of PG is higher than 1200 °C, the desulphurization degree of PG at 1200 °C under reducing-oxidizing atmosphere can exceed 90%, and the decomposition products of PG have high hydration activity. This means that little liquid phase will occur if PG is decomposed at1200°C, so PG can be decomposed using a fluidizing furnace. The new process of PG decomposition for producing sulfuric acid and lime has many advantages over the traditional process of PG decomposition for producing sulfuric acid and cement, and has a broad application prospects.