Reactions of Chromium during the Calcination of Cement Clinker Produced Using Steel Slag

We investigated the effects of calcination temperature(950-1450℃),steel slag content,and the total chromium content of steel slag on the Cr^(6+)contents of clinker samples produced using steel slags with different chromium contents.Additionally,the reactions of chromium in clinker(produced using steel slag)during calcination were studied.It is found that Cr^(6+)conversion increases with increasing calcination temperature to 1250℃,reaching a maximum of 43%-79%,before decreasing to 18%-42%at 1450℃.Cr^(6+)is mainly formed by the oxidation of trivalent chromium(Cr^(3+))during the solid-phase reaction stage of clinker calcination.Furthermore,the Cr^(6+)content of a clinker sample is proportional to the chromium content of its raw meal precursor and is mainly in the form of water-insoluble calcium chromate(CaCrO_(4)).The chromium in clinker is mainly distributed in tricalcium aluminate and tetracalcium aluminoferrite,however,some is present in silicate minerals.We expect to inform the monitoring and control of the Cr^(6+)content of clinker(produced using steel slag)and resulting cement.

STUDY ON STRENGTH AND PETROGRAPHIC STRUCTURE OF CLINKER BY LOW-TEMPERATURE BURNING

In this paper,the strength and petrographic structure of clinker by low-temperature burning are studied. The results show that both the calcining temperature of Ca-CO3 and sintering temperature clinker decreases by 150 degrees C compared with those in traditional rotary kiln,the rate of f-CaO in the clinker sintered at 1300 degrees C is 0.29% similar to 2.81%, the strength of the clinker is 62. 5MPa with maximum 69. 4MPa at a specific area of 2900 similar to 3400cm(2)/g. The results also show that the types of petrographic structure of the clinker can be classified as: homogeneous structure, inlaid or edged structure,stain-melting structure and porous structure. The clinker sintered at 1300 +/- 15 degrees C temperature and with enough retention period is mainly in homogeneous structure.

Prediction of Free Lime Content in Cement Clinker Based on RBF Neural Network

Considering the fact that free calcium oxide content is an important parameter to evaluate the quality of cement clinker, it is very significant to predict the change of free calcium oxide content through adjusting the parameters of processing technique. In fact, the making process of cement clinker is very complex. Therefore, it is very difficult to describe this relationship using the conventional mathematical methods. Using several models, i e, linear regression model, nonlinear regression model, Back Propagation neural network model, and Radial Basis Function （RBF） neural network model, we investigated the possibility to predict the free calcium oxide content according to selected parameters of the production process. The results indicate that RBF neural network model can predict the free lime content with the highest precision （1.3%） among all the models.

Composition Design for High C_3S Cement Clinker and Its Mineral Formation

A new composition of Portland cement clinker was studied, in which KH, SM and IM was 0.98,2.4 and 2.4 respectively as well as its meal added 1%CuO （in mass）. Fired at 1 200℃,1 350℃,1 400℃ and 1 450℃ for 30 min, the resultant mineral phases component and mineral morphology were analyzed. The performances of the cement which was made of clinker burned at 1 450℃ and fly ash were determined. By means of QXRD, XRD and optical microscopy, it is shown that the clinker burnt at 1 450℃ has the larger size crystals and distinct crystal interface, in which the C3S content is 73.37% and the mineral phases is dominantly C3S, following by minor C2S, C3A and tetracalcium aluminoferrite. The results reveal that a new type of high C3S content clinker can completely be made by traditional temperature-time schedule. The performances of the cement produced from this clinker with addtion of 50% fly ash and 5% gupsum were in agreement with the 32.5 strength grade of Portland fly-ash cement. The results also show that the clinker has a significant effect of saving energy and utilizing waste slag.

Effect of CuO on the Burnability and Mineral Formation of High C_3S Cement Clinker

The effect of CuO on the clinkering process and mineral structure, components and morphology of high C3S cement clinker was studied. One reference mixture was prepared according to the potential mineral phase components C3S=75%, C3A=7%, C4AF=18% and then was mixed, respectively, with 0.5%, 1%, 1.5%, 2%, 2.5% and 4% CuO. All samples were heated at a rate of 10°C/min to the design temperatures and then maintained for 40 min. Analyses by the glycerol-ethanol method, XRD and SEM-EDS show that the minimum of free lime （f-CaO） content was related to temperature and CuO amount. The higher the temperature, the lower the amount of CuO corresponding to the f-CaO minimum content. CuO promotes the formation and growth of C3S and C4AF and a new compound is found. In addition, these phenomena are discussed theoretically. In conclusion, CuO alters the burnability and the formation and structure of C3S in a high C3S cement system.

Simulation of clinker grinding circuits of cement plant based on process models calibrated using GA search method

Particle size distributions of obtained samples from several sampling campaigns were determined and raw data were mass balanced before being used in simulation studies.After determination of breakage function,selection function,Bond work index,residence time distribution parameters,and Whiten's model parameters for air separators and diaphragms between the two compartments of tube ball mills,performance of the circuits was simulated for given throughputs and feed particle size distribution.Whiten's model parameters were determined by GA(genetic algorithm) toolbox of MATLAB software.Based on implemented models for modeling and simulation,optimization of circuits was carried out.It increased nearly 10.5% and 15.8% in fresh feed capacity input to each tube ball mill.In addition,circulating load ratios of circuits are modified to 118% and 127% from low level of 57% and 22%,respectively,and also cut points of air separators are adjusted at 30 and 40 μm from high range of 53 and 97 μm,respectively.All applications helped in well-operation and energy consumption reduction of equipments.

Catalytic performance of cement clinker supported nickel catalyst in glycerol dry reforming

The paper reports the development of cement clinker-supported nickel （with metal loadings of 5 wt%, 10 wt%, 15 wt% and 20 wt%） catalysts for glycerol dry （CO2） reforming reaction. XRF results showed that CaO constituted 62.0% of cement clinker. The physicochemical characterization of the catalysts revealed 32-folds increment of BET surface area （SBET） with the addition of nickel metal into the cement clinker, which was also corroborated by FESEM images. Significantly, XRD results suggested different types of Ni oxides formation with Ni loading, whilst Ca3SiO5 and Ca2Al0.67Mn0.33FeO5 were the main crystallite species for pure cement clinker. Temperature-programmed reduction analysis yielded three domains of H2 reduction peaks, viz. centered at approximately 750 K referred to as type-Ⅰ peaks, another peaks at 820 K denoted as type-Ⅱ peaks and the highest reduction peaks, type-Ⅲ recorded at above 1000 K. 20 wt% Ni was found to be the best loading with the highest XG and H2 yield, whilst the lowest methanation activity. Syngas with lower H2/CO ratios （0.6 to 1.5） were readily produced from glycerol dry reforming at CO2-to-Glycerol feed ratio （CGR） of unity. Nonetheless, carbon deposit comprised of whisker type （Cv） and graphitic-like type （Cc） species were found to be in majority on 20 wt%Ni/CC catalysts.

NMR Research on Cement Clinker and Its Structures in Early Age Hydration

Clinker has long been regarded as a critical factor for cement hydration and solidification.α-C2S and β-C2S in 2CaO·SiO2（C2S） phase and C3S Monoclinic 1（C3S M1） and C3S Monoclinic 3 （C3S M3） in 3CaO·SiO2 （C3S） phase were clearly recorded in the 29Si MAS NMR spectra.The content of C3S phase in the clinker deduced from the fine peak analysis coincides with the phase quantification analysis calculated by the Taylor-Bogue method based on XRF,which also accords to the statistical data in industrial production.NMR provides a proof that C3S M1 and β-C2S phases have a prior reaction in the early age hydration of clinker,and demonstrates that aluminum coordination changes from tetracoordinated 4CaO·Al2O3·Fe2O3（C4AF） to hexacoordinated [Ca2Al（OH）6]（SO4）0.3·3H2O（Aft） in one day hydration and changes to the 3CaO·Al2O3·CaSO4·nH2O （Afm） in a seven-day hydration.

Quantitative XRD Analysis of Cement Clinker by the Multiphase Rietveld Method

Quantitative phase analysis of Portland cement clinker samples was performed using an adaptation of the Rietveld method.The Rietveld quantitative analysis program,originally in Fortran 77 code,was significantly modified in visual basic code with windows 9X graph user interface,which is free from the constraint of direct utilizable memory 640 k,and can be conveniently operated under the windows environment.The Rietveld quantitative method provides numerous advantages over conventional XRD quantitative method,especially in the intensity anomalies and superposition problems.Examples of its use are given with the results from other methods.It is concluded that,at present,the Rietveld method is the most suitable one for quantitative phase analysis of Portland cement clinker.

Effect of Microwave Processing on Aluminate Cement Clinkering

When raw materials were preheated to 1000-1300 ℃ by electricity and microwave was inputted for 1 min 5 s-4 mins, then alunminate clinkers were obtained. The f-CaO contents,XRD patterns and lithofacies analysis show that the microwave processing accelerates the clinkering reaction,and Fe_2O_3 is contributed to the aluminate cement clinkering. The appearance of liquid phase in process of microwave heating increases the microwave absorbability of materials greatly.

Behavior of SiO_2 in the leaching process of alumina clinker with high concentration

It is essential for alumina production by alkaline process to know the behavior of minerals containing Al and Si in basic solution,and the behavior of SiO2 in the process of clinker leaching is an important portion. To study the behavior of SiO2 in the process of high concentration clinker leaching,experiments were carried out in home-made reactors. The results indicate that factors,such as temperature,time,Al2O3 concentration,as well as SiO2 concentration,have profound impact on the SiO2 and Al2O3 concen-tration of pregnant liquor during the high concentration leaching. However,sodium carbonate and free caustic soda concentrations have no remarkable effect on it,thus they are the secondary factors compared with Al2O3 concentration. The concentration of SiO2 in the pregnant liquor could be reduced to a lower level when the major effect parameters of this process are controlled properly.

Study on Sintered Synthetic Hercynite Clinker

Special grade bauxite and roll scale were used as raw materials to investigate the influences of reducing atmosphere and firing temperature on sintering clinker. The results showed that: 1) The mixture of the materials could be sintered enough to synthesise hercynite under reducing atmosphere by adding reducing reagent; 2) The hercynite clinker could be sintered to high density and the content of FeAl 2O 4 may attain 80～90% under the firing temperature of 1550℃.

Effect of Fused MgO-ZrO_2 Clinker Addition on Thermal Shock Resistance of MgO-ZrO_2 Unfired Bricks

MgO -ZrO2 unfired bricks with ZrO2 content up to 8% at the interval of 2% were prepared, using fused magnesia （ MgO ： 97% ） and fused MgO - ZrO2 clinker （ ZrO2 ： 14. 33% ） as starting materials and phenolic resin as binder. The effects of ZrO2 content on thermal shock resistance （TSR） and other properties such as cold and hot modulus of rupture have been investigated. Re- sidual cold modulus of rupture ratio after heating at 1 000 ℃ and quenching by air blowing was adopted to characterize TSR. Addition of the MgO -ZrO2 clinker improves TSR, attributing to the microcrack toughening effect by thermal expansion mismatch between different phases. When ZrO2 content goes above 4%. the impro- ving effect tends to be moderate. The introduction of MgO- ZrO2 clinker can also improve the HMOR at 1 500 ℃, while the increased ZrO2 content reduces CMOR of the bricks prefired at 1 600 ℃, due to the thermal expansion mismatch effect. Compromising the overall properties, the optimal ZrO2 content for such magnesia based unfired brick is suggested to be 4%.

Optimization of the Content of Tricalcium Silicate of High Cementing Clinker

Optimization of the content of tricalcium silicate（C 3 S）of high cementing clinker was investigated.The content of free-CaO（f-CaO）,mineral composite,the content of C 3 S in the clinker and the hydration product were analyzed by chemical analysis and X-ray diffraction（XRD）.＂K Value＂method of QXRD was selected as a quantitative analysis way to measure the content of C 3 S,and the strength of cement paste was determined.The results show that at a water cement ratio of 0.29,the strength of cement paste with 73%C 3 S can be up to 97.5 MPa at 28 days age.The strength at 28 d of cement with 73%C 3 S is 16%higher than that with 78%C 3 S at water requirement for normal consistency.The relationship between the strength of high cementing Portland cement and the content of C 3 S in the clinker is nonlinear.According to the strength of cement paste,the optimal content of C 3 S in cement clinker is around 73%in this paper.

Predictive Model for Cement Clinker Quality Parameters

Managers of cement plants are gradually becoming aware of the need for soft sensors in product quality assessment. Cement clinker quality parameters are mostly measured by offline laboratory analysis or by the use of online analyzers. The measurement delay and cost, associated with these methods, are a concern in the cement industry. In this study, a regression-based model was developed to predict the clinker quality parameters as a function of the raw meal quality and the kiln operating variables. This model has mean squared error, coefficient of determination, worst case relative error and variance account for (in external data) given as 8.96 × 10–7, 0.9999, 2.17% and above 97%, respectively. Thus, it is concluded that the developed model can provide real time estimates of the clinker quality parameters and capture wider ranges of real plant operating conditions from first principle-based cement rotary kiln models. Also, the model developed can be utilized online as soft sensor since they contain only variables that are easily measured online.

Inter-comparative Study of Quantitative Methods of Industrial Clinker

Impurities from the raw materials, the grinding and the homogenization of the raw materials, the kiln instability and the complexity of the cooling step, all these factors make it difficult to obtain a perfect evaluation of the mineralogical composition of Portland clinker. We studied the limitations of the most commonly used quantitative methods and recommend some procedures to obtain reliable and reproducible results of quantitative analyses. Different clinker samples（provided by the Bizerte Cement Company（Tunisia）） were subjected to an elemental analysis by X-ray fluorescence and the mineralogical composition was determined by the Bogue calculation and by X-ray powder diffraction combined with the Rietveld method（Different softwares were used： XPert High Score Plus version 2.0 and TOPAS version 4.2）. We then compared the results obtained by the Rietveld method and the Bogue calculation to the specific peak areas of each phase. The content of each phase, determined by the Rietveld method, varied proportionally to the change in peak area; a significant difference in these results was found by using the elementary Bogue calculation.

Effect of Minor Elements on Silicate Cement Clinker

The effect of rare-earth and HX addition agent on the burn-ability of silicate cement dinker was investigated by orthogonal experiment. The result shows, compared with blank sample, f CaO of the .samples added with rare-earth and HX agent drops by 84.95% , its 3 d and 28d compressive strength enhances by 24.40% and 16.90% , respectively. It was discovered by means of X-ray diffrnction and high temperature microscope analysis that sintering temperature of the sample added with rare-earth and HX addition agent is about 1320℃. At the same time, the tmrning temperature of triealeium silicate desends and its crystal growth forming- rate increases. Tricalcium silicate content in burning clinker is higher and its crystal is larger.

Effects of Clinker Contents of Different C_3A and C_4AF on the Performance of PSC Cement

Phosphogypsum-slag-clink （PSC） cement were prepared by original phosphogypsum（PG）, which was grinded after dried at 60 ℃combined with different contents of phosphogypsum （15%, 20%, 30%）, and a small amount of different C3A, C4AF contents of finely ground cement clinker, and ground granulated blast furnace slag （GGBFS）. Physical mechanical and sugaring properties were studied. The results show that compressive strength of PSC cement with 20% phosphogypsum at 3 d ages would be higher than 17 MPa and even 50 MPa at 28 days. Compressive strength at longer curing stage and sugaring properties of PSC with lower content of C3A higher C4AF clinker were improved, pH value of PSC cement system at early stage was relatively low, and pH gradually increased with the addition of clinker, pH increased firstly and then decreased with the hydration stage. SEM analyses showed that the amount of ettringite, which was influenced by pH and content of A1, must be controlled in PSC cement system, which may cause damage to microstructure or even expansive cracks if large amount of ettringite formed in hardened paste.

THE FORMATION MECHANISM OF PORTLAND CEMENT CLINKER MINERALS IN RAPID BURNING

Cement clinker is burnt at the rapid heating rate has the obvious effect of saving energy due to the low burning temperature and short burning time. This kind of technique is being researched actively in recent years, but the systematical theory investigation about the formation mechanism of clinker minerals under this condition has not been reported. In this paper, the formation mechanism of Portland cement clinker minerals in rapid burning was studied by means of DTA, SEM, EPMA, XRD and other conventional testing methods by using a special burning equipment.

A STUDY ON THE KINETICS AND SOME MECHANISMS OF CEMENT CLINKER FORMATION

In this paper for saving energy two different burning methods of cement clinker formation have been studied.One is the rapid burning method and the other is ordinary burning method simulating rotary kiln,and they are compared by the kinetic point of view.The result reveals that the activation energy of rapid burning is much lower than ordinary burning.For looking into the cause, the main raw material—lime stone was burnt by the same two methods and the structure of product CaO has been detected.It can be found that the microstructure of CaO produced by rapid burning is looser;lattices constants are greater;crystal defects are more and particle size is smaller than that produced by ordinary burning.These cause the chemical reaction more active.So the activation energy of clinker formation of rapid burning is much lower than that of the ordinary burning.