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.

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.

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

In this paper,the strength and petrographicstructure 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℃com-pared with those in traditional rotary kiln,the rate of f-CaOin the clinker sintered at 1300℃ is 0.29%～2.81%,thestrength of the clinker is 62.5MPa with maxium 69.4MPa ata specific area of 2900～3400cm2/g.The results also showthat the types of petrographic structure of the clinker can beclassified as:homogeneous structure,inlaid or edged struc-ture,stain-melting structure and porous strncture.The clinkersintered at 1300±15℃ temperature and with enough reten-tion period is mainly in homogeneous structure.

EFFECTS OF DIFFERENT BURNING PROCESSES ON THE FORMATION KINETICS OF CEMENT CLINKER

Two different methods of burning cement clinker, a rapid burning method and an ordinary burning method used in rotary kiln, respectively, were compared in the laboratory. By means of determining fCaO in the clinkers, rule constant Kr and diffusion activation energy Ea in the two processes of clinker formation were calculated by using Ginstling-Brounshtein diffusion equation and Arrhenius equation. The results show that two processes have very different kinetic constants at the same temperature range 1280-1320C. The rate constant Kr at each temperature in the rapid burning process is much greater than that in the ordinary burning process and the former activation energy Ea is much smaller.

Research of green cement clinker calcinated from ferrochrome slag

Ferrochrome slag is a kind of industrial waste containing Cr\+\{6+\} and is produced in the process of silico ferrochrome smelting. On the basis of analyzing the chemical composition and mineral composition of ferrochrome slag, this paper has put forward a technology of green portland cement clinker calcinated from ferrochrome slag. In the experiment, physical chemical changes of cement clinker in the burning process of ferrochrome slag were investigated. The effects of calcinating temperature and clinker cooling rate on the solubility value of Cr\+\{6+\} were analyzed. The results indicated that when the calcinating temperature is above 1450℃, and the cooling rate is beyond 120 ℃/min, Cr\+\{6+\} in cement clinker is almost insoluble.

CORRELATION OF THE COMPONENTS OF PORTLAND CEMENT CLINKER AND SINTERING PROCESS BY MEANS OF XRD QUANTITATIVE ANALYSIS

In this paper,the cement clinkers fromvarious industrial kilns were investigated by a superposingpeaks method for X-ray quantitative analysis（XRQA）ofclinker minerals,the results show that the clinker mineralcontents measured by XRQA method better accord with thereality of clinkers made in different conditions than theo-retic contents calculated by Bouge formula do.The mea-sured contents of C3S of clinkers manufactured in rotarykilns are higher than theoretically calculated values,where-as,the results of clinker manufactured in shaft kilns arecontrary to that.This is because in rotary kiln,the rawmeals are fully pre-heated and have high sintering temper-ature,the clinkers are well solid-solutioned and rapidlycooled,on the contrary,owing to the struetural defects,it iseasy to exist reduing atmosphere and lower temperature inshaft kiln,moreover the cooling rate is slower,all these canevidently lead to worse clinker quality.Adding CaF2-Ca-SO4 complex mineralizer can remarkably modify the sinter-ing

RESEARCH ON RELATION BETWEEN MELTING POINT OF CEMENT CLINKER AND HEATING RATE

The relation between the melting point of Portland cement raw meal and its heating rate have been studied. The raw meal was burnt at different heating rate ranging from 10-900℃/min by the following methods: (A) in electric resistance furnace; (B) in DTA-TG analyzer with infrared ray focused heating; (C) in high temperature microscope with electron stream heating.

THE FORMATION MECHANISM OF PORTLAND CEMENT CLINKER MINERALS IN RAPID BURNING

Cement clinker is burnt at the rapid heatingrate has the obvious effect of saving energy due tothe low burning temperature and short burning time.This kind of technique is being researched activelyin recent years,but the systemetical theoryinvestigation about the formation mechanism ofclinker minerals under this condition has not beenreported.In this paper,the formation mechanism ofportland cement clinker minerals in rapid burningwas studied by means of DTA,SEM,EPMA,XRDand other conventional testing methods by using aspecial burning equipment.

EFFECT OF BURNING METHOD ON THE FORMING PROCESSES OF PORTLAND CEMENT CLINKER

The forming temperature of Clinker meltunderdifferent burning conditions has been studiedby appearance examination and thermal shrinkerdetermination, and the viscosity of melt has beendiscussed by studying the coordination number ofAl3+ and Fe3+ in cement clinker burned by differentmethod with x- ray fluorescence analysis and Moss-bauer spectroscopy. The results show that the clin-ker melt under rapid burning may come into exis-tence at lower temperature and It’s viscosity islower. So the forming processes of clinker may bedifferent at rapid burning from ordinary burning.They are probably an important factor to promote theformation of clinker burned at lower temperaturewith rapid burning method.

MgO ACTS THE BURNING OF WHITE CEMENT CLINKER

In this paper,how and why MgO acts on theburning of white cement clinker and increases thewhiteness were found by means of common detectionand EPMA.It was shown that MgO is a kind ofeffective mineralizer and brightener.

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.

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

In this paper for saving energy two differentburning methods of cement clinker formation havebeen studied.One is the rapid burning method andthe other is ordinary burning method simulatingrotary kiln,and they are compared by the kineticpoint of view.The result reveals that theactivation energy of rapid burning is much lowerthan ordinary burning.For looking into the cause,the main raw material—lime stone was burnt bythe same two methods and the structure of productCaO has been detected.It can be found that themicrostructure of CaO produced by rapidburning is looser;lattices constants aregreater;crystal defects are more and particlesize is smaller than that produced by ordinaryburning.These cause the chemical reaction moreactive.So the activation energy of clinkerformation of rapid burning is much lower thanthat of the ordinary burning.

Corrosion of Basic Refractories in Contact with Cement Clinker and Kiln Hot Meal

This paper investigates the new phases formation in the magnesia-spinel, magnesia-zirconia-cal- cia and magnesia-hercynite refractory products as a result of their reaction with kiln hot meal and cement clinker (both rich in SO3 and Cl ions) at the temperature range 1200°C - 1450?C. The labor- atory corrosion tests were conducted by means of pulverous method and by special coating test. The phase identity of the products as well as the mixes after corrosion tests was established by powder X-ray diffraction method. The microstructure development of the contact zones between coating and the products were studied using scanning electron microscopy SEM with EDS spectroscopy. The differences in the reactions proceeding between the phases of the test bricks and the phases of kiln hot meal and cement clinker in dependence on the temperatures have been discussed.

Crystallization Characteristic of Periclase in Clinker and Effect of Mg2+ on Hydrate of Cement Pastes

Crystallization characteristic of periclase in clinker and effect of Mg^2+ on hydrate of cement pastes were investigated. Morphologies and relative content of periclase were characterized with scanning electron microscopy and X-ray diffraction. Derivative thermogravimetry analysis and backscattered electron imaging were used to characterize the effect of Mg^2+ on hydrate of cement pastes. The experimental results show that in ample space, periclase forms octahedron structure, and subhedral or anhedral crystal is formed in limited space. Due to the accelerated burning temperature and prolonged holding time, coarse pericalase crystals are formed. Mg(OH)2 particle thickness increases due to faster crystal growth rate along c axis at later age. Mg^2+can substitute Ca^2+ in C-S-H or C-A-H to form magnesium silicate hydrate(M-S-H) or magnesium aluminate hydrate(M-A-H), and the substitution extent for C-A-H is higher than that for C-S-H. Cured in 80 ℃ water, the decalcification rate of C-A-H in pastes is higher than that cured in 50 ℃ water. M-A-H with an atomic Mg/Al ratio of 2 is formed through substitution of Ca by Mg in C-A-H.

Effect of High Temperature Calcination on Structure and Properties of Bauxite-based Homogeneous Clinkers

In this paper,the effect of high temperature calcination on the structure and properties of bauxite-based homogeneous clinkers calcined at different temperatures for different durations was studied.The results show that with the rising of calcination temperature and the prolonging of holding time,the volume density of bauxite-based homogeneous clinkers increases and the apparent porosity decreases.After high temperature calcination,the linear expansion of bauxitebased homogeneous clinker is smaller than that of the non-calcined ones.Whether calcined at high temperatures or not,the thermal shock resistance of bauxite-based homogeneous clinkers is good.The crystalline phases of bauxite-based homogeneous clinkers are mainly mullite and corundum.There is more glass phase in the bauxite-based homogeneous clinkers without calcination.After calcination at high temperatures the glass phase content decreases significantly,and the mullite crystals develop better forming the cross-network structure.

Development of Lightweight Concrete Using Industrial Waste Palm Oil Clinker

Concrete is a major material used in the construction of buildings and structures in the world.Gravel and sand are the major ingredients of concrete but are non-renewable natural materials.Therefore,the utilisation of palm oil clinker(POC),a solid waste generated from palm oil industry is proposed to replace natural aggregate in this research to reduce the demand for natural aggregates.One mix of ordinary concrete as control concrete;while four mix proportions of oil palm clinker concrete were obtained by replacing 25%,50%,75%,and 100%of gravel and sand of control concrete with coarse and fine oil palm clinker respectively by volume,with same cement content and water cement ratio.Compressive strength test was carried out of concretes with different percentages of oil palm clinker;whereas water absorption tests according to respective standard,were carried out to determine the durability properties of various mixes.Based on the results obtained,the study on the effect of percentage of clinker on strength and durability properties was drawn.According to ACI classification of light weight concrete only the 100 percentage replacement can achieve the definition of light weight concrete since its density is less than 1,900 kg/m3 and strength larger than 17 MPa.Eventually the 25%replacement of the normal aggregate by the OPC will improve the strength and durability of the concrete.

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.

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.

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 C 3S, following by minor C2S, C3A and tetracalcium aluminoferrite. The results reveal that a new type of high C 3S 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.