Thermal analysis of raw meals doped with Li, Cu and S for burning of Portland cement clinker

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Calcium looping (CaL) is a promising carbon capture and storage (CCS) technology that has the potential to significantly reduce CO2 emissions in cement production. Integrating CaL with cement production provides a viable solution to the high CO2 emissions generated during the calcination process. This study examines the behavior of two industrial cement raw meals from different sites (A-RM and B-RM) under CaL conditions, focusing on phase composition, particle size distribution, and clinker phase evolution up to 1450 °C. Calcination and CaL experiments were conducted in a CO2-rich atmosphere, with materials characterized using quantitative X-ray diffraction (Q-XRD) and high-temperature X-ray diffraction (HT-XRD). The results showed that both raw meals absorbed similar amounts of CO2 during the cyclic CaL experiments. A-RM formed C2S and other silicates, while B-RM retained more free CaO due to a less effective reaction with coarser quartz (SiO2) particles. HT-XRD revealed delayed clinker-phase evolution in the 1000–1400 °C range in CaL-treated raw meals. However, CaL-treated raw meals achieved low free CaO at 1450 °C, suggesting that optimal kiln conditions can produce the desired phase composition. These findings indicate that integrating CaL-treated raw meals into cement production requires careful optimization of operational parameters to maintain clinker quality and minimize energy consumption. Further research should focus on improving the efficiency and reactivity of CaL-treated raw meals to enhance their suitability for industrial cement production.

The influence of clinkering conditions and cooling rate on the phase composition of Belite-Ye’elimite-Ferrite (BYF) clinker

One of the severe environmental problems in developing countries involves hazardous waste. The traditional management of hazardous wastes usually employs physical and chemical processes to stabilize or reduce the toxicity of them. Then, the wastes are taken away to a secure landfill, which is nowadays hard to site, build, operate, and maintain effectively. A viable waste management option is co-processing in cement production. The co-processing technology consists of partial application of hazardous waste as alternative fuels and raw materials (AFR). It can reduce the use of non-renewable energy and natural resources as well as environmental problems stemming from mishandling by other management options. This research studied leaching of heavy metals from cement produced from the co-processing of industrial sludge containing petroleum and heavy metals as an alternative fuel. The sludge was utilized up to 20% by weight in raw meal. Analysis results of industrial sludge containing petroleum and heavy metals were used as a basis for selection of four heavy metals; namely, Cr, Ni, Pb and Zn. To study the sequential extraction test, approximately 5% to 45% of heavy metals were distributed in Fraction 3 (bound to iron and manganese oxide), and a major concentration of the heavy metals (54% to 87%) were found in Fraction 5 (residual fraction). The more the percentage of sludge increased, the more the concentrations of heavy metals in the clinker increased. In addition to the analysis, compressive strengths and leaching tests of cement mortars were also evaluated. The compressive strengths results were satisfactory according to ASTM C109/C109M–95 and the leached metal concentrations did not exceed the limits set by the Notification of the Ministry of Industry No.6 B.E.2540 (1997), the Notification of the Ministry of Industry B.E.2548 (2005) and the US Regulatory Toxicity Characteristic Leaching Procedure (TCLP).

The production route for cement clinker, including the clinkerization protocol and temperature, is highly dependent on the selection of raw materials. Natural resource reserves used in cement manufacturing are steadily declining due to rapid urbanization and the growing demand for building materials. Consequently, there is an urgent need to identify alternative resources, potentially from cost-effective primary raw materials or waste products. This study aims to evaluate the feasibility of incorporating recycled concrete as construction and demolition waste (C&DW) with unconventional clayey materials (bentonite and zeolite) into clinker synthesis at a reduced temperature of 1300 °C. The effect of mechanical pretreatment of the clinker raw meal, applied for durations of 10 to 30 min, was investigated. Mix designs combining traditional and alternative raw materials, along with different mechanical pretreatment durations, were systematically tested to assess their impact on raw meal clinkerization and the resulting cement mechanical properties. Despite variations in raw meal composition, the produced clinkers consistently exhibited phase compositions comprising C3S, C2S, C3A, and C4AF, as confirmed by XRD, FTIR, and SEM/EDS analyses. Among the studied raw materials, clayey components played a dominant role in controlling the formation of the main cement minerals, demonstrating that zeolite and bentonite can effectively substitute standard clays. Additionally, C&DW did not impede clinkerization; rather, it functioned as a silica source, replacing quartz sand. Short mechanical pretreatments (10 min) enhanced the content of cement minerals, whereas longer treatments adversely affected clinkerization. This study offers new insights into cement clinker production at reduced temperatures through the use of C&DW combined with unconventional clayey materials. The clinkerization temperature was reduced by approximately 100 °C from the conventional 1400-1450 °C, while still producing cements with mechanical performance comparable to ordinary Portland cement (OPC). The resulting zeolite- and bentonite-based cements, either mechanically untreated or subjected to short pretreatment, are potentially suitable for structural concrete applications, while cements produced with longer mechanical pretreatments may be more appropriate for lower-demand or non-structural uses.

The cement industry is one of the major sources of CO2 emissions and is likely to contribute to further increases in the near future. The carbonate looping process has the potential to capture CO2 emissions from the cement industry, in which raw meal for cement production could be used as the sorbent. Cyclic experiments were carried out in a TGA apparatus using industrial cement raw meal and synthetic raw meal as sorbents, with limestone as the reference. The results show that the CO2 capture capacities of the cement raw meal and the synthetic raw meal are comparable to those of pure limestone. The CO2 capture capacity of limestone in the raw meal is lower than for pure limestone. The difference in the CO2 capture capacity decreases with an increase in cycle number. The calcination conditions and composition are major factors that influence the CO2 capture capacity of limestone. At 850 °C in N2, the capacity of synthetic raw meal was similar to that of pure limestone, whereas at 950 °C in N2 and in a CO2-rich atmosphere there was a significant difference. The SEM and BET analyses indicate that sintering is the main reason for the lower capture capacity of the limestone in the raw meal. The main components of the raw meal used along with the limestone have different effects on the CO2 capture capacity of the limestone. Al2O3 has the most negative effect, followed by Fe2O3, whereas SiO2 showed no effect. These interactions can be observed as a correlation between the measured surface area and the CO2 capture capacity. The XRD results indicated an increase in crystallite size and the formation of new phases due to the reaction between the main components of the raw meal and the limestone, which also has an effect on the CO2 capture capacity. The formation of dicalcium silicate was also observed by XRD analysis in the calcined synthetic raw meal. The effect of calcination conditions and compositions on the CO2 capture capacity as a function of cycle number is described by a correlation equation. This equation is used to determine the decay constant (k) and residual CO2 capture capacity (Xr). This shows that raw meal could be used as a sorbent for the easy integration of the carbonate looping process into the cement pyro process for reducing CO2 emissions from the cement production process.

Both copper and lithium act as strong fluxes and lower the temperature of the clinker melt formation. Sulphur promotes the stabilisation of more hydraulically active modification of alite M1. It is expected that this combination could produce an alite clinker at significantly lower temperatures with high quality technological parameters. In this paper, the effect of combined oxides of copper, lithium and sulphur addition on the phase composition and clinker structure of Portland cement was investigated. The reference raw meal was prepared from common cement raw materials. Each of the mentioned oxides was added to the reference raw meal in two different concentrations, and 8 combinations were prepared. Chemically pure compounds (NH4)2SO4, CuO and Li2CO3 were used as a source of these oxides. The raw meals were burned to equilibrium at 1450°C. Their phase composition was determined by X-ray diffraction analysis, the microstructure was monitored by optical microscopy, and the microchemistry of the clinker phases was observed by electron microscopy with EDS analysis. It was found that in samples with high lithium or copper content, there is an increase in belite and free lime at the expense of alite. The combination of Cu + Li has the most negative effect, followed by Li alone and Cu alone. The higher SO3 content slightly offsets this negative effect.

The article deals with the study of the effects of alternative fuels and raw materials on the cement clinker quality. The clinker quality was expressed by the content of two principal minerals alite C3S and belite C2S. The additions of alternative fuels ashes and raw materials, in principle, always increased the belite content and conversely reduced the amount of alite. The alternative fuels with high ash content were used such as the meat-bone meal, sewage sludge from sewage treatment plants and paper sludge and the used alternative raw materials were metallurgical slags - granulated blastfurnace slag, air cooled blastfurnace slag and demetallized steel slag, fluidized bed combustion fly ash and waste glass. Meat-bone meal, sewage sludge from sewage treatment plants and paper sludge were evaluated as moderately suitable alternative fuels which can be added in the amounts of 2.8 wt. % addition of meat-bone meals ash, 3.64 wt. % addition of sewage sludge ash and 3.8 wt. % addition of paper sludge ash to the cement raw mixture. Demetallised steel slag is suitable for production of special sulphate resistant cement clinker for CEM I –SR cement with addition up to 5 wt. %. Granulated blastfurnace slag is a suitable alternative raw material with addition 4 wt. %. Air cooled blastfurnace slag is a suitable alternative raw material with addition 4.2 wt. %. Waste glass is not very appropriate alternative raw material with addition only 1.16 wt. %. Fluidized bed combustion fly ash appears not to be equally appropriate alternative raw material for cement clinker burning with less potential utilization in the cement industry and with addition 3.41 wt. %, which forms undesired anhydrite CaSO4 in the cement clinker.

The cement industry is a major source of mercury emissions to the atmosphere. In order to reduce mercury emissions and mercury content in cement industry products, it is necessary to achieve a thorough understanding of its distribution in all stages of the process. Cement production can be divided into two main stages: clinker burning and grinding. These underwent a two-year balance investigation. The main raw material used in the clinker burning process is limestone, in which mercury concentration varied from 16.2 to 33.4 μg/kg. Heat for the clinker burning process is obtained from solid fuels: fine coal, containing from 30.3 to 44.0 μg Hg/kg, alternative fuels – from 170.6 to 408.4 μg Hg/kg and rubber waste, containing from 60.2 to 68.9 μg Hg/kg. The major additive used in both clinker and cement production is gypsum. Concentration of mercury varied widely depending on the supplier, ranging from 199.6 to 467.1 μg/kg. Ferrous additives were the raw material with highest mercury content – 3695.4 μg Hg/kg on average. Average mercury concentration in products was as follows: clinker – 4.0 μg/kg, furnace cement – 12.0 μg/kg, portland cement – 10.1 μg/kg. Performed mass balances enabled determination of mercury flows in production processes: limestone with ferrous additive – 119.4 mg Hg/h, rotary kiln-produced clinker produced – 0.21 mg Hg/h, furnace cement – 22.2 mg Hg/h, portland cement – 12.5 mg Hg/h. Indexes of mercury emissions to air were also determined for production processes: clinker burning – 8.952 mg Hg/Mg of clinker, furnace cement production – 4.085 mg Hg/Mg of cement and portland cement – 8.561 mg Hg/Mg of cement. Average mercury content in flue gases was 5.82 μg/m3, with a variability range of 0.4–81.5 μg/m3, including approximately 20% of oxidized mercury Hg2+. Applying additional mercury emission reduction methods, i.e. adsorption on activated charcoal and SCR or SNCR will enable a reduction of emissions to 4.924, 2.247 and 4.709 mg Hg/Mg respectively and average mercury concentration in flue gas to approximately 2.5 μg/m3.

In recent years, the variability in the composition of cement raw materials has increasingly impacted the quality of cement products. However, there has been relatively little research on the homogenization effects of equipment in the cement production process. Existing studies mainly focus on the primary functions of equipment, such as the grinding efficiency of ball mills, the thermal decomposition in cyclone preheaters, and the thermal decomposition in rotary kilns. This study selected four typical pieces of equipment with significant homogenization functions for an in-depth investigation: ball mills, pneumatic homogenizing silos, cyclone preheaters, and rotary kilns. To assess the homogenization efficacy of each apparatus, scaled-down models of these devices were constructed and subjected to simulated experiments. To improve experimental efficiency and realistically simulate actual production conditions in a laboratory setting, this study used the uniformity of the electrical capacitance of mixed powders instead of compositional uniformity to analyze homogenization effects. The test material in the experiment consisted of a mixture of raw meal from a cement factory with a high dielectric constant and Fe3O4 powder. The parallel plate capacitance method was employed to ascertain the capacitance value of the mixed powder prior to and subsequent to treatment by each equipment model. The fluctuation of the input and output curves was analyzed, and the standard deviation (S), coefficient of variation (R), and homogenization multiplier (H) were calculated in order to evaluate the homogenization effect of each equipment model on the raw meal. The findings of the study indicated that the pneumatic homogenizer exhibited an exemplary homogenization effect, followed by the ball mill. For the ball mill, a higher proportion of small balls in the gradation can significantly enhance the homogenization effect without considering the grinding efficiency. The five-stage cyclone preheater also has a better homogenization effect, while the rotary kiln has a less significant homogenization effect on raw meal. Finally, the raw meal processed by each equipment model was used for clinker calcination and the preparation of cement mortar samples. After curing for three days, the compressive and flexural strengths of the samples were tested, thereby indirectly verifying the homogenization effect of each equipment model on the raw meal. This study helps to understand the homogenization process of raw materials by equipment in cement production and provides certain reference and data support for equipment selection, operation optimization, and quality control in the cement production process.

Influence of NaF, KF and CaF2 addition on the clinker burning temperature and its properties

The use of alternative fuels and raw materials in cement industry leads to the incorporation of some undesirable compounds into the clinker phases. One of them is barium oxide which influences the formation of clinker phases and related properties of the produced cement. Barium in clinker was already studied; the phase composition is changed depending on the amount of barium. However, detailed research focused on hydration properties of these clinkers and cements has not been carried out, yet. A clinker with barium oxide addition to raw meal was prepared. As a source of barium oxide, barium sulphate (baryte) was used in amount of 4% calculated to BaO in the clinker. Barium incorporated in clinker inhibits formation of alite; therefore, lime saturation factor was slightly reduced. Compared to barium carbonate—another source of barium oxide—barium sulphate influences the ratio of clinker phases less significantly. This clinker and a reference sample without barium were milled with and without addition of gypsum. Hydration of barium clinker and cement was examined by XRD in situ hydration and isothermal calorimetry. Hydration products were evaluated by means of thermogravimetric and differential thermal analysis. An increase in total heat of hydration can be seen in samples with barium. The heat is influenced by different hydration of clinker phases with incorporated barium, sulphates and by higher content of free CaO and C3A. According to XRD in situ hydration, hydration of samples with barium is suppressed, the amount of portlandite during the whole measurement is much higher in samples without barium.

With the developing technology, devices that can fully control the quality of cement and clinker in cement production have been produced. These devices can give accurate results in a short time and with minimum error margins, with all necessary analyzes and phase compositions. Although these methods are very useful for cement factories in practice, they cannot fully reveal some parameters such as crystal structure and morphology of clinker phases, size distribution and clinker porosity. In microscopic studies, the formation, size, distribution and amount of clinker phases in the examined cross-sectional area can be determined. In this study, optical microscope examination and image processing techniques were used to determine the clinker characteristics. Raw meal was formed by mixing limestone and clay from cement raw materials in certain proportions. Then, clinker was obtained as a result of burning the raw meal at approximately 1400 oC. In addition to performing rapid phase analysis using image processing programs, information about the crystal properties of the phases was obtained. The size, number, average equivalent diameter, distribution of clinker phases and porosities can also be examined with the help of image processing programs. According to the result of the image processing method, Portland cement clinker with easy burning properties, high alite and low belite content was obtained.

Co-processing between waste and raw material in cement plant was the one method to reduced concentration of the waste and decreased consumption of raw material and fuel. However, the heavy metal in waste made the effect to cement properties. This study investigated the physical and chemical characteristics of various mixtures of cement clinker. The 2.5% of mixture between shale core and clay was added in the raw meal for made the samples suitable in burning process with one meter of the pilot-scale rotary cement kiln. From the study, different ratio of Cr in raw meal did not make the effect moisture content and loss on weight in ignition process. When compared with control, high concentration of Cr increased percent free lime but decreased percent C3S and compressive strength in the clinker phase. Cr reacted with Al to get calcium aluminum chromium oxide. Likely to Cr, different ratio of Ni did not make in moisture content and loss on weight in ignition process of raw meal. In contrast, high concentration of Ni reduced percent free lime but increase compressive strength in clinker phase. Ni reacted with Mg to get Magnesium nickel oxide. High concentration of Zn in raw meal increased moisture content and loss on weight in ignition process of raw meal. High concentration of Zn reduced free lime in clinker phase. High concentration of Zn also increased concentration in both C3S and C2S. The Zn made the effect in setting time of cement mortar and created high compressive strength in 28 days. Zn reacted with other heavy metal included Fe, Mn, and Cr to got zinc iron manganese chromium oxide. From the leaching test, the all of different ratio of each three heavy metals still in the range when compared with Thai standard.

This study investigates the effects of a high-CO 2 atmosphere on phase evolution, burnability, and clinker mineral formation in cement raw meals using high-temperature X-ray diffraction (HT-XRD). The cement industry is a significant CO 2 emitter, primarily from limestone decomposition and fuel combustion. Innovative solutions such as carbon capture and storage (CCS) are critical, with electrification and oxy-fuel combustion showing promise. Electrification using plasma technology, which employs CO 2 as a carrier gas, offers a pathway to near-zero emissions. Four industrial raw meals from northern Europe were analyzed under conventional (20% CO 2 ) and high-CO 2 (95% CO 2 ) conditions. Chemical composition, particle size distribution, and coarse fraction analyses preceded HT-XRD data collection across temperatures up to 1500 °C. High-CO 2 conditions delayed calcite decomposition, reducing free-CaO availability and altering burnability. The timing of calcite decomposition relative to C 2 S formation suggests a reaction pathway in which free CaO, released from calcite, rapidly reacts with thermally activated SiO 2 to form C 2 S. Additionally, spurrite decomposition released reactive CaO and C 2 S, enhancing C 3 S formation at 1300–1400 °C in spurrite-rich samples. Above 1400 °C, melt formation promoted further C 3 S development, leading to similar final levels in both tested atmospheres. These findings indicate that high-CO 2 conditions significantly influence clinker phase evolution and reactivity. Practical implications include optimizing raw meal composition and kiln temperature profiles in electrified and oxy-fuel systems to enhance burnability while minimizing operational issues such as spurrite-induced kiln buildup. Future research should further explore industrial scalability and raw material adjustments to enhance CO 2 efficiency during clinkerization. • High CO 2 delays calcite decomposition, affecting burnability and clinker formation. • Spurrite decomposes to reactive C 2 S and CaO, increasing C 3 S at lower temperatures. • Melt formation above 1400 °C equalizes C 3 S levels across high and conventional CO 2 . • High CO 2 atmospheres require optimized raw meal and burnability for efficiency.