Introduction Cement industry is one of the major carbon-emitting industries, which is characterized by a thermal efficiency below 54% and an energy consumption ranging from 3-4 GJ per ton of cement clinker. China annual average cement production reaches 2 341 million tons, contributing to approximately 14.3% of the total CO2 emissions. In addition to the CO2 emissions resulting from the high-temperature decomposition of limestone, which serves as a primary raw material, the cement production process significantly contributes to elevated CO2 emissions due to its substantial energy consumption. The cement rotary kiln is a pivotal equipment in the production process, with its high energy consumption primarily attributed to subpar performance of certain refractory materials and an irrational configuration. Consequently, this leads to elevated temperatures (reaching up to 350-400 ℃) in both the transition zone and firing zone of the kiln shell, resulting in a substantial energy loss accounting for 8%-15% of the total heat input. Previous studies demonstrated that the implementation of light weight refractory materials could effectively mitigate heat loss from the kiln shell, thereby enhancing energy efficiency. The CA6/MA composite material C2M2A14 has the excellent high-temperature performance and chemical stability of both CA6 and MA. It is proven to be an effective ladle lining material in the non-slag line part. Incorporating a proper quantity of Fe2O3 during the synthesis process of C2M2A14 results in a denser product under identical firing conditions. In this paper, C2M2A14 was introduced into magnesite refractories to achieve light weighting of magnesite refractories. In addition, the mechanism of achieving light weighting and the effects of addition amount and particle size on the microstructure and properties of magnesite refractories were also investigated.Methods Magnesium hydroxide, calcium carbonate and calcined α-alumina fine powders as raw materials were mixed. Also, 1% Fe2O3 was added to the mixture according to a specific mass ratio. The mixture was then pressed into cylindrical samples with a diameter of 36 mm×36 mm. C2M2A14 was synthesized via firing at 1 780 ℃ for 5 h. The synthesized material was crushed and sieved to obtain fine particles with different sizes of 1-3 mm, 0.088-1.000 mm, 0.5-1.0 mm, 0.088-0.500 mm, and≤0.088 mm. Magnesia and materials such as C2M2A14 were mixed according to the specified ratio, and then pressed into cylindrical samples with dimensions of 36 mm×36 mm and 36 mm×50 mm, as well as crucible samples with the dimensions of 50 mm×50 mm. These samples were fired at different temperatures (i.e., 1 600, 1 650 ℃ and 1 700 ℃) for 3 h. The bulk density, apparent porosity, true density, and cold crushing strength at room temperature of A sample with the size of 36 mm×36 mm were characterized according to national standards. The load softening temperature of a sample with the size of 36 mm×50 mm was measured. The pore size distribution of the original brick was determined by a fully automatic mercury porosimeter. Cement material in crucible was heated at 1 350 ℃ for 6 h to investigate its corrosion-resistance to cement material. The microstructure before and after corrosion of the crucible samples and original bricks was determined in a backscattered electron imaging mode by field corrosion scanning electron microscopy. The phase composition of the samples was characterized by X-ray diffraction with a software named Jade .Results and discussion The results show that at 1 600 ℃, the apparent porosity of sample increases while their bulk density and cold crushing strength decrease as the amount of C2M2A14 increases. Also, the load softening temperature decreases. The apparent porosity of samples with particle sizes ranging from 0.5-1.0 mm increases from 23.2% to 32.8% with increasing C2M2A14 from 10% to 40%. The bulk density decreases from 2.70 g/cm3 to 2.36 g/cm3, which is lower than the one of dense refractory (which is also made of the same material) at 2.94 g/cm3, indicating a trend towards light weighting. At the same addition amount of 10%, the particle size of C2M2A14 becomes smaller, the apparent porosity of the sample decreases, and the bulk density and cold crushing strength both increase. The load softening temperature is closer. The apparent porosity of samples with different particle sizes (i.e., 0.5-1.0 mm and 0.088-0.500 mm) gradually decreases, while the bulk density increases as the firing temperature increases. However, there is no corresponding increase in cold crushing strength. The maximum cold crushing strength is 56.6 MPa, and the particle sizes both exhibit a load softening temperature of >1 540 ℃, meeting the requirements for application in cement kiln transition zones. The presence of magnesia in the matrix during firing induces the decomposition of C2M2A14, as evidenced by XRD and SEM analysis. In the magnesite-spinel-aluminate ternary system, a liquid phase forms at elevated temperatures, facilitating a pore formation through liquid-assisted Kirkendall effect and achieving a light weighting in the samples. Furthermore, increasing the amount of C2M2A14 results in a higher apparent porosity, while leading to a decrease in bulk density, cold crushing strength, and load softening temperature. The corrosion resistance of group D and E samples with particle sizes of 0.5-1.0 mm and 0.088-0.500 mm was investigated at 1 350 ℃ by a static crucible method with the addition of 10% C2M2A14. The crucibles of D series samples exhibit a visible corrosion penetration, while those of group E samples show a negligible corrosion penetration. No adhering slag appears on the side walls in either group. The microstructural analysis reveals that different sizes of C2M2A14 particles are responsible for variations in penetration depth between the two group samples. Larger and more pores occur in group D samples, allowing cement material to penetrate through them. The introduction of C2M2A14 particles with the sizes of 0.088-0.500 mm in group E results in smaller pores resulted from the reaction between C2M2A14 particle and magnesia matrix, making them denser and effectively inhibiting the penetration by a low melting point cement phase.Conclusions 1) Introducing Ca2Mg2Al28O46 was introduced into magnesium refractor during firing. Magnesite-spinel-aluminate ternary system formed a liquid phase at a high temperature. The pores formed with a liquid phase assisted the Kirkendall effect and resulted in magnesium refractory to achieve lightweight. The apparent porosity of samples increased, the bulk density, compressive strength and the refractoriness under load decreased with increasing the amount of Ca2Mg2Al28O46 additions. At the same amount of Ca2Mg2Al28O46 added, the performance could be improved via reducing its particle size. 2) As the firing temperature increased, the apparent porosity of specimen decreased, the bulk density increased, but their compressive strength did not increase, and the refractoriness under a load maintained at a high level (>1 540 ℃). The refractoriness under a load could reach 1 603 ℃ when 10% (in mass fraction) of Ca2Mg2Al28O46 particles with the sizes of 0.50-1.00 mm were added and fired at 1 700 ℃. 3) The static crucible experiments at 1 350 ℃ showed that the specimens with the introduction of Ca2Mg2Al28O46 particles with the sizes of less than 0.50 mm at 10% addition had the optimum corrosion resistance to cement materials when the specimens were fired at 1 650 ℃.