Synthesis of CaC₂ and the Adsorption Mechanism of Alkaline Metals on the CaC₂ Surface

Acetylene is an important chemical raw material produced by the reaction of CaC2 and water. During the synthesis reaction process of calcium carbide, the coke formed from the highly alkaline coal and limestone results in a large amount of ash, which not only increases energy consumption but also significantly affects the purity of CaC2. In order to explore the effect of ash on CaC2, first, CaC2 was synthesized by a high-temperature solid-state reaction, and its purity was identified. XRD results indicate that the main phase of this crystal is CaC2 with a space group of I4/mmm. To further investigate the adsorption properties of inorganic minerals on CaC2 surfaces, the adsorption of the alkali metals Na and K from the ash to the CaC2 surface was calculated by Density Functional Theory (DFT) calculations. The surface energy calculation results demonstrate that CaC2 has the lowest energy and most stable crystal faces, which are in good agreement with the experimental results. Among them, on the crystalline face (110), the most stable configuration for Na is the Ca–C bridge site, while the most stable configuration for K is the Ca–Ca bridge site. The atomic population and charge density difference values show that the charge transfer of K on the CaC2 surface is significantly larger than that of Na. PDOS analysis demonstrates a deep hybridization of K, which inferred that K is more easily combined with calcium carbide than Na.