Abstract: To reveal the regulatory mechanisms and differential impacts of Ca²⁺ concentration on the coal slime flotation process, optimize flotation parameters, and enhance flotation efficiency, this study systematically investigates the effects of varying Ca²⁺ concentrations on collector adsorption, coal-bubble interactions, and flotation performance. Using flotation feeds of different coal types (1/3 coking coal, fat coal, and coking coal) from the Linhuan Coal Preparation Plant in Huaibei as research objects, methods such as contact angle measurement, adsorption rate determination, coal particle-bubble attachment angle testing, and flotation index analysis were employed.The results indicate that Ca²⁺ significantly alters the contact angle of collector oil droplets and influences collector adsorption behavior, with distinct differences observed across different coal types; coking coal exhibits the optimal adsorption performance, followed by fat coal. Increasing Ca²⁺ concentration generally leads to an increase in the coal particle-bubble attachment angle, thereby enhancing the affinity between coal and bubbles. The impact on clean coal yield, ash content, and flotation perfection indices varies by coal type: at low concentrations, the impact on 1/3 coking coal and fat coal is minimal, while high concentrations significantly increase the ash content. For coking coal, flotation indices show an initial increase followed by a decrease, with an overall decline in the flotation perfection index. By regulating the electrochemical properties of the coal particle surface, collector adsorption behavior, and coal-bubble interactions, Ca²⁺ significantly affects flotation outcomes. These differential impact patterns provide a theoretical basis for the optimization and precise regulation of industrial flotation processes.