Inorganic modified green mudstone (MGM) was prepared from the green mudstone (GM) residue of Fushun West Open Pit Mine and characterized by XRF, XRD, FTIR, and SEM of GM and MGM. According to the calculation of pore size and the BET equation, the pore size and specific surface area of the MGM were larger. The results of adsorption kinetics and isothermal adsorption experiments showed that the adsorption capacity of MGM for phosphate increased from 0.1 mg/g to 0.71 mg/g, which was obviously better than that of GM. The GM and MGM accorded with the quasi-second-order kinetic model. The isothermal adsorption data of GM accorded with the Freundlich model, and the isothermal data of MGM accorded with the Langmuir model, which indicated that the model of GM and MGM was an adsorption process from a double layer to a single layer. Thermodynamic data showed that the increase in temperature was beneficial to the adsorption of MGM. The internal diffusion model showed that due to the change of pore size structure after modification, the number of adsorption sites that could provide phosphate was increased, and at the same time, the change of internal elements led to the extension of the chemical reaction time by 700 min. Because of the ligand exchange and electrostatic interaction between phosphate, GM, and MGM, the adsorption results showed that acidity was better than alkalinity. To improve the recycling ability of MGM, hydrochloric acid with a concentration of 0.1 mol/L was determined as the best phosphorus resolving agent, and the resolving rate was still close to 80% after five cycles. The results showed that the MGM could be a promising adsorbent for the removal of phosphorus, providing a new way for resource utilization of mining waste residue.