Abstract: This study investigated the efficiency and mechanisms of Cd removal with sepiolite(SP) modified by heat and acidification(HHSP). The optimal acid concentration, reaction time and temperature was firstly explored. On this basis, the dynamics and isotherms of Cd adsorption by SP and HHSP were compared and the adsorption mechanisms were further investigated with SEM-EDS, XRD and XPS. The results show that the HHSP prepared with 0.9 mol/L HCl for 24 h and heating at 500℃ for 1h exhibited the highest Cd sorption capacity. The Cd sorption by both SP and HHSP followed the pseudo-second order kinetics, and 73.13% and 85.96% of adsorption occurred in the first 2 h, respectively. The adsorption reached equilibrium after 24 h when the initial Cd concentration was 50 mg/L. The maximum Cd adsorption capacity of HHSP was estimated to be 22.147 mg/g based on Langmuir model, which was 4.23 times as high as that of SP (4.200 mg/g). The pH and pHpzc of SP apparently decreased with acidification, indicating an increase in the adsorption sites for cations on the modified SP. SEM-EDS showed that the acidifying and heating treatment had little effect on the fibrous structure of SP, and the mass ratio of the adsorbed Cd increased from 1.57% for SP to 2.13% for HHSP. XPS analysis indicated that both Cd complexation by the surface hydroxyl (-OH) and precipitation of CdCO₃, CdCl₂, CdO and Cd (OH)₂ contributed to the Cd removal by SP and HHSP. XRD analysis demonstrated that the specific surface area of SP was increased by acid activation due to the removal of CaCO₃. The results of this study highlighted that the pre-treatment with acidification and heat can improve the effectiveness of HHSP for Cd immobilization, and provide a useful way to apply HHSP in mitigation of Cd bioavailability in paddy soil.