Abstract: Low−grade Attapulgite (LGPal) is often regarded as an inefficient adsorbent material or waste due to co−occurring minerals (e.g., dolomite, quartz, etc.), which limits its efficient utilization. In addition, the efficient removal of anionic azo dyes (e.g., Congo red) still faces challenges such as high adsorbent cost and low efficiency. LGPal from Xuyi, Jiangsu Province was selected as the research subject. It was modified through high−temperature calcination to investigate the effects of calcination temperature on its chemical composition, structure, and adsorption capacity for Congo red. The adsorption mechanism of calcination−modified LGPal toward Congo red was analyzed using methods such as X−ray photoelectron spectroscopy (XPS). Results indicate that calcination at 750 ℃ yields optimal Congo red adsorption capacity of LGPal, reaching 220.35 mg/g—a 148.32% increase compared to the uncalcined sample. At this temperature, dolomite diffraction peaks nearly disappear, MgO forms, while the silica tetrahedra within the attapulgite crystal structure remain intact. LGPal−750 exhibited a specific surface area of 63.15 m²/g and a total pore volume of 13.34 cm³/g. However, its average pore diameter increased by 5.5 nm (70.15%) compared to the uncalcined sample. This increase results from the desorption of adsorbed water, zeolite water, and coordination water within LGPal, coupled with the high−temperature calcination of dolomite to produce MgO and CO₂. The enlarged average pore size enhances the sample's adsorption capacity for Congo red. Conversely, the protonated hydroxyl groups (−OH₂⁺) on the surface of calcined magnesium oxide attracts negatively charged −SO₃− groups, thereby enhancing Congo red adsorption.The preparation of low−cost and high−performance adsorbents by utilizing the thermal decomposition characteristics of the “dolomite− attapulgite” coproducts provides a feasible solution for the treatment of industrial wastewater and the resource utilization of mineral solid waste.