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Phosphogypsum (PG) modified by milk of lime (namely lime‐preconditioned phosphogypsum, PPG) is investigated to evaluate the adsorption thereof for removing Congo Red (CR) from aqueous solution. The experimental parameters, such as adsorbent dosage, pH, adsorption temperature, initial CR concentration and contact time, are carefully studied in the batch system. FT‐IR, XRD, BET and SEM are used to characterize the structure and morphology of PPG in the various conditions. The adsorption kinetic and isotherm of PPG onto CR from aqueous solution are fitted using quasi‐first‐order and quasi‐second‐order kinetic equations, and Langmuir and Freundlich models, respectively. The quasi‐second‐order kinetic equation is more suitable to describe the adsorption kinetics of CR by PPG than the quasi‐first‐order kinetic equation. The equilibrium data of CR is found to best fit to the Langmuir model. The adsorption capacity for CR achieved 79.5 mg/g according to Langmuir model. Further, the thermodynamic results show that the adsorption is an endothermic and spontaneous process. Meanwhile, desorption experiments are performed to verify and reveal the adsorption behavior. And the packed micro‐channel is firstly applied to remove CR from aqueous solution. Finally, the adsorption mechanism is speculated according the structure of CR and PPG. PG can be employed as waste‐recycling alternatives for recalcitrant dye removal from aqueous solution. [ABSTRACT FROM AUTHOR]