A dual functional adsorbent (EDA/MMA/OA/Fe3O4) with amino group magnetite has been synthesized to behave as an anionic or cationic adsorbent (for the adsorption of phosphate or copper) by adjusting the pH value to make amino group protonic or neutral. The adsorptions of phosphate and copper ions by the dual functional adsorbent were investigated using kinetic, equilibrium, thermodynamic, and surface characteristic experiments. The adsorption behaviors for both copper ions and phosphate by EDA/MMA/OA/Fe3O4 were in good agreement with the Langmuir adsorption isotherm with the maximum adsorption capacities of 7.096 for the copper ion and 34.5071 mg g−1 for phosphate, respectively. The optimum conditions for the desorption of copper ions and phosphate were 0.1M HNO3 and 0.05 M NaOH, respectively. After three cycles, the adsorption capacity of the recycled EDAMMA/OA/Fe3O4 for copper ions and phosphate exhibited a loss of about 17.1% and 28.1%, respectively.