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Adsorption using magnetic adsorbents makes the phosphorus removal from water simple and efficient. However, most of the reported magnetic adsorbents use chemically synthesized nanoparticles as magnetic cores, which are expensive and environmentally unfriendly. Replacing the nanomagnetic cores by cheap and green magnetic materials is essential for the wide application of this technique. In this paper, coal-fly-ash magnetic spheres (MSs) were processed to produce a cheap and eco-friendly magnetic core. A magnetic adsorbent, ZrO2 coated ball-milled MS (BMS@ZrO2), was prepared through a simple chemical precipitation method. Careful structural investigations indicate that a multipore structural amorphous ZrO2 layer has grown on the MS core. The specific surface area of BMS@ZrO2 is 48 times larger than that of the MS core. The highest phosphorus adsorption is tested as 16.47 mg g-1 at pH = 2. The BMS@ZrO2 adsorbent has a saturation magnetization as high as 33.56 emu g-1, enabling efficient magnetic separation. Zeta potential measurements and X-ray photoelectron spectroscopy analysis reveal that the phosphorus adsorption of BMS@ZrO2 is triggered by the electrostatic attraction and the ligand exchange mechanism. The BMS@ZrO2 adsorbent could be reused several times after proper chemical treatment.