Phosphorus (P) removal from aqueous solutions was investigated using modified bentonite, calcite, kaolinite, and zeolite with FeCl3, CaCl2, and NaCl. The maximum sorption capacity of P was obtained by modified adsorbents with Fe3+ ions (Fe-adsorbents). The results showed that P sorption capacity by Fe-adsorbents (bentonite (1.31 mg g−1), calcite (1.97 mg g−1), kaolinite (1.31 mg g−1), and zeolite (1.58 mg g−1)) was improved by ∼467, 107, 409, and 427 %, respectively, compared to unmodified adsorbents (bentonite (0.28 mg g−1), calcite (1.82 mg g−1), kaolinite (0.32 mg g−1), and zeolite (0.37 mg g−1)). Sorption isotherms were well described by the Freundlich model. Desorption experiments showed that the desorption capacity was in order of unmodified adsorbents>modified adsorbents with Na+ ions (Na-adsorbents)>modified adsorbents with Ca2+ ions (Ca adsorbents)>Fe-adsorbents. Effect of pH and ion strength was also investigated. At different pH, changes in the ionic strength had little effect on the adsorption. Results showed that double-layer model (DLM) could model P adsorption onto modified adsorbents over a wide range of pH and varying ionic strength. According to the scanning electron microscopy (SEM) images and saturation indices (SIs), high P removal by adsorbents was partly due to the P precipitation.
