Abstract
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 Fe(3+) ions (Fe-adsorbents). The results showed that P sorption capacity by Fe-adsorbents (bentonite (1.31mgg(-1)), calcite (1.97mgg(-1)), kaolinite (1.31mgg(-1)), and zeolite (1.58mgg(-1))) was improved by ∼467, 107, 409, and 427%, respectively, compared to unmodified adsorbents (bentonite (0.28mgg(-1)), calcite (1.82mgg(-1)), kaolinite (0.32mgg(-1)), and zeolite (0.37mgg(-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 Ca(2+) 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.
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