Application of Thermally Treated Crushed Concrete Granules for the Removal of Phosphate: A Cheap Adsorbent with High Adsorption Capacity

The aim of this study was to investigate phosphate removal using crushed concrete granules (CCGs). The CCGs were thermally treated at different temperatures (300, 500, 700, and 900 degrees C) for 3 h under anoxic conditions. The results showed that CCGs thermally treated at 700 degrees C (700TT-CCGs) were the most effective for the removal of phosphate. The equilibrium adsorption data fitted well the Langmuir isotherm model with a maximum phosphate adsorption capacity of 21.522 mg/g, higher than that of granular adsorbents in the literature. In pH experiments, phosphate adsorption by 700TT-CCGs decreased as initial pH increased from 3 to 5, but sharply increased above pH 5 (final pH 9.1), which was favorable for the formation of calcium phosphate precipitate. The effect of competing anions on phosphate adsorption follows the order: HCO3- > SO42- > NO3-, which is consistent with the reverse order of the shared charge. Column experiments showed no breakthrough of phosphate in the column packed with half 700TT-CCGs and half sand for over 300 h. This study demonstrates that CCGs can be used for phosphate removal from aqueous solution after thermal treatment, which is a simple and cheap way to improve the phosphate removal capacity of CCGs.