Contrasting Perfluorooctanoic Acid Removal by Calcite Before and After Heat Treatment

Calcites before and after calcination at 1000 degrees C were evaluated for their potential removal of perfluorooctanoic acid (PFOA) from water. After heat treatment, the PFOA sorption capacity increased by 25%, from 3.2 to 3.9 mg g-1, and the affinity increased by 2.7 times, from 0.03 to 0.08 L mg-1. Kinetically, the initial rate, rate constant, and equilibrium sorption were 8.7 mg g-1 h-1, 2.6 g mg-1 h-1, and 1.8 mg g-1 for heat treated calcite, in comparison to 6.4 mg g-1 h-1, 3.1 g mg-1 h-1, and 1.4 mg g-1 for calcite without heat treatment. X-ray diffraction analyses showed phase changing from calcite to calcium oxide after calcination. However, after contact with PFOA solutions for 24 h, the major phase changed back to calcite with a minute amount of Ca(OH)2. These results suggest that using raw cement materials derived from heat treatment of limestone may be a good option for the removal of PFOA from water. Thus, further studies are needed to confirm this claim.