Kinetic and Equilibrium Studies of Cr(VI) from Wastewater with Modified Fly Ashes

This study focused on the characteristics of the removal of Cr(VI)(Cr⁶⁺) from wastewater with fly ashes (FAs), a by-product from coal-fired electric power plants. The influences of NaCl dose, pH, agitated time and fly ash (FA) dose (the temperature is 50°Cin the test) were investigated in batch experiments, and the removal of Cr⁶⁺ and sorption capacity with modified fly ashes (MFAs) were compared to those with original fly ashes (OFAs). With the initial Cr⁶⁺ concentration 2mg/L at pH=2, the removal of Cr⁶⁺ was 98.7% in 60min with 2g/L MFAs by 0.25M H₂SO₄ solution. The equilibrium process was described well by the Langmuir isotherm model with maximum sorption capacities of Cr⁶⁺ on MFAs. Good correlation coefficient was obtained for the pseudo second-order kinetic model. In the end, some mine wastewater containing low concentration of Cr⁶⁺ was treated by MFAs. It could be proposed that MFAs by 0.25M H₂SO₄ is an effective adsorbent for the removal of Cr⁶⁺ from wastewater. Meanwhile, Our objective is to search a kind of low-cost adsorbent as a replacement for costly conventional methods of removing heavy metal ions (Cr⁶⁺) from wastewater with FAs, to improve the utilization ratio of FAs and to pursue a new approach for environmental protection and recycle treatment of a coal combustion by-product. Study on the associative methods for MFAs and advanced treatment which should be strengthened will offer the theoretical foundation for the practical application, and finally, this will realize zero emission of Cr⁶⁺.