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)(Cr
⁶⁺
) 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 Cr
⁶⁺
and sorption capacity with modified fly ashes (MFAs) were compared to those with original fly ashes (OFAs). With the initial Cr
⁶⁺
concentration 2mg/L at pH=2, the removal of Cr
⁶⁺
was 98.7% in 60min with 2g/L MFAs by 0.25M H
₂
SO
₄
solution. The equilibrium process was described well by the Langmuir isotherm model with maximum sorption capacities of Cr
⁶⁺
on MFAs. Good correlation coefficient was obtained for the pseudo second-order kinetic model. In the end, some mine wastewater containing low concentration of Cr
⁶⁺
was treated by MFAs. It could be proposed that MFAs by 0.25M H
₂
SO
₄
is an effective adsorbent for the removal of Cr
⁶⁺
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 (Cr
⁶⁺
) 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 Cr
⁶⁺
.