Adsorptive treatment of coking wastewater using raw coal fly ash: Adsorption kinetic, thermodynamics and regeneration by Fenton process.

Raw coal fly ash (RCFA) was used directly as adsorbent to treat coking wastewater. The results show that the RCFA can introduce COD (14, 4, and 11 mg L-1 at pH = 1.0, 7.0, and 14.0, respectively) into water due to the dissolution of reductive components from RCFA, this can be avoided by washing (6 times) using distilled water. The concentration of leached metal elements in wastewater is lower than the standard in GB18918-2002, China. The adsorption process accords with the pseudo-second order adsorption kinetic model and Langmuir thermodynamics model better than other ones, and it belongs to a physical and exothermic process. More loading of RCFA (10-60 mg L-1) means less adsorption capacity, and 40 g L-1 is the optimal value. The variation of regeneration rate of SRCFA for the first time (RR1) with regeneration time accords with the behavior of hyperbolic function (1RR1=0.986+53.913t), and the [H2O2], [Fe2+] and regeneration temperature can affect the RR1 at the manner of exponential function ( [Formula: see text] , [Formula: see text] , and RR1=2.064·e-251.048T). At the optimal regeneration condition of SRCFA ([H2O2] = 5 mM, [Fe2+] = 8 mM and temperature = 293 K), the RR1 can reach 87.1% after 270 min. The stability of RCFA shows two different stages, i.e., within the first 4 regenerations the RR increases from 87.1% to 89.7% and then decreases gradually and always. This variation trend can be confirmed by the results of SEM and BET tests.