Use of coal fly ash for simultaneous co-adsorptive removal of phenol and cyanide from simulated coke wastewater

The present study deals with the process parameter optimization and modeling of simultaneous adsorption of phenol and cyanide from simulated coke wastewater onto acid treated coal fly ash. At a temperature of 30 °C, pH of 9 and adsorbent dose of 40 g L-1, optimum removal of phenol and cyanide was found to be 67 and 82%, respectively for initial concentration of 200 mg L-1 phenol and 20 mg L-1 cyanide. Both single-component and multi-component isotherms were applied to the experimental data in the range of initial concentration of 100-1000 mg L-1 of phenol and 10-100 mg L-1 of cyanide. Extended Langmuir and extended Freundlich isotherms were found to be best fitted model for phenol and cyanide, respectively. The monolayer capacity of fly ash as calculated by extended Langmuir isotherm was 248 mg phenol g-1 of fly ash and 1.2 mg cyanide g-1 of fly ash. Kinetic studies revealed chemisorptions to be the mechanism of adsorption of both phenol and cyanide. Thermodynamic parameters viz, ΔG0, ΔH0 and ΔS0 were calculated as -1.7, -7.3 kJ mol-1, -0.05 kJ mol-1 K-1 for phenol and -3.8, 24 kJ mol-1 and 0.09 kJ mol-1 K-1 for cyanide adsorption, respectively indicating process of phenol adsorption onto fly ash as exothermic and spontaneous while that of cyanide as endothermic in nature.