Removal of cyanide from steel plant effluent using coke breeze, a waste product of steel industry

Cyanide contamination in steel industry wastewater is a long-standing environmental problem. The present work demonstrates the usability of coke breeze, a carbon rich by-product of steel industry for successful adsorption of free cyanide from the wastewater. The coke breeze was characterized by scanning electron microscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Elemental analysis by energy dispersive X-ray clearly showed the presence of elemental nitrogen after adsorption of cyanide. XRD and FTIR analyses confirmed the cyanide adsorption on coke breeze matrix. pH(zpc) of the adsorbent was found to be 7.4. Maximum Langmuir adsorption capacity of coke breeze for cyanide was 12.3 mg/g at pH 7 and 298 K. Adsorption kinetics revealed that cyanide concentration was reduced rapidly in initial two hours and slowly thereafter. Continuous column experiments were conducted to observe the scalability of the process using real life steel plant wastewater. First principle based pore diffusion model was used to quantify the performance of continuous column experiments and relevant model parameters were estimated. Using these parameters a complete scale up study was undertaken for treatment of actual steel plant wastewater.