Cyanide removal from blast furnace effluent using layered double hydroxide based mixed matrix beads: Batch and fixed bed study

Abstract

Effluent tailings from steel industries contain huge amount of cyanide either in free form or as metal complex. The nanoparticle-based technologies for treatment of cyanide effluent are limited in practical application due to leaching and causes severe operational problems. In this study, the synthesized nickel aluminium layered double hydroxide (NiAl LDH) was impregnated inside the polysulfone matrix at different loadings of 2, 4, 6 and 8 wt% to form mixed matrix beads (MMBs) that serve as an alternative for the upscaling of adsorptive column and thereby overcome the shortcomings adequately. The basal spacing of the LDH impregnated inside the MMB is 8.8 Å. The characteristic peak at 2120 cm^-1 in the post-adsorption FTIR indicated the successful adsorption of cyanide in LDH. The mean free energy value suggested that adsorption occurs via ion-exchange. The morphological stability of the impregnated LDH nanoparticles at elevated loading (6 and 8 wt%) was asserted using Field emission scanning electron microscopy and Transmission electron microscopy analysis. The maximum adsorption capacity of the optimum MMB was 80 mg/g at 303 K. The adsorption mechanism was established based on the speciation chemistry of cyanide present in the actual steel plant effluent. A fundamental macroscopic transport model was used to predict the adsorption kinetics to evaluate the mass transfer and diffusion time scales. The information about the effective pore diffusivity obtained from kinetic macroscopic model along with the adsorption isotherm parameters were used in a first-principle based model to simulate the breakthrough behaviour of continuous column mode experiments and axial dispersion and mass transfer coefficient were estimated in due process. These parameters were used to scale-up the adsorption columns and a performance curve was generated correlating the life of the filter, flow rate, feed concentration and amount of adsorbent required.