Cyanide adsorption on activated carbon impregnated with ZnO, Fe2O3, TiO2 nanometal oxides: a comparative study

Nanocrystalline metal oxides including TiO2, Fe2O3, and ZnO and their combinations were impregnated on activated carbon (AC) and characterized by XRD, FTIR, and FESEM analyses. The results showed the size of most Fe2O3/AC, TiO2/AC, TiO2/Fe2O3/AC, ZnO/AC, and ZnO/Fe2O3/AC particles are in the range of 25–60 nm. BET analysis verified the high surface area of the six adsorbents (201–448 m2/g). The adsorption results confirmed that the modification could improve the adsorption capacity and removal efficiency as the maximum monolayer adsorption capacity and cyanide removal efficiency were observed for ZnO/Fe2O3/AC (101.0 mg/g, 82.5%), TiO2/Fe2O3/AC (96.2 mg/g, 75.1%), ZnO/AC (91.7 mg/g, 73.5%), TiO2/AC (90.9 mg/g, 72.4%), Fe2O3/AC (86.2 mg/g, 69.2%,), and AC (78.1 mg/g, 66.3%), respectively. Moreover, the study of different isotherm models including Langmuir, Freundlich, and Redlich–Peterson indicated that the Langmuir model was the most suitable one for the six adsorbents with 0.56 < RL < 0.64. The kinetic modeling of experimental data revealed the cyanide adsorption on all adsorbents followed the pseudo second-order model confirming chemisorption can be a main mechanism of adsorption. The regeneration and reusability results showed modified AC adsorbents have more reusable and stable structure than AC to be used as adsorbents in industrial wastewaters. The performance of adsorption process was compared with different methods of cyanide removal. The results approved that adsorption process as a cost-effective and simple design method using bioadsorbents can be highly effective in full-scale applications for the removal of high concentration of cyanide.