Performance of Natural Zeolite and Sepiolite in the Removal of Free Cyanide and Copper-Complexed Cyanide ([Cu(CN)3]2−)

Abstract

AbstractThe chemical and biological methods employed to date in the removal of free cyanide (CN−) and metal-cyanide complexes from aqueous fluids have proved expensive and problematic. A simpler and more economical approach was attempted in the present study using zeolite and sepiolite. The effectiveness of zeolite from Manisa-Gördes (Turkey) and of sepiolite Eskişehir-Sivrihisar (Turkey) at removing free and Cu-complexed cyanide, [Cu(CN)3]2− was investigated. For removal of CN−, the system performance was examined in terms of concentration, particle size, and retention time. Material with smaller particle sizes (<0.106 mm) performed better, particularly in the case of sepiolite. The maximum CN− removal capacities of zeolite and sepiolite were calculated as 571 and 695 meq/100 g for free CN adsorption, and 455 and 435 meq/100 g for Cu-complexed CN adsorption, respectively. The time to reach equilibrium was calculated as 1050 min. Acid activation, a simple cation adsorption removal method, did not improve the process, instead leading to reduced CN adsorption. Hydroxylated surfaces of metal oxides at the edges of zeolite develop charges and exchange with anions in water. Mg2+ ions located at the edges of the octahedral sheet can create complexes with CN− anions. Moreover, hydrogen bonding with anions (CN− in this case) and H+ of zeolitic water bonded to coordinated water molecules can also create complexes. These two complexes are considered to be effective mechanisms for sepiolite. The effects of both acid activation and CN adsorption were clearly observed in the Fourier-transform infrared spectra. Removal of CN was characterized by the Langmuir isotherm, indicating monolayer coverage with chemical bonding to the surface, which deteriorated during acid activation. The study indicated that zeolite and sepiolite can be used efficiently and easily for removal of free and Cu-complexed CN.