Abstract
Nowadays, mining effluents have several contaminants that produce great damage to the environment, cyanide chief among them. Ferrites synthesized from transition metals have oxidative properties that can be used for cyanide oxidation due to their low solubility. In this study, cobalt and copper ferrites were synthesized via the precipitation method, using cobalt nitrate, copper nitrate, and iron nitrate as precursors in a molar ratio of Co or Cu:Fe = 1:2 and NaOH as the precipitating agent. The synthesized ferrites were impregnated in specific areas on active carbon. These composites were characterized using X-Ray Diffraction (XRD) and Scanning Electron Spectroscopy (SEM). The XRD results revealed a cubic spinel structure of ferrites with a single phase of cobalt ferrite and two phases (copper ferrite and copper oxides) for copper. The CoFe2O4 impregnated on active carbon reached a cyanide oxidation of 98% after 8 h of agitation; the composite could be recycled five times with an 18% decrease in the catalytic activity. In cobalt ferrites, a greater dissolution of iron than cobalt was obtained. In the case of copper ferrite, however, the copper dissolution was higher. These results confirm that ferrites and activated carbon composites are a novel alternative for cyanide treatment in mining effluents.
Highlights
The effluents generated during metallurgical operations, galvanizing, gold and silver extraction, crude refining, among others, contain metal complexes of cyanide or free cyanide [1].The Environmental Protection Agency (EPA) catalogs this waste as highly dangerous for nature and human health, its treatment prior to discharge in water bodies is a very important issue [2].several methods have been applied through the years in order to oxidize cyanide to cyanate ions
As it was mentioned in the Materials and Methods section, two activated carbons of different specific area were employed as supports for ferrites deposition
Copper ferrite and cobalt ferrite impregnated on activated carbon were successfully synthesized using the precipitation method
Summary
The effluents generated during metallurgical operations, galvanizing, gold and silver extraction, crude refining, among others, contain metal complexes of cyanide or free cyanide [1]. In the last few years, several composites based in biomass or active carbon have been employed for waste water treatment The importance of these composites lies in their easy separation of products or reagents without operations such as filtration, centrifugation, or decantation. In the particular case of cyanide ions oxidation coming from metallurgical operations, activated carbon may transform this toxic reagent into more environmentally friendly substances. Ferrites formed from transition metals are widely studied, due to their use as magnetic materials, semiconductors, pigments, and catalysts. The catalyst may follow the Mars van Krevelen mechanism in order to oxidize cyanide ions into cyanates [12]. The oxygen in the catalyst migrates to the surface to oxidize the adsorbed reagent (cyanide ions in this case) and form the products. If instead of a cobalt oxide, a cobalt ferrite or a nickel ferrite is used, the percentage of oxidation is 85%, which shows that the catalytic activity of the cobalt ferrite is superior to that of the oxide systems
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