Photocatalytic degradation of ferricyanide as synthetic gold mining wastewater using TiO2 assisted by H2O2

Abstract

Ferricyanide Fe(CN) 6 3is one of the most stable cyanometallic complexes present in the gold mining effluents. This cyanocomplex is hard to degrade by natural attenuation and generates a negative impact on aquatic environments. Although free cyanide (CN-) can be obtained by acidifying the solution, the CNis lethal for all forms of life. The oxidation of Fe(CN) 6 3in a typical photocatalitic system was evaluated with the addition of H 2 O 2. To verify the degradation, chemical parameters, such as free cyanide, the formation of ammonia, nitrate, and total iron were analyzed at the end of the process. Different parameters were evaluated to analyze the behavior of the degradation: 1. dark stage adsorption using the catalyst, 2. the TiO 2 dosage, 3. Addition of H 2 O 2 , 4. UV radiation power (120 and 200W) and finally a test of TiO 2 with solar radiation. The photolysis effect from a ferricyanide solution at 100 mg L-1 at alkaline pH 13, showed that the complex studied is highly stable since under UV irradiation conditions (λ> 300 nm), a low rate of dissociation was observed. After 24h of irradiation, the cyanocomplex was under 20%, whereas degradations up to 70% were obtained in a heterogeneous photocatalysis system with TiO 2. The best result was achieved with the H 2 O 2 and TiO 2 photocatalytic system, and the stoichiometric concentration was about 2.5 times less than the peroxide used in the gold mining industry, reaching 83% degradation. The photocatalytic process obtained less toxic byproducts than the original synthetic ferricyanide used as mining wastewater.

Efficiency of Adsorption and Photodegradation of Composite TiO2/Fe2O3 and Industrial Waste in Cyanide Removal

“…The irradiation of the solution was carried out with a lamp of 300 W, with a wavelength of 300 nm; a flow of 4 L/min H2O2 (pH 13) was added. A degradation of 83% was achieved in one hour [24].…”