Cyanide Detoxification of Mining Wastewaters with TiO2 Nanoparticles and Its Recovery by Electrocoagulation

Due to the widespread use of cyanide in mining operations, its recovery and destruction is important for both the environmental aspects of wastewater and its treatment, and the economic aspects associated with the high consumption of chemicals by the process itself. A photoelectrocatalytic detoxification technique with titanium dioxide microelectrodes is one of the most innovative ways for the treatment of wastewater containing cyanide. However, this technique has a disadvantage for industrial application in that the separation of titanium dioxide after the photocatalytic degradation of cyanide is rather difficult due to the fineness of the particles, and therefore, the reuse of the titanium dioxide has not been attained for the treatment of cyanide-containing wastewater. To overcome this weak point, an electrocoagulation (EC) technique is used to recover the titanium dioxide from its aqueous suspensions. The results show that photodegradation of cyanide is 93% in 30 min using a 450 W halogen lamp. The recovery of anatase with the EC process is 98%. The results indicate that this technique has the potential to serve as a reliable and economical method because sunlight can be used efficiently as the power source. The Langmuir isotherm is used to obtain the thermodynamic parameters, i.e., free energy, enthalpy and entropy. The evaluation of these parameters, i.e., Delta G degrees = -37 kJ/mol, Delta H degrees = -54 kJ/mol and Delta S degrees = 0.524 kJ/mol K, indicates the spontaneous and exothermic nature of the adsorption of the anatase particles on the iron species.