Abstract
The photocatalytic oxidation of cyanide by titanium dioxide (TiO2) supported on activated carbon (AC) was evaluated in a continuous flow UV photo-reactor. The continuous photo-reactor was made of glass and covered with a wood box to isolate the fluid of external conditions. The TiO2-AC synthesized by the impregnation of TiO2 on granular AC composites was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), Scanning Electron Microscopy (SEM), and nitrogen adsorption-desorption isotherms. Photocatalytic and adsorption tests were conducted separately and simultaneously. The results showed that 97% of CN− was degraded within 24 h due to combined photocatalytic oxidation and adsorption. To estimate the contribution of only adsorption, two-stage tests were performed. First, 74% cyanide ion degradation was reached in 24 h under dark conditions. This result was attributed to CN− adsorption and oxidation due to the generation of H2O2 on the surface of AC. Then, 99% degradation of cyanide ion was obtained through photocatalysis during 24 h. These results showed that photocatalysis and the continuous photo-reactor’s design enhanced the photocatalytic cyanide oxidation performance compared to an agitated batch system. Therefore, the use of TiO2-AC composites in a continuous flow photo-reactor is a promising process for the photocatalytic degradation of cyanide in aqueous solutions.
Highlights
Cyanide is a highly toxic pollutant, which, even at low concentration, may cause human health and environmental problems [1]
The textural properties determined by N2 physisorption and BET (Brunauer-Emmett_Teller) modeling listed in Table 1 show that activated carbon (AC) support and TiO2-AC catalyst had more than 900 m2/g of specific surface area
Design operational conditions were established into the photoreactor where a minimum distance between UV source and fluid/composites and a stable continuous flow though immobilized composites were achieved
Summary
Cyanide is a highly toxic pollutant, which, even at low concentration, may cause human health and environmental problems [1]. Cyanide is rapidly and extensively absorbed by the human body through the oral inhalation and dermal routes. It prevents the transport of oxygen, which affects the cellular respiration process, leading to suffocation in the worst case and eventually to death [2]. Cyanide is present in industrial wastewaters such as coal gasification, electroplating, plastics, pharmaceuticals, and the mining industry These wastewaters are discharged in the water bodies causing serious threats to the environment [1,3,4]. Large-scale gold mining projects as “Fruta del Norte” and “Cascabel” have been developed in the last years. Both small- and large-scale gold mining industries use cyanidation to recover gold from ores
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