Anoxic photocatalytic treatment of synthetic mining wastewater using TiO2 and scavengers for complexed cyanide recovery.

The wastewater from gold exploitation is well known for the toxic nature of recalcitrant cyanide metallic complexes. In this work the selectivity in the photocatalytic degradation of gold mining wastewater (Fe(CN)63-) using suspended TiO2 with alcoholic and organic acid scavengers in a mini-CPC photoreactor with a 30 W UV-A LED as an artificial source of light was evaluated. The study was done in four stages: 1. load catalyst determination, 2. combination of scavengers in a typical photocatalytic degradation, 3. evaluation of scavenger concentration and 4. kinetic study. The decomposition into CN- and Fe removal of the cyanocomplex were tracked. It was observed that formic acid (FA) and t-butanol (t-ButOH) were the best scavengers for the photocatalytic degradation under anoxic conditions. The best concentrations of acceptors used in the study were 10 mM FA and 10 mM t-ButOH at 20 W m-2 of UV-A power, reaching 80% degradation of Fe(CN)63-, 40% Fe removal and 18 ppm of free cyanide CN release to the liquid phase. The electrical efficiency of oxidation per order (EEo) was increased by about 50% with the addition of scavengers instead of traditional anoxic photocatalytic treatment. It was proved that the photocatalytic decomposition of the Fe cyanocomplex was done through the photoreduction path of the metal complex.

An approach to utilize the artificial high power LED UV-A radiation in photoreactors for the degradation of methylene blue.

Utilization of UV LED light is trending in the development of photoreactors for pollutant treatment. In this study, two different geometries were studied in the degradation of methylenebBlue (MB) using high power UVA LED as a source of light. The dosage, initial concentration, electric power, and H2O2 addition were evaluated in the two geometries: a mini CPC (Cilindrical Parabolic Collector) and a vertical cylindrical with external irradiation both coupled with LED UVA. Best degradation was obtained for 0.3 g L-1 TiO2, 40 min, and 15 ppm of MB of initial concentration in the standard batch reactor. It was found that the best system was a cpc geometry. Also, hydrogen peroxide was used as an electron acceptor and 97% degradation was obtained in 30 min with 10 mM H2O2 and 0.4 g TiO2/L. Power of the LEDs was also evaluated and it was found that 20 W m-2 is the best operational condition to achieve the best MB degradation avoiding the oxidant species recombination.