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Background and purpose: Cyanide (CN-) is of dangerous pollutants in the environment from industries such as electroplating, mining and paint entering into environment. The present study aimed to review the efficiency of cyanide removal by zirconia photocatalytic process with and without hydrogen peroxide (H2O2). Materials and methods: This was an applied-fundamental study and was conducted in Environmental Health Research Center. After constructing photoreactor, by changing variables nanoparticle dosage (0.25-4 g/l), pH (4-11), H2O2 amount (0.1-1 ml), cyanide concentration (2.5-75 mg/l) and exposure time (5-90 min), efficiency of the photocatalytic processes was studied with zirconia ZrO2 and H2O2 in the cyanide removal. Experiments were followed on real wastewater samples. 200 synthetic samples and 20 real samples were tested. Results: The maximum cyanide removal (2.5 mg/l) was about 96% by UV/ZrO2/H2O2 process under optimal conditions (0.75 g/L nanoparticles, 0.5ml H2O2 and pH = 8). Removal of cyanide (20 mg/l) by the UV/ZrO2/H2O2 was, 35, 38.75, 55, 56, 59, 61.25, 65, 71.5, 81 and 88.5%, respectively in 5-90 minutes. The efficiency of cyanide removal with UV/ZrO2/H2O2 process decreased from 95.6% to 50.4% in 2.5 to 75 mg/l of cyanide. The maximum cyanide removal (2.5 mg/l) was approximately 85.6% by UV/ZrO2 process under the optimal conditions (0.75 g/l nanoparticles and pH = 4). UV/ZrO2 process efficiency in the cyanide removal decreased from 85.6% to 36.4% in 2.5-75 mg/L of cyanide. The maximum cyanide removal from real wastewater was 54.08% and 72.8% with UV/ZrO2 and UV/ZrO2/H2O2 processes, respectively. Conclusion: Increasing nanoparticle, exposure time and reducing pH increased UV/ZrO2 process efficiency. Increasing cyanide concentration decreased efficiency of the both processes. Increasing H2O2 to optimum dosage (0.5 ml/100 ml CN) increased UV/ZrO2/H2O2 process efficiency, but higher levels of H2O2 decreased the process efficiency.

Keywords: Zirconia nanoparticle, photocatalytic processes, cyanide removal, hydrogen peroxide, electroplating industries

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