Influencing Factors of Ammonia Nitrogen Removal by Electro-oxidation in Seepage Drainage of Uranium Tailings Pond

Abstract

Ammonia nitrogen wastewater is one of the most difficult water treatment problems in the world. In the process of uranium mining, beneficiation and smelting, radioactive solid waste will be produced which cann’t be effectively treated, and will be stored in uranium tailings pond for a long time. Due to the role of rainwater, tailings pond will produce a large amount of wastewater, leach harmful substances into the water to form percolation drainage. Uranium tailings percolation drainage has the characteristics of high salt, high ammonia nitrogen, poor biodegradability and high chloride ion content, and the components in different regions of tailings pond are greatly different. Existing ammonia nitrogen treatment methods can’t effectively treat complex wastewater. Electro-oxidation method is a clean and efficient method to remove ammonia nitrogen in wastewater. By using electric energy and catalytic oxidation of anode and cathode plates, as well as indirect oxidation, chlorine ions in water are converted into highly oxidizing hypochlorite ions, and ammonia nitrogen is converted into harmless nitrogen by strong oxidation, so as to achieve harmless treatment of wastewater and no secondary waste is generated. In this paper, the principle and chemical reaction process of ammonia nitrogen removal by electro-oxidation were analyzed, and the factors affecting the removal rate of ammonia nitrogen were clarified, including chloride ion concentration, plate material, current density, pH, etc., and the influence of each factor on the electro-oxidation process was determined by single factor test. Through orthogonal analysis, the influence degree of each factor on the ammonia nitrogen removal rate was explored, and the influence degree of each factor was ranked from high to low, in order of chloride ion concentration>plate material>current density. pH is a secondary factor, which provides alkaline environment for electrochemical reaction and has little effect on ammonia nitrogen removal. The removal rate of ammonia nitrogen is significantly improved under different conditions, among which chloride ion is the most obvious, and the removal rate of ammonia nitrogen increases from 43.4% at 369 mg/L chloride ion concentration to 96% at 1000 mg/L. Finally, the Ti/RuO2-IrO2-SnO2 electrode set is recommended. The optimal conditions are chloride ion concentration of 1 000 mg/L, current density of 20 mA/cm2, electrolytic time of 3 h, pH=9-11, under which the removal rate of ammonia nitrogen is 100%. The effluent of ammonia nitrogen meets the requirements of ‘Regulations on Radiation Protection and Radiation Environment Protection for Uranium Mining and Metallurgy’ and ‘Comprehensive Sewage Discharge Standard’.

Keywords

• seepage drainage of uranium tailings
• ammonia nitrogen wastewater
• electro-oxidation