pH值对氨氮电化学氧化产物与氧化途径的影响

Effect of pH for the Electrochemical Oxidation Products and Oxidation Pathways of Ammonia

研究了含氨氮废水在循环流动式电解槽中的电化学氧化,讨论了pH值对氨氮电化学氧化效果、产物及其途径的影响.结果表明,在弱碱性条件下,有利于电解过程中羟基自由基和游离氯的生成,氨氮的电化学氧化速率较大.在有氯离子存在的情况下,氨氮电化学氧化过程中有氯胺生成,氯胺的组成与体系的pH值有关.当pH>9时,一氯胺占优势;当pH=7时,一氯胺和二氯胺同时存在,并且近似相等;当pH<5时,主要是二氯胺;pH值>5时,可以避免三氯化氮的生成.在电流密度为20mA/cm2时,电解产生的羟基自由基<5×10-15mol/L,氨氮电化学氧化的2种途径中间接氧化起主要作用.

The electrochemical oxidation of ammonia in wastewater was investigated in a flow electrochemical cell.The effect of pH on ammonia removal efficiency,oxidation products and oxidation pathways was elucidated.The experimental results indicated that,the higher production efficiency of free chlorine and hydroxyl radical can be obtained under the moderate alkaline condition,and the electrochemical oxidation rate of ammonia was higher in this condition.In existence of chloride ions,chloramines produced during the electrolysis of ammonia.The constituent of chloramines related with the pH of reaction system. When pH was higher than 9,monochloramine was dominant;When pH was equal to 7, monochloramine and dichloramine existed at the same time and the concentration of the two chloramines was an approximation of the same;When pH was smaller than 5,most of the production was dichloramine.The production of nitrogen trichloride can be avoided when pH was higher than 5.Under the current density of 20 mA/cm^2,the concentration of hydroxyl radical produced by electrolysis was smaller than 5×10^-15mol/L.The indirect oxidation was the dominant reaction in the two pathways of electrochemical oxidation of ammonia.