UV/氯联合处理含溴溶液中溴酸根的生成

研究了UV和氯联合作用下溴酸根离子(BrO^-₃)在低浓度含溴溶液中的生成,旨在探讨pH、次氯酸钠(NaOCl)浓度、溶解氧(DO)、光强和温度等因素对其生成的影响.研究表明,暗反应条件下H₂O-NaOCl-Br^-体系较稳定,而UV照射可使游离氯浓度持续降低,同时伴有部分Br^-（6 .6%～32%）被氧化成BrO^-₃离子;pH、温度和光强恒定时余氯的分解可用拟一级反应速率方程拟合;实验条件下（I为610～1 896 μW/cm²,T为12 .2～36 .1℃）,拟一级反应速率常数分别与体系温度和光强值有线性关系;BrO^-₃的生成大致可以分为快速、慢速和平缓3个阶段;在慢速生成阶段,BrO^-₃的生成量与余氯的分解量有良好的线性关系（绝大部分相关系数在0 .96以上）;实验范围内（pH为4 .41～11 .07,DO为1 .5～9 　mg/L,Cl₂为1 .23～4 .50 　mg/L）,低pH、低DO和高初始NaOCl（以氯计）浓度有利于溴酸根的生成,提高温度与光强均不同程度提高溴酸根生成速度,但同时因加速余氯的分解而减少了溴酸根的总生成时间.

Bromate Ions Formation in UV/Chlorination Processes for Bromide-Containing Solutions

Bromate ions formation in UV/chlorination processes was systematically investigated. Experimental conditions were explored, such as pH, initial concentration of NaOCl, dissolved oxygen, UV light intensity and water temperature. The results showed impalpable changes of the H2O-NaOCl-Br(-) system was observed in dark, whereas in UV/chlorination processes free chlorine was continuously reduced and a considerable ratio (6.6 - 32 percent) of bromide was oxidized to bromate. The chlorine decomposition followed pseudo-first order rate equation when the reaction conditions, including pH, temperature and UV light intensity, was nearly fixed. Within the light intensity range of 610 - 1 896 microW/cm2 and temperature range of 12.2 - 36.1 degrees C the pseudo-first order rate constants had a linear relationship with temperature and light intensity, respectively. Bromate formation could be divided totally into three stages: quick-form stage, slow-form stage and plateau stage. In slow-form stage the production of bromate had a good linear relationship with the amount of decayed chlorine, of which the regression coefficients were higher than 0.96 in most cases. Under the conditions in these experiments (pH 4.41 - 11.07, DO 1.5 - 9 mg/L, Cl2 1.23 - 4.50 mg/L), production of bromate was favored under the circumstance with low pH value, low DO value and high chlorine concentration. Both increasing temperature and increasing light intensity improved the creation of bromate, as well as reduced the duration of bromate forming process because of the acceleration of chlorine decomposition.