氯酸盐对电镀废水COD检测的掩蔽机理初步分析

Preliminary Analysis of Masking Mechanism of Chlorate on COD Detection in Electroplating Wastewater

向电镀废水中投加氯酸盐,分析了氯酸盐在COD检测过程中的掩蔽作用,研究了氯酸钠投加量、pH值等因素对掩蔽作用的影响,并结合COD、TOC、Cl^-、ClO_3^-等指标,初步揭示了检测COD过程中氯酸盐掩蔽作用的机理。结果表明,向电镀废水中投加氯酸盐并不能有效降解有机物,出水COD数值降低是因为检测COD过程中氯酸盐的掩蔽作用,且在一定范围内,其掩蔽能力随着投加量的增加而增大。探索掩蔽机理发现,在酸性高温消解过程中,ClO_3^-与水中的有机物发生了氧化还原反应,减少了Cr_2O_7^(2-)的消耗量,同时大部分的ClO_3^-转化为了Cl^-,并与Hg^(2+)(氯离子掩蔽剂)络合生成HgCl_4^(2-)稳定下来,导致COD的检测值较低。另外,在COD检测过程中pH值并不会影响氯酸盐的掩蔽作用。

The masking effect of chlorate on detection of COD was analyzed through adding chlorate into the electroplating wastew on effluent COD were investigated ater.The effects of sodium chlorate dosage,pH value and other factors ,and the masking mechanism of chlorate on COD detection was preliminarily revealed according to the results of COD, TOC,Cl^-and ClO3^-.It turned out that the organic pollutants could not be degraded effectively through the addition of chlorate into the electroplating wastewater,and the main reason for the decrease of the effluent COD was the masking effect of chlorate during the detection.It was also found that the masking effect of chlorate was enhanced with the increase of its dosage within a certain range.Moreover,the results indicated that the ClO3^- and organic pollutants were subjected to an oxidation-reduction reaction during the acidic and high temperature digestion process,resulting in the decreased consumption of Cr2O7^2-.Meanwhile,most of the ClO3^- was converted into Cl^-,which was then reacted with mercuric sulfate (chloride ion masking agent)to form stable HgCl4^2- through complexation,and it finally led to the reduction of detected COD value.In addition,pH value had no effect on the masking effect of chlorate during the detection of COD.