三种波长测定COD比较兼论无汞对测定值的影响以及汞银的回收

综述密封高温快速测定COD在610 nm、420 nm和348 nm三种波长条件下的特点。前二者已定为国家标准方法,研究发现348nm灵敏度最高,可以测定超低量程的COD,其准确度4.5%、精密度5.2%,检出限1.6 mg/L,建议也将其定为国家标准方法。COD测定都加Hg^2＋掩蔽Cl^-,无汞法不加Hg^2＋,只加Ag＋或加Ag＋又加Cr^3＋;前者COD测定值偏高,后者的Cr^3＋使Cr（V1）/Cr^3＋电极电势下降,虽然有抑制Cl^-的氧化作用,但灵敏度下降,有机物氧化率下降,测定结果偏低较大。如果要求测定准确度高,无汞不行。测定废液中加入铁或铜,回收汞银。

Comparison of COD Values Determined by 3 Wavelengths and the Discussion on the Influence of Mercury-free on Determine Value and the Recovery of Mercury-silver

An overview on the characteristics of COD rapidly determined in the condition of seal and high temperature under 3 different wavelengths of 610 nm,420 nm and 348 nm. The determination methods under the first two wavelengths have been accepted as the national standard measurements,while from the research,we find that under the wavelength of 348nm,the sensitivity of COD is highest so ultra-low-range COD can be determined and we suggest to list COD determination under 348nm wavelength as another national standard measurement. The accuracy、precision and detection limit of this methods are ,4.5%、5.2%and 1.6 mg/L,respectively.COD measurement is required to add Hg^2＋and mask Cl^-and mercuryfree method is free of Hg^2＋and only adding Ag＋or Ag＋and Cr^3＋. Only adding Ag^＋,COD determine value will be higher than the actual value and if adding Ag＋and Cr^3＋,Cr^3＋will decline electrode potential of Cr（Vl）/Cr^3＋which though is able to restrain the oxidation of Cl^-,the sensitivity of COD decreases and oxidation rate of organic matter decreases leading a lower COD determine value. Mercury cannot be free if an accurate determine result is required. Add copper or iron in the waste liquid could recovery mercury-silver.