非银汞试剂密闭消解-电位滴定检测废水中COD

DETERMINATION OF COD BY CLOSED DIGESTION COUPLED TO POTENTIOMETRIC TITRATION WITH NON-MERCURY-SILVER REAGENTS

建立了非银汞复合试剂+硫磷混酸+重铬酸钾+大体积密封瓶消解样品,进行电位滴定批量测定COD的方法。自制了消解/滴定一体瓶与相应的消解器,非银汞复合试剂加量0.5 g(由硫酸锰/硫酸铜/硫酸铝钾/硫酸铬钾(质量比)=3∶2∶1∶1),0.1 mol/L K2Cr2O7加量10 mL,体积比为3∶1的硫磷混酸15 mL,水样加量10 mL,(160±5)℃温度下密封消解20 min,消解液直接由黄金电极电位滴定。实验结果表明:50 mg/L水平的实际样品COD,RSD≤4.78%,与HJ 828—2017的结果相对误差≤5.80%,应用于石化废水和其他水质分析,效果满意。

A new detection method of CODCr was established using a high volume of closed digestion mode coupled to gold electrode potentiometric titration with mixed reagent free of silver-mercury which consists of mixture of sulfuric phosphoric acid and potassium dichromate.The digestion//titration integrative bottle and the corresponding digester were custom-made.Theoptimized procedure for determining COD were as follows:adding 0.5 g mixed reagents of MnSO4,CuSO4,KAl(SO4)2,and KCr(SO4)2(mass ratio 3∶2∶1∶1)to mixture of sulfuric phosphoric acid(volume ratio 3∶1,15 mL)with 0.1 mol/L K2Cr2O7(10 mL)as the oxidant;closed digestion time was 20 min at(160±5)℃,and the sample of addition were 10 mL.The relative standard error(RSD)of COD was≤4.78%at 50 mg/L level,The relative error compared to results from HJ 828—2017 was≤5.80%.The improved method for determining COD overcame a lot of disadvantage andshortened the analysis time byone-third.The mixed reagents can be easily acquired and is cost effective.The method has been applied to petrochemical wastewater and other water COD analysis whereit showed satisfying result.