高氯废水化学需氧量测定中硫酸汞掩蔽氯离子的影响因素

Influencing Factors of Mercury Sulfate Masking Chloride Ions in Determination of Chemical Oxygen Demand in High Chlorine Wastewater

在按照标准方法HJ 828-2017和HJ/T 70-2001测定高氯废水的化学需氧量时,氯离子对测定结果具有明显的正干扰,但是系统性研究硫酸汞掩蔽氯离子影响因素的文献尚未见报道,因此考察了消解温度、消解方法、催化剂、硫酸汞与氯离子质量比、共存次氯酸根和共存溴离子等因素的影响,并进行了方法验证。以含1 000,2 000,5 000,7 500,10 000 mg·L^(-1)氯离子的100mg·L^(-1)(以氧计,通过邻苯二甲酸氢钾换算)化学需氧量标准溶液为待测对象,以重铬酸钾作氧化剂,硫酸亚铁铵滴定法测定,比较了消解温度分别为180,220,260℃,消解方法分别为回流消解和密闭消解,添加或不添加硫酸银催化剂,硫酸汞与氯离子质量比分别为10∶1、20∶1和30∶1,共存次氯酸钠质量浓度分别为0,10,20,30mg·L^(-1)(氯离子质量浓度为1 000mg·L^(-1)),共存溴离子质量浓度分别为0,200,400,800mg·L^(-1)(氯离子质量浓度为1 000mg·L^(-1))时化学需氧量测定值的相对误差以及相对标准偏差(RSD,n=5),并以优化的试验条件测定化学需氧量标准溶液和实际样品。结果显示:不添加催化剂,硫酸汞与氯离子质量比为20∶1,180℃密闭消解等条件有利于硫酸汞掩蔽氯离子,共存次氯酸根以及溴离子会对硫酸汞掩蔽氯离子产生显著的负、正干扰;用上述优化的方法测定氯离子质量浓度小于7 500mg·L^(-1)且不含难氧化有机物的加标样品和化学需氧量标准溶液,测定值的相对误差和RSD(n=5)均小于10%和5.3%,回收率为81.4%~107%;对比标准方法 HJ 828-2017和HJ/T 70-2001,优化方法的准确度和精密度以及样品的适用范围大幅提高,并且无需使用复杂的回流装置,提高了测定效率。

When determining the chemical oxygen demand of high chlorine wastewater according to the standard methods of HJ 828-2017 and HJ/T 70-2001,chloride ion has obvious positive interference on determined results,but the references for systematic research on the influencing factors of mercury sulfate masking chloride ions has not been reported.Therefore,the influencing factors including digestion temperature,digestion method,catalyst,mass ratio of mercury sulfate to chloride ion,coexisting hypochlorite and coexisting bromine ion,were investigated,and method validation was carried out.The 100 mg·L^(-1) chemical oxygen demand standard solutions(calculated by oxygen with potassium hydrogen phthalate)containing 1000,2000,5000,7500,1o 000 mg·L^(-1) chloride ion were used as the analyte,potassium dichromate was used as the oxidant,and ammonium ferrous sulfate titration method was used for determination.The relative errors and RSDs(n=5)of the determined values of chemical oxygen demand were evaluated when digestion temperatures were 180,220,260°C,digestion methods were reflux digestion and sealed digestion,silver sulfate catalyst was added or not added,mass ratios of mercury sulfate to chloride ion were 10:1,20:1 and 30:1,mass concentrations of coexisting sodium hypochlorite were 0,10,20,30 mg·L^(-1)(the mass concentration of chloride ion was 1000 mg·L^(-1)),and mass concentrations of coexisting bromine ion were 0,200,400,800 mg·L^(-1)(the mass concentration of chloride ion was 1000 mg·L-1).The chemical oxygen demand standard solutions and actual samples were determined under the optimized test conditions.It was shown that conditions(no addition of catalyst,the sealed digestion,digestion temperature of 180 C,mass ratio of mercury sulfate to chloride ion at 20:1)were conducive to the masking of chloride ions by mercury sulfate,and the coexistence of hypochlorite and bromine ion had significant negative and positive interference on the masking of chloride ions by mercury sulfate.The above optimal method was applied to the analysis of the spiked samples and chemical oxygen demand standard solutions without difficult to oxidize organic compounds and with chloride ion mass concentration less than 7500 mg·L^(-1),and relative errors and RSDs(n=5)of the determined values were less than 10%and 5.3%,giving recoveries in the range of 81.4%-107%.Compared with the standard methods of HJ 828-2017 and HJ/T 70-2001,the accuracy and precision of the optimized method,as well as the applicability range of samples,had been greatly improved,and there was no need to use complex reflux devices,thus improving the determination efficiency.