石墨精制废水中氟离子浓度测定偏差问题的解析

随着高纯石墨日益成为现代科技与工业发展的重要原料,石墨精制产生的酸性含氟废水量也会越来越大,其处理结果监测的准确性对控制该行业的环境冲击有着重要作用.实验中发现氟离子选择电极法测定石墨精制废水沉淀处理出水时,测量结果随水样稀释倍数增加而增高的问题.本文通过水质分析和理论计算对可能存在的氟化钙微晶稀释溶解、离子强度波动、共存离子干扰等因素进行排查,并用离子色谱法对测量结果进行核对.结果表明:稀释液中过量的掩蔽剂TISAB将溶液中络合态的氟离子释放出来,是导致离子选择电极法氟离子质量浓度测定结果随稀释倍数增加而增高的主要原因;石墨精制废水处理出水中氟离子质量浓度在0~30 mg/L,用国家标准方法对其氟离子质量浓度测定需先将水样稀释100倍.

Analysis of measurement deviation problem of fluoride ion concentration in graphite refining wastewater

With high purity graphite becoming an important raw material in modern science, technology and industrial development, more and more fluoride-containing wastewater will be produced.The accurate monitor plays an important role in the control of the industry''s environmental impact. It is found that fluorine ion concentration measured by fluoride ion selective electrode increased with the increasing of dilution ratio in graphite refining wastewater measurement. Reasons like dissolution of suspended calcium fluoride micro-crystal, the interference of impurity ions and the effect of ionic strength were analyzed through water quality analysis and theoretical calculation. Ion chromatography was used to check the result of experiments. Results show that the release of fluorine ion with complexing state from masking agent of TISAB is the main reason of what was found in the experiment. The fluorine ion concentration of graphite refining wastewater is about 0 to 30 mg/L.The water needs to be diluted 100 times when the fluoride ion concentration is measured by the national standard method.