焦化废水硫氰化物检测过程中氰络合物的硫酸锌屏蔽作用

SHIELDING EFFECT OF ZINC SULFATE ON CYANIDE COMPLEX DURING THIOCYANIDE DETECTION FOR COKING WASTEWATER

焦化废水中含有大量的氰化物(CN^(-))和硫氰化物(SCN^(-))等有毒有害污染物,在预处理过程中,一般采用硫酸亚铁(FeSO_(4))混凝沉淀去除硫化物(S^(2-))、油分、悬浮物并降低废水毒性。上述过程同时会形成亚铁氰化物([Fe(CN)_(6)]^(4-)),[Fe(CN)_(6)]^(4-)再与Fe^(3+)形成亚铁氰化铁沉淀(普鲁士蓝,Fe_(4)[Fe(CN)_(6)]_(3)),干扰硫氰酸铁(Fe(SCN)_(3))分光光度法对SCN^(-)检测的准确性。为解决上述问题,提出在SCN^(-)显色前加入硫酸锌(ZnSO_(4))的方法,屏蔽过量的[Fe(CN)_(6)]^(4-),并分析ZnSO_(4)对SCN^(-)检测的影响程度。结果表明:Fe(SCN)_(3)-ZnSO_(4)分光光度法能屏蔽工业废水中[Fe(CN)_(6)]^(4-)和大部分金属氰络合物的干扰,从而能快速准确地测定SCN^(-)。方法中SCN^(-)适用质量浓度为0.2~34.8 mg/L,统计方差为1.86%,回收率达到94%~103%。该方法适用于多点多频率采样分析,可为工业废水SCN^(-)的现场监测提供一种新手段。

Coking wastewater contains a large amount of cyanide(CN^(-))and thiocyanide(SCN^(-))and other toxic and harmful pollutants.In the pretreatment process prior to the biological process,generally,ferrous sulfate(FeSO_(4))was used to coagulate and precipitate sulfide,oil,and suspended matter to reduce the toxicity of wastewater.At the same time,ferrocyanide([Fe(CN)_(6)]^(4-))was formed,and then[Fe(CN)_(6)]^(4-)was combined with Fe^(3+)to form iron ferrocyanide precipitation(Prussian blue,Fe_(4)[Fe(CN)_(6)]_(3)),which interfered with the accuracy of ferric thiocyanate[Fe(SCN)_(3)]spectrophotometric method for SCN^(-)detection.To solve the above problems,it was proposed that zinc sulfate(ZnSO_(4))should be added to shield excessive[Fe(CN)_(6)]^(4-)before Fe(SCN)_(3)color development;moreover,the influence of ZnSO_(4)on the analysis and detection of SCNwas analyzed.The results showed that the Fe(SCN)_(3)-ZnSO_(4)spectrophotometry could shield the interference of[Fe(CN)_(6)]^(4-)and most metal cyanide complexes in industrial wastewater,so that SCN^(-)can be determined quickly and accurately.The applicable concentration range of this method was 0.2~34.8 mg/L of SCN^(-),the statistical variance was 1.86%,and the recovery rate was 94%~103%.This method is suitable for multi-point and multi-frequency sampling analysis,and is a novel method for the site monitoring of SCN^(-)in industrial wastewater.