用自行设计的自动分析系统测定高含量SO3--对硫酸钡浊度测定法的改进

Determination of SO3 in High Content by Self-Designed Automatic Analyzer System--Modification of the Turbidimetric Determination of BaSO4 in Suspension

为了解决湿法磷酸生产中高含量SO3的测定,对硫酸钡浊度测定法的反应条件进行了改进,并自行设计制造了自动化的分析系统。测定时样品由蠕动泵(P)推入酸化盘管(AC)中进行酸化和稀释,由定量环(Sv)取样25μL,注入反应系统。在第一反应盘管(RC1)中,SO3与第一混合试剂中的BaCl2溶液反应生成BaSO4悬浊液,该溶液中的聚乙二醇-4000(PEG-4000)和乙醇通过协同作用避免了BaSO4颗粒的团聚,降低粒子间的相互作用,使BaSO4的生成减少,降低了测定的灵敏度,提高了稳定性。在第二反应盘管(RC2)中,BaSO4与第二混合试剂中的NH3·H2O/乙二胺四乙酸二钠(Na2EDTA)溶液发生络合反应同时被Na2EDTA包裹,进一步降低其灵敏度。最后反应溶液进入流通式光度检测器,在680.0nm波长处测试BaSO4悬浊液的吸光度。经优化试验条件,上述第一混合试剂中3种组分的质量分数或体积分数为:BaCl24%,PEG-4000 3%和乙醇2%;第二混合试剂中Na2EDTA的质量分数为6%,NH3·H2O的体积分数为6%。对实际按本方法及重量法分析进行测定,两种方法所得结果的相对偏差在±2%以内,且不受共存的高含量PO43-和F-的干扰。

For determination of SO3 in high content in production of phosphoric acid by wet process,a selfdesigned automatic analyzer system was fabricated and modification of reaction condition for turbidimetric determination of BaSO4 suspension was made.In the determination by the automatic analyzer,the sample was pumped into the AC coil where the sample was acidified and diluted.25μL of the sample was taken by a volumetric vessel and injected into the reaction system of RC1 and RC2.In reaction coil RC1,SO3 in the sample was reacted with BaCl2 in mixed reagents solutionⅠto form BaSO4 suspension;and through co-reaction of 2 other reagents in the mixed reagents solution Ⅰ,i.e.PEG-4000 and ethanol,coagulation of BaSO4 particles was avoided and interaction among particles were reduced,leading to less formation of BaSO4 and lowering the sensitivity of determination and raising of stability.The reaction mixture was then passed through the reaction coil RC2 where complexation reaction was occured between the BaSO4 and Na2EDTA present in mixed reagent solution Ⅱ,and BaSO4 was simultaneously wrapped up by Na2EDTA,thus leading to further lowering of sensitivity.Finally,the reaction solution was passed to the flowing cell of the spectrophotometer,and the absorbance of the BaSO4 suspension was measured at the wavelength of 680.0 nm.By the optimizing test,the mass fraction or volumic fraction of the reagents found were as follows:in mixed reagent solutionⅠ,BaCl24%,PEG-4000 3%and ethanol 2%;in mixed reagents solution Ⅱ,Na2EDTA 6%,aq.ammonia 6%.Five substantial samples were analyzed by the proposed method and checked by the gravimetric method,the results obtained by the 2 methods were checked quite well,giving relative deviations within ±2%.Interferences of macro amounts of coexisting PO43- and F- were eliminated by controlling the acidity at pH 2.