The New Method Research About The Determination Of Trace Amounts Of Chloride And Heavy Metals In Nitric Acid

The research project is aimed to establish a new method to analyze some important impurity materials in HNO₃ which not only has the characteristics of strong oxidation and erosion, but is widely used in scientific and industrial fields. The significance of this research is that it is closely related to industrial safety of HNO₃ production .The principle on the main experiments is briefly introduced. Several analytical methods of traditional industrial standard for HNO₃ were concisely reviewed. The deficiency of these methods were pointed out. It is necessary that a new standard method for HNO₃ analysis should be developed.The items involved in this thesis were demonstrated as principle and technical flow chart, specific operation in the experiments and their results, etc. The details are shown as flowing:(I) Sample pretreatment250 mL HNO₃ was sampled under unpolluted condition. The HNO₃ was neutralized with Na₂CO₃ to making analysis solution (pH=7). Physical vibration method was used to drive carbon dioxide out of solution in flask. The sample should be cooled to room temperature before syringe injection step.(II) Analytical technology by high-pressure ion chromatography(HPIC) with two columnsThe analytical conditions for PIC-8 were optimized. The solution was analyzed by IC double-columns (YSA-8). The correlation coefficient is 0.9997 for calibration curve. The content of Cl^- in HNO₃ is 6.06mg/L.The accuracy of the analytical results was assessed by standard addition .The range of recovery are 96.5⁹9%. The range of reproducibility(RSD) are 1.84%².83%(n=5).The analysis results are satisfactory..(III) The method of anodic stripping voltammetry(ASV) was established for the determination of heavy metals, Pb²⁺etc in HNO₃. The optimization of specific experimental conditions were fixed. The concentration of heavy metals, Pb²⁺etc in HNO₃ and in Na₂CO₃ solution were determined respectively. The Pb²⁺content in HNO₃, 0.237 mg/L, was obtained with subtract calculation.(IV) The comparative experimentsA pre-treatment with high pure Cu was required for Cl" determination. The Cl" ion is fixed up by Na₂CO₃.After the redox reaction between Cu and HNO₃, Cu(NO₃)₂, the main product, is heated and decomposed at 250℃. Finally, the solution is analyzed with thesingle-column's IC method and better Cl'peak was observed.(V) The economics assessment for the researchThe ratio of performance to price for the equipments and chemicals expenses used in this research were counted. It has been proved that this experimental method is closely correspond to economic situation of chem-engineering in our country .(VI) Some issues related to IC theory and analytical techniques were discussed. The ideas for improvements of HPIC analytical method were raised referring to the most advanced IC technology in today's world.