Study On The Removal Of Trace Iodine From Dilute Brine In The Production Process Of Ion-exchange Membrane Caustic Soda

Ionic membrane caustic soda production is the mainstream caustic soda production technology in the world’s chlor-alkali industry.As its core,the ionic membrane has high costs and harsh operating conditions.Iodine in dilute brine can shorten the service cycle of the ionic membrane and increase the cost of caustic soda production.Due to multiple recycling,the iodine in the dilute brine will be enriched to a higher concentration and oxidized into high-valent IO₃^-,IO₆^5-,etc.in the electrolytic tank.These high-valent iodine will combine with Na⁺,Ba²⁺,etc.to form Na₃H₂IO₆,Ba₃H₄（IO₆）₂ and other insoluble precipitates on the ionic membrane,resulting in shorter service life of the ionic membrane and increased production energy consumption.Iodine in dilute brine has complex forms.The key to deiodination of dilute brine is to select the appropriate iodine conversion method.This paper establishes a research method for dynamically analyzing the forms of iodine in dilute brine by measuring its potential.Use the improved GB/T 13882-1992 to determine the content of iodine in the dilute brine,study the effect of oxidant Na Cl O and reductant Na H₂PO₂,Fe Cl₂ on the transformation of iodine form in the dilute brine under different process conditions,deiodination by adsorption with composite adsorbent,the optimal process parameters for iodine removal from dilute brine were determined.The main contents include:（1）The improved detection method has high accuracy and sensitivity,with a detection limit below 0.4μg/L,the recovery rate of spiking is96.00%～103.00%,and high concentration Na Cl has no significant interference with the improved method;（2）The reductant Na H₂PO₂ was used to remove iodine from the dilute brine.At p H=2.0 and Eh=513 m V,the iodine content in the brine is reduced from 11.49 mg/L to 3.08 mg/L,and the iodine removal rate was 73.19%;（3）It is determined that the potential of the dechlorinated dilute brine immediately rises from 550 m V to 670 m V when the iodine ion is converted into iodine.The potential of the dechlorinated dilute brine is controlled by adding Na Cl O.When p H=1.5 and Eh=606 m V,the residual iodine content of the dechlorinated dilute brine is 2.33 mg/L,and the deiodination rate is 60.17%;（4）When Fe Cl₂ is used as reducing agent,the deiodination study was conducted by using a combined addition of starch and Fe Cl₂,under the conditions of p H=1.5,starch concentration is 0.15%,Fe Cl₂ concentration is 0.24 g/L,and reaction time is 120 min,the remaining iodine content in the dilute brine is 1.31 mg/L,and the deiodination rate reaches 83.05%.