Determination And Removal Technology Of Iodine In Brine During Ionic Membrane Caustic Soda

Ionic membrane production of caustic soda is the mainstream technology in the world's alkali industry.Among them,the ionic membrane is expensive,but the presence of iodine in the raw material brine will have a serious impact on the service life of the ionic membrane,thereby increasing the cost of the alkali.The iodine in the brine initially begins in the form of I-,but the I-will be oxidized to IO3-,IO65-,etc.during electrolysis,which is the predominant form of iodine in the dilute brine.As the number of times of dilute brine recycling increases,these ions will accumulate,resulting in higher levels of iodine in the secondary brine.When the iodine concentration is higher than 0.2 mg/L(in terms of I-),it will combine with Na+,Ba2+,Mg2+,Ca2+,Sr2+ and other ions to produce indissolvable precipitates such as Ba5(IO6)2,Mg5(IO6)2,Ca5(IO6)2,Sr5(IO6)2,etc.deposited on the ionic membrane,resulting in increased cell voltage,reduced current efficiency and increased energy consumption.Therefore,accurate analysis and detection of the iodine content in the process brine,the use of appropriate removal method to remove iodine in the process brine,is of great significance for the protection of the ion membrane.This task establishes the determination method of iodine content in brine prepared by ionic membrane production of caustic soda process,through the discussion of improved ceric sulfate catalytic spectrophotometry and iron thiocyanate-nitrite spectrophotometry.The composite adsorbent adsorption method was used to remove iodine from dechlorinated brackish brine and high brine,and most of the iodine contained in these two brines was successfully removed.The main research results of the thesis are as follows:(1)An analytical method for the iodine content in the chlor-alkali process brine was established.The method has high sensitivity and accuracy,and the detection limit is 0.3 ?g·L-1,and the lower limit of determination is less than 1.0 ?g·L-1.The recovery experiment of the secondary brine and dechlorinated brackish water in the production process was carried out.The recovery rate was in the range of 95.00%?104.0%,and the relative standard deviation(RSD)was less than 8.0%.In addition,the high concentration of sodium chloride in the brine has no significant effect of this measurement.(2)The deiodination technology of dechlorinated pale salt water was studied.And the deiodination conditions were determined by experiments are:adjust the pH value of the solution to about 2.5,after reacting for 30 min,add 1.8 mL of a reducing agent solution with a concentration of 1.0 g/L,react for 40 min,then pass into the composite adsorbent adsorption column,flow out at a flow rate of 5 mL/min.After removal,the iodine content in the solution is about 0.31 mg/L,and the iodine removal rate is above 90%.(3)The deiodination technology of high brine in power plants was studied.And the deiodination conditions were determined by experiments are:adjust the pH value of the solution to about 2.0,add 0.3 mL of 5%oxidant solution to 100 mL of high brine,after oxiding for 50 min,pass into the composite adsorbent adsorption column,then flow out at a flow rate of 6 mL/min.After removal,the iodine content in the solution is about 0.04 mg/L,and the iodine removal rate is above 95%.