Inveastigation Of Selective Bromine Removal/Recovery By Electrochemical Method

As an important chemical material,bromine is extracted commonly by air blow-out method and steam distillation method in industry.However,both these two methods have drawbacks such as high energy consumption,large equipment capital,high footprint and low security.Also,there is no mature new methods to replace them so far.In terms of extraction technology,electro-oxidation method is attracting more and more attention because of its low energy consumption,simple procedure and clean production.In this article,elecro-oxidation method was creatively applied to extracting bromine from concentrated seawater and underground brine,and thus,several sections in air blow-out method could be replaced.By using of the differece of standard redox potential between Br~-and Cl~-,the selective oxidation of bromide from chloride-rich solution was realized,and therefore,the separation and recovery of bromine was then achieved.In this article,the feasibilities of electro-oxidation method in the application of bromine extraction from concentrated seawater and underground brine were both verified in theory and practice,and their kinetic models were also discussed.On this basis,the effects of co-existing ions on bromide oxidation were investigated as well.Finally,the laws in bromine extraction from concentrated seawater and underground brine were studied,and their optimal operating time was also determined.The results are as follows:With the graphite electrode as the working electrode and its potential between1.0 V and 1.5 V vs.SHE(standard hydrogen electrode),the selective oxidation of bromide was feasible in theory.Chloride oxidation was difficult to occur at the selected potential(1.350 V)even though its concentration was very high,while the oxidation of bromide at three orders of magnitude lower concentration than chloride could be achieved at precisely controlled potential.That meant bromine extractions from concentrated seawater and underground brine at this potential were both feasible in practice.The bromide oxidation from concentrated seawater and underground brine both followed the second-order kinetic reaction model.In bromine extraction from concentrated seawater,due to the presence of chloride,the total conductivity of solution rose,which in turn showed a strong promoting effect on the electro-oxidation of bromide.And sulfate also showed a promoting effect for the same reason.Moreover,the presence of hardness ions such as calcium ions and magnesium ions had little effect on the electro-oxidation of bromide.In addition,the enhancement of water electrolysis at chloride concentration of 37.32 g/L leaded to not only the decrease of current efficiency but also the increase of energy consumption.And in bromine extraction from concentrated seawater,the optimal operating time may be from 4 h to 10 h.In bromine extraction from underground brine,chloride had both effects of promotion and inhibitition on the electro-oxidation of bromide.The promoting effect might result from inreasing total conductivity of solution with the increase of chloride concentration.The inhibitory effect might be due to the adsorption competition between chloride and bromide on the graphite electrode surface.Before 32.0 g/L of chloride concentration,the promoting effect was dominant.After the concentration of chloride reached 32.0 g/L,inhibition began to outweigh promotion.Energy consumption deceased with the increase of chloride concentration,and current efficiency was relatively unaffected by the concentration of chloride.And in bromine extraction from underground brine,operating time from 6 h to 10 h may be optimal in this process.