Study Of Valorization Of Seawater Concentrate Via Electrodialysis And Bipolar Membrane Electrodialysis

Nowadays,reverse osmosis(RO)as a kind of advanced membrane technology is widely applied in water treatment,seawater desalination,materials concentration,etc.However,its application is effected by the treatment of RO concentrate,to a certain extent.Based on this,in this paper,electrodialysis(ED)and bipolar membrane electrodialysis(BMED)technology was used for the valorization of seawater concentrate.In this paper,monovalent-selective electrodialysis concentrated seawater concentrate to produce coarse salt,which is researched,and the technical feasibility is verified.In the laboratory condition,an ED system which is divided into three-stage operation to treat seawater concentrate.Monovalent-selective ED as the first stage of system was used to separate multivalent ions;ordinary ED as the latter two-stage of system was used to concentrate brine to produce coarse salt after evaporation process.Two types of monovalent-selective membrane(CIMS/ACS,CSO/ASV)were used to compare the separation performance of divalent ions under the same conditions.Results indicated that CIMS/ACS stack is superior to CSO/ASV stack in the case of concentration and desalination performance either the final concentration of divalent ions or the separation efficiency.In addition,lowering current density is effective to improve the selectivity in monovalent ions to divalent ions with either the CIMS membrane or the CSO membrane.Then,considering the current efficiency and energy consumption,it shows technical feasibility to treat seawater concentrate for the production of coarse salt with the purity of?85%under the ultimate optimal condition(4 mA/cm2,CIMS/ACS stack,desalination rate of 70%of the first-stage ED operation).In addition,on the basis of first work,a new scheme by coupling BMED and ED technology was designed to realize the valorization of seawater concentrate and obtain a series of target products(acid,base,salt).Specific scheme was shown below:chemical precipitation as the first step was used to remove a part of Ca2+,Mg2+ ions,CIMS/ACS stack was applied to remove divalent ions further as the second step to obtain NaCl abundant brine,pellet reactor was employed to remove divalent ions finally as the last step in order to fulfill the requirement of the follow-up experiment.Besides,a part of acid and base of in situ production by BMED can be used as precipitant of the first step as well as the third step.The effects of types of bipolar membrane(FBM,BP-1),current density,and feed concentration were investigated during BMED experiment.It is suitable to attain acid/base with a purity of-95%/-85%under the ultimate optimal condition(10 mA/cm2,a feed conductivity of 100 mS/cm,BMED stack equipped with BP-1 membrane),meanwhile,energy consumption(1.75 kWh/kg)and current efficiency(70%)are best.In addition,at the current density of 10 mA/cm2,a purity(?92%)of coarse salt was obtained.Finally,process economic was evaluated,the total process cost was estimated at $0.50/kg at optimal condition(10 mA/cm2),believing that the operation cost and energy consumption will be significantly reduced with the expanding of the scale of production,hence,it predicted that it was technological feasible for the production of acid and base by BMED.