Study On Extraction/Recovery Of Bromine From Shale Gas Wastewater By Electrochemical Oxidation

Bromine as a basic chemical raw material,its demand is growing with the development of industry,agriculture,and medical industries,prices continue to rise.Industrial bromine extraction methods mainly include the air blowing method and steam distillation method,both of them have some disadvantages.As a new bromine extraction technology,electrochemical oxidation has attracted more and more attention due to its simple process,clean products,and strong selectivity.Simultaneously,a large amount of wastewater generated in the process of shale gas exploitation contains a certain amount of bromine.Direct emission will not only cause waste of resources but also pollute the environment.Based on this,the extraction process of bromine from shale gas wastewater（SGW）by electro-oxidation was studied in this paper.To achieve efficient recovery of bromine in real wastewater and provide further theoretical support for the application of bromine extraction technology by electro-oxidation method,the influence conditions of bromine extraction process by electro-oxidation of simulated shale gas wastewater were investigated,and the process of bromine extraction by the electro-oxidation method of real shale gas wastewater was explored.Specific studies include:（1）The effects of electrode potential,electrode area,Cl-Br ratio,coexisting ions,and temperature on bromine extraction by electro-oxidation were investigated.It was found that bromine extraction from shale gas wastewater by electro-oxidation fits the pseudo-first-order reaction kinetic model.The bromine extraction yield was affected by the anode potential,and the reaction rate increased with the increase of potential in the range of 1.13-1.18 V.However,when the electrode potential reached 1.17 V,Cl^-gradually oxidized,and 1.13-1.16 V was the suitable potential range for selective bromine extraction by electro-oxidation.With the increase of electrode area,the reaction rate increases,and the unit energy consumption decreases first and then increases,the 9 cm²graphite plate was selected as the optimal area ofΦ6×14 cm³bottle for reaction.With the increase of the Cl-Br ratio,the inhibition effect of Cl^-competitive adsorption gradually increased.Coexisting ions(including Ca²⁺,Mg²⁺,K⁺,Ba²⁺,NO₃^-)had no significant effect on bromine extraction by electro-oxidation.And the increase in temperature promoted bromine extraction by electro-oxidation.（2）The experimental study of bromine extraction from real shale gas wastewater by electro-oxidation was carried out.It was found that the direct bromine extraction effect was poor due to the interference of organic matter,and the bromine extraction yield was only 25.4%at 6 h.The presence of methanol and polyacrylamide in shale gas wastewater can affect the bromine extraction process.The adhesion of organic matter on the electrode surface and the degradation of organics by hypobromic acid are two reasons leading to the poor bromine extraction effect.After advanced oxidation pretreatment of shale gas wastewater with thermally-activated Na₂S₂O₈,bromine extraction yield can be increased to 77.8%after 6 h electro-oxidation.（3）In the process of bromine extraction by electro-oxidation,the cathode can produce hydrogen by side,and the average hydrogen production at 6 h is 1.01 mmol/L.After bromine extraction,the mixture of cathode and anode was neutral,indicating that the electro-oxidation process was environmentally friendly and had good environmental benefits.