Improved Technology On Capacitive Deionization For Desalination Performance

With more and more people realizing the global shortage of fresh water resources,capacitive deionization(CDI)technology has become a new widely concerned desalination technology due to low energy consumption,low-cost and no secondary pollution.This paper mainly focuses on the poor desalination efficiency of CDI technology,proposes the technological means,and optimizes the process parameters to further improve the desalination performance of CDI.Firstly,in order to solve the problem of co-ion effect of CDI technology,ion-exchange membrane was introduced.Meanwhile,nickel foam was used to replace graphite current collector to enhance the desalination performance by improving the contact conductivity.In exploring electrode material,voltage and brackish stream's flow rate to membrane capacitive deionization(MCDI)desalination performance,without any carbon materials(ACO)and three different activated carbon(AC1,AC2,AC3)to treat brine,the electrodialysis process simulated by AC0 was significantly worse,indicating that electroadsorption process played a major role in the MCDI desalination process.The phenomenon with the highest desalination efficiency of AC1 was consistent with the results of their specific surface area.It was concluded that the adsorption performance of electrode material was closely related to the specific surface area.As the driving force,1.6 V is more suitable voltage parameter on the premise of avoiding side reactions.If the brackish flow rate is too fast or low,the electroadsorption efficiency will be worse due to the shorter hydraulic residence time and the desorption of ions adsorbed in electrode pores.Therefore,the optimal flow rate is 10 mL·min-1.The adsorption capacity of electrode was 9.0 mg·g-1 when NaCl aqueous solution of 500 mg·L-1 was treated under the optimal parameters.The adsorption and desorption experiments show that the existence of ion exchange membrane improves the regeneration performance.Then,due to the problem of intermittent desalination by MCDI technology,the flow electrode of serpentine channel was designed to replace the plate electrode.It can enhance the desalination performance by avoiding the desorption process and increasing the utilization rate of electrode material.The 1000 mg·L-1 NaCl solution was treated by the flow electrode capacitive deionization(FCDI)desalination system,and the electrolyte concentration,electrode flow rate,voltage and flow rate of brackish stream parameters of the desalination system were optimized to further improve the desalination performance.The results show that the concentration of electrolyte affects both resistance and concentration polarization,and the optimal concentration is 10.0 g·L-1.Voltage is positively correlated with desalination efficiency,but 1.6 V was determined to the appropriate voltage parameter by considering energy consumption and charge efficiency.Due to the close relationship between flow rate of brackish stream and residence time,the optimal flow rate is 10.0 mL·min-1.When the electrode flow rate was 36 mL·min-1,the average desalination rate was 0.35 ?g·cm-2·s-1,indicating that the technique improves the processing capacity of MCDI.Finally,to solve the problem of high internal resistance caused by discontinuous electrode materials in FCDI technology,an electric catalyst was innovatively introduced to couple FCDI technology with electrochemical reaction and enhance the desalination performance of FCDI by improving the ion migration rate.The novel FCDI technology with Co3O4 and Co(OH)2 as catalysts was compared with the traditional FCDI technology by desalination experiment on 1000 mg·L-1 NaCl brine solution.The desalting ratio is increased by 25%as a result of the novel FCDI technology.At the same time,the energy consumption decreases,while the charge efficiency increases.Furthermore,the experimental parameters of the novel FCDI technology were optimized,and the optimal voltage,electrolyte concentration,flow rate of brackish stream and electrode were determined to be 1.6 V,5.0 g·L-1,12.5mL·min-1 and 36 mL·min-1.Under these parameters,the average desalination rate was 0.45 ?g·cm-2·s-1.