Research On Rice Husk Based Capacitance Carbon For Capacitance Deionization Technology

Seawater and brackish water desalination have emerged to become the strategic supply of water for many countries around the globe,especially for the Arabian Gulf countries.Though technological advancement in multi-stage flash distillation(MSF),reverse osmosis(RO)commenced with great improvement in desalination cost reduction and increased flux and selectivity with reduced fouling during the past decades,there are still high energy consumption,secondary pollution,cost and other issues.Among all of the conventional energy-intensive desalination technologies,capacitive deionization(CDI)is regarded as a promising desalination technology due to its unique properties of low electricity consumption and environmental friendliness.CDI utilizes electrosorption process with highly porous carbon-based electrodes to remove charged dissolved substances from aqueous solution through external electric field.Notably,CDI does not require a high pressure pump in operation phase,and its energy can be recovered during desorption process.As a source of low-cost,abundant and raw materials,the rice husk is made into the rice husk based capacitance carbon(RHC)with high specific surface area and specific capacitance characteristics.Therefore,this paper aims at the realization of RHC for the application of capacitance deionization technology,exploring the principles and application conditions of RHC for CDI technology.Firstly,RHC is characterized with various porous structure and high specific surface area,which are tested by BET,SEM and other physical analysis methods.RHC exhibits a regular rectangle in the cyclic voltammetry test,showing well capacitance and owning the basic property as CDI electrode material.The basic conditions that affect the performance of CDI are studied by controlling single factor variables(influent flow rate,influent solution concentration and operation mode).The low flow rate is beneficial to the full electrostatic adsorption of ions.The ohmic resistance of solution with the higher concentration is lower,which can improve the adsorption capacity of the electrode material.The constant current-voltage mode is put forward by comparing the advantages and disadvantages of different operation modes,which can satisfy the adsorption capacity and reduce energy consumption effectively.The adsorption capacity of RHC under 1.0V and 10 mM NaCl solution was 9.7 mg/g and RHC as CDI electrode material is competitive with commercial carbon cloth(5.85 mg /g)and the corresponding literature data.Secondly,the problem that the carbon powder on the electrode surface tend to fall off is found in the system.We present the production method of RHC-carbon cloth composite electrode to solve that.A layer of carbon cloth is bonded over the RHC electrode,which can inhibit powdering off and increase the quantity of carbon per area effectively.Correspondingly,the removal rate of ion was improved from 34.91% to 72.32% under 1.0V and 5mM NaCl solution.In the practical application,the deionization process will be used to treat the aqueous solution of different components.Finally we study the processing ability of CDI for different anions and cations.The hydrated radius and the number of charges of ions are important parameters for ions adsorption.The small hydrated radius is favorable for ion distribution,and the electrostatic force between the ions with high charge and the electrode is strong.The parameter Z(the ratio of ion hydrate radius and the number of charge)expresses the common effect of the two factors.The smaller the Z is,the greater the equivalent adsorption capacity(the product of the ion adsorption capacity and the number of charges)is.At the same time,it is found that the RHC-carbon cloth composite electrode was consistent with RHC electrode on the influence of Z on adsorption capacity.