| At present,all over the world are facing different degrees of arsenic pollution,which seriously threatens human health.Electrocoagulation has been widely concerned because of its simple equipment,convenient operation,short treatment time and no additional chemical reagents.There have been many studies on arsenic removal by electrocoagulation,but they usually use inexpensive and easy-to-obtain aluminum and iron as electrode materials.Iron electrocoagulation not only brings about chromaticity problems,but dissolved iron may also stimulate the growth of bacteria,while aluminum electrocoagulation can lead to high concentration of dissolved aluminum ions in the solution due to chemical dissolution of the electrode.In this paper,the removal of arsenic was investigated by using the electrode group（aluminum anode-graphite cathode）,which is different from conventional aluminum electrocoagulation,and a new non-toxic and harmless electrode material-titanium（titanium anode-titanium cathode）.The effects of electrochemical parameters and water quality parameters on the removal of arsenic were investigated.The experimental parameters were optimized by response surface experimental design method,and the removal mechanism of arsenic was analyzed by various characterization methods.The treatment effect of electrocoagulation in actual arsenic-containing water was studied in order to provide theoretical guidance for its practical application.The main conclusions are as follows:（1）Compared with conventional aluminum electrocoagulation,aluminum-graphite electrocoagulation was able to adjust the p H of the solution and reduce the residual of total dissolved aluminum in the solution while ensuring the removal rate of arsenic.In the single-factor experimental results,a 9 mm plate spacing was chosen,taking into account arsenic removal efficiency,energy consumption and mass transfer.When the current density was increased from 1.25 A/m2 to 5 A/m2,the anode loss and total dissolved aluminum concentration increased from 0.002 k Wh and 0.33 mg/L to 0.024 k Wh and 0.50 mg/L respectively.The initial p H of the solution affected the reaction rate:neutral>acidic>basic.The presence of background electrolyte affected the removal of arsenic,removal rate:no electrolyte>Na Cl>Na NO3>Na2SO4.Response surface experimental results showed the degree of influence of each factor on the experimental results:initial p H>plate spacing>current density.Under the revised optimum process parameters（plate spacing of 9 mm,current density of 2.5 A/m2 and initial p H of 6.9）,the total arsenic removal could reach over99%.（2）The results of Al species analysis by Ferron method showed that the aluminum-graphite group contained higher Alb content than the aluminum-aluminum group,and the presence of Alb would make the system have higher positive charge.Zeta potential test results showed that the zeta potential was higher in the aluminum-graphite system,while the zeta potential in the aluminum-aluminum system showed an increasing and then decreasing trend,which was related to the p H changes.XRD analysis of the floc products showed that the aluminum-graphite system corresponds to bayerite and the aluminum-aluminum system corresponds to alumina trihydrate and bayerite.（3）The single-factor experimental results of arsenic removal by titanium electrocoagulation showed that the arsenic removal effect did not vary greatly under different plate spacing,and the total arsenic removal ranged from 97.24%to 98.82%after30 minutes of treatment.When the current density was increased from 15 A/m2 to 25 A/m2,the cost of treating 1 m3of water increased from RMB 4.41 to RMB 10.86.The rate of arsenic removal in solutions with different initial p H was different,with removal rates of:acidic>neutral>alkaline.The background electrolyte affected the corrosive performance of the titanium electrode and thus the removal of arsenic,with total arsenic removal rates of97.30%,53.93%and 8.31%for Na Cl,Na NO3 and Na2SO4 as the background electrolyte respectively.The higher the Na Cl concentration the faster the electrode corrosion rate and the faster the arsenic removal rate.The response surface experimental results showed that the influence of each factor on the experimental results:initial p H>current density>plate spacing.Under the revised optimum process parameters（plate spacing of 9 mm,current density of 15 A/m2 and initial p H of 6.4）,the total arsenic removal could reach over 99%.（4）The adsorption experiment of titanium electrocoagulation floc products showed that the floc products of electrocoagulation had adsorption effect on arsenic,and the in-situ removal of arsenic by electrocoagulation was more effective than the adsorption of floc products.FTIR and XPS analysis of the floc products revealed the presence of arsenic in the flocs produced by electrocoagulation.To investigate the source of As（III）in the As 3d patterns of XPS,HPLC-ICP-MS was used to analyze the changes of arsenic in the solution during the electrocoagulation process.The results showed that the prepared raw water contained As（III）,and As（III）was removed by flocculation and adsorption during the reaction.（5）When aluminum-graphite electrocoagulation and titanium electrocoagulation were used to treat different arsenic-containing actual water,because the actual water quality was complex and coexisted with various ions,SS and other impurities,it was necessary to increase the current density or prolong the treatment time to make the arsenic concentration meet the standard. |
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