Study On Removal Of Arsenic From Water By Electrocoagulation

The removal of arsenic in water is one of the most active research issues.The electroflocculation method has received widespread attention in the treatment of arsenic pollution in water because of its simple device,high processing efficiency,low energy consumption,small footprint,low cost,and wide application range.Existing researches mostly focus on arsenic removal efficiency,removal kinetics and power consumption.The mechanism of electroflocculation removal of arsenic is still lacking,especially the influence mechanism of coexisting interfering substances in the water on the removal of arsenic is still unclear.This paper systematically studies the kinetics of arsenic removal in the process of electroflocculation under different conditions,focusing on the changes of iron morphology and combining it with the removal of arsenic,to comprehensively and deeply understand the process of arsenic removal by electroflocculation and the interference factors Influence Mechanism.In order to improve the efficiency of arsenic removal by electricflocculation,provide theoretical guidance for the design of interference elimination measures.Firstly,the electrode materials,current intensity and reaction p H conditions were optimized.The results show that the iron electrode,aluminum electrode and copper electrode can effectively remove As（Ⅴ）,and the iron electrode has the best effect.In the process of electrocoagulation with iron electrodes,the removal efficiency of As（Ⅴ）increases with the increase of current intensity.When the current intensity is 3 m A and the p H is in the range of 5.0 to 9.0,the current efficiency reaches 90.5 to 116.4%.As（Ⅴ）with an initial concentration of 400μg/L can be reduced to less than 10μg/L in1 hour.The removal efficiency of As（Ⅴ）is less affected by p H.When the p H is increased from 5.0 to 7.0,the alkaline conditions are more conducive to the oxidation and precipitation of Fe²⁺,the amount of insoluble iron increases,and the removal rate of As（Ⅴ）increases.When the p H was further increased to 9.0,due to the formation of Fe（OH）₄^-anion complex,the proportion of insoluble iron slightly decreased,and the removal rate of As（Ⅴ）also decreased.Although the removal rate of As（Ⅴ）is slow when the p H is too low or too high,the final removal efficiency is roughly equivalent in the range of p H 5.0-9.0,indicating that the electroflocculation method can work effectively in a wider p H range.On this basis,the effects of co-existing oxyacids（phosphate,silicate）,humic acid（HA）and calcium ions on the removal of As（Ⅴ）by electroflocculation were further studied.It was found that the oxygen-containing anion phosphate and silicate have significant inhibitory effects on the process of electroflocculation removal of As（Ⅴ）.In the p H range of 5.0-9.0,the higher the phosphate/silicate concentration,the lower the As（Ⅴ）removal rate.This is because phosphate and silicate have similar chemical properties as As（Ⅴ）and can compete with As（Ⅴ）for adsorption sites.Phosphate and silicate have no significant effect on the distribution of iron morphology during electroflocculation.HA has a strong inhibitory effect on the removal of As（Ⅴ）by electroflocculation.On the one hand,HA can compete with As（Ⅴ）for adsorption sites.On the other hand,HA can form Fe（III）-HA complexes with Fe（III）to suppress the formation of iron oxide/hydroxide precipitates.When the silicate/HA coexists with calcium ions,the removal rate of As（Ⅴ）is greatly improved compared to when it exists alone,but the As（Ⅴ）removal rate does not change much when phosphate and calcium ions coexist.Calcium ions can significantly reduce the inhibitory effect of HA on the formation of iron oxide/hydroxide precipitates.In order to further explore the mechanism of electroflocculation removal of As（Ⅴ）and the influence mechanism of coexisting substances.XRD and FTIR were used to analyze the products of electroflocculation solidified body.The results show that:in the range of p H 5.0-9.0,the solid products produced by electrolysis mainly exist in the form of Lepidocrocite,Goethite and Magnetite,and with the increase of p H,the content of Lepidocrocite decreases and the content of Goethite and Magnetite increases.In the presence of phosphate alone,the content of Lepidocrocite increses.When silicate is present alone,the content of Lepidocrocite decreases.For HA,although it affects the yield of precipitation,it does not show a significant effect on the crystal form of precipitation.Calcium ions can promote the formation of more stable Goethite and Magnetite precipitates,thereby reducing the impact of silicate or HA on As（Ⅴ）removal.In the presence of phosphate,the precipitated crystal form is basically not affected by calcium ions.Therefore,when calcium ions coexist with phosphates,calcium ions have less promoting effect on the removal of As（Ⅴ）.Finally,we verified the application of the electro-flocculation method in actual water bodies.Use tap water,river water and groundwater to conduct electroflocculation experiments.Although the water quality parameters of different water bodies are different,the final removal rate is different,but by changing the reaction conditions,the As（Ⅴ）content can reach the drinking water standard.