Study On Regeneration Of Iron Base Complex Denitration Liquid

Ferrous chelates can effectively absorb NO from flue gas,which is a potential efficient way to control NOx pollution,but the existence of oxygen in flue gas can oxide ferrous ion into ferric iron,making the chelates lose the ability of absobing NO,which makes it diffulcult for industrial application of NOx controlling,so it needs to find a way to reduce ferric iron to ferrous ion for ferrous chelates regeneration.Therefore,preventing ferrous from being oxidized and promoting the reduction of ferric iron is an important content of the denitration technology.This paper investigates direct electrochemical reduction progress and electrochemistry cooperating with reductants reduction progress of ferric iron chelates.In the study of direct electrochemical reduction progress,this paper explores the effects of operating voltage,current density,pH of cathode electrolyte,Fe(Ⅲ)and the ligand concentration on the direct electrochemical reduction process of Fe(Ⅲ)TEA/Fe(Ⅲ)-EDTA,and also explores kinetic study of Fe(Ⅲ)EDTA/Fe(Ⅱ)EDTA on graphite electrode and Fe(III)TEA/Fe(II)TEA on stainless steel electrode.In the study of electrochemistry cooperating with reductants reduction progress,this paper firstly investigates the synergy between electrochemi-stiy and reductants,and analyses the reason.Then this paper investigates electrochemistry cooperating with Na2S2O4,Na2SO3 and Na2S reduction progresses,and investigates the effects of voltage,pH of cathode electro-lyte,reducting agent concentration on reduction progress.At last,this paper studies the removal efficiency of NO by Fe(III)L liquid after regeneration and analyses the absorption products.Experiments are done in H type electrolytic cell with cation membrane.The results showed that in direct electrochemical reduction,reduction rate of Fe(III)EDTA rose first and then declined when potential rose from 3 V to 8 V,and current density had the same effect when it varied from 0.6 to 1.9 mA·cm-2,increasing Fe(III)EDTA concentration was in favour of reduction rate when its concentration rose from 0.01 mol·L-1 to 0.025 mol·L-1 with potential of 6 V.The cyclic voltammogram indicated that the electrode reaction process of Fe(III)EDTA/Fe(II)EDTA on graphite electrode was electrochemically reversible,and the reduction diffusion coefficient Dr was 1.47×10-6 cm2·s-1,the oxidation diffusion coefficient Do was 3.19×1 0-7 cm2·s-1,the electron number n closed to 1.Fe(III)TEA had better reduction rate in alkaline condition,increasing operating voltage or current density was helpful for reduction when the operating voltage varied from 6 V to 14 V and the current density varied from 0.9 mA cm-2 to 1.8 mA·cm-2,Adjusting pH of cathode electrolyte from 6 to 11,reduction rate of Fe(III)TEA rose.Increase of Fe(III)or TEA concentration helped to increase reduction rate.Reduction rate of Fe(III)TEA was better when the cathode electrode was stainless steel wire not that Stainless steel sheets under same conditions.In the study of Fe(III)EDTA reduction by electrochemistry cooperating with reductant,the results showed that reduction by electrochemistry cooperating with reductants were better than single reductant or electrochemistry reduction.The potentiometric titration curve indicated that a strong reductant sodium hydrosulfite was produced by alkaline sodium hydrosulfite under the influence of current.Further study indicated that increase of operating voltage or sodium hydrosulfite concentration was in favor of reduction rate.When initial pH of cathode electrolyte varied from 6.7 to 9.5,reduction rate at 9.5 was the best,and reduction rate of Fe(III)EDTA increased not obviously.When electrochemistry cooperated with sodium sulfite,HSO3-could be reduced to S2O42’ in the electrolysis process,increase of sodium sulfite concentration promoted reduction,neutral cathode electrolyte was the optimal condition.When electrochemistry cooperated with sodium sulfide,increase of operating voltage helped reduction progress,reduction rate rose first and then declined with increase of sodium sulfide concentration or pH of cathode electrolyte.The results also showed that electrolysis promoted absorption of NO by Fe(II)EDTA under aerobic condition.When 0.02mol·L-1 Fe(III)EDTA was reduced for 40 minutes,and then absorbed NO,the initial removal efficiency of NO can be up to 50%,and the removal efficiency of NO with electrolysis during absorption was 15%higer than non-electrolysis progress.NO was transformed into NO2-and NO3-after being absorbed by ferrous chelates,and it could be converted into NH4+ by electrolysis or sodium hydrosulfite reduction.