| The accurate determination of complexing agent helps to prove the type of metal complexes in electroplating wastewater in order to select suitable treatment method.Many analytical methods are used to determinate the complexing agent,but the influence of metal ions and other complexing agents on the analytical results are seldom considered.This article investigated the influence of metal complexation of nickel-oxalic acid on the analysis of oxalic acid by high performance liquid chromatography(HPLC),the influence of three complexing agents on EDTA analysis by ion chromatography and the influence of nickel ions on EDTA analysis by semi-quantitative test paper.The experimental results showed that nickel ions had significant influence on the quantitative analysis of oxalic acid,and hydroxide precipitation eliminated the metal complexation effectively.Sodium citrate and oxalic acid had little impact on the quantitative analysis of EDTA while sodium gluconate had great influence.Semi-quantitative test paper was used to preliminarily determine whether EDTA existed in electroplating wastewater,but the metal complexation of nickel-EDTA would interfere with the identification of EDTA.There are many mature treatment methods for electroplating wastewater containing high-concentration metal ions.However,for electroplating wastewater containing low-concentration metal ions,the common treatment method is too ineffective to reach the emission limit of electroplating pollutant because of the low-concentration metal complexes formed by metal ions and stable complexing agents.Therefore,advanced oxidation processes are considered to treat low-concentration metal complexes.The research object was low-concentration Ni-EDTA complexed by 5.0mg/L nickel ions and 25.0mg/L EDTA.Ozone method,heat activated persulfate,Fenton method,UV/O3,UV/persulfate,electrocoagulation and other advanced oxidation processes were used.The influence of initial pH,reaction time,dosage and other factors on the removal of Ni-EDTA was further researched and the optimal experiment condition was obtained by comparing different methods,which helped to select proper treatment method of real wastewater.For the ozone method used to treat low-concentration Ni-EDTA in simulated wastewater,the concentration of nickel ions decreased with the increase of reaction time,ozone concentration and initial pH.The optimal experiment conditions were as follows:initial pH was 11.0,reaction time was 5min,ozone concentration was 15mg/L,and the removal rate of Ni-EDTA was 98.3%.For the heat activated persulfate method used to treat low-concentration Ni-EDTA in simulated wastewater,with the increase of reaction time,sodium persulfate dosage and temperature,the concentration of nickel ions increasingly decreased.The optimal experiment conditions were as follows:reaction time was 60min,molar ratio of persulfate and EDTA was 25:1,temperature was 90?,initial pH was 4.6,the removal rate of Ni-EDTA was 98.4%.For Fenton method used to treat low-concentration Ni-EDTA in simulated wastewater,the concentration of nickel ions decreased with the increase of H2O2 dosage,nFe2+:nH2O2 and reaction time.The optimal experiment conditions were as follows:initial pH was 2.5,hydrogen peroxide dosage was 180mg/L,nFe2+:nH2O2 was 1:1,reaction time was 60min,and the removal rate of Ni-EDTA was 98.7%.When using UV/O3,UV/persulfate,electrocoagulation and other advanced oxidation processes to treat low-concentration Ni-EDTA in simulated wastewater,the performance of UV/persulfate had reached the emission limit of electroplating pollutant and the removal rate of Ni-EDTA was up to 100%.The optimal experiment conditions were as follows:12W of UV lamp,molar ratio of persulfate and EDTA was 25:1 and reaction time was 60min,and initial pH was 3.8.The performance of ozone method and heat activated persulfate method,Fenton method and UV/persulfate for low-concentration Ni-EDTA in simulated wastewater is good.The data results of these four methods have reached emission limit of electroplating pollutant.Under the optimal experiment conditions,different advanced oxidation processes are ordered according to the removal rate of Ni-EDTA:UV/persulfate method>Fenton method>heat activated persulfate method>ozone method>UV/H2O2>electrocoagulation method>UV/O3>UV method>sodium hypochlorite method>hydrogen peroxide method. |
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