Preliminary Study On The Combined Treatment Of Heavy Metals And Organic Matter In The Sedum Sedum Juice With Chemical Precipitation And Electric Fenton Method

Sedum plumbizincicola,a hyperaccumulator,has been potentially used in the remediation of cadmium?Cd?polluted soil.As a result of containing a lot of heavy metals in the biomass after phytoremediation,it is necessary to dispose the biomass for avoiding secondary pollution.At present,the most economic and feasible method to dispose S.plumbizincicola biomass is thermal disposal?incineration?.In order to make the biomass fast dehydration chopping and squeezing are used to meet the demand of thermal disposal.However,as this process would produce plenty of juice containing a lot of heavy metals and organic materials,it cannot be irrigated unless be treated to achieve emission standard.This study combines chemical flocculation precipitation and Electron-Fenton?EF?to treat S.plumbizincicola juice.The impacts of pH,dosage of PAC and agitation speed on removal of Cd and chemical oxidation demand?COD?are studied in process of flocculation precipitation,then orthogonal test is used to optimize the condition of reaction.After treatment of flocculation precipitation,EF is utilized to dispose the juice further.Similarly,the impacts of pH,current density and H₂O₂ dosage on removal of Cd and COD are researched by single test.Furthermore,response surface analysis?RSA?is used to study the interaction and order of impact among the three factors.Besides,the chemical fraction of heavy metal is significant for its removal rate and mechanism.The concentrations of different chemical fraction of heavy metals in S.plumbizincicola tissues were studied by sequential extraction procedures;the change of ionic Cd in S.plumbizincicola juice is acquired by Cd ion-selective electrod?ISE?;Visual MINTEQ is used to calculate speciation of heavy metals before and after EF.The result of flocculation precipitation shows that with the rise of pH,PAC dosage and agitation speed,both removal rate of Cd and COD increase first and then decrease.The optimal conditions of flocculation precipitation are pH 10,PAC 2%and agitation speed at 400 r·min^-1.At this condition,the concentration of Cd,Pb,Zn and COD decrease from 1.25?1.18?92.60?51980 mg·L^-11 to 0.23?0.27?22.7?23376mg·L^-1,and the removal rate of Cd,Pb,Zn and COD are 81.9%,77.0%,76.4%and55.0%,respectively.The result of EF shows that,with the increase of pH,the removal rate of Cd is gradually increased,while that of COD is decreased;with ehance of both current density and H₂O₂ dosage,removal rate of Cd and COD increase first and then decrease.Moreover,both the impact order of three factors on the removal rate of COD and Cd is pH>current density>H₂O₂ dosage.Furthermore,the adding of H₂O₂in EF process can greatly enhance the removal rate of Cd and Zn.After treatment through flocculation precipitation,the juice is disposed by EF at the condition of pH=5,current density=15 mA?cm²,and H₂O₂ dosage=9 g?L^-1.In this condition,the concentration Cd,Zn and COD decrease to 0.0011?0.0075?9497mg·L^-1,the removal efficiency of Cd,Zn and COD achieve 99.45%,99.90%and 55.50%.Moreover,the consumption electric energy of EF is about 0.1 KWh?L^-1.These results of speciation analysis show that NaCl,HAc and HCl soluble forms were main fractions for Cd and Pb in plant tissues,while water and ethanol soluble forms which possess high chemical activity were main fractions for Zn.Furthermore,Cd²⁺concentration accounted for roughly 20%of the total Cd in the juice,while the dominating forms of Cd were non-ionic.Besides,most of Cd and Zn in the juice are organic complex and inorganic complex,which cause Cd and Zn cannot be further removed by flocculation precipitation.The mechanism of Cd and Zn removal of EF is that OH oxides organic materials,which can release Cd²⁺and Zn²⁺into the solution.Furthermore,OH may possess the merit of destroying complexing structure.In total,most of heavy metals in the juice are non-ionic,which determines that traditional chemical precipitation-a economical method-can not remove these heavy metals effectively.While the combination of chemical precipitation and EF can thoroughly remove heavy metals in the juice.Moreover,this method can also remove some organic materials.