Removal Of Heavy Metals From Desulfurization Wastewater By Hybrid Zero-valent Iron System

Desulfurization wastewater comes from wet desulfurization of boiler flue gas,which contains many harmful heavy metals such as lead,cadmium,selenium,and arsenic.Because these pollutants pose a serious damage to living organisms,desulfurization wastewater need to be properly treated.This experiment takes the flue gas desulfurization wastewater from a power plant of Datang Environment Company as an example to study the feasibility of hybrid zero-valent iron system（ZVI/Fe3O4/Fe（Ⅱ））.The effects of Fe²⁺ concentration,initial p H,hydraulic retention time,dissolved oxygen,organic pollutants and other factors on the removal efficiency of heavy metals are investigated.Combined with scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray electron spectroscopy（XPS）and other characterization methods,the reaction mechanism is studied.The results are as follows:The hydraulic retention time and Ca²⁺ concentration have a negligible effect on the treatment of simulated wastewater.Most heavy metals can be quickly removed in solution with high Ca²⁺ concentration.The initial concentration of heavy metals,initial p H and organic ligands（humic acid）are significant factors that affect the performance of the hybrid zero-valent iron system.The removal rates of Cd（Ⅱ）,Mn（Ⅱ）,Cr（VI）and Se（IV）with high concentrations reduce from 95% to 88%,35%,70% and 85%,respectively.p H has a great influence on the removal of Cd（Ⅱ）,Mn（Ⅱ）and Cr（VI）.The removal rate of Cd（Ⅱ）and Mn（Ⅱ）increases with the increase of p H.In the system with added humic acid,the removal rate of Cu（Ⅱ）,Hg（Ⅱ）,Cr（VI）and Se（IV）by hybrid zero-valent iron significantly reduce.As（Ⅲ）,Pb（Ⅱ）and Cr（VI）are relatively less affected by humic acid.Compared with the system without adding humic acid,the removal rate of As（Ⅲ）,Pb（Ⅱ）and Cr（VI）drops by 10-20%.XPS spectrum analysis showed that the reaction of hybrid zero-valent iron with common heavy metals mainly involves reduction,complexation,electrostatic attraction and co-precipitation.Cr（VI）,As（Ⅲ）,Se（IV）and other high-valence heavy metals can be removed through synergies.For complex actual wastewater systems,using the smaller iron powder particle size can effectively increase the removal rates of Cd（Ⅱ）,Mn（Ⅱ）and Cr（Ⅲ）.Compared with Fe²⁺ concentration,the change of dissolved oxygen concentration will have a greater impact on the system.In a system with low dissolved oxygen concentration,the removal of Cu（Ⅱ）,Cd（Ⅱ）,As（Ⅲ）and Se（IV）can reach equilibrium in a shorter time.