Effect Of Environmental Factors On The Surface-mediated Removal Of Tetrabromobisphenol A By Iron Based Materials

Iron is the fourth most abundant element in the earth’s crust,and a large number of iron minerals exist in nature.Iron based materials have good adsorbability,excellent redox ability,and economic and efficient restoration of the environment.Therefore,in recent years,many scholars have carried out a large number of studies on the removal of environmental pollutants by iron-based materials.Tetrabromobisphenol A（TBBPA）is the most widely used brominated flame retardant,which has been detected in the atmosphere,water,sediment,soil and other environmental media and organisms.It has lipophilic and bioaccumulative properties.In this paper,several iron-based materials were selected to study the removal of TBBPA（20 mg/L）under different environment factors,and the mechanisma of TBBPA removal at the interface of different iron-based materials were compared.The main research results are as follows:（1）Sulfate green rust（GR）was synthesized in situ by intermittent titration method,and the removal effects of in situ GR（in-GR）and ex situ GR（ex-GR）on TBBPA were compared under anaerobic and aerobic alternating environment and aerobic environment only.The results showed that both in-GR and ex-GR could adsorb～100%of TBBPA.The removal efficiency of in-GR system was higher than that of ex-GR system by methanol elution of TBBPA at the interface.After 48h of anaerobic and 24h of aerobic,only 20%of TBBPA existed in in-GR system,while 30%of TBBPA remained untransformed in ex-GR system.Through FTIR analysis,in-GR and ex-GR are mainly converted to magnetite and goethite,while the characteristic peak of ex-GR system was more obvious.The reduction products and oxidation products of in-GR system were detected by liquid mass spectrometry in the anaerobic and aerobic alternating environment,and the possible degradation path of TBBPA was further analyzed.Compared with the aerobic system only,it was found that the removal efficiency of TBBPA in the anaerobic and aerobic alternating environment in-GR and ex-GR systems was higher and the yield of·OH in the system was slightly higher.By XRD detection,it was found that only the aerobic system GR was mostly converted into magnetite.However,the presence of humic acid（HA）can inhibit the removal of TBBPA by in-GR under anaerobic and aerobic alternation.（2）Zero-valent iron（ZVI）,ferrous sulfide（Fe S）and iron oxide（Fe₃O₄）were prepared by physical ball milling or chemical precipitation method.It was found that the TBBPA in solution of these iron based materials could be 100%adsorbed on their interfaces at first.After the elution of TBBPA at the interface,it was found that ZVI had the best removal effect on TBBPA in the anaerobic and aerobic system,and the removal rate of TBBPA was higher.Compared with Fe₃O₄ system and Fe S system under aerobic condition only,it was found that the Fe S prepared by ball milling method had the best TBBPA removal effect,reaching 71%removal rate,and produced more·OH.However,in the presence of HA,by detecting the debromination products of TBBPA in the ZVI system,it was obvious that HA could inhibit the removal of TBBPA by ZVI.With the increase of HA concentration,the removal rate of TBBPA decreased and the debromination products decreased.（3）Based on the above findings that HA has a significant effect on ZVI’s removal of TBBPA,in order to gain more insight into deposition behaviors of environmental matrixes on ZVI interfaces as well as the properties of deposited layers,quartz crystal microbalance with dissipation（QCMD）equipped with ZVI-coated sensor prepared by spraying ZVI suspension was applied to investigate the deposition processes of co-present HA and calcium ion（Ca（II））on ZVI interface,including dosing sequence of HA and Ca（II）,and the effects of Ca（II）concentrations.A more stable layer with larger mass was deposited on ZVI surface when HA was initially introduced into the reaction system than that formed when Ca（II）was first injected.The deposition of Ca（II）was promoted after HA deposition,whereas HA deposition was less significant after Ca（II）deposition,which could be attributed to the difference in the structure composition of outer deposition layer.In addition,it was found that both of the deposition rate and layer mass were increased with the increasing Ca（II）concentration from 10 to 200 mg/L.In particular,the value of change in dissipation（ΔD）gradually decreased when Ca（II）concentration increased from 10 to 100 mg/L,indicating the more rigid layer formed.However,if continually increasing Ca（II）concentration to 200mg/L,ΔD presented an increasing tendency,with an indication of a more loose and softer conformation of the deposition layer.To sum up,it was found that the dynamic and in-situ process of ZVI passivation layer formation could be monitored via QCMD technique,and the characteristics of ZVI adsorption layer could also be provided.