Elimination Of Vanadium From Wastewater Using Zero-Valent Iron Activated By Ball Milling: Performance And Mechanism

Zero-valent iron（ZVI）is considered as a promising material for pollutant remediation owing to its high reduction capacity,environmental friendliness,and cost-effectiveness.For the ZVI/H₂O system,the effect of decontamination is highly dependent on the corrosion evolution of ZVI.The interface electron transfer between the Fe~0 core and contaminants is a crucial process.Besides,the surface electrical conductivity and interface structure of ZVI is also critical to ZVI reactivity.Nonetheless,surface passivation usually occurs in the synthesis and application process because of the accumulation of oxides and the organic layer.The oxidation of shell with a high steric hindrance influences the performance of ZVI seriously.Notably,the activation effect of improving surface properties of ZVI was more significant than the simple decrease of the size to increase the specific surface area.The ball-milling technology,a highly efficient and cost-effective method,had excellent application prospects for overcoming passivation issues of ZVI to enhance the decontamination efficiency.Therefore,in this work,we investigated the influence and mechanism of the introduced process control agent（PCA）,technological parameters and different environmental factors to ZVI^bm on the removal of V⁵⁺.The main conclusions are as follows:（1）During the ball milling process,a mechanochemical reaction may have occurred between Na Cl and ZVI,so that the oxide shell on the surface of ZVI was replaced by Na Cl and Fe Cl₂,thus realizing the physicochemical modification of the ZVI surface.（2）Under near-neutral conditions,the removal rate of V⁵⁺by ZVI^bm has nearly an order of magnitude higher than that of ZVI.Besides,ZVI^bm also enables efficient removal of V⁵⁺over a wider p H range（3-9）.（3）The contamination removal reaction in the initial stage can occur immediately without induction time,while as the reaction progresses,the surface passivation effect intensifies,resulting in slow subsequent reaction stages.（4）The enhanced agglomeration effect and significantly reduced surface pore volume of ZVI^bm due to excessive energy input weakens the reactivity of ZVI^bm.In contrast,adding Na Cl during ball milling not only effectively alleviates the agglomeration of ZVI^bm,but also increases the specific surface area of the product and generates more active sites.（6）From the perspective of economy and effect,the optimal conditions for ball milling to activate ZVI are at 300 rpm,4 h,Na Cl 3 wt.%.The optimal conditions for the removal of V⁵⁺pollution are that the concentration of V⁵⁺solution is 10 mg/L,p H=7,25℃,and 5.0 g/L.Thermodynamic analysis shows that the reaction between ZVI^bm and V⁵⁺is endothermic.Kinetic model and adsorption isotherm model indicate that the adsorption rate is mainly controlled by chemisorption,which is a multi-layer heterogeneous adsorption.（7）The removal of V⁵⁺in wastewater by ZVI^bm is mainly based on reduction.