Weak Magnetic Field Drive Cr(Ⅵ)/As(Ⅴ) Removal By Zero-Valent Iron: The Efficiency

With the development of industry,chromium and arsenic pollution in industrial waste water as an environmental issue has drawn more and more attention.A certain concentration of Cr（Ⅵ）and As（Ⅴ）can cause the human body acute or chronic poisoning;indiscriminate discharge in natural water system is bound to affect the health and safety of humans,animals and plants.Currently,the treatment methods of Cr（Ⅵ）-contaminated water mainly include reduction,coagulation,adsorption,ion exchange,electrochemical,and membrane separation,etc.There are problems that low processing capacity,complex operation process,and are easy to cause secondary pollution.This thesis proposed a new technology to strengthen the zero valent iron（ZVI）remove Cr（Ⅵ）and As（Ⅴ）program by weak magnetic field（WMF）.Studied ZVI removes Cr（Ⅵ）strengthen laws under WMF,determined its kinetic parameters;analysised the forces of charged ions stress distribution in WMF,and observed the removal rate effects by the coexistence of water anions in WMF.A rational and efficient basis provided for designing and controlling the process of remove chromium and arsenic.By researching the Cr（Ⅵ）removal by ZVI strengthen behavior in WMF showed that regardless the external magnetic field,the reaction rate of Cr（Ⅵ）removed by ZVI increased with the increasing amount of iron dosage.The removal rate of Cr（Ⅵ）by ZVI was significantly improved in the presence of external uniform magnetic field.When the magnetic field intensity was 2³ mT,the reaction rate reached the maximum:0.159 mg·L^-1·min^-1,and compared to the reaction without WMF,the reaction rate could be improved 3⁴ times.In the range of 5¹0 mT,the reaction rate increased at first phase and soon slowed down,indicated that the faster the reaction rate,the higher degree of iron surface corrosion.This confirmed the magnetic field can accelerate the corrosion of ZVI,thereby accelerating the reaction between Cr（Ⅵ）and ZVI.Iron corrosion products are mainly magnetite and maghemite.The results of the three-dimensional numerical simulation of WMF showed that the induced magnetic field is not uniform and the maximum field intensity occured in the ZVI surface and interior,about twice of the applied field strength.Magnetic field gradient force drives paramagnetic Fe²⁺to move in the direction of larger magnetic field intensity,provided by the superimposed magnetic field.Lorentz force eacting on ZVI particles could be negligible.Magnetic gradient force was the main force to accelerate the ZVI corrosion.There were some interactions between the presence of a weak magnetic field and the water contained in the coexisting ions,the combined effected of zero-valent iron and As（Ⅴ）of the reaction rate.Under the condition of no WMF,chloride and nitrate could accelerate rate to a certain extent,and acceleration increased with the corresponding ion concentration.Low concentrations of humic acid had little effect on the system,a high concentration could increase the removal rate of ZVI and As（Ⅴ）.Promoting degree followed the trend of Cl^->NO₃^->HA.Silicate and phosphate could suppress ZVI removal arsenic,with the corresponding inhibitory concentration increases more obvious.Phosphate inhibitory effected more evidence than silicate.Application of WMF could weaken inhibitive effect of silicate and phosphate,and strengthened the positive effect of chloride,nitrate and humic acid.