Removal Of Heavy Metals And Inorganic Anions From Water With Liquid Nitrogen Treated Iron Powder

With the development of the human economy,the earth faces relatively serious environmental problems,such as heavy metal and inorganic anion pollution.These pollution problems have seriously affected ecological security and sustainable social development,so environmental restoration has become a hot topic of research.In environmental management,zero-valent iron is widely used due to its high efficiency and low toxicity.However,micron zero-valent iron particles have large size and low effective utilization rate,and are easy to form an oxide film in contact with air and water to reduce activity.In this paper,we use liquid nitrogen to soak iron powder to induce cracks on the surface of iron powder at low temperature,thus exposing more zero-valent iron and ferrous iron.Liquid nitrogen treatment has a distinctly different effect on different heavy metal contaminants.The removal of zinc(Zn),cadmium(Cd),mercury(Hg),and silver(Ag)by iron powder after liquid nitrogen treatment is enhanced.On the contrary,for nickel(Ni),lead(Pb),and copper(Cu)Removal is suppressed.We find that this is mainly related to the redox potential and removal mechanism.After the iron powder treated with liquid nitrogen,Fe(0)will increase,and more OH-will be produced in the solution,which will promote the coprecipitation of Zn(?)and Cd(?).At the same time,both increased Fe(0)and Fe(?)can promote the reduction of Hg(?)and Ag(?).However,the reduction of-OH or other functional groups on the surface of the iron powder after treatment with liquid nitrogen may inhibit the removal of nickel(Ni),lead(Pb)and copper(Cu).In addition,we find that liquid nitrogen treatment can promote the efficiency of iron powder removal of nitrate.Under neutral or alkaline conditions,iron powder can hardly remove nitrate,while acidic conditions can accelerate removal.Nitrate is mainly reduced to NH4+,and a small amount of NO2-,N2 and other species.At the same time,the addition of oxygen accelerates the process of nitrate removal,zero-valent iron is oxidized to iron oxide or iron hydroxide such as hematite and magnetite.Magnetite has good electrical conductivity and can accelerate the ability of zero-valent iron to transport electrons,thereby promoting the removal of nitrate.In this paper,iron powder was treated with liquid nitrogen to remove a series of heavy metals and inorganic anions,and the surface of micron zero-valent iron is modified to some extent.The method of liquid nitrogen treatment of iron powder is simple and easy to operate,and economical and safe,and provides a new idea for the modification of zero-valent iron.In addition,the iron powder before and after liquid nitrogen treatment shows the different properties of different pollutants,which lays a foundation for us to study the removal of different pollutants.