Removal Of As(Ⅲ) And Cu(Ⅱ) By Supported And Sulfidated Nanoscale Zero-valent Iron From Aqueous Solution

Heavy metal is the main pollutant that causes water pollution.Nano-zero-valent iron（NZVI）provides a new method for tremediation of heavy metal polluted water and treatment of heavy metal wastewater.To solve the problem of aggregation and passivation of nano zero-valent iron,sulfurized nanoscale zero-valent iron supported on attapulgite was prepared by using attapulgite as carrier and sodium thiosulfate as sulfidation reagent.As（III）and Cu（II）were chosen as representatives,and the performance and reaction mechanism of removal of As（III）and Cu（II）by ompound materialwere studied.In addition,the effects of initial pH of solution,temperature,dissolved oxygen content and coexisting ions on the removal of As（III）and Cu（II）were investigated.The main results are as follows:（1）Attapulgite was chosen as carrier,the appropriate mass ratio of Fe to attapulgite was 2:1,Na₂S₂O₃ was chosen as sulfidation reagent,the appropriate mole ratio of S to Fe was 25%.It was observed from SEM and TEM that after loading and vulcanization modification,nano-iron aggregates became smaller,the size of beads formed by magnetic attraction dcreased and some aggregations of nano zero-valent iron was even dispersed into a single spherical particle.The experimental results showed that the BET specific surface area of compound material was 2.3 times that of NZVI（The BET specific surface area increased from 19.60 m²/g to 46.04 m²/g）.（2）The removal efficiency of of As（III）and Cu（II）by sulfurized nanoscale zero-valent iron supported on attapulgite wass significantly increased compared with nano-zero-valent iron.The quality of iron in composite materials was only 2/3 compared with nano-zero-valent iron,so the cost of use can be greatly reduced.（3）The removal of As（III）by compound material fitted well with the Langmuir adsorption model,and the maximum adsorption capacity was 193.83 mg/g.The removal mechanism of As（III）was clarified by XRD and XPS analysis of the reacted materials.On the one hand,the coordination between H₂AsO₃^-/HAsO₄^2-（produced by H₂AsO₃^-）and iron oxide on the surface of zero-valent iron;on the other hand,arsenic can also be removed by the forming of FeAsO₄ chemical precipitation.（4）The removal process of Cu（II）was fitted well with adsorption-reduction（L-H）model.The adsorption capability of Cu（II）by the composite reached 587.8 mg/g（9.25mmol/g）.The mechanism of Cu（II）removal can be attributed to that Cu²⁺in aqueous solution was reduced to Cu⁰ by Fe⁰ and FeS was changed to CuS with smaller solubility product constant.（5）When the pH value was between 3 and 6,the material had a good removal rate of As（III）;higher temperature was beneficial to the removal of As（III）.The removal process of As（III）required the participation of appropriate dissolved oxygen,too much dissolved oxygen was not conducive to the removal of As（III）.When the pH value wass between 2and 11,the material had a good removal rate of Cu（II）;higher temperature was beneficial to the removal of Cu（II）.The material had the best removal effect of Cu（II）when the dissolved oxygen concentration was close to 0.