The Fundamental Research Of Selenite Se(IV) Removal In Aqueous Solution By Green Rust

This paper investigated that GR（Cl^-） treated the simulate wastewater containing selenite in the laboratory in anaerobic and aerobic conditions. We investigated the effcts of different environmental factors on the efficiency of Se（IV） removal by GR（Cl^-）, including the dosing quantity of GR（Cl^-）, initial solution pH value, dissolved oxygen, and coexistence of anion and cation,etc.Various characterization techniques such as SEM, XRD, XPS were employed and discuss the reaction mechanism.From the study, following conclusions are obtained.（1） The reaction time of GR（Cl^-） and Se（IV） was short.Se（IV） with an initial concentration of 15 mg/L can be completely removed by GR（Cl^-） with 98 mg/L added in anaerobic condition and 140 mg/L in aerobic condition.（2） Dissolved oxygen has inhibiting effect on Se（IV） removal by GR（Cl^-）, because oxygen accelerates oxidation of GR（Cl^-） and changes its surface structure.（3） Alkaline solution facilitates the Se（IV） removal by GR（Cl^-） in both anaerobic and aerobic conditions, however, a high pH value（>10） will affect the removal efficiency seriously.（4） Cations differ in the effects on the Se（IV） removal when they exist in the aqueous solution. Ca²⁺and Mg²⁺ have little influence on Se（IV） removal by GR（Cl^-） in both aerobic and anaerobic conditions. Characterized by SEM and XRD, Ca²⁺、Mg²⁺ have little influence on the structure of GR（Cl^-）.Al³⁺ shows inhibiting effect on Se（IV） removal by GR（Cl^-） in anaerobic condition, but facilitates it in aerobic condition. The reason why it inhibits the reaction was that Al³⁺ reduces pH greatly, which results in the structure of GR（Cl^-） destroyed. Precipitate covers on the surface of GR（Cl^-） easily, affecting the adsorption and reduction of GR（Cl^-）. And the reason why it facilitates the removal was that the floc Al（OH）3 can flocculate and remove Se（IV）. Cu²⁺ exhibits inhibiting effect on Se（IV） removal by GR（Cl^-） in anaerobic conditions, but facilitates it in aerobic condition. Cu²⁺ was reduced to Cu、CuO and Cu2 O by GR（Cl^-） in anaerobic condition, and the precipitate Cu（OH）2 formed by hydrolysis covers on the surface of GR（Cl^-） easily, affecting the adsorption and reduction of GR（Cl^-）. But in the aerobic condition, Cu²⁺ was just reduced to a small amount of Cu、CuO and Cu2 O without Cu（OH）2, showing that Fe-Cu galvanic cell may be formed in the process which is favorable to the reaction.（5） Anions differ in the effects on the Se（IV） removal when they exist in the aqueous solution. NO3- facilitates the Se（IV） removal by GR（Cl^-） in anaerobic condition. Mainly because the presence of NO3-makes the material particles become smaller. In aerobic condition, NO3-shows inhibition effect on Se（IV） removal. PO43- has inhibition effect on Se（IV） removal in both aerobic and anaerobic conditions. Because the precipitate formed by PO43-, Fe²⁺ and Fe³⁺ covers the surface of GR. A little SiO32- facilitates the reaction in the anaerobic condition. Although the crystal of the product has changed, the appearance and characteristics of the material changes little. Because pH increases dramatically which results in poor reaction effects. In the anaerobic condition, SiO32- exhibits inhibition effect on the reaction. In this process, the change of pH has an important effect on reaction.（6） Reaction Kinetic shows that the reaction model approaches two-order kinetics model. Through to the GR（Cl^-） and Se（IV） reaction to the fitting of the three adsorption model, it shows that Se（IV） removal by GR（Cl^-） was a complex form of adsorption. Through the characteristis of reaction product, pH value during the reaction process and changes of ORP with time, it shows that the Se（IV） removal by GR（Cl^-） was a complex reaction process which includes reduction and adsorption conducting together.