Preparation And Simulation Of Green Rust

A new preparation process with high yield was proposed for Green Rust,which is an important intermediate product during the synthesis of iron oxides.In a near neutral condition,ferric iron was titrated into ferrous iron aqueous solution,and NaOH was fed to adjust the pH.Compared with co-precipitation process,the solution kept greenish during the reaction,without yellowish,and the TEM images showed only hexagonal plates or small octahedral crystals but no needle ones,the new method improved the yield.Amorphous Green Rust was produced,and TEM images analysis showed that nucleation rate of Green Rust was very slow,at room temperature,more than ten days were needed,while,enhancing the aged temperature(at 70℃)may quicken that process.The synthesis of Green Rust was a complex process including the hydrolysis of iron ions,oxidation of ferrous and nucleation of goethite.Reaction mechanism study was performed to enhance the selectivity.Cyclic Voltammetry was used to measure the concentration of Fe²⁺instantly.The production rate of Green Rust was found to be a function of the concentration of both Fe²⁺and Fe(OH)₃.Based on the oxidation rate of Fe²⁺and nucleation rate of amorphous Fe(OH)₃ from literature,the kinetic coefficient was estimated to be 0.33 M^-1·s^-1.Taylor-Couette reactor was selected to provide a good condition for the growth of Green Rust.Numerical model was set up for the process of Green Rust preparation. Three dimensional numerical simulation were conducted to obtain steady state flow pattern of Taylor-Couette reactor,which agreed well with the theory analysis.From different numerical simulation with different rotating velocities and feeding positions, the best operation mode was adding Fe³⁺from the inner wall of the reactor and NaOH from the outwall of the cylinder under Couette pattern.