Studies On Reaction Kinetics Of Oxidation Of Nitrogen-and Sulfur-containing Compounds By Potassium Ferrate

Potassium ferrate（Ⅵ）has super oxidizing properties and is a multifunctional green water treatment agent that combines oxidation,sterilization,adsorption and flocculation.Nitrogen-and sulfur-containing compounds are important substances of water pollution.Their existence is closely related to various environmental issues such as the formation of disinfection by-products,membrane fouling,water eutrophication and increase of chemical oxygen demand.Potassium ferrate can oxidize such pollutants quickly and effectively,does not produce carcinogenic by-products,the reduction product Fe（Ⅲ）will not cause harm to human body and environment.Most literatures focus on the extensive application of potassium ferrate,few reports have been made on its kinetic data and mechanism.This paper focuses on the kinetics of oxidation of several nitrogen-and sulfur-containing compounds by potassium ferrate.Firstly,the oxidant potassium ferrate was synthesized according to hypochlorite oxidation method and characterized by ultraviolet and infrared spectroscopy.The reaction kinetics of oxidation of the amines,amino acids and inorganic sulfides by potassium ferrate were studied by using the stop-flow techniques.The reaction product was detected and the active center of the reaction was proposed.Based on this,the possible reaction mechanism was designed.The rate expression was obtained,the rate constant k₂ at different temperatures and the activation parameters E_a,Δ_r^≠S_m andΔ_r^≠H_m of 298.2K are calculated too,which explains the experimental phenomenon well.Specific conclusions are as follows:（1）Under the pseudo first-order condition,the reaction is a first-order reaction for both potassium ferrate and reducing agent;the reaction rate constant decreases with the increase of[OH^-],which is negative fraction for OH^-.（2）Fe（Ⅵ）is finally reduced to Fe（Ⅲ）,which exists in the form of Fe（OH）₃ colloid in water.It can absorb suspended substances and large particles in water and play a role in purifying water.（3）The precipitate was obtained by derivatization with 2,4-dinitrophenylhydrazine,and the main oxidation products of amines and amino acids were detected by mass spectrometry.The results showed that when K₂FeO₄ oxidized amines and amino acids,the carbon associated with the amino group was oxidized,and form the corresponding aldehydes or ketones.The inorganic sulfur compound is oxidized to sulfate.These oxidation products are harmless to the environment or less harmful than before,and can be further treated to get non-toxic and harmless products.（4）Under alkaline conditions,Fe（Ⅵ）exists mainly in the form of FeO₄^2-,but HFeO₄^-formed by its hydrolysis can easily form an intermediate complex with the reducing agent,and then get the product through double electron transfer.The reaction mechanism based on this design is consistent with the experimental variation.（5）When potassium ferrate oxidizes compounds with similar structure,the amino group in ethanolamine is more easily involved in the reaction than hydroxyl group;ethylenediamine with more amino groups reacts faster than ethanolamine.In the reaction with inorganic sulfur-containing compounds,Na₂S₂O₃ has a larger space resistance than Na₂SO₃ when forming an activated complex with HFeO₄^-,the formation ability is weakened,so the reaction rate is slow.In this paper,the reaction kinetics of oxidation of nitrogen-and sulfur-containing compounds by potassium ferrate is studied,the oxidation products were determined,which provides theoretical basis for the study of such substances in wastewater treatment.