Study On The Oxidative Leaching Mechanism Of Potassium Manganate Preparation By Liquid Phase Metho

Potassium manganate,as an intermediate in industrial synthesis of potassium permanganate,is one of the most important manganese salts,which can only exist stably under strong alkali conditions.As a common manganese salt,potassium permanganate is widely used in the fields of electrochemistry,water disinfection and wastewater organic degradation due to its advantages of safe storage and transportation,convenient operation and no harmful gas to human body and environment.At present,the production method of potassium permanganate is mainly divided into two steps,among which the second step of potassium permanganate electrolysis,crystallization,separation and drying process of potassium permanganate technology has been relatively mature,but the preparation of the first step of potassium permanganate has been a problem in industrial production of potassium permanganate due to high energy consumption,low efficiency and serious environmental pollution.Therefore,the preparation technology of intermediate product potassium manganate becomes the key to the improvement of potassium permanganate industry.The preparation of potassium manganate by liquid phase method greatly alleviates the depletion of medium and high grade pyrolusite in our country.This paper combined liquid phase pressure oxidation to prepare potassium manganate and response surface method to optimize the reaction parameters;systematically explored the phase transition law of reaction products under different reaction temperature,reaction time,initial potassium hydroxide concentration,initial alkali-manganese ratio and different oxygen pressure;studied the kinetics of alkaline leaching process.The research contents are as follows:（1）The stable morphology of leaching residue under different potential and alkalinity during preparation of potassium manganate by liquid phase method.With the increase of temperature,manganese dioxide can be oxidized to form a new phase—Mn O₄^2-in strong alkaline solution,indicating that the increase of temperature is conducive to the conversion of Mn⁴⁺to Mn⁶⁺.（2）Analysis of response surface during preparation of potassium manganate by liquid phase method.The response surface method was used to establish the continuous variable surface model,and the expectation function was used to evaluate the influence factors and their interactions.The optimal process parameters were determined:The leaching temperature was 200℃,the leaching time was 174.37 min,the initial alkali-Mn ratio was 14.33,the initial potassium hydroxide concentration was 66.41%,the oxygen pressure was 0.15 MPa,and the potassium manganate conversion rate reached the maximum.（3）Phase transition of potassium manganate prepared by liquid phase method.Pure manganese dioxide was used as raw material to prepare potassium manganate continuously by pressure oxidation in a sub-molten salt system.The changes in the composition and morphology of the reaction products under different reaction temperature,reaction time,initial potassium hydroxide concentration,initial alkali-manganese ratio and oxygen pressure were investigated by the control variable method.The results show that with the increase of reaction temperature,the reaction time should be increased,the initial potassium hydroxide concentration should be decreased or the initial alkali-manganese ratio should be decreased to reach the maximum crystallinity of the reaction products.The crystallinity of the reaction products reached the maximum when oxygen pressure was 0.3 MPa at different temperatures.（4）Using pyrolusite as raw material,the process of preparation of potassium manganate by liquid phase method was studied.It was determined that the process of preparation of potassium manganate by liquid phase method under pressure alkaline leaching was controlled by surface chemical reaction.The kinetic equation of chemical reaction was obtained as follows:1-（1-α）^1/3=t·exp（17.06-101.07/RT）.