Study On The Regulation Mechanism Of Purification Of Rhodochrosite Leaching Solution To Prepare Battery-grade Mn₃O₄

Low-grade rhodochrosite has limited its application range due to many kinds of impurity elements,high content and low grade,especially in high purity lithium ion battery cathode manganese materials.Starting from broadening the application channels of low-grade rhodochrosite,this paper studies the mechanism of precipitation-reverse precipitation method to remove impurity ions in rhodochrosite leaching solution,the law of solid-liquid phase distribution and process conditions,the performance regulation mechanism of battery-grade manganese tetroxide prepared by manganese sulfate solution,and the process influencing factors and influencing mechanism of lithium manganate prepared by manganese tetroxide,so as to realize the integrated preparation of low-grade rhodochrosite from mineral hydrometallurgy to lithium ion battery cathode manganese series materials.The main research is as follows:（1）Study on purification mechanism of rhodochrosite leaching solution.Deep purification of rhodochrosite leaching solution was carried out by precipitation-reverse precipitation method.The results show that K⁺and Na⁺enter the manganese-rich phase precipitation in the form of inclusions under the condition of purification system.Ca²⁺and Mg²⁺ions mainly enter the manganese-rich phase precipitation as insoluble hydroxides.When the reaction p H is less than 8,Co²⁺and Ni²⁺ions do not react with hydroxide,and react with precipitant R to form nickel-manganese double salt and cobalt-manganese double salt,and all of them enter the manganese-rich phase precipitation.When the reaction p H exceeds 8,it can react with hydroxide and enter the precipitation in the form of double salt and hydroxide.Iron and copper ions enter the precipitate as insoluble hydroxides.Silicon mainly enters the precipitation by wrapping inclusions,and a small amount of silicate and cation form insoluble double salts.The sulfur element is mainly precipitated as Mn（NH₄）₂（SO₄）₂和Mn₂（OH）₂SO₄ double salts.In 1L rhodochrosite leaching solution(Mn²⁺:38g·L^-1),using precipitant R,under the reaction conditions of p H 7,temperature 70℃,time 3h,and precipitant feeding acceleration of 0.5 L·h^-1,the high-purity Mn SO₄ solution that meets the requirements of battery-grade Mn₃O₄preparation process can be obtained after the dissolution of manganese-rich phase precipitation.（2）Study on the regulation mechanism of battery-grade Mn₃O₄ preparation.The Mn SO4 liquid phase direct oxidation method was used,and ammonia was used as p H regulator and complexing agent.Mn²⁺and NH₃ formed[Mn（NH₃）_x]²⁺,which could effectively slow down the oxidation rate of Mn²⁺and help to control the crystal morphology and particle size.[Mn（NH₃）_x]²⁺can promote the growth of grains along the（211）,（103）and（112）crystal planes to form spinel Mn₃O₄ with octahedral morphology.The nucleation rate and growth rate were controlled to control the grain size of Mn₃O₄.When the nucleation rate is fast,the grains are small,the agglomerated particles are small,and the voids are large.When the grain growth rate is fast,the grain grows,and no longer grows when the interface energy of the crystal is minimized.It was found that the content of impurity elements in Mn₃O₄ prepared under the conditions of Mn²⁺of 80 g·L^-1,ammonia concentration of 8%,reaction p H of 8,reaction temperature of 80°C,reaction time of 12 h and oxygen flow rate of 3L·min^-1 met the requirements of Mn₃O₄ for lithium batteries.The XRD pattern of the product had a flat baseline,narrow diffraction peak and high strength,which was completely corresponding to the standard card,indicating that the product had good crystallinity and high purity.According to the Scherrer formula,the grain size is 300nm,which is consistent with the electron microscope results.According to XPS valence analysis,the manganese of Mn₃O₄ is+2 and+3 valence,and its chemical formula can be expressed as Mn O·Mn₂O₃.（3）Preparation and electrochemical properties of lithium manganate cathode materials.Lithium-ion cathode material LiMn₂O₄ was prepared by high temperature solid state method with octahedral Mn₃O₄ as manganese source and Li OH as lithium source.Under the conditions of Li/Mn of 0.5,calcination temperature of 800℃and calcination time of 10 h,the product LiMn₂O₄ has a Fd-3m spatial structure,good crystallinity,high purity,small cell size,and the cell volume is 557.6?³.Compared with electrolytic Mn O₂ as a manganese source,LiMn₂O₄ better inherits the octahedral morphology of Mn₃O₄,the particle size is uniform,the degree of distortion is small,the R value is 1.013,the crystal structure is stable and greatly improved,which is conducive to improving the electrochemical performance.At a current density of 0.2C,the initial discharge specific capacity is 121.9 m Ah·g^-1.After 100 cycles,the discharge specific capacity is 114.1 m Ah·g^-1,and the capacity retention rate is 93.6%.In the rate mode,the discharge specific capacity is about 87 m Ah·g^-1 at 10C current density,and the discharge specific capacity is 110 m Ah·g^-1 at 0.2C.The results show that LiMn₂O₄ inherits the octahedral morphology of Mn₃O₄ and effectively improves the crystal structure change during the sintering process.The stable crystal structure is conducive to the deintercalation of lithium ions during the charge and discharge process.This process is less destructive to the crystal structure,and the cycle performance and rate performance of LiMn₂O₄ are improved.In summary,the mechanism of precipitation-reverse precipitation of rhodochrosite leaching solution to remove impurity ions was revealed,and the solid-liquid phase distribution law of impurity ions was clarified,which enriched the preparation theory of battery-grade Mn₃O₄ and expanded the high-end application channels of low-grade rhodochrosite.