Extraction Of Potassium From Biotite By Alkli-earth Metal Ions (M²⁺) Exchange Method And Electrochemical Properties Of Hydrate M²⁺-biotite

In this paper,biotite was taken as the raw material.Soluble potassium ions were extracted from biotite by alkaline earth metal ions(Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺)exchange method.It provided a new method for extracting potassium from silicate minerals containing insoluble potassium.The best scheme of potassium removal was studied.The method of extracting soluble potassium ions after potassium removal was determined.The evolution of structure after potassium removal by different alkaline earth metal ions(M²⁺)exchange method was revealed.The mechanism of“Coulomb effect”and“vacancy effect”in the process of potassium removal by Mg²⁺/K⁺ions-exchange was put forward,which provided theoretical guidance for the process of potassium removal from mica.The vermiculite-type hydrate biotite(Mg²⁺-biotite)obtained after potassium removal can be used as electrode material with small capacitance.A new application way and electrochemical performance of biotite were explored.The specific research contents and conclusions are as follows:1.In essence,alkaline earth metal ions(Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺)are used as ion exchanger.Dilute HCl is used as p H regulator and weak oxidant.These measures make the insoluble potassium ions in biotite exchange with alkaline earth metal ions(Mg²⁺,Ca²⁺,Sr²,Ba²⁺).K⁺ions came out of the biotite layer and went into the filtrate.The rate of potassium removal can reach 98%in 8 h by Mg²⁺/K⁺ions-exchange method.The rate of potassium removal can reach 89%in 24 h by Ca²⁺/K⁺ions-exchange method.The rate of potassium removal can reach 94%in 10 h by Sr²⁺/K⁺ions-exchange method.The rate of potassium removal can reach 96%in 20 h by Ba²⁺/K⁺ions-exchange method.In the same ions-exchange time,the rate of potassium removal was positively correlated with P（effective space coefficient）and H（expansion coefficient of biotite layer）.The larger the effective space coefficient P between the biotite layers and the expansion coefficient H between the biotite layers,the higher the potassium removal rate.Considering the rate of potassium removal and reaction time,the best scheme of potassium removal is Mg²⁺/K⁺ions-exchange method.2.The results of XRD and HRTEM showed that the basal plane（001）spacing of biotite d_（001）=1.006 nm in the process of alkaline earth metal ions(Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺)exchange from biotite.The basal plane（001）spacing of Mg²⁺-biotite increased to d_（001）*=1.433 nm.The basal plane（001）spacing of Ca²⁺-biotite increased to d_（001）*=1.429 nm.The basal plane（001）of Sr²⁺-biotite is increased to d_（001）*=1.517 nm.The basal plane（001）of Ba²⁺-biotite is increased to d_（001）*=1.175 nm.A large number of structural water molecules entered the interlayer domain of biotite in the form of hydrate M²⁺(Mg²⁺,Ca²⁺,Sr²,Ba²⁺),which makes K⁺layer structure of biotite change to hydrate vermiculite-type layer structure.Biotite transformed into vermiculite-type hydrate M²⁺-biotite.3.The bond structure changes of Si-O-Si（Al）,Si-O-Si and Si（Al）-O in the silicon oxygen tetrahedral layer of biotite were studied by XRD and FTIR during the process of removing potassium from biotite by Mg²⁺/K⁺ions-exchange method.It was found that the bond length of Si-O-Si（Al）and Si-O-Si in the silicon oxygen tetrahedral layer increased,while the bond length of Si（Al）-O decreased.This was because the hydrate Mg²⁺occupied the original position of K⁺in the interlayer domain of biotite.Compared with the original K⁺ion,the charge of Mg²⁺is larger.So the Coulomb force of Mg²⁺on the bridge oxygen is stronger,which made the bond length of Si-O-Si（Al）and Si-O-Si increase.The increase of the bond length of Si-O-Si（Al）and Si-O-Si increased the traction of Si（Al）-O on the active oxygen.So the bond length of Si（Al）-O decreased.4.The mechanism of“Coulomb effect”in the process of removing potassium by Mg²⁺/K⁺ions-exchange method was found by XRD and Mossbauer spectrum:when the p H of the reaction solution was 3,the H⁺provided by dilute HCl and NO₃^-provided by Mg（NO₃）₂ formed HNO₃.HNO₃ had a proper oxidizability,which made most of Fe²⁺in the alumina octahedron of biotite oxidized into Fe³⁺[Fe³⁺→Fe²⁺].A Fe²⁺was oxidized into Fe³⁺.A new positive charge was generated in the alumina octahedron,which can be used to compensate the amount of interlayer positive charge caused by Al substituted Si[Al³⁺→Si⁴⁺].So one K⁺ion was released from the biotite interlayer.The mechanism of“Coulomb effect”in the process of potassium removal by Mg²⁺/K⁺ions-exchange method can be expressed as follows:3Fe²⁺+4H⁺+NO₃^-=3Fe³⁺+2H₂O+NO↑pH=3.0 [Fe³⁺→Fe²⁺]∞[Al³⁺→Si⁴⁺]∝K⁺5.The mechanism of“vacancy effect”in the process of removing potassium by Mg²⁺/K⁺ions-exchange method was found by XRD characterization:in order to keep the charge conservation between layers,one Mg²⁺can replace two K⁺.At this time,a point defect vacancy appeared.Because the generation of this vacancy reduces the vacancy resistance of interlayer ions-exchange.The rate of Mg²⁺/K⁺ions-exchange increased.The mechanism of“vacancy effect”in the process of Mg²⁺/K⁺ions-exchange can be expressed as follows:Mg²⁺+vacancy→2K⁺6.The electrochemical test results shown that the discharge time of vermiculite-type hydrate Mg²⁺-biotite electrode can reach 109.63 s after being charged and discharged at a constant current of 0.005 m A.The discharge specific capacity was mainly provided by the oxidation reaction in the electrode.When charging,due to the unstable and rapid transformation of the oxidized material,the charge specific capacity was almost completely provided by the double-layer capacitor.The discharge specific capacity was3.43 F/g.The discharge time of the biotite electrode was only 35.17 s,and the specific capacity of charge and discharge of the biotite electrode is almost completely provided by the double-layer capacitor.The discharge specific capacity was 1.10 F/g.