Study Of Extracting Potassium From Mica By Oxidation-ionexchange Methods And Its Mechanism

With the increasingly depleting of lacking soluble potassium resources originated from over-exploitation,in order to ensure the further development of agriculture,a sufficient process to extra soluble potassium from insoluble minerals with large reserves is necessary.As one kind of insoluble potassium-bearing mineral,mica contain high potassium ratio and the reserves are plenty.The study on the extraction of potassium ions in the interlayer is mainly concentrated on the acid hydrolysis,high temperature calcination and other destructive means,which is not conducive to the full utilization of resources.In this paper,hydromica and biotite were used as the object of potassium extraction,and soluble potassium ions were extracted from the interlayer of mica under the premise of ensuring the mica layer structure by oxidation-ion exchange method.Firstly,the structural characteristics of raw mica ore were studied by elemental analysis,XRD and FT-IR analysis.It was found that the hydromica was hydroxy muscovite and biotite was pure biotite.Then,the effects of the reaction temperature,reaction time,the value of hydrochloric acid,the species of exchange cations and the concentration of the cation on the extraction rate were studied.XRD,XPS,and Mossbauer spectroscopy were used to characterize the change of crystal grain distance,valence vibration mode and octahedral element valence.According to the change of mica microstructure in the process of extracting potassium,the"coulombian effect"mechanism during the extracting potassium from mica by oxidation ion exchange was proposed.The specific research contents and conclusions are as follows:?1?In the experiment of extracting potassium from hydromica,among the four exchange cations of Mg,Ca,Sr,and Ba,the exchange rate of barium ion was the highest.In the reaction temperature range of 30-80 ^oC,the potassium extraction rate increased first and then decreased with the increase of temperature,and reached the peak at 45 ^oC.When reaction time was in the range from 0.5 to 4 hours,the potassium extraction rate gradually increased with the increase of reaction time.When the barium ion concentration is in the range of 0.25-1.75 mol/L,the potassium extraction rate of barium ion was the highest.The oxidation treat in the ion exchange process can further improve the potassium extraction rate.The layered structure characteristic of hydromica after oxidation-ion exchange treatment remained unchanged.The low valence cations V³⁺and V⁴⁺in the octahedral position were oxidized to high valence V⁵⁺.?2?In the experiment of extracting potassium from biotite,the effect of oxidation treat on the extracting rate of potassium ions was conspicuous.In the reaction temperature range of 30-60 ^oC,the temperature and the potassium extraction rate were positively correlated,the coefficient of proportionality was K₁.When came to 60-90^oC,the temperature and the potassium extraction rate were also positively correlated,the ratio coefficient was K₂,and the coefficient of proportionality became larger.With the increase of the dosage of hydrochloric acid,the pH value of the reaction solution decreased,meanwhile,and the potassium extraction rate increased first and then decreased.In the continuous reaction time of 3-24 h,the potassium extraction process showed two effects:"vacancy effect"and"blocking effect".The interaction between the two effects led to the relationship between the potassium extraction rate and the reaction time curve of“double peak”type,the peak point in?9 h,37.2%?and?15 h,42.3%?,interval of about 6 h.The potassium ions extracted from the solution was removed in time by the method of fractional extraction,which can reduce the effect of"blocking effect",resulting in the relationship between potassium extraction rate and time was"ascending"type.The potassium extraction rate can reach to 92.1%after four times extraction.?3?To extracting potassium from biotite by oxidation-ion exchange method,the oxidation process occurs in the octahedral structure layer,the Fe²⁺of the octahedral structure layer of the biotite was oxidized to Fe³⁺by strong oxidizing nitric acid,and with the deepening of the oxidation degree,some Fe³⁺will escape from the biotite lattice to form octahedral vacancies,due to the escape of Fe³⁺,the remaining iron ions in the octahedron will be reordered,resulting in the redistribution of iron ions in M1 and M2octahedron,which shown the preferential occupation of M1 octahedron.The barium potassium exchange process occurs in biotite layer,which is a dynamic reversible process,the entry of barium ions will form a layer of vermiculite-type crystal structure with spacing slightly higher than that of the biotite layer as well as created vacancy in the interlayer structure of mica.The tetrahedral layer of biotite is affected by the oxidation process and the barium potassium exchange process both created vacancy in mica structure,the vibration mode is more intense from the plane vibration to the vertical direction.?4?The mechanism of extracting potassium from mica by oxidation/ion-exchange method with no structural breaking is that oxidating the octahedral oxidizable cation(Fe²⁺,V³⁺,V⁴⁺)to high oxidation states,resulting in the electronegativity of silicon oxygen tetrahedral layer caused by the substitution of aluminum in silicon was reduced,and then the coulombian bondage interlayer K⁺was weakened,then the potassium extraction ability of exchange cations was improved.All of this can be called as"coulombian effect".