Study On Purification Of Flake Graphite By High Pressure Alkaline Leaching And Normal Pressure Acid Leaching

Graphite with unique crystal structure has many excellent physical and chemical properties. As deep processing products of graphite, high purity graphite is also extensively used in advanced sealing, composite materials, nuclear industry, aerospace and other fieldsThis paper firstly introduces the structure of graphite and its usage in industry.And points out the contradiction between the rapid development of modern industry and the shortage of high quality graphite.On the basis of the over view of the domestic and international research results about demineralization techniques and the application status of these techniques, the direction in studies of the demineralization processing for high quality graphite from natural flake graphite are proposed. There by, significance and main contents of this research are put forward explicitly.The research chooses natural flake graphite concentrate from Qingdao as study object. According to the existing form of ash minerals in graphite and the thermodynamics analysis results of demineralization by pressure-leaching method, the technical route of pressure alkali leaching followed by acid leaching at atmospheric on demineralization is put forward, and the theory foundation on demineralization are investigated.The element categories and contents, the phase composition and distribution characteristics of ash in graphite are analyzed with modern analysis and testing technology. The main ash elements in graphite are Si, Al, Fe, etc, which exist generally as the oxide. The main phase compositions of ash minerals are quartz, mullite, hematite, etc. The maximum mineral particles are mixed with carbon particles, and a few fine minerals particles are intimately associated with the carbon matrix. It is difficult to separate minerals particles from carbon particles by the physical method. The chemical leaching is more suitable for demineralization of graphite.The thermodynamics laws of pressure leaching of graphite are analyzed. The lga-pH diagrams of Si, Al, Fe, the φ-pH diagram of Al-Si-H2O system at different temperature.The effects of leaching agents, concentration of NaOH and H2SO4, leaching temperature, leaching duration, liquid-to-solid ratio, etc. On the degree of demineralization are examined from the technological angle. The reasonable technological conditions obtained by factor experiments are that:Alkaline leaching:temperature 200 ℃; NaOH concentration of 15%; holding time 30min; liquid to solid ratio of 10:1;Acid leaching:temperature 90℃; H2SO4 concentration of 12%; holding time 30min; liquid-solid ratio 10:1.Under the best process conditions of purification, the fixed carbon content of graphite reached 98.71%, impurity content lower than 1.5%, impurity removal rate over 93%, among them> 87%, the degrees of removal of Si and Al is more than 87%, the degrees of removal of Fe is more than 90%, the degrees of removal of Ca and Mg is more than 95%, the degrees of removal of Na and K is more than 98%.