Basic Study On Preparation Of High Purity Quartz From Sandy Kaolinite Tailings

High-purity quartz is the basic raw material in strategic emerging industries such as information technology,new energy and electric light sources.China’s high-purity quartz raw materials,such as natural crystal and quartz vein,account for less than 1%of the total quartz resources.There are a large number of quartz resources in the sandy kaolin tailings,which have greater recycling value.The study of preparing high-purity quartz with sandy kaolin tailings as raw materials not only realized the comprehensive utilization of tailings resources,but also provided a theoretical basis for enriching the sources of high-purity quartz.In this paper,quartz resources of sandy kaolin tailings in Jiangxi are used as raw materials.First,based on the research results of process mineralogy,a kaolin tailings sorting quartz sand test was carried out,and the obtained quartz sand coarse concentrate was analyzed for impurities.Then,a comparison test of the effect of conventional roasting and microwave roasting on the removal of Al element in quartz sand was carried out.Next,a single-factor condition test of microwave roasting-leaching separation of Al in quartz sand was carried out.Finally,the effect and mechanism of microwave roasting on the separation of muscovite,potash feldspar and other gangue minerals and fluid inclusions in quartz sand are discussed.The tailings of sandy kaolin in Jiangxi Province are purified by the classification-grinding-scrubbing-magnetic separation-gravity separatio-two stage reverse flotation to obtain coarse quartz sand concentrate with 99.59%SiO₂ content.Its main impurity elements and the contents are Al 821μg/g,Fe 36.1μg/g,Na 38.4μg/g,K 237μg/g,Li22.3μg/g,Ti 21.6μg/g,respectively.Through the analysis of process mineralogy,it is clear that the gangue minerals such as muscovite and K-feldspar are the most important factors affecting the quality of quartz sand.Through the comparison test of conventional roasting of quartz sand coarse concentrate and microwave roasting.It is confirmed that roasting-water quenching has the effect of increasing the content of SiO₂ in the quartz sand coarse concentrate and strengthening the leaching and separation effect of Al element,and the microwave roasting-water quenching effect is better.Acdroding to the single-factor condition test of microwave roasting-leaching separation of Al in quartz sand coarse concentrate,the optimum conditions are as follow:900℃microwave roasting 180min-water quenching,leaching temperature 80℃,leaching time600min,c（HCl）=2.0mol/L,c（HNO₃）=2.0mol/L,c（HF）=1.5mol/L,stirring speed 500r/min,solid liquid ratio 1g:5mL.Under these conditions,high purity quartz sand with the aluminum element content of 236μg/g and total impurity elements less than 500μg/g can be obtained.The test results of KCl doped roasting-leaching purified quartz sand coarse concentrate show that:Under the process conditions of c（H₂SO₄）=3.68mol/L,leaching temperature80℃,leaching time 120min,stirring speed 500r/min,solid-liquid ratio 1g:5mL,the removal rate of the aluminum element in quartz sand ofmicrowave roasting at 900℃for180min with 1%KCl doping,conventional roasting at 900℃for 180min with 1%KCl doping and 900℃microwave roasting for 180min with undoping were 22.11%,19.06%and 17.53%.It was confirmed that KCl doping roasting has the effect of improving the leaching and separating effect of the aluminum element in quartz sand,but the improvement effect is weak.Based on different calcination conditions of pure mineral dissolution behavior of gangue minerals in quartz sand,the variation law of the content of characteristic element Na in fluid inclusions and the change of quartz sand morphology,the mechanism of microwave roasting to strengthen the separation effect of impurity elements in quartz sand is confirmed in three aspects.First,the high temperature changes the microwave response capability of muscovite and the microwave roasting promotes the finer cracking particle size of muscovite,which strengthen the dissolution and separation effect of muscovite in quartz sand in mixed acid.Second,the main component of fluid inclusions in quartz sand is H₂O,which can be selectively heated by microwaves to form high temperature hot spots.So the burst separation effect of fluid inclusions in quartz sand be enhanced.Third,mineral inclusions or connected bodies such as muscovite and potash feldspar in quartz sand are selectively heated by microwave under the action of high temperature,but quartz does not have this characteristic,which promotes cracks between quartz and gangue minerals and further enhancing the effect of mixed acid dissolution and separation of impurity elements in quartz sand.Research shows that it is feasible to prepare low-iron（Fe₂O₃<50μg/g）quartz sand and high-purity quartz sand with total impurity elements less than 500μg/g from sandy kaolin tailings as raw materials,and it is necessary to conduct in-depth research.The research in this paper provides new ideas for the comprehensive utilization of sandy kaolin tailings and the processing of high-purity quartz.