Research On Preparation Of 4N High Purity Quartz Sand From Nigeria Silica Ore By Microwave Chlorination

High purity quartz sand is the basic raw material in high-tech industries such as electric light source,solar cell and semiconductor integrated circuit.As the best raw material of high purity quartz sand,the crystal resources are almost exhausted.It is important to produce high purity quartz sand with quartz ore instead of crystal.Nigeria is rich in quartz mineral resources.The proven quartz mineral resources amount to260 million tons.At present,the quartz mineral exported to China is cheap,and it is only used for simple rough processing as ordinary quartz sand,resulting in a serious waste of resources.In this paper,Nigeria quartz silica ore was used as the research object for the preparation of 4N high-purity quartz sand by removing metallic impurities and gas-liquid inclusions from quartz sand through crushing-grinding-screening-roasting-acid leaching processes.（1）The mineralogy of Nigeria quartz ore was studied by inductively coupled plasma spectrometer,scanning electron microscope,optical microscope,X-ray diffractometer and infrared spectrometer.The results show that the main metal impurities in Nigeria quartz ore are Al,Fe,Na,K,Li,Ca,Mg and Ti,and the total content of metal impurities is 478 mg/kg,among which the highest content of Al impurities is 270 mg/kg.These metal impurities mainly exist in impurity minerals such as pyrite,feldspar,mica,ruruite and fluorite,and quartz ore also contains a large number of gas-liquid inclusions.According to infrared spectrum analysis,the gas-liquid inclusions contain a large number of water molecules.（2）The quartz sand was roasted at high temperature in Muffle furnace and microwave furnace respectively,and the effects of roasting method,roasting temperature and roasting time on the removal of gas-liquid inclusions in quartz sand were studied.The experimental results show that high temperature roasting can effectively remove gas-liquid inclusions in quartz sand,and microwave roasting is better than muffle roasting in removing gas-liquid inclusions from quartz sand.The optimal temperature of microwave roasting is 900℃,and the optimal time is 4 h.XRD analysis showed that no new crystal shape was formed after microwave roasting.（3）Through the experimental study on the removal of metal impurities in quartz sand by microwave roasting and acid leaching,the optimal concentrations of the three acid solutions were determined as follows:c（HCl）=4 mol/L,c（HNO₃）=3 mol/L,c（H₂SO₄）=4 mol/L;the three single acid solutions were configured into a mixed acid solution according to the volume ratio of 1:1:1 for acid leaching experiments,and the results showed that the optimal acid leaching temperature was 80℃and the acid leaching time was 4 h.The quartz sand after mixed acid leaching was analyzed by ICP-OES.The total content of metal impurities in the quartz sand was 179.2 mg/kg,and the content of Si O₂ in the quartz sand was99.98%.（4）The removal of metal impurities in quartz sand by microwave chlorination roasting-hot pressed acid leaching showed that KCl among three chlorination agents KCl,Na Cl and Ca Cl₂ had the best removal effect on metal impurities in quartz sand.After quartz sand doped with 2.0 wt.%KCl was calcined by microwave at 900℃for 4 h,hot pressed acid leaching was performed with mixed acid solution consisting of hydrochloric acid,sulfuric acid and nitric acid in a volume ratio of 1:1:1.The leaching temperature was 200℃and the leaching time was 4 h.After hot pressed acid leaching,the total content of metal impurities in quartz sand was 85.1mg/kg,and the total impurity removal rate reached 82.20%.At which time the content of Si O₂ in quartz sand reached 99.9915%,reaching the standard of 4N.