Study On Purification Of Quartz Sand By Microwave Chlorination Calcination And Its Mechanism

In the 21st century,with the rapid development of high-tech enterprises and the sharp decrease of natural crystal reserves,quartz is urgently needed as an alternative crystal to make up for the shortage.Compared with traditional electric furnace heating,microwave heating is safer,more efficient,energy-saving and environmentally friendly.The selective heating of the microwaves makes it be widely used in the mineral processing and the mineral purification industry.Chlorination calcination is widely used in the purification of rare earths and the separation of heavy metals,and its application in the purification of quartz has a remarkable effect.Therefore,microwave calcination and chlorination calcination are combined to remove inclusions and lattice impurities in quartz.Based on the above,this paper does the following research:(1)By studying the effect of long-time mixed acid leaching on the removal of impurity aluminum in quartz,the functional relationship between the leaching time and the remaining aluminum impurities in the quartz was established.Within 80 minutes,the removal of aluminum in the quartz was controlled by the surface reaction;when the leaching time exceeds 80 minutes,the removal of aluminum in the quartz is controlled by the diffusion of the insert solid reaction product layer;thus,the existing form of aluminum in the quartz is determined.(2)Three kinds of chlorinating agents,NaCl,KCl and NH4Cl,were mixed with Fengyang quartz and calcined at different doping ratios at 900℃ under microwave for 2 hours to remove aluminum impurities in the quartz after water quenching and leaching.The results show that when the chlorinating agent is NH4Cl and the doping ratio is 2 wt.%of quartz,after microwave calcination at 900℃ for two hours,HF-HCl-HNO3(1 mol/L HF,2 mol/L HCl,2 mol/L HNO3,solid-liquid ratio is 1:10)After leaching at 110℃ for two hours,the content of aluminum in the quartz was reduced from 738.8 ppmw to 17.9 ppmw,and the removal rate of aluminum reached 97.58%.(3)The effects of different microwave calcination temperature and calcination time on the removal of aluminum in quartz were discussed.The experiment found that with the increase of calcination temperature,the removal rate of aluminum in the quartz also increased.When the temperature is 1100℃,the removal rate of aluminum reached 98.29%.With the increase of temperature,quartz undergoes two phase transformations.These phase transformations change the volume of the quartz,and the transformation of crystal form leads to changes in the internal structure of the quartz.These two changes greatly increase the volume of the quartz,the probability of exposure of the internal impurities to the outside.With the increase of the calcination time,the internal changes of the quartz tend to be complex,so there is no special rule in the trend of changes with time.(4)The difference in the removal of aluminum impurities between microwave chlorination calcination and traditional resistance furnace chlorination calcination is compared.Since the traditional resistance furnace heats the quartz through thermal radiation or heat conduction,the quartz is uniformly heated.Whereas the microwave is selective heating,which leads to a large temperature difference between the quartz matrix and the impurities in the inclusions,resulting in thermal bursting,cracks forming.These increase the probability of internal impurities being exposed,make the chlorinating agent more likely to react with the impurities,and expound the mechanism of microwave chlorination calcination.(5)By studying the change of lattice parameters of vein quartz under different microwave treatment conditions,it is shown that the phase transformation has occurred inside the quartz.By studying the relative position changes of Si(111)(2θ=28.44°)and SiO2(101)(2θ=26.65°)in XRD spectrum,the relationship between the impurities in the quartz before and after microwave treatment and the position change of spectrum was explored.This paper provides a fast and easy method to remove aluminum from quartz,utilizing the selective heating of microwaves and the easy decomposition of NH4Cl during heating,the quartz sand and NH4Cl doped with microwave calcination combined with acid leaching,making low-grade common quartz reaches the standard of highpurity quartz after the treatment,and the mechanism of the impurity removal is described.