Li Feifei,Jiang Xuesong,Zuo Qiuxia,Li Jingwei,Ban Boyuan,Chen Jian
Iron is a major impurity in quartz sand and must be strictly removed in many applications. However, the iron removal rate in most of the conventional purification process is not high enough. In this study, a fast, low-energy consuming, environment-friendly and simple process for purifying quartz is demonstrated by a combination of microwave heating and ultrasound-assisted acid leaching treatment. Using the characteristics of selective heating of microwave, the micro-inclusions burst and generate cracks in the surrounding quartz matrix far below the α/β phase transition temperature, which enables removal of the impurities in the subsequent processing steps and reduces iron diffusion into the quartz matrix. Microwave process sequence, time, and temperature are all important factors, and appropriate parameters need to be explored. Ultrasound can assist acid leaching removal of Fe impurities through the cracks. Under optimized conditions, the iron content can be reduced to below 0.167 ppmw with one single purification pass.
A new purification method for molybdenum disulfide via NaNO 3 –HCl–HNO 3 synergistic leaching at 80 °C was developed. The effects of the concentration of NaNO 3 , HCl, and HNO 3 , and liquid–solid ratio and the leaching time on the purification of molybdenum disulfide were investigated by orthogonal array design methodology. The results of Taguchi method utilizing L 25 (5 5 ) orthogonal array indicated that the NaNO 3 concentration had the greatest impact on the purification of molybdenum disulfide. The optimum conditions for the purification of molybdenum disulfide were as follow: concentration of NaNO 3 = 2.5%, concentration of HCl = 11%, concentration of HNO 3 = 1.0%, liquid–solid ratio = 3, and the leaching time = 10 h. Under optimum conditions, the content of molybdenum increased from 55.1 to 59%, and the contents of iron, copper, lead, and calcium decreased from 0.35 to 0.21%, 0.027 to 0.008%, 0.054 to < 0.005%, and 0.27 to 0.035%, respectively. Based on molecular formula of molybdenum disulfide, the content of molybdenum disulfide increased from 91.93 to 98.44%. XRD and SEM indicated that this method removed only the impurities and did not affect the phase and particle size of molybdenum disulfide. The results show that the new purification method avoids the roasting process and will achieve the “green” production. The new method based on orthogonal array is effective for the purification of molybdenum disulfide via acid leaching.
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