This article introduces the purification and preparation process of quartz sand for photovoltaic glass. The project utilizes a purification process involving "grading-regrinding-magnetic separation-leaching" to obtain high-quality quartz products, meeting the standards of silicon raw materials for photovoltaic glass.
The SiO2 content in the ore sample is 97.36%, with harmful impurities including 0.25% Fe2O3, 1.12% Al2O3, 0.073% TiO2, 0.100% CaO, and 1.95g/t Cr2O3. According to the industry standards for silicon raw materials used in photovoltaic glass, the main issue with this quartz sand mine is the insufficient SiO2 content, and excess Fe2O3, Al2O3, and TiO2 content.
Particle size is a crucial indicator for industrial applications of quartz sand. Currently, the requirements for quartz raw materials in the float glass and photovoltaic glass manufacturing sectors are mostly in the range of 0.106~0.50mm. The product after crushing contains a higher proportion of coarse particles larger than +0.50mm. Therefore, ore grinding and classification are necessary before ore dressing.
Rod mills have a large processing capacity, produce uniformly sized products, and are less prone to overgrinding. They are commonly used in quartz sand grinding operations.
After crushing and screening the original ore, 34.11% of quartz sand with a particle size of 0.106~0.50mm is obtained. Subsequently, a three-stage rod mill is used to obtain suitable-grade quartz sand, with respective yields of 31.30%, 8.98%, and 1.16%. Since the proportion of suitable-grade quartz obtained in the third stage is relatively low, and adding an extra grinding stage would increase ore dressing costs, the grinding system is set to two stages with grinding times of 30s and 60s, resulting in a 74% yield of quartz sand that meets the particle size requirements.
The impurity element Fe corresponds to weakly magnetic minerals such as hematite, so magnetic separation is employed to remove it. As different magnetic field strengths have a significant impact on ore dressing indicators, experiments are conducted using the ZQS-1500 magnetic separator with varying magnetic field strengths.
Experimental results show that increasing the magnetic field strength reduces the Fe2O3 and TiO2 content in the magnetic separation concentrate of quartz. When the magnetic field strength reaches 2.0T, the removal rate of impurity iron in quartz is the highest. Considering all factors, 2.0T is selected as the magnetic separation intensity for this quartz sand.
The mineral rutile corresponding to TiO2 has a relatively high density, so gravity separation is employed to separate it from quartz. Before magnetic separation, some rutile is pre-removed through gravity separation to reduce the pressure on magnetic separation. This further lowers the Fe2O3 and TiO2 content in the gravity-magnetic joint concentrate. In this case, both a shaking table and a high-gradient magnetic separator are used for gravity-magnetic joint ore dressing, effectively removing titanium and iron from quartz sand.
Since most of the impurity minerals in this quartz sand have fine particle sizes and are sparsely distributed in the interstitial spaces of quartz sand, physical methods such as gravity separation and magnetic separation have limitations in removing impurities. Therefore, chemical leaching is necessary for deep impurity removal to obtain high-quality silicon raw materials for photovoltaic glass.
Through ore dressing experiments and analysis, it is determined that the acid leaching process uses a mixed acid of hydrochloric acid and hydrofluoric acid. The concentrations of hydrochloric acid and hydrofluoric acid are 15% and 5%, respectively, with a solid-liquid ratio of 1:1. When the quartz sand ore is leached at 75°C for 6 hours, the SiO2 content reaches 99.79%, and the three main impurities, Fe2O3, Al2O3, and TiO2, have contents of 0.0075%, 0.063%, and 0.008%, respectively. All indicators meet the industry standard requirements.
Through the "grading-regrinding-magnetic separation-leaching" ore dressing process, impurity minerals such as plagioclase, mica, rutile, and hematite in quartz sand are removed. The SiO2, Fe2O3, Al2O3, and TiO2 contents are 99.79%, 0.0075%, 0.063%, and 0.008%, respectively. Finally, a high-quality quartz sand concentrate with a yield of 67.61% is obtained, meeting the requirements of qualified products.
