Quartz sand is a widely used mineral raw material, which can be found in industries such as glass, casting, electronic materials and construction. High-purity quartz sand is more valuable and is used in many high-end fields, such as electronics, photovoltaics, semiconductors, etc. However, the presence of aluminum affects the purity of quartz sand, and it needs to be separated. This article will introduce you to the separation method of quartz and aluminum.
The aluminum impurities in quartz sand mainly come from feldspar, mica and clay minerals. Feldspar and mica are rich in aluminum, and clay substances, due to their high viscosity, may introduce aluminum into quartz sand through adsorption or encapsulation.
The impact of aluminum impurities on the performance of quartz sand mainly includes three aspects.
(1)Aluminum impurities will reduce the purity of quartz sand, making it unable to be used in high-end fields such as photovoltaics and semiconductors, and naturally reduce the selling price of quartz sand.
(2)Aluminum impurities may react with other elements, affecting the physical, chemical and optical properties of quartz sand. For example, during the sintering process, aluminum elements will participate in the replacement reaction in the silicate structure, causing the sintering performance of quartz sand to decrease; quartz sand with high aluminum content will have a relatively higher melting point, an increased thermal expansion coefficient, and a decreased electrical insulation performance.
(3)Aluminum impurities increase processing costs. The presence of aluminum impurities will inevitably increase the cost of quartz sand processing, and more advanced technology and more equipment will be used to remove aluminum impurities, thereby improving the purity of quartz sand.
Now that we know the source of aluminum in quartz sand and the effect of aluminum on the properties of quartz sand, how can we separate quartz sand from aluminum stone? Common methods include the following:
（1）Scrubbing and graded desludging
Scrubbing and graded desludging are a common pretreatment method for processing quartz sand. They mainly remove clay minerals and fine impurities on the surface of quartz sand through mechanical scrubbing to reduce the content of aluminum impurities. In actual production, scrubbing operations are usually completed with the help of scrubbers, rod mills and other equipment. Graded desludging usually uses equipment such as hydrocyclones to classify according to particle size, reduce the content of clay impurities, and take away some aluminum impurities.
（2）Flotation method
Since aluminum impurities are usually present in gangue minerals such as feldspar and mica, the common method for separating these gangue minerals is flotation. Flotation methods are mainly divided into two methods: fluorine flotation and fluorine-free flotation.
Fluoride flotation is the use of cationic collectors and hydrofluoric acid activators to float quartz sand minerals within an acidic pH range. This method has good industrial application effects and was once the main process for separating feldspar and quartz. However, due to the toxicity of hydrofluoric acid and its environmental damage, its use has been gradually reduced or banned.
Fluoride-free flotation uses the structural differences between quartz and feldspar to prepare anionic and cationic mixed collectors, and preferentially floats feldspar according to their different Zeta potentials.
（3）Acid leaching method
The acid leaching method is a method in which acid reacts with aluminum impurities to dissolve aluminum impurities and remove them.
15%-20% single hydrochloric acid can be used to replace the mixed acid composed of hydrochloric acid and sulfuric acid, the weight ratio of hydrochloric acid: quartz sand is 1:1, and the industrial pure quartz sand is leached for at least 5 hours at a temperature of 80℃-90℃ with mechanical stirring; 0.4%-0.6% oxalic acid and 1.0%-4.5% hydrochloric acid can also be used to remove aluminum from quartz sand. The weight ratio of oxalic acid to hydrochloric acid is 0.5:99.5, the weight ratio of mixed acid: quartz sand is 1:1, and ultrasonic stirring is performed for at least 1 hour.
When using the acid leaching method, parameters such as acid concentration, temperature and time need to be controlled to avoid excessive erosion of quartz sand.
（4）Heat treatment method
The heat treatment method causes feldspar and other aluminum-containing minerals to undergo phase change or decomposition through high-temperature calcination, thereby reducing their content in quartz sand. However, this method may increase production costs and cause environmental pollution problems.
（5）Combined treatment method
The combined beneficiation method is to use a variety of methods to remove aluminum impurities according to the specific conditions and production requirements of quartz sand. The single beneficiation method introduced above may not be able to remove aluminum impurities completely, so a combined treatment method is often used. For example, first remove some clay impurities by scrubbing and desludging, then use flotation to remove feldspar and mica, and finally use heat treatment or acid leaching to remove stubborn aluminum impurities.
The above are five commonly used methods for separating quartz sand and aluminum stone, among which flotation and combined treatment are more commonly used. It is recommended to conduct a beneficiation test before determining the treatment method, and determine the appropriate beneficiation method based on the test data to achieve the effect of removing aluminum impurities and purifying quartz sand.
