How to remove aluminum impurity in quartz sand?

Aluminum is the main impurity element of high-purity quartz sand. It often substitutes si4 + in the crystal lattice and introduces balanced charge ions (Na +, Li +) and so on) γ Al3+ will produce color center under irradiation, which will harm the radiation resistance of quartz glass.
There are three main forms of aluminum in quartz sand as below.
One is in feldspar, mica and clay.
Second, it exists in quartz crystal as inclusion.
Third, it exists in quartz lattice in the form of isomorphism.
For aluminum in different forms, there are also the following removal methods
(1) Clay minerals can be removed by desliming.
(2) It is difficult to remove the aluminum impurities and fluid inclusions in the quartz lattice network by general treatment methods, so high temperature roasting and hydrofluoric acid pickling can be used.
(3) For feldspar type aluminous ore, feldspar is a framework silicate mineral formed by the substitution of si4 + in quartz crystal by Al3+ and mixing with metal cations such as K+, Na+, etc., so the physical properties of feldspar and quartz are similar. Gravity separation and magnetic separation are difficult to separate feldspar and quartz, and flotation is the most effective method to separate them.
The flotation methods of feldspar and quartz can be divided into hydrofluoric acid method and fluorine-free flotation method.
Hydrofluoric acid flotation is a traditional method for separation of feldspar and quartz. It is also a mature and widely used technology. When pH = 2 ~ 3, HF and cationic collector are added to the pulp to make feldspar float out preferentially, so as to achieve the purpose of flotation separation of feldspar and quartz.
Hydrofluoric acid method has a good effect in industrial application. It used to be the main process for separation of feldspar and quartz. However, HF is highly toxic and harmful to the environment. Now it is less or forbidden to use, so it is replaced by fluorine-free flotation process.

Fluoride free flotation is a process developed to change the serious harm of fluoride method to the environment. There are three methods: alkaline pumice quartz method, neutral pumice feldspar method and acid pumice feldspar method. The acid method is widely used in sand washing plants because of its maturity.
1）Acid flotation method is the main separation method of feldspar and quartz flotation, which is about pH = 2 ~ 3, using mixed collector of cation and anion to float feldspar preferentially. Using quartz sand flotation machine can produce good flotation effect and obtain high purity quartz sand.
2）Neutral flotation feldspar method is a method of preferential flotation feldspar in neutral medium with sodium hexametaphosphate as inhibitor and mixed collector of cation and anion.
3）Alkaline pumice quartz method is a method of preferential flotation of quartz with alkyl sulfonate at pH = 11 ~ 12, using alkaline earth metal ions such as Ca2 + and Na + as activators. Through the test of feldspar surface in alkaline feldspar system ζ Potential and Ca2 + adsorption indicate that feldspar is inhibited; The recovery of quartz increases obviously when 1-dodecanol is added. The surface tension is tested and the mechanism is analyzed. It is concluded that the surfactant acts as a promoter in the adsorption of neutral complex semi micelle formed by sulfonate and metal cation on quartz surface, and as a dispersant when long-chain alkyl sulfonic acid is used.

The removal of aluminum impurities is mainly desliming and flotation. The flotation separation of feldspar and quartz has gone through the development process from fluoride and acid to fluoride free and acid free. At present, the acid flotation feldspar method is the most widely used and mature in industry, but this process needs to be carried out under strong acid, which is not easy to operate and easy to corrode equipment. Therefore, the industrial application of fluoride free and acid free method will become a new development direction, The selection of anionic and anionic collectors is a research hotspot.