How to remove aluminum from quartz sand

Aluminum is the main impurity element in high-purity quartz sand. It often replaces Si4+ in the crystal lattice and introduces balanced charge ions (Na+, Li+, etc.) γAl3+ will produce color centers under irradiation, damaging the radiation resistance of quartz glass.

Aluminum in quartz sand mainly comes in the following three forms.

First, it is found in feldspar, mica and clay.

Second, it exists in the quartz crystal in the form of inclusions.

Third, it exists in the quartz lattice in an isomorphic form.

For different forms of aluminum, there are several removal methods:

(1) Clay minerals can be removed by desliming.

(2) It is difficult to remove aluminum impurities and fluid inclusions in the quartz lattice network with general treatment methods. High-temperature roasting and hydrofluoric acid pickling can be used.

(3) For feldspathic aluminum ore, feldspar is a skeleton silicate mineral formed by replacing si4+ in quartz crystal with Al3+ and mixed with metal cations such as K+ and Na+. Therefore, the physical properties of feldspar and quartz are similar. . It is difficult to separate feldspar and quartz by gravity and magnetic separation, but 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 the traditional method for separating feldspar and quartz. It is also a mature and widely used technology. When pH=2~3, add HF and cationic collector to the slurry to make the feldspar float out first, thereby achieving the purpose of flotation separation of feldspar and quartz.

The hydrofluoric acid method has good industrial application results. It was once the primary process for separating feldspar and quartz. However, hydrofluoric acid is highly toxic and harmful to the environment. Its use has now been reduced or banned, so it has been replaced by a fluorine-free flotation process.

Fluorine-free flotation is a process developed to change the serious harm to the environment caused by fluorination. There are three methods: alkaline pumice quartz method, neutral pumice feldspar method and acidic pumice feldspar method. The pickling method is widely used in sand washing plants because of its maturity.

1) Acid flotation is the main separation method for feldspar and quartz flotation. When pH=2~3, a mixed collector of anion and cation is used to preferentially float feldspar. The use of quartz sand flotation machine can produce good flotation effect and obtain high-purity quartz sand.

2) The neutral feldspar flotation method is a method of preferential flotation of feldspar in a neutral medium using sodium hexametaphosphate as a corrosion inhibitor and a mixed collector of anions and cations.

3) The alkaline pumice quartz method uses alkyl sulfonate with pH=11~12 and uses alkaline earth metal ions such as Ca2+ and Na+ as activators to preferentially flotate quartz. Testing the ζ potential and Ca2+ adsorption of the feldspar surface in the alkaline feldspar system shows that the feldspar is inhibited; after adding 1-dodecanol, the recovery rate of quartz is significantly improved. Surface tension was tested and the mechanism analyzed. It is concluded that surfactants act as accelerators in the adsorption of neutral composite semimicelles formed by sulfonates and metal cations on the quartz surface, and act as dispersants when using long-chain alkyl sulfonic acids. .