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Anyone who knows quartz sand knows that quartz sand is widely used and is a non-metallic mineral raw material. In the above, we also know that the purification of quartz sand is difficult, mainly because it contains some other impurity minerals. The impurity minerals containing iron are: goethite, hematite, limonite, ilmenite, magnetic yellow. Iron ore, tourmaline, amphibole, biotite, etc. The presence of these impurities greatly reduces the use value of quartz sand. Therefore, the removal of iron from quartz sand is very important. Let's take a look at the six methods of removing iron from quartz sand. The high quality ore of iron method is the key factor of high quality quartz sand, but there are some impurities in quartz sand more or less, and the quartz sand beneficiation and purification, mostly with iron removal as the main purpose, then all the iron removal methods can be approximated. Divided into the following three categories:

The first category: physical-mechanical methods such as magnetic separation, re-election, flotation, ultrasonic beneficiation and water washing, etc. These methods are suitable for the treatment of coarse-grained impurities;

 The second type: chemical method, which is leached by a mineral acid, and removes an iron oxide film on fine-grained iron-titanium mineral or quartz particles by a chemical reaction. Although this method is more efficient, the cost is higher, the technical conditions are harsh and the environment is harmful;

The third category: microbial beneficiation method is to separate iron from oxidized ore by various bacteria, and the process is slow. At present, industrialization has certain difficulty.

1. Water-eluting mud Scope of application: It is suitable for simple washing of clay to remove clay minerals. Generally, the size of quartz sand is 0.075-1.0mm, while the size of clay mineral is less than 50μm, generally less than 20μm.

Iron removal method:

① Advanced coarse screening to remove the gravel, remove the gravel with a hole diameter of 5cm.

② Use a 0.5-1.0 mm wet sieve to remove coarse sand particles that are detrimental to glass production. Quartz sand and clay minerals can be separated from each other in an aqueous medium.

③ cleaning can use different equipment, such as cleaning tank, cyclone, rising water flow hydraulic classifier. Nowadays, the ascending water flow hydraulic classifier is often used, the fine mineral is discharged from the top overflow port in the form of mud, and the coarser and heavier particles are discharged from the bottom.

 2, re-election

Scope of application: When iron in quartz sand is mainly in the form of heavy minerals (mines with a relative density greater than 2.9), re-election should be considered.

The criteria for re-election are: E = (heavy mineral density - medium density) / (light mineral density - medium density). When E is greater than 2.5, it is easy to reselect and separate. When the value is lowered, the reselection efficiency is lowered. When the value is less than 1.25, it is not suitable for gravity beneficiation.

The role of reselection: reselection is generally effective for the entire particle size range of quartz sand. However, flotation is generally ineffective for the upper limit of the particle size range. In contrast, for mixed particles, flake particles, light mineral particles, and medium density minerals, re-election becomes difficult.

3, magnetic separation

Scope of application: The strong magnetic field concentrator is mainly suitable for quartz sand beneficiation. The magnetic separation investment is relatively high, but the operation is simple and the production cost is low.

Advantages of magnetic separation: It has high selectivity and can obtain high-yield quartz sand while effectively removing impurity minerals. The content of strong magnetic minerals (such as magnetite) in quartz sand is small. Few sand mines can reduce iron content with a low magnetic field magnetic separator.

4. Flotation

In order to remove heavy minerals containing iron, flotation is relatively simple. A common collector for iron oxide is sodium petroleum sulfonate. Petroleum sulfonates can also be replaced by fatty acids.

Advantages of flotation: Removal of iron from minerals by flotation can achieve better results than other methods. Because it not only removes iron minerals, it also removes time-dependent particles with iron and clay minerals. Therefore, many foreign quartz sand concentrators use flotation methods.

Disadvantages of flotation: In order to remove iron impurities, it is necessary to further reduce the particle size of the quartz sand to the monomer dissociation state. Therefore, flotation has poor adaptability to coarse particles, while quartz sand has a relatively coarse particle size range. In addition, special consideration should be given to the contamination of the surrounding environment by flotation reagents.

5, the method of removing thin film iron

Due to the existence of thin film iron, after simple water washing and heavy magnetic separation process, it still can not meet the requirements of producing qualified sand. Therefore, removing thin film iron is a common problem. The method for removing the thin film iron mainly includes a stirring scrubbing, an ultrasonic cleaning and a pickling method.

(1) Stirring and scrubbing

 Stirring scrubbing is accomplished by intergranular friction caused by vigorous agitation of the blades, and is typically used in Denver forging machines. This method usually removes clay minerals and some loose oxides that adhere to the surface. However, since the iron oxide film is thin and strong, this method is unlikely to remove them. Chemical reagents can be added if necessary.

 (2) Ultrasonic cleaning 

The principle of ultrasonic cleaning of mineral surface is to introduce ultrasonic waves into the cleaning liquid, which produces strong cavitation in the cleaning liquid. The cavitation produces strong mechanical force and peels off the impurities attached to the mineral surface. The frequency of the ultrasonic vibration and the residence time of the mineral in the ultrasonic action zone depend on the nature of the surface mineral and its binding strength to the main mineral. Under the action of ultrasonic waves, the film on the surface of the mineral dissociates from other impurities, enters the liquid phase in the form of fine mud, and is removed by washing and dehydration. The method not only removes impurities on the surface, but also removes uneven parts, minute gaps and impurities, thereby ensuring a high-purity cleaning effect. In order to improve the ultrasonic cleaning effect, a small amount of a reagent such as sodium carbonate and a surfactant such as water glass may be added.

(3) Chemical treatment

Quartz sand chemical treatment has good iron removal effect, but the cost is high, the technical requirements are strict, and it is harmful to the environment. However, in order to obtain quartz sand of higher purity, chemical methods will inevitably be used in the future.

Acid leaching and pickling are common chemical treatment methods and can be divided into cold acid treatment and thermal acid treatment. Under static conditions, the treatment by acid-dissolving minerals is called acid leaching. Scrubbing in an acidic medium can be referred to as pickling. Acid leaching takes a considerable amount of time, especially cold acid dissolution.

Alkaline treatment: NaOH and Na2CO3 are commonly used alkaline reagents. The principle of action is to convert insoluble valuable metals into soluble metal sodium salts, thereby achieving the purpose of purifying quartz sand.

Chlorination method: the chlorine gas, sodium chloride, ammonium chloride and quartz sand are heated together, so that the iron in the sand becomes FeCl3 gas volatilization, and the purpose of removing iron can also be achieved.

 6, microbial law

Studies have shown that Aspergillus niger strains can remove iron from quartz sand, but the treatment time is longer. Various physical and mechanical methods and chemical methods can be used alone or in combination to remove iron from quartz sand, and their efficiency depends to a large extent on the nature of the mineral raw material.

Selection principle of quartz sand beneficiation and purification process 
In fact, the purification technology of quartz sand is more and more advanced. In practical applications, it is rare to use only one method to produce qualified sand. Generally, a variety of methods are needed. For a certain type of quartz sand, the following factors should be considered in determining the beneficiation process:

(1) the original composition of the quartz sand to be treated and the state of occurrence of iron;

(2) The user's quality requirements for quartz sand concentrate;

(3) The limits of investment and production costs of the concentrator;

(4) Pollution problems with the surrounding environment.