How to effectively remove iron from silica sand?

Ore dressing and purification of silica sand is mostly aimed at removing iron. The methods of removing iron can be generally divided into physical-mechanical method, chemical method and microbial method. Physical-mechanical methods, such as magnetic separation, gravity separation, flotation, ultrasonic mineral processing and water washing, are suitable for the treatment of coarse impurities. Chemical method is to leach with inorganic acid and remove iron oxide film on fine iron-titanium minerals or quartz particles by chemical reaction. Although this method has high efficiency, it also has high cost, harsh technical conditions and harmful to the environment. There are also microbial beneficiation methods, which are used to separate iron from oxidized ores by various bacteria. The process is slow and industrialization is still difficult at present. The quartz sand raw ore situation is different, the method used is also different, below we will introduce in detail.

1. Water elution and desliming

It is very simple to remove clay minerals and fine minerals from silica sand. Because of the obvious difference between the grain size of silica sand and clay minerals, the grain size of silica sand ranges from 0.075 to 1.0 mm, while that of clay minerals is less than 50 micron and generally less than 20 micron. Therefore, simple washing can remove clay minerals.

Ore washing is generally a preparatory operation in mineral processing. But for silica sand, it is almost inseparable from washing operation, because silica sand often contains more weathered clay. These clays even encapsulate quartz particles to form cements. Therefore, it can be said that ore washing is an independent separation operation in quartz sand beneficiation. Sometimes qualified quartz sand can be obtained after washing.

Before cleaning, coarse screening (e.g. pore size 5 cm) is usually used to remove gravel, and then wet screening with 0.5-1.0 mm is used to remove coarse sand which hinders glass production. As a water spraying device is installed on the screen to assist in screening, quartz sand and clay minerals can be separated from each other in the water medium. Cleaning can be done with different equipment, such as sand washing machine, attrition scrubber, hydraulic classifier, etc. At present, hydraulic classifier is widely used. Fine minerals are discharged from the top overflow in the form of mud, and coarse and heavy particles are discharged from the bottom.

attrition scrubber

It should be pointed out that water-elution of quartz sand not only removes clay minerals, but also removes fine minerals below 0.1mm, mainly quartz. But the content of feldspar and heavy minerals is higher, removing them can greatly reduce the iron content, and the size range of quartz sand is more in line with the requirements of glass industry.

2. Gravity separation

When iron in quartz sand is mainly in the form of heavy minerals (minerals with relative density greater than 2.9), gravity separation should be considered. Gravity separation is often used effectively in the whole grain size range of quartz sand, while flotation is invalid to the upper limit of grain size range. On the contrary, for mixed particles, flake particles, light mineral particles and medium density minerals, gravity separation becomes difficult.

The criterion of gravity separation is: E=(heavy mineral density-medium density)/(light mineral density-medium density). When E is greater than 2.5, gravity separation is easy, and the efficiency of gravity separation decreases with the decrease of this value. When the value is less than 1.25, it is not suitable for gravity separation.

3. magnetic separation

The advantage of magnetic separation is that it has strong selectivity and can obtain high output of quartz sand while maintaining effective removal of impurity minerals. The content of strong magnetic minerals (such as magnetite) in quartz sand is very small. Few placers can reduce iron content with a weak magnetic field separator. Therefore, the high gradient magnetic separator is mainly suitable for quartz sand beneficiation. The investment of magnetic separation is relatively high, but the operation is simple and the production cost is low.

4. flotation

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

Flotation is difficult if quartz and feldspar are to be separated. Feldspar is separated from quartz mainly to reduce the content of alumina. Iron content usually decreases with the decrease of aluminium. In the past, fluorine flotation was used, that is, hydrofluoric acid (HF) was used as adjusting agent and amine as collector. However, due to the enormous harm of fluoride to the environment and the continuous improvement of environmental protection standards, there is no reason to develop this method any more. Therefore, the fluorine-free flotation process has been greatly developed. This method uses dodecyl propylene diamine (dodecyl diamine) as collector in acidic condition regulated by hydrochloric acid or sulphuric acid. Removal of iron from minerals by flotation can achieve better results than other methods. Because it can remove not only monomer containing iron, but also quartz particles with iron film and clay minerals. Therefore, many foreign quartz sand concentrators have adopted flotation method.

The disadvantage of flotation is that in order to remove iron impurities, it is necessary to further reduce the size of quartz sand and make it monomer dissociation. Therefore, flotation has poor adaptability for coarse grains, and the size range of quartz sand is relatively coarse for flotation. In addition, special consideration should be given to the environmental pollution caused by flotation reagents.

flotation machine

5. Removal methods of thin film iron

Owing to the existence of thin film iron, the process of washing and gravity and magnetic separation can not meet the requirements of producing qualified sand. Therefore, the removal of thin film iron is a very common problem. The main methods of removing thin film iron are stirring scrubbing, ultrasonic cleaning and pickling. A. Stirring and scrubbing

Stirring scrubbing is accomplished by the friction between particles caused by the violent stirring of blades. Denver scrubber is commonly used. This method can generally remove clay minerals adhering to the surface of quartz and some loose oxides, but it is unlikely to remove them because of the thin and strong iron oxide film. Adding chemicals can be used when necessary. B. Ultrasound cleaning

The principle of ultrasonic cleaning mineral surface is to introduce ultrasonic wave into the cleaning solution, which causes strong cavitation in the cleaning solution, and produces strong mechanical force by the cavitation, which strips the impurities adhering to the mineral surface. The frequency of ultrasonic vibration and the duration of mineral residence in the ultrasonic zone depend on the properties of surface minerals and the degree to which they bind to the main minerals. Under the action of ultrasound, the film and other impurities on the surface of minerals dissociate and enter the liquid phase in the form of fine mud, which is removed by washing and dehydration. This method can not only remove the impurities on the surface of quartz, but also remove the inhomogeneous and tiny cracks and impurities, which ensures the cleaning effect of high purity. In order to improve the effect of ultrasonic cleaning, a small amount of reagents (such as sodium carbonate), surfactants (such as sodium silicate) C. chemical treatment can be added.

Chemical treatment of quartz sand has a good iron removal effect, but its cost is more expensive, technical requirements are more stringent, and it is harmful to the environment. But in order to obtain higher purity quartz sand, chemical treatment will be inevitable in the future.

Acid leaching and pickling are common chemical treatment methods, which can be divided into cold acid treatment and hot acid treatment. Under static conditions, the treatment of minerals by acid dissolution is called acid leaching, and the scrubbing operation in acidic medium can be called acid pickling. Acid leaching takes quite a long time, especially cold acid dissolution takes a long time.

A. Alkali treatment: NaOH and Na2CO3 are commonly used alkaline agents. Its principle is to convert insoluble valuable metals into soluble sodium metal salts, so as to achieve the purpose of silica sand purification.

B. Chlorination method: heating chlorine, sodium chloride and ammonium chloride with quartz sand to make iron in sand volatilize into FeCl3 gas, which can also achieve the purpose of iron removal. It should be pointed out that chemical treatment is not limited to the treatment of iron oxide films, they are effective for iron in thin film iron and fine clay, and also have partial dissolution for other iron-bearing minerals.

6. Microbiological method

The results show that Aspergillus Niger can remove iron from quartz sand, but the treatment time is longer. Various physical-mechanical and chemical methods can be used to remove iron from quartz sand individually or jointly, and their efficiency depends largely on the properties of mineral raw materials.

7. Selection principle of quartz sand beneficiation and purification process

In practical application, it is rare that qualified sand can be produced by using only one method. Generally, many methods are needed to cooperate with each other. For a certain kind of quartz sand, the following factors should be taken into account in determining the beneficiation process:

A. The original composition of quartz sand to be treated and the occurrence state of iron;

B. Quality requirements of quartz sand concentrate for users;

C. Limits of investment and production costs of concentrators;

D. Pollution of the surrounding environment.