Quartz sand, also known as silica sand, is a common non-metallic mineral raw material. After beneficiation and purification, it can be made into high-purity quartz sand, which is widely used in glass, ceramics, metallurgy, casting and refractory materials industries. So, what are the common methods of quartz sand beneficiation and purification?

1.Quartz sand washing, graded desliming method

The grade of SiO2 in quartz decreases as the particle size of quartz becomes finer, while the grade of impurity minerals such as iron and aluminum increases instead. This phenomenon is particularly obvious in quartz containing a large amount of clay minerals, so before selection Water separation of raw quartz ore is carried out through equipment such as spiral scrubber, trommel, hydrocyclone, desliming bucket, and hydraulic classifier. Grading desliming is necessary and the effect is obvious. Water washing and grading desliming, as a pretreatment method before ore selection, has been applied earlier and widespread. However, the removal effect of thin-film iron and adherent impurity minerals existing on the surface of quartz is not significant.

2.Quartz sand scrubbing method

The scrubbing method mainly uses mechanical force and the abrasive force between the sand grains to remove the thin film iron, bonding and muddy impurity minerals on the surface of the quartz sand, and to further smash the mineral aggregates that are not monomeric, and then the grading operation reaches the quartz sand The effect of further purification. At present, the quartz sand scrubbing method mainly includes two methods: rod friction scrubbing and mechanical scrubbing. For the mechanical scrubbing method, the factors that affect the scrubbing effect are mainly from the structural characteristics and configuration of the scrubbing machine, followed by process factors, including scrubbing time and scrubbing concentration.

Magnetic separation can remove as much as possible the weakly magnetic impurity minerals such as hematite, limonite and biotite, including conjoined particles. Strong magnetic separation usually uses wet strong magnetic separator or high gradient magnetic separator. Generally speaking, for quartz whose impurities are mainly weak magnetic impurity minerals such as limonite, hematite, biotite, etc., the wet-type strong magnet machine can be used to select above 10,000 Oe; For magnetic minerals, it is better to use weak magnetic machine or medium magnetic machine for sorting.

Studies have shown that the number of magnetic separations and the intensity of the magnetic field have an important effect on the effect of magnetic separation. With the increase of the number of magnetic separations, the iron content gradually decreases. Under a certain magnetic field intensity, most of the iron can be removed, but afterwards the magnetic field intensity Even if it is increased a lot, the iron removal rate has not changed much. In addition, the finer the particle size of the quartz sand, the better the effect of removing iron, which is due to the high amount of iron-containing impurity minerals in the fine-grained quartz sand. When the raw quartz sand contains many impurity minerals, only scrubbing, desliming and magnetic separation cannot be used to purify the quartz sand into high-purity sand.

4.Quartz sand flotation method

The flotation method is mainly to remove non-magnetic associated impurity minerals such as feldspar and mica in the quartz sand. Quartz sand flotation mainly includes fluorine flotation and fluorine-free flotation. Among them, fluorine flotation is carried out in the acidic pH range using cationic collectors and hydrofluoric acid activators. The disadvantage is that fluorine-containing wastewater seriously pollutes the environment and needs to be treated and discharged. Fluorine-free flotation is to use the difference in the structure of quartz and feldspar to reasonably adjust the ratio and amount of anion and cation mixed collectors, and use their different zeta potentials to preferentially flotate feldspar to achieve separation.

Generally speaking, after scrubbing, desliming, magnetic separation and flotation, the purity of quartz can reach 99.3%-99.9%, which can basically meet the needs of industrial sand.

Acid leaching utilizes the characteristics that quartz is insoluble in acid (except HF) and other impurity minerals can be dissolved in acid, so as to achieve further purification of quartz.

Commonly used acids for acid leaching include sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid, and reducing agents include sulfurous acid and its salts. Studies have found that the above-mentioned acids have a good removal effect on non-metallic impurities in quartz, but they have a significant effect on different metal impurities, acid types and their concentrations. It is generally believed that various dilute acids can remove Fe and Al. Both have significant effects, and the removal effect of Ti and Cr is acid leaching treatment with concentrated sulfuric acid, aqua regia or HF. The mixed acid composed of the above-mentioned acids is usually used for acid leaching and removal of impurity minerals. Considering the dissolving effect of HF on quartz, the HF concentration generally does not exceed 10%. In addition to the concentration of acid, the amount of acid, acid leaching time, temperature and slurry mixing can all affect the quartz acid leaching effect. The control of various factors of acid leaching should be based on the requirements of the final grade of quartz, try to reduce the acid concentration, temperature and dosage, and reduce the acid leaching time, so as to realize the purification of quartz at a lower beneficiation cost.

The above are the five common methods of quartz sand beneficiation and purification. As for which purification method to choose, it needs to be decided according to various factors such as the nature of the quartz sand ore, the conditions of the dressing plant, and the investment budget. It is recommended that when making a selection, you should first understand the quartz sand and stone itself, and select a single or combined process in a targeted manner through the beneficiation test report in order to strive for the ideal technical and economic benefits.