In nature, pure quartz minerals are rare; they are usually associated with gangue minerals such as feldspar, mica, iron, aluminum, etc. To obtain high-purity quartz sand, purification is necessary, and the commonly used process for purification is quartz sand flotation technology. This article provides a comprehensive introduction to the principles, process, and types of impurities that flotation can separate in quartz sand.
The principle of quartz sand flotation technology relies on the difference in hydrophobicity between quartz sand and gangue minerals. Through stirring, mineral particles collide with bubbles and adhere to them. The bubbles carry the mineral particles to the bubble layer, achieving the purpose of mineral separation.
However, the physical and chemical properties of silicate minerals are similar, and their surface characteristics are alike. Therefore, selecting suitable flotation reagents, controlling the interaction between mineral surfaces and water, and adjusting the pH to control surface charge become the core issues in flotation.
Crushing: After quartz mining, the ore undergoes crushing using a crusher and vibrating screen, reducing the quartz ore to 20-30mm.
Grinding: The grinding stage follows crushing, where the crushed ore is further ground to smaller particles (200 mesh or even finer) using a rod mill. This stage is completed with the cooperation of a rod mill and classification equipment.
Scrubbing: The surface of quartz sand may sometimes have a thin film of iron, and grinding may cause sludging. Using scrubbing equipment to remove the thin film of iron and sludge helps achieve initial purification.
Stirring: After mixing quartz sand with reagents, stirring and washing are performed to disperse the reagents thoroughly in the quartz sand. This allows impurities on the surface of quartz sand to react with the reagents, forming bubbles.
Flotation: Using density and gravity differences, flotation methods are applied to separate quartz sand and impurities.
Dewatering: Concentrate dewatering is achieved using concentration machines, dewatering screens, and other dewatering equipment to reduce the water content of the quartz concentrate.
Drying: The floated high-purity quartz sand is directly subjected to heating or natural drying.
The above completes the entire process of quartz sand flotation, resulting in high-purity quartz sand. However, quartz ore contains various impurities, and different flotation methods and reagents should be used for different impurities.
Mica: Rapid separation of quartz sand and mica can be achieved through two flotation methods:
a. In alkaline pulp, using an anionic collector, direct flotation can selectively separate quartz, and mica enters the tailings.
b. In acidic pulp, using a cationic collector, reverse flotation can selectively separate mica, and the tailings containing quartz are recovered.
Feldspar: To remove feldspar from quartz sand, three flotation methods can be employed:
a. Acidic flotation of feldspar, mainly under strong acid conditions (usually sulfuric acid H2SO4, pH=2~3), using a mixed anionic-cationic collector for selective flotation of feldspar.
b. Neutral flotation of feldspar, in a neutral medium, using a mixed anionic-cationic collector and an inhibitor to separate quartz and feldspar.
c. Alkaline flotation of quartz, which can be divided into anionic collector method and cationic collector method.
Iron-containing Minerals: For magnetic minerals, magnetic separation is recommended for iron removal in quartz sand. When magnetic separation is not feasible, three flotation methods can be used to separate iron-containing minerals:
a. Fluorine and acid method. This method has good flotation effects, easy control, and stable indicators but causes significant erosion of the land and environmental damage.
b. Fluorine-free acid method. This method eliminates fluoride ions, reducing environmental damage. The production indicators are stable, but strong acid corrosion of beneficiation equipment is severe.
c. Fluorine-free and acid-free method. This method, under natural pH conditions, creates a high-concentration slurry flotation environment through the rational allocation of anionic and cationic collectors to achieve the purpose of selectively floating impurity minerals. However, this method has high requirements for the treatment of original sand and is not easy to control in production, and it is not widely used.
Apatite: Quartz sand's phosphorus minerals are generally present in the form of apatite. Two flotation methods can be used to separate apatite from quartz sand: a. In alkaline conditions, flotation separation of apatite and quartz sand is recommended using Na2CO3 as the pH adjuster and sodium silicate as the inhibitor.
