The existence of iron-containing impurities in quartz sand greatly reduces the use value of quartz sand and affects the quality of products. For example, in glass production, iron-containing impurities will cause great harm to the production and quality of glass, especially for glass melting. The thermodynamic properties of the process and the light transmission of the finished glass. Therefore, quartz sand iron removal technology has always been an important part of quartz sand ore processing. Selecting a suitable quartz sand iron removal method is of great significance for effectively controlling the purity of quartz sand products and improving corporate profits.
The iron-containing impurity minerals in quartz sand mainly include: goethite, hematite, limonite, ilmenite, pyrrhotite, tourmaline, amphibole, biotite, garnet, etc. The existing states of iron impurities in quartz sand include: associated iron impurities in clay and accompanying heavy minerals, argillaceous and thin-film iron on the surface of particles, iron impurities inside quartz sand particles and primary inclusions distributed in crystals. In the processing and production process of quartz sand, the selection of iron removal process should be carried out according to the existence of different iron impurities in order to ensure the control standard of iron content.
At present, the iron removal process of quartz sand generally first carries out water desilting of raw materials, and then selects mechanical scrubbing, magnetic separation, ultrasonic wave, flotation, acid leaching, microorganisms and other methods to remove iron in quartz sand and improve the quality of quartz sand. industrial value.
Mechanical scrubbing is to remove the iron film on the surface of the quartz sand and the iron-containing minerals adsorbed on the surface of the quartz sand by means of the collision and friction between the external force and the sand, so as to achieve the purpose of iron removal. Mechanical scrubbing processes include rod friction scrubbing and traditional mechanical scrubbing.
For mechanical scrubbing, it is generally believed that the factors affecting the scrubbing effect are mainly the structural characteristics and configuration of the scrubbing machine, followed by technological factors, including scrubbing time and scrubbing concentration.
The efficiency of mechanical scrubbing increases with increasing pulp concentration, as increasing pulp concentration increases the probability of particle-to-particle collisions. Studies have shown that the sand scrubbing concentration between 50% and 60% is the best.
In principle, the scrubbing time is based on the preliminary product quality requirements, and should not be too long, because if the time is too long, it will increase the wear and tear of the equipment, increase the energy consumption and increase the cost of beneficiation and purification.
If high-efficiency and strong scrubbing is used with dosing, with appropriate technology and equipment, the effect of rod friction will be better, because dosing can increase the electrical repulsion between the surface of impurity minerals and quartz particles, and enhance the separation of impurity minerals and quartz particles. Effect.
In general, the mechanical scrubbing iron removal process is the most widely used quartz sand iron removal process. It has the characteristics of good quality, large output, low cost and simple operation, and can meet the requirements of float glass for high-quality silica sand. The first choice for large-scale production and processing enterprises.
The acid leaching iron removal method mainly utilizes the characteristics that quartz is insoluble in acid (except hydrofluoric acid), and other impurity minerals can be dissolved by acid, so as to further purify quartz sand. The acid leaching method can not only remove iron from quartz sand, but also has a good effect on non-metallic impurity minerals.
At present, acid leaching mainly includes single acid leaching and mixed acid leaching. The single acid leaching method is mainly aimed at the quartz sand with relatively single impurities. The mixed acid leaching method is to mix different acids together to synergistically remove various impurities in the quartz sand, with higher removal efficiency and better product purity.
Acids commonly used in acid leaching include sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid, and oxalic acid, which is less harmful to the environment, is also used for iron removal.
Since the harmful components in quartz sand are mineral aggregates rather than pure minerals, the effect of mixed acid leaching is better than that of single acid leaching. The proportion of various acids and the order of addition also have a great influence on the removal of impurity minerals.
The acid concentration should be suitable. If the acid concentration is too low, it will take a long time, the output is low and the impurity removal effect is not good. If the acid concentration is too high, it will not only increase the cost, aggravate the corrosion of the equipment, but also reduce the SiO2 output.
The acid leaching temperature has a great influence on the removal rate of impurities in quartz. The lower the temperature, the slower the reaction speed and the longer the time required; the higher the temperature, the faster the volatilization of the acid, thus increasing the amount of acid. In addition, acid leaching time, mineral particle size and slurry agitation all affect the removal effect.
When the impurity content in the product does not meet the requirements after one acid leaching, secondary acid leaching and multiple acid leaching can be carried out until the impurity iron content reaches the requirement.
Generally speaking, the use of sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid is expensive and has a large impact on the environment. The main advantage of using oxalic acid as a leaching agent to remove iron from quartz sand minerals is that a soluble complex is formed during leaching, which can be decomposed under the action of microorganisms and sunlight.
In addition, the use of oxalic acid to remove iron has certain requirements on the particle size of the ore. Generally, it is required to grind the ore to an average particle size of about 20 μm, and to treat the ore for more than three hours, the iron removal rate can reach 80~100%. After acid leaching, low-iron quartz sand with SiO2 purity of 99.99% and Fe content of ≤ 235ppm can be obtained.