Flotation is to use the natural or modified hydrophobic surface of minerals. Through stirring, the ore particles collide with the air bubbles and adhere to them. The air bubbles load the ore particles and float to the air bubble layer to achieve the purpose of mineral separation. Quartz flotation is mainly used to remove mica and feldspar minerals that are symbiotic with quartz ore, and can also float phosphorus and iron-containing minerals. In addition, flotation can also remove secondary iron mixed in crushing and grinding.
The physical and chemical properties of silicate minerals are relatively similar, resulting in similar surface properties. The core issue of flotation is to choose a suitable flotation agent to control the interaction between the mineral surface and water and use pH to control the surface site.
Quartz and feldspar are framework silicate minerals. After the quartz is dissociated, a large number of Si-O bonds are broken and interact with water molecules to bond hydroxyl groups to the surface of the mineral. Adjusting the pH value can change the distribution of OH- or H+ on the mineral surface and charge the mineral surface.
The silicate minerals of the mica family have a layered structure, and the interlayers rely on alkali metal ions to interact with each other. The bonds are weak and the ions are highly active. Therefore, after mica dissociation, it has a relatively high negative charge in aqueous solution, and a low pH value can also attract cations. absorbing agent to make it hydrophobic.
According to the value of the point of zero charge (PZC), in theory, adjust the pH to the isoelectric point of quartz. At this time, the surface of quartz is neutral, and the surface of mica and feldspar is negatively charged to generate electrostatic adsorption with cationic flotation agents; apatite and The surface of iron ore is positively charged, which is easy for anion flotation agent to generate electrostatic adsorption.
Flotation Separation of Mica Minerals and Quartz
After dissociation of layered mica, the surface exposes a large number of anions O2- and F-, and the zero charge point is extremely low (pH<2), so cations can be used in a wide range of pH values (pH=2~13). catch.
In the cation collection system, although feldspar has buoyancy, the pH range of flotation (pH=4~11) is narrower than that of mica, so mica can be floated preferentially under strong acidic conditions.
Flotation Separation of Feldspar Minerals and Quartz
The effective separation of feldspar and quartz has always been a difficult point in the mineral processing industry. The two belong to the framework silicate minerals, which are similar in physical properties, chemical composition, structure, etc., and cannot be separated by gravity and magnetic separation; the charging mechanism of the two in aqueous solution is also basically the same, and the hydrophilicity is relatively strong. , the zero electricity point is very low. However, in the structure of feldspar, aluminum-oxygen tetrahedrons replace silicon-oxygen tetrahedrons, and alkali metal ions such as K+ and Na+ are introduced as electricity price compensation. Alkali metal ions such as K+ and Na+ are easy to dissociate in water, which makes the surface of the mineral negatively charged, making the zero-electric point of feldspar lower than that of quartz, making it possible to float feldspar from quartz.
At present, the separation of feldspar by quartz flotation mainly adopts acidic conditions, and can be divided into fluorine flotation and fluorine-free flotation according to the different reagents used.
The conventional process is the fluorine flotation method that began in the 1940s, that is, under the activation of strong acidity and fluorine ions, feldspar is preferentially floated with cationic collectors. The key to realize flotation selectivity is to adjust the pH value of the pulp solution. At pH=2, quartz is near the zero-electric point, and feldspar has a general zero-electric point (pH=1.4~1.7). Under the activation of fluoride ions, the surface The negative potential is enhanced, and the quartz surface is basically uncharged. Amine cations are the first to adsorb on the surface of feldspar, making the surface hydrophobic.
Flotation Separation of Iron-bearing Minerals and Quartz
The types of iron-containing ores in quartz impurities include pyrite (FeS2), ilmenite (FeTiO3), hematite (Fe2O3), magnetite (Fe3O4), etc. Its occurrence state in quartz is in the form of iron oxide film adhered to the surface of quartz, or in the form of iron-containing minerals as mineral inclusions, and in the form of diffusion in the interior of the quartz crystal lattice or in the presence of Exist in other mineral impurities, such as iron contained in minerals such as mica and hornblende.
It is the key to determine the appropriate selection process to remove iron to find out the occurrence form of iron impurities and the distribution form in each particle size. Most of the iron-containing minerals have a zero-electric point above 5, which is positively charged in an acidic environment, and is theoretically suitable for anion collectors.
Flotation Separation of Apatite Mineral and Quartz
In quartz, phosphorus generally exists in the form of apatite. In industrial phosphate rock flotation, fatty acid soap anionic collectors are commonly used, such as sodium oleate, oxidized paraffin soap, tall oil, etc. for recovery.
Because fatty acids are afraid of hard water and have low solubility at low temperature, to improve their adaptability, it is necessary to mainly target the carboxyl group and the methylene group at the α position, and improve the water solubility and adaptability of the collector by introducing functional groups to modify the polarity of the carboxylic acid molecule. . Such as sulfuration of fatty acids, carboxylation into more polar sulfonic acid groups, increase the water solubility and low temperature resistance of collectors, and improve the flotation adaptability. Studies have shown that the flotation performance of fatty acid sulfonate is equivalent to that of sodium oleate, but it has better selectivity and stronger resistance to hard water. Derivatives such as α-nitro fatty acid, α-sulfonic acid carboxylic acid, chloronaphthenic acid, etc. produced by modification of the methylene group at the α-position of fatty acid have a good collection effect on phosphate rock.
For fatty acid flotation of apatite, in order to solve the problem of low water quality and low temperature in winter, mineral oils such as heavy oil and kerosene are generally added to enhance the hydrophobic surface to achieve the effect of co-collection. Studies have shown that mixed collectors are better than single collectors.