Feldspar minerals are extremely complex minerals, and there are many types of feldspar. The main types of feldspar are mainly potassium feldspar, albite, and calcic feldspar. The former two are more important in glass and ceramic industry, and are more common in the utilization of feldspar resources.
Among the common feldspar species, potassium feldspar is mostly found in three forms: permittic feldspar, feldspar, and microplagioclase. It belongs to potassium sodium mixed feldspar, and its potassium sodium ratio is 1:1, 2:1, 4:1, respectively. The latter two are more common in industry. Among them, high potassium feldspar is mostly microplagioclase, and its sodium feldspar content is generally about 20 %. Sodium feldspar belongs to the plagioclase family, and its Na2O theoretical content is 11.80 %. It can be understood that the common feldspar is a mixed mineral of potassium sodium feldspar.
Feldspar beneficiation mainly adjusts ore dressing indexes to meet the requirements of qualified products. Generally more pure feldspar silicon and aluminum are qualified, but if there is quartz, it will increase the content of the feldspar and reduce the content of aluminum, potassium and sodium. At this time, quartz needs to be selected through mineral processing and the flotation process is used only.
Iron index is a harmful element of feldspar. The existence of iron has an effect on the color of ceramics and glass products, especially for high quality products. The required iron content should be as low as possible. The following figure is the requirement for different glass industry to contain iron.
In order to reduce the iron content in feldspar, the main processes that can be used are scrubbing, magnetic separation, flotation, gravity separation, acid washing and so on. The scrubbing is mainly aimed at the situation that the surface contains more thin film iron or more clay minerals. The magnetic separation is mainly for the removal of all kinds of iron minerals with coarser granularity, and the flotation can be used to remove the mica or silicon containing it. Acid and gravity separation are used to remove iron from coarse-grained or fine-grained (desliming) iron. Acid washing is mainly used to remove film iron.
When magnetic selection is used for iron removal of feldspar, magnetic separators with different magnetic fields need to be used, but mainly strong magnetism, because the iron in feldspar is mostly in the form of weakly magnetic iron-bearing minerals. Although the iron index in conventional feldspar tests is expressed in the form of Fe2O3, in fact, the iron in feldspar may be magnetite, hematite, ferrosilicate, iron sulfide or even iron carbonate or other iron-containing salts. In addition to iron sulfide, iron in feldspar can be removed by strong magnetic selection.
The magnetic separator used for removing iron from feldspar can be dry or wet. The difference between them is the requirements of mineral processing and investment, equipment and so on. Dry magnetic separation is not suitable for fine-grained feldspar mineral processing. Part of -0.074mm in feldspar will be lost in a large portion of the magnetic minerals. In the dry magnetic separation process, the fine feldspar can easily form the dust, causing air pollution and need related dust removal equipment. The advantage of dry magnetic separation is that the investment cost of the mineral processing equipment is low. The general dry magnetic separation is directly selected after the crushing crusher is broken, and the grinding cost of all kinds of grinding equipment for wet ore dressing is high and the treatment ability is low.
Wet magnetic separation is suitable for more clay minerals, higher iron content and higher content of powdered ore. The separation accuracy of magnetic mineral and feldspar in wet magnetic separation is high, and the loss of powdery feldspar in dry magnetic separation will not occur. Wet magnetic separation is suitable for micro fine separation. Feldspar micro powder should first choose wet magnetic separation.
The granularity of feldspar ore dressing has a significant influence on the iron removal effect of magnetic separators. When +3 mm feldspar ore dressing, whether dry or wet magnetic dressing, it will be due to the fact that the coarse feldspar containing part of magnetic minerals has its own gravity. Too large causes it to be unselective. The appropriate particle size for dry magnetic selection requirements should be -1mm, and the lower limit of particle size is more appropriate at 0.1 mm. At this time, the mobility of Sandy feldspar is better, and the feldspar particles containing iron are also easier to be adsorbed. When wet magnetic selection, the content of fine particles should be reduced as much as possible. If there are strict requirements for particle size, dehumidification and grading can create better ore dressing conditions for wet magnetic selection.
In the narrow grain range of 0.15 mm, the iron removal effects of dry magnetic and wet magnetic selections are similar.The magnetic separation of long stone requires multiple magnetic separators to be connected in series to perform multistage sweep and magnetic separation.