Feldspar is one of the most common minerals in the continental crust. Its main components include SiO2, Al2O3, K2O, Na2O and so on. It contains potassium, sodium, calcium and a small amount of barium and other alkali metals or alkaline earth metals. As strategic non-metallic mineral resources, feldspar minerals are widely distributed in the earth’s crust, and are the most widely distributed silicate rock-forming minerals except quartz. About 60% of them occur in magmatic rocks, 30% in metamorphic rocks, and 10% in sedimentary rocks, with a total weight of 50% of the earth’s total weight. There is a well-developed isomorphism in feldspar minerals, and the chemical composition is often expressed by OrxAbyAnz (x+y+z=100), where Or, Ab and An represent three components of potassium feldspar, albinite and calcium feldspar, respectively.
The melting point of feldspar is generally about 1300℃, the density is about 2.58g/cm3, Mos hardness 6.5, the specific gravity fluctuates between 2.5-3, brittle, compression resistance, good grindability and development performance, easy to crush.Good chemical stability, corrosion resistance, except high concentration of sulfuric acid and hydrofluoric acid; Helps melt function, commonly used as flux in ceramic and glass industry; Low index of refraction and birefraction. It has a glassy luster, but often has a different color because it contains impurities. Most of feldspar minerals are used as raw materials for glass and ceramic industry, and can also be used for fertilizer treatment, abrasives and tools, glass fiber and other industries.
Factors affecting feldspar quality
The first is the element with dyeing ability, such as Fe, Ti, V, Cr, Mn, Cu, etc.
Under normal circumstances, Fe and Ti are the main dyeing elements, other elements content is very small, white degree has little influence.
The second category is dark minerals, such as biotite, rutile, chlorite and so on. The content of dark minerals in mineral rocks is low, but it has great influence on the quality of feldspar concentrate.The third type is the organic carbon deposited with feldspar, which gives the ore a gray-black color. In most cases, the organic carbon is easy to be removed at high temperature, and the whiteness has little effect. The main elements of the industry products are iron, titanium, and iron, and the surface of the product will appear black spots, the calcium content is too high, the surface of the product is uneven, so to improve the quality of the long stone minerals, the application of the long stone, the content of dark minerals and calcium must be reduced, especially the removal of iron oxide.
The existence of iron in feldspar mainly has the following forms: 1. It is mainly monomer or aggregate of hematite, magnetite and limonite with the particle size of >0.1mm. It is spherical, needle-like, flakelike or irregular, highly dispersed in feldspar minerals and easy to remove. Second, the surface of feldspar is polluted by iron oxide in the form of seepage, or along the cracks, minerals and cleavage joints of feldspar penetration distribution, the iron oxide formed by iron dye greatly increases the difficulty of iron removal. Third, it exists in the form of iron-bearing gangue minerals, such as biotite, limonite, pyrite, ferrotitanium ore, amphibole, epidote and so on.
Commonly used beneficiation methods of feldspar ore
At present, the main process flow of domestic feldspar ore purification is generally “crushing – grinding classification – magnetic separation – flotation”, according to different feldspar mineral impurity content and gangue mineral embedded characteristics, and hand separation, desudging, classification and other operations.
（1） crushing and grinding
The crushing of feldspar is divided into coarse crushing and fine crushing. Most ores have to go through the two processes of coarse crushing and fine crushing.Coarse crushing most of the jaw crusher, crushing equipment mainly impact type crusher, hammer type crusher, impact type crusher, etc.
The grinding of feldspar is mainly divided into dry grinding and wet grinding.
The efficiency of wet grinding is higher than that of dry grinding, and the phenomenon of “over-grinding” is not easy to appear.Grinding equipment are mainly ball mill, rod mill, tower mill, sanding mill, vibration mill, airflow mill, etc.
（2）Washing and desliming
Feldspar ore in the process of formation more or less will contain a certain amount of slime.Washing is mainly to remove impurities such as clay, fine mud and mica in feldspar. Washing can reduce the content of Fe2O3 in the ore, and also improve the content of K2O and Na2O. Ore washing is to separate from coarse-grained minerals under the action of water flow by taking advantage of the characteristics of small particle size and slow settling speed of clay, fine mud and mica.The commonly used ore washing equipment is scrubbing machine, vibrating screen and ore washing tank.
The main purpose of the removal of the mud is to remove the native ore from the ore and the secondary ore of the middle class of the broken grinding process, and prevent the effect of the subsequent selection of the powder. The commonly used deputer equipment has hydraulic cyclone, classifier, centrifuge and depuff.
Using the magnetic difference between various ores, the process of iron removal under the action of external magnetic field is called magnetic separation. Feldspar has no magnetism, but Fe2O3 and mica in feldspar have weak magnetism, so under the condition of strengthening the external magnetic field, Fe2O3, mica and feldspar can be separated.At present, the commonly used magnetic separation equipment in China mainly includes rare earth roller magnetic separator, permanent magnet drum magnetic separator, wet magnetic plate magnetic separator, vertical ring high gradient magnetic separator, electromagnetic slurry high gradient magnetic separator and superconducting high intensity magnetic separator.
Flotation method refers to the addition of adjustment agent, collector, foaming agent and other agents in the grinding raw material pulp, so that the iron impurities attached to the bubble, so that it and the pulp solution, and then mechanical scraping out, so that the iron impurities and raw material fine powder separation.Flotation is an effective way to remove impurity of feldspar. On the one hand, it can remove impurities such as iron and mica, and on the other hand, it can increase the content of potassium and sodium.When the mineral is different, the choice of capture agent is different, but the reverse flotation process can be adopted.
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