Feldspars are an integral part of every ceramic product produced. Potassium feldspars are used to produce high strength electric insulators, fine china, and specialty ceramic products. Sodium feldspars are used in the manufacture of glass. Finely ground feldspar is used to produce sanitary ware such as toilets and lavatories and comprises up to 50 percent of their composition. It is also used as a pigment for high traffic paints such as the traffic lane stripes on highways and it is also a key component of foam rubber.
Feldspars are found either as pegmatite (hard rock) or as highly weathered in situ deposits. Both types can be concentrated via flotation but the weathered feldspars are usually more difficult as the grain surfaces are pitted and eroded creating a large increase in the surface area of the feldspar particles. The weathered feldspars are also softer and break down in processing, creating slimes which absorb greater quantities of reagents.
In either case, the feldspar minerals are usually associated with silica sand, micaceous minerals (muscovite and biotite), tourmaline, garnets, ilmenite, and other iron oxides. Feldspar can be separated from the other minerals through the use of multi-stage flotation. The following procedures are normally used:
- Attrition scrubbing at 70% solids or greater if required.
- Thorough desliming to remove all finely disseminated minerals.
- To remove the mica, condition the feed at 50-60% solids with the pH adjusted to 3.0-3.5 with sulfuric acid. A tallow amine (cationic collector) such as AEROMINE 3030C or AEROMINE 3035C promoter is added at a dosage of 0.25 – 0.5 Kg per tonne and the feed conditioned for three minutes. The feed should be diluted to 20-30% solids in the flotation cell. It is often necessary to add fuel oil to the mica conditioner at a dosage of 0.25 – 0.5 Kg per tonne for optimal removal.
- To remove the iron and other heavy minerals, the tailings from the mica float should be dewatered and placed in a conditioner, where very high solids conditioning (70-75%) for five minutes with the pH adjusted to 2.5-3.0 is required. An anionic collector such as AERO 869 promoter is added at a dosage of 0.25 – 0.5 Kg per tonne. After conditioning, the feed enters a flotation cell where it is diluted to 20 30% solids.
To separate the feldspar from the silica sand, the tailings from the heavy mineral float are again dewatered and placed in a conditioner where solids are adjusted to 50-60%. Sulfuric acid is added to attain a pH of 2.0 2.5 and hydrofluoric acid is added at a dosage of 0.38 – 0.75 Kg per tonne. A tallow amine such as AEROMINE 3030C or AEROMINE 3035C promoter (cationic collector) is added at a dosage of 0.25 - 0.5 Kg per tonne. Conditioning time of 3 minutes is recommended. The conditioned feed is diluted to 20-30% solids in a flotation cell where the feldspar is removed from the silica sand. It is often necessary to add kerosene, #2 fuel oil, or some other light oil for optimum removal of the feldspar in particular the weathered feldspars.