why to brighten feldspar?

1.       What is Feldspar used for?

Orthoclase and Albite are more used for industrial process. In 2011,  20.7 million Tones of feldspar were produced, mostly by three countries: Turkey (5 Mt), Italy (4.7 Mt) and China (2.1 Mt)(USGS).

Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. Feldspar is ground to about 20 mesh for glassmaking and to 200 mesh or finer for most ceramic and filler applications.

In glassmaking, alumina from feldspar improves product hardness, durability, and resistance to chemical corrosion. In ceramics, the alkalis in feldspar (calcium oxide, potassium oxide, and sodium oxide) act as a flux, lowering the melting temperature of a mixture. Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fiber. Pottery (including electrical insulators, sanitary ware, tableware and tile) and other uses, such as fillers, accounted for the remainder.

2.       How to use Feldspar?

Feldspars shall be pure enough for industrial purpose. Impurities, such as muscovite, hematite, limonite, biotite, chlorite, hornblende, tourmaline, etc, impact the whiteness and performance of feldspars. 

General Industrial Standard for Feldspar

用途 Use	长石种类与品质 Type and Class of Feldspar		化学成分Chemical Composition (%)
			SiO2	Al2O3	Fe2O3	K2O+Na2O	K2O	Na2O	CaO+MgO
玻璃 Glass	钾长石K-feldspar		≤70	≥18	≤0.2
	钠长石Na-feldspar		63-70	16-20	≤0.3		≤1	≥8
陶瓷 Ceramic	钾长石 K-feldspar	I 级品Class-I		≥17	≤0.2	≥11		＜4	＜2
		II级品Class-II		≥17	≤0.5	≥11			＜2
	钠长石Na-feldspar		63-70	16-20	＜0.5	≥11
搪瓷Enamel				＜0.4	12-14

  

Feldspar Product Standard for Domestic Ceramics

类别 Type	等级 Class	化学成分Chemical Composition (%)
		Fe2O3·TiO2	TiO2	K2O·Na2O	K2O	Na2O
钠长石 Na-feldspar	优等品High-class	≤0.15	≤0.03	≥10.00		≥9.00
	I等品Class-I	≤0.25	≤0.05	≥9.00		≥8.00
	合格品Accepts	≤0.50	≤0.10	≥8.00	Na2O>K2O
钾长石 K-feldspar	优等品High-class	≤0.15	≤0.03	≥14.00	≥12.00
	I等品Class-I	≤0.25	≤0.05	≥13.00	≥10.00
	合格品Accepts	≤0.50	≤0.10	≥10.00	K2O> Na2O

Feldspar Product Standard for flat glass

等级 Class	化学成分Chemical Composition (%)
	Fe2O3	Al2O3	K2O+Na2O	SiO2
优等品 High-class	≤0.10	≥18.00	≥12.00	≤65
I级品 Class-I	≤0.20	≥16.00	≥11.00	≤70
II级品 Class-II	≤0.35	≥15.00
合格品 Accepts	≤0.50	≥14.00

Moisture: ≤1% by dry process, and ≤5% by wet process