A paper on how to prepare high-purity silicon powder in quartz sandstone

High-purity silicon micropowder has the characteristics of good insulation, low thermal expansion coefficient and high chemical stability, and is widely used in semiconductor raw materials, silicone raw materials, solar cell substrates, optical glass electronic packaging materials, and the like.

The silicon micropowder is usually a micropowder which is processed by a process such as crushing, purifying, grinding and grading of natural quartz or fused silica (amorphous SiO2 which is melted and cooled by natural quartz at a high temperature).

The use of quartz sandstone as raw material to prepare high-purity silicon micropowder by ball-scraping, magnetic separation and other mineral processing and purification processes is of great significance for the development and utilization of quartz sandstone.

1. Analysis of quartz sandstone

The quartz sandstone in a certain area of ​​Sichuan Jiangyou was used as raw material to analyze the mineral composition and chemical composition.

(1) Mineral composition

The volume fraction of single crystal quartz in the quartz sandstone is above 95%, the roundness of sorting is better, the quartz is in the shape of his shape, the particle size is mainly concentrated in the range of 0.05-0.2 mm, and the gangue mineral filling is filled in the crack, the particles There is a small amount of clay matrix between them.

(2) Chemical composition

The purity of SiO2 in the quartz sandstone is 99.47%, and the impurities with higher content are mainly Al2O3, Fe2O3, TiO2, K2O, CaO, MgO, and the sum of the six main impurities reaches 0.0603%.

If the quartz sandstone is directly ground and utilized, the SiO2 content of the product only reaches the level of ordinary silicon micropowder, and the content of other impurity elements must be reduced by related processes, and can be applied to the insulation casting of electric components and high-voltage electrical appliances, epoxy resin potting and the like. .

(3) Composition analysis of quartz sandstone micro-region

Quartz sandstone fine particles mainly composed of quartz, the particle size of 20-30 m, the ore containing Al, K, P, Ca, and Ce and other impurities, may occur in phosphate minerals or clay mineral, by ball milling scrub The process can dissociate it from the quartz grains.

2, quartz sandstone preparation of high purity silicon powder

(1) Process conditions

Using a jaw crusher to crush and sieve to obtain -0.20mm quartz sand, magnetic separation by dry magnetic separator (1.0T), preliminary removal of magnetic minerals and impurities in quartz sand;

After being scrubbed by a planetary ball mill, the quartz sand is ground to a desired particle size, and the iron film, clay mineral, etc. on the quartz surface are scrubbed. The planetary ball mill has a rotational speed of 600 r/min, a pulp mass fraction of 50%, and a ball milling time of 80 min. The content of SiO2 in the fine sand obtained by ball scrubbing increased to 99.76%, the whiteness increased from 52.7% of the ore to 86%, and the content of each impurity decreased.

The quartz sand is scrubbed by ball milling. Although the SiO2 content is improved while grinding, the residual impurities in the silicon micropowder need to be acid leached, and the purification effect by mixed acid leaching is more obvious. The acid mass fraction is 12%, the mass ratio of oxalic acid, sulfuric acid and hydrochloric acid is 2.5: 3.75: 3.75, the liquid-solid ratio is 3mL/g, the temperature is 50°C, the ultrasonic acid leaching treatment is 2h, and the high-purity silicon micropowder is obtained by drying and dispersing.

(2) Analysis of the composition of the obtained high-purity silicon micropowder

After the quartz sandstone is mined and purified by crushing, sieving, magnetic separation, ball scrubbing, acid leaching, etc., the indexes of the high-purity silicon micropowder are as follows: SiO2 99.95%, Al2O3 0.0038%, Fe2O3 0.0019%, K2O 0.0008%, TiO2 0.0054 %, CaO 0.0024%, MgO 0.0009%, whiteness of 87.5%, fully meet the requirements of electrical grade silicon micropowder.

Note: The above table shows the physical and chemical indicators of silicon micropowder (SJ/T10675-2002) for the electronics and electrical industry.

China's quartz resources are abundant, but there are relatively few enterprises that can produce high-purity silicon micropowder. The preparation of high-purity silicon micropowder from quartz sandstone is very important for the development and utilization of quartz sandstone resources in China and the destruction of high-purity quartz sand. Significance.