High value-added utilization of micro-silica fume

Micro-silica fume is the dust formed by Si and SiO gas generated during the production of ferrosilicon alloy and metal silicon in the submerged arc furnace, which is oxidized with air in the flue and condensed rapidly, also known as silica fume (or condensed silica fume). With the strengthening of environmental protection, the output of micro-silicon fume is increasing year by year. If it is directly discharged or dumped, it will cause environmental pollution and waste of resources. Therefore, how to resource and utilize these huge quantities of micro-silicon fume has become an urgent problem for ferrosilicon smelting enterprises. The problem.

Microsilica fume is a by-product of ferrosilicon and metal silicon smelting. It is widely used in metallurgical pellets, special concrete, special cement, refractory materials, chemical products and other fields due to its excellent and magical properties.

1. Characteristics of silica fume

The main chemical composition of micro-silica fume is SiO2, in which SiO2 mainly exists in non-crystalline phase (or amorphous SiO2), with a content of ≥80%, less impurity components, a specific surface area of 20-28㎡/g, and a particle size of less than 10μm Accounting for more than 80%, it has high chemical activity, is easy to react with alkali, and has the characteristics of light weight, high refractoriness and strong activity. It is widely used in construction, refractory materials, metallurgy, ceramics, chemical industry and other fields.

2. The hazards of silica fume

Microsilica dust is a kind of fine, light, and easily floating inhalable particles. If it is discharged directly, it will cause the dust to be difficult to settle.
Floating in the air, seriously affecting human health and the surrounding environment. Microsilica dust particles can directly enter the lungs after being inhaled by the human body, causing lung cancer and other dust diseases.

3. High value-added utilization of micro-silica fume

Generally speaking, the higher the grade of SiO2 in silica fume, the higher its added value.

(1) Used in concrete industry

Concrete mixed with silica fume has the characteristics of high strength, good adhesion and cohesion performance, and can increase the molding thickness. In water conservancy and hydropower projects such as long-span bridges and offshore oil drilling platforms, micro-silica fume-doped concrete can improve its anti-seepage, corrosion resistance and abrasion resistance. In the process of road construction, micro-silica fume can greatly improve the early strength and wear resistance of concrete.

(2) As a cement admixture

Microsilica fume is used as a blending material for the production of special cement. The special cement mixed with silica fume can be made into dense concrete whose strength is 2~3 times that of ordinary concrete. It has good wear resistance, corrosion resistance, impermeability, insulation, frost resistance and resistance to chloride ions. blocking performance, etc.

(3) Used in the refractory industry

Micro-silica dust has excellent properties such as high refractoriness, and is widely used in the refractory industry. It is mainly used to prepare high-temperature ceramics, ladle materials, high-temperature wear-resistant materials, breathable bricks, and refractory castables.

(4) Metallurgical pellets

In the metallurgical industry, most enterprises use micro-silicon fume as a return material. Using silica and micro-silica fume mixed pellets as the raw material for electric furnace reduction and smelting of silicon can achieve normal silicon recovery rate and constant energy consumption per unit product. Wet the silica fume with water and make a pellet to form a pellet of about 4cm, which can be directly reduced and smelted in an electric furnace without roasting or drying. The pellets can also be sintered at high temperature, there are no problems such as bursting during the sintering process, and the product sintered ore has high strength.

(5) Preparation of nano-silica (nano-SiO2)

(6) Preparation of metal silicon

(7) Preparation of high performance adsorbent

(8) Preparation of gel material

Since micro-silica fume can be calcined at high temperature or alkali-dissolved to prepare water glass, no matter whether micro-silica fume or water glass is used as the silicon source to prepare silica aerogel, high value-added utilization of micro-silica fume can be realized. Silica airgel prepared from silicon fume has high porosity, high strength, low density, good heat insulation performance, and non-toxic characteristics. It is expected to be widely used in aerospace, construction, medicine and other industries.