Production Process of Silicon Metal from Silicon Slag

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Silicon metal is used silica as raw material, carbonaceous material as a reducing agent, and smelting in the electric furnace. The silicon content of industrial silicon is more than 97%. The industrial is mainly used as an alloying agent, Semiconductor material, silicone oil, etc.

About 100kg of silicon slag is produced for every ton of silicon metal produced. For a long time, silicon slag is used for paving or dumping as waste slag, which occupies a lot of land resources. Silicon slag contains more than 15% elemental silicon. How to recycle the silicon slag?

Raw Materials

The new method of silicon metal production uses silicon slag as raw material and removes the CaO, Al2O3, and FeO from it.

silicon slag
silicon slag

The silicon slag chemical composition.

 SiSiO2CFeOAl2O3CaO
Silicon Slag16.248.7150.34.94.9
chemical composition of silicon slag

The Impurities of Silicon Metal

The impurities exist in the silicon metal in the form of elemental and compounds. The thermodynamic calculation shows that, under normal pressure, Fe2O3 reduction temperature is lower than SiO2, Al2O3, MgO, and CaO. Due to the different reduction temperature, the Fe2O3, and SiO2 is totally reduced, while the Al2O3, MgO, and CaO can be partially reduced. The unreduced SiO2, Al2O3, MgO, and CaO from the molten slag. Part of the slag forms a light-colored slag, which can be removed when broken, and the other part is mixed with silicon and becomes an impurity in the metal silicon.

Separation principle of silicon and slag

Extract industrial silicon from silicon slag. Firstly, the light-colored slag and the dark-colored slag in the silicon slag are separated with a manual hammer to increase the silicon content in the silicon slag, and then smelted and separated to remove the impurities in the molten silicon.

Silicon slag

The Silicon Metal Production Process from the Silicon Slag

According to the properties of silicon slag, the smelting process contains manual separation, machine separation, adding raw materials, refining in the furnace, casting, crushing, dust separation, etc.

  • Separated silicon slag fall in the machine separation workshop, and then, the materials are transported to the mixing compartment by the forklift.
  • The prepared materials are added to the electric furnace for smelting. The smelting period is 2-3 hours. When one furnace is charging or discharging, the other furnace is smelting, and it will not be charging and discharging simultaneously.
  • The molten silicon is injected into the ladle, transported to the pouring area by the traveling crane, and crushed after cooling.
  • After passing the inspection, pack it in ton bags and put them into storage.
  • Dust extraction. Using a bag type of dust collector to collect the powder and discharge the purified flue gas into the atmosphere.

Chemical composition of selected silicon slag

 SiSiO2FeOAl2O3CaO
Silicon Slag87.921.50.300.10.06
Chemical composition of selected silicon slag

Chemical composition of prepared materials

 SiSiO2FeOAl2O3CaO
prepared materials88.906.310.30.104.19
Chemical composition of prepared material

Chemical composition of furnace slag

 3Al2O3.2SiO2CaO.SiO2FeO.2SiO2SiCSi
Furnace slag0.63940.8032
Chemical composition of furnace slag

Chemical composition of silicon metal product

 SiCFeOAl2O3CaO
Si metal99.500.020.30.060.03
Chemical composition of silicon metal product

Silicon metal equipment

The industrial silicon enterprise is a high energy-consumption enterprise, therefore, it should be selected in areas with low energy prices. The workshop of silicon slag refining should be close to the origin of raw materials.

Cost analysis of silicon metal production from silicon slag

The cost of producing industrial silicon from silicon slag is about 8,000 yuan/ton, of which the variable cost ratio is 90.77% and the fixed cost ratio is 9.23%. The cost of raw materials and power accounted for 62.0% of the total cost, which is the key factor affecting the benefit. The company increases the recovery rate, reduces energy consumption, and strengthens internal management to increase the benefit.

The production cost of silicon metal

Raw materialIngredientsEnergy powerLabor costOthers
72.740.1617.862.776.47
the production cost of silicon metal

Conclusion:

Silicon slag contains more than 15% of silicon metal. The silicon metal mixed with silicon slag is used as paving material. Using an industrial frequency furnace to smelt silicon slag can obtain industrial silicon with low processing cost, which is a new technology for producing metallic silicon.

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