METHOD FOR REFINING CRUDE SILICON MELTS USING A PARTICULATE MEDIATOR

Abstract

A process for the oxidative refining of crude silicon melts during the production of technical-grade silicon. The process includes oxidative refining a crude silicon melt during the production of technical-grade silicon, where during the refining of the crude silicon melt, a finely divided mediator having a particle size parameter d.sub.50 of 1 to 200 μm is added. The finely divided mediator contains a minimum content of metallic silicon of 8% by mass and also at least one or more of the elements H, C, O, F, Cl, Ca, Fe and Al. Additionally, the finely divided mediator is added to the crude silicon melt by means of pneumatic conveying with a gas.

Claims

1-9. (canceled)

10. A process for the oxidative refining of crude silicon melt, comprising: oxidative refining a crude silicon melt during the production of technical-grade silicon, wherein during the refining of the crude silicon melt a finely divided mediator having a particle size parameter d.sub.50 of 1 to 200 μm is added, wherein the finely divided mediator contains a minimum content of metallic silicon of 8% by mass and also at least one or more of the elements H, C, O, F, Cl, Ca, Fe and Al, wherein the finely divided mediator is added to the crude silicon melt by means of pneumatic conveying with a gas.

11. The process of claim 10, wherein the technical-grade silicon has an Si content of at least 95% by mass.

12. The process of claim 10, wherein the finely divided mediator contains silicon residues which are selected from by-products or wastes arising in the production or in the mechanical processing of silicon.

13. The process of claim 10, wherein the finely divided mediator is added to the crude silicon melt by means of a lance.

14. The process of claim 10, wherein the gas with which the finely divided mediator is added to the crude silicon melt contains constituents selected from Cl.sub.2, O.sub.2, SiCl.sub.4, wet H.sub.2 and CO.sub.2, and combinations of these.

15. The process of claim 10, wherein the finely divided mediator has a proportion by weight of oxygen of at most 0.4% by mass.

16. The process of claim 10, wherein the finely divided mediator has a water content of at most 5% by mass.

17. The process of claim 10, wherein the proportion by weight of reactive carbon in the finely divided mediator, based on the total mass of the finely divided mediator, is not more than 0.1, wherein reactive carbon is the proportion of carbon in the finely divided mediator which reacts with O.sub.2 by thermo-oxidative degradation up to a temperature of 1100° C.

18. The process of claim 10, wherein the mass ratio of mass (finely divided mediator) to mass (crude silicon melt) when adding the finely divided mediator is 0.01 to 0.15.

Description

EXAMPLES

[0047] Liquid crude silicon from a continuous production process for metallurgical-grade silicon was collected in a treatment vessel and then, with the addition of various mediators (having a particle size parameter d.sub.50 of 25 μm; addition by pneumatic conveying with air via a refractory injection lance directly into the liquid crude silicon), was oxidatively refined over a period of 100 min (refining gas: oxygen/air mixture [oxygen content at 30% by volume based on the total volume of the gas mixture]; volume flow rate of the mixture: 16 Nm.sup.3/h per 1 t of liquid crude silicon), and the silicon phase was decanted into a trough and finally solidified. After cooling down to room temperature and mechanically removing the silicon from the trough, the specific energy consumption per ton of silicon product and the purity of the silicon product were determined. The tests were evaluated by comparison with conventional processes: usually, the specific energy consumption per ton of silicon product is 13.0 MWh/t, with the purity of the silicon product being approx. 98.5%. Table 1 gives an overview of the mediators used—the results of the tests are summarized in Table 2.

TABLE-US-00001 TABLE 1 Si [% by Accompanying Content [% by mass] Mediator mass] elements Water O C A 10 Fe, Ca, Al, F, Cl 1 35 7 B 10 Fe, Ca, Al, F, Cl 0.05 0.5 5 C 10 Fe, Ca, Al, F 0.1 5 2 D 10 Fe, Ca, Al 0.1 5 1.5 E 10 Fe, Ca, Al 0.1 15 1.5 F 20 Fe, Ca, Al 0.1 5 1.5 G 40 Fe, Ca, Al 0.1 5 1.5 H 50 Fe, Ca, Al 0.1 5 1.5 I 60 Fe, Ca, Al 0.1 5 1.5 J 80 Fe, Ca, Al 0.1 5 1.5

TABLE-US-00002 TABLE 2 Mass ratio Specific energy Purity m(mediator)/ consumption [% by mass Test Mediator m(crude silicon) [MWh/t] of Si] 1 A 0.07 12.92 98.8 2 B 0.07 12.91 98.8 3 C 0.07 12.91 98.7 4 D 0.07 12.9 98.8 5 E 0.07 12.9 98.8 6 F 0.07 12.85 98.9 7 G 0.07 12.87 98.8 8 H 0.07 12.8 98.9 9 I 0.07 12.78 98.9