METHOD FOR REFINING CRUDE SILICON MELTS USING A PARTICULATE MEDIATOR

Abstract

A process for refining crude molten silicon. The process includes oxidatively refining the crude molten silicon in the production of technical silicon. The crude molten silicon is admixed during the refining with a particulate mediator which has a minimum amount 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. The particulate mediator is described by a characteristic number K which has a value of 0.03 to 6 mm.sup.−1 and is calculated using the formula

[00001]$K=\frac{6.Math.\left(1-{\mathrm{.Math.}}_{m,M}\right)}{d_{50,M}}$

where d.sub.50,M is the particle size (diameter) at 50% of the mass undersize of the grading curve of the particulate mediator [mm] and the ε.sub.m,M is the mean effective porosity of the particulate mediator.

Claims

1-7. (canceled)

8. A process for oxidatively refining crude molten silicon in the production of technical silicon, comprising: admixing the crude molten silicon during refining with a particulate mediator which comprises a minimum amount 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 particulate mediator is described by a characteristic number K which has a value of 0.03 to 6 mm.sup.−1 and is calculated as follows: $\begin{array}{cc}K=\frac{6.Math.\left(1-{\mathrm{.Math.}}_{m,M}\right)}{d_{50,M}},& \left(\mathrm{equation}1\right),\end{array}$ wherein d.sub.50,M is the particle size (diameter) at 50% of the mass undersize of the grading curve of the particulate mediator [mm]; and wherein ε.sub.m,M is the mean effective porosity of the particulate mediator.

9. The process of claim 8, wherein the technical silicon has an Si content of at least 95% by mass.

10. The process of claim 8, wherein the particulate mediator comprises silicon residues selected from by-products or wastes which are obtained in the production or in the mechanical working of silicon.

11. The process of claim 8, wherein a weight fraction of reactive carbon in the particulate mediator, based on the total mass of the particulate mediator, is at most 0.1, with the reactive carbon being that carbon fraction of the particulate mediator that reacts with 02 up to a temperature of 1100° C. with thermo-oxidative degradation.

12. The process of claim 8, wherein the particulate mediator has a water content of not more than 5% by mass.

13. The process of claim 8, wherein the particulate mediator has an oxygen weight fraction of not more than 0.4% by mass.

14. The process of claim 8, wherein the mass ratio of mass (particulate mediator) to mass (crude molten silicon) on addition of the particulate mediator is 0.01 to 0.5.

Description

EXAMPLES

[0047] The experiments described below were carried out in ambient air and at room temperature (20° C.).

[0048] Liquid crude silicon from a continuous production process for metallurgical silicon was captured in a treatment vessel and then subjected over a period of 100 minutes, with addition of different mediators, to oxidative refining (refining gas: oxygen/air mixture [oxygen content at 30% by volume, based on total volume of the gas mixture]; volume flow rate of the mixture: 16 Nm.sup.3/h per tonne of liquid crude silicon), and the silicon phase was decanted into a trough and finally solidified. After cooling to room temperature and mechanical removal of the silicon from the trough, determinations were made of the specific energy consumption per tonne of silicon product and the purity of the silicon product. The experiments were analyzed in comparison to conventional processes: the specific energy consumption per tonne of silicon product is typically 13.0 MWh/t, with the purity of the silicon product being around 98.5%. Tables 1 and 3 provide an overview of the mediators used—the results of the experiments are summarized in Tables 2 and 4.

TABLE-US-00001 TABLE 1 Me- K Si [% by Accompanying Amount [% by mass] diator [mm.sup.−1] mass] elements Water O C A 0.09 10 Fe, Ca, Al, F, Cl 5 40 10 B 0.09 10 Fe, Ca, Al, F, Cl 0.05 0.5 5 C 0.09 10 Fe, Ca, Al, F 5 15 2 D 0.09 10 Fe, Ca, Al 5 15 2 E 0.09 10 Fe, Ca, Al 5 15 2 F 0.09 20 Fe, Ca, Al 1 15 2 G 0.09 40 Fe, Ca, Al 0.5 10 2 H 0.09 50 Fe, Ca, Al 1 15 2 I 0.09 60 Fe, Ca, Al 1 15 2 J 0.09 80 Fe, Ca, Al 1 15 2

TABLE-US-00002 TABLE 2 Mass ratio Specific energy Purity Experi- m(mediator)/ consumption [% by ment Mediator m(crude silicon) [MWh/t] mass Si] 1 A 0.1 12.92 98.8 2 B 0.1 12.91 98.8 3 C 0.1 12.91 98.7 4 D 0.1 12.9 98.8 5 E 0.1 12.9 98.8 6 F 0.1 12.85 98.9 7 G 0.1 12.87 98.8 8 H 0.1 12.8 98.9 9 I 0.1 12.78 98.9 10 J 0.1 12.75 98.9

TABLE-US-00003 TABLE 3 Me- K Si [% by Accompanying Amount [% by mass] diator [mm.sup.−1] mass] elements Water O C K 0.03 50 Fe, Ca, Al 1 13 2 L 0.04 50 Fe, Ca, Al 1 13 2 M 0.06 50 Fe, Ca, Al 1 13 2 N 0.09 50 Fe, Ca, Al 1 13 2 O 0.11 50 Fe, Ca, Al 1 13 2 P 0.18 50 Fe, Ca, Al 1 13 2 Q 0.42 50 Fe, Ca, Al 1 13 2 R 0.96 50 Fe, Ca, Al 1 13 2 S 1.14 50 Fe, Ca, Al 1 13 2 T 3.6 50 Fe, Ca, Al 1 13 2 U 6 50 Fe, Ca, Al 1 13 2

TABLE-US-00004 TABLE 4 Mass ratio Specific energy Purity Experi- m(mediator)/ consumption [% by ment Mediator m(crude silicon) [MWh/t] mass Si] 11 K 0.1 12.81 98.8 12 L 0.1 12.81 98.8 13 M 0.1 12.77 98.8 14 N 0.1 12.8 98.9 15 O 0.1 12.75 99.0 16 P 0.1 12.74 99.1 17 Q 0.1 12.72 99.0 18 R 0.1 12.63 99.1 19 S 0.1 12.65 98.9 20 T 0.1 12.82 98.7 21 U 0.1 12.85 98.6 22 R 0.01 12.94 98.6 23 R 0.5 12.32 99.5 24 R 0.25 12.44 99.2 25 R 0.02 12.93 98.7 26 R 0.15 12.57 99.2 27 R 0.03 12.92 98.8 28 R 0.04 12.90 98.9

[0049] The examples show that the inventive use of mediators in the production of metallurgical silicon is advantageous economically.