EA029631B1 - Method for producing metallurgical silicon of improved purity from silicon-containing semiproducts (quartz fines, silicon production dust (microsilica)) by the aluminothermic process - Google Patents

Abstract

The invention is related to the process for producing metallurgical silicon of improved purity from silicon-containing semiproducts by the aluminothermic process, the silicon being inexpensive and environmentally pure, and can be used in production of silicon for solar batteries and semiconductor electronics. Improved purity of the metallurgical silicon is due to provision of a method wherein cleaning of difficult-to-remove boron and phosphorus impurities is carried out simultaneously, in a single operation, aluminothermic silicon recovery and refining by active silicate slags to remove boron and phosphorus are performed by the aluminothermic process with optimum selection of the CaO/SiOratio and selection of quantity of aluminium dissolved in silicon. Solution of the problem by the proposed method allows attainment of a new technical result consisting in producing silicon of improved purity; and, for the purposes of economy, it is proposed to use highly aluminous cement produced as a building material.

Description

The invention relates to the technology of obtaining metallurgical silicon of high purity from silicon-containing intermediates by the method of aluminothermy with low cost, environmentally friendly for use in the manufacture of silicon for solar cells and semiconductor electronics. Production of metallurgical silicon of high purity is ensured by the fact that purification of hard-to-remove impurities of boron and phosphorus occurs simultaneously in a single technological operation. Aluminothermic reduction of silicon and refining it with active silicate slags from boron and phosphorus is carried out by the method of aluminothermy with an optimal selection of the CaO / 8U ₂ and selection of the amount of aluminum dissolved in silicon. When solving the problem by the proposed method, a new technical result is achieved, which consists in obtaining silicon of increased frequency, as well as for the purpose of economic feasibility, the resulting high-alumina cement is supposed to be used as a building material.

029631

The invention relates to the technology of obtaining metallurgical silicon of high purity from silicon-containing intermediates by the method of aluminothermy with low cost, environmentally friendly for use in the manufacture of silicon for solar cells and semiconductor electronics.

The known method according to the Eurasian patent No. 009888, published 08/31/2008, IPC C01B 33/023. The essence of the method consists in obtaining pure silicon by aluminothermic reduction of silicon dioxide in silicon-containing phosphoric slags for the photoelectronic industry. Phosphoric slag was loaded into a graphite crucible, brought to melting by induction heating at an efectic temperature, after which aluminum was added. Silicon, formed as a result of redox reactions, was separated from the slag and floated on its surface. A new batch of slag and aluminum was loaded onto it. The operation was repeated several times until complete precipitation of the reacted slag and separation with silicon, which filled the upper part of the reactor.

The disadvantage of this patent is that in this way silicon can be obtained only in the presence of waste phosphorus production.

The known method is closest to the claimed technical solution, taken as a prototype (see US patent No. 4457903, published 07/03/1984, IPC S01B 33/02). According to the patent, silicon dioxide can be reduced by aluminum to silicon in the presence of slag. In this process, aluminum behaves simultaneously as a reducing agent with respect to the dioxide and as a solvent for the resulting silicon. At the beginning, slag composition was prepared: 48% CaO, 52% δίθ ₂ , mixed and loaded into the crucible. Using induction heating, the mixture was melted, then a mixture of δίΟ ₂ + Α1 was added in portions to the melt in a stoichiometric ratio and kept until complete melting and reduction of silicon from aluminum dioxide. The resulting silicon was collected on the surface of the melt. Separation of silicon from slag was carried out using a drainage system, which consists of two graphite tubes for separate draining of silicon and slag and a graphite septum located 5 mm from the bottom of the crucible. The drainage system allows you to separately drain the silicon and slag into the mold.

The disadvantage of this system is the complexity of the manufacture and operation of the drainage system in the industrial version, the release of aluminum from the oxide dissolved in the electrolysis slag and the fact that no pure silicon is purified from phosphorus using the aluminothermy method.

The technical task of the invention is to obtain pure silicon from intermediates (quartz fines, silica dust production (silica fume)).

The proposed solution allows to obtain metallurgical silicon of high purity, due to the fact that the purification of hard-to-remove impurities of boron and phosphorus occurs in a single technological operation at the same time, aluminothermic reduction of silicon and refining of its active silicate slag from boron and phosphorus.

When solving the problem by the proposed method, a new technical result is achieved, which consists in obtaining silicon of increased frequency from intermediates (quartz fines, silica dust (microsilica)), and for economic expediency, the high-alumina cement formed is supposed to be used as a building material.

The method is as follows:

The separation of slag from silicon during cooling occurs due to the phase transition of dicalcium silicate from the β-phase to the γ-phase. In the present invention, the mixture of the composition (CaO, δίθ ₂ , CaP ₂ ), in which the amount of δίθ ₂ (oxidizer) is greater than the reducing agent (Α1) by the stoichiometric ratio, was mixed and 1/4 of the mixture was loaded into a graphite crucible and melted with induction heating . The remaining mixture was divided into three equal parts, which were portionwise loaded into the molten mixture with the addition of metallic aluminum. The amount of aluminum is taken in an excess amount necessary for the recovery of silicon from dioxide.

Then a mixture of slag and silicon is poured into a mold, and the melt is subsequently refined from aluminum and calcium. Due to the different density of silicon and slag, the separation of these components occurs. When cooling the mixture, the slag disintegrates into powder. Due to this, the slag is separated from silicon.

Purification of metallurgical silicon by aluminothermy of phosphorus is carried out by by selecting the optimum ratio of CaO / occupies 8 ₂ and the amount of dissolved aluminum in silicon. The cleaning coefficient for phosphorus is 100%.

Using the method of the invention, silicon was obtained from hard-to-remove impurities of the following purity, rsh: B - 1.5; P <0.5.

A distinctive feature of the proposed technical solution is that due to the selection of the slag composition in a single technological operation, two stages are simultaneously combined: aluminothermic reduction of silicon and refining it with active silicate slags from boron and phosphorus, as well as from calcium and aluminum, which are separate in traditional technologies. Production of metallurgical silicon of high purity for hard-to-remove impurities

- 1 029631

boron and phosphorus is carried out by aluminothermy through optimal selection ratio CaO / ₂ occupies 8 and selection of the amount of aluminum dissolved in the silicon.

The method of obtaining metallurgical silicon of high purity for stubborn impurities of boron and phosphorus from quartz fines and waste silicon and ferroalloy production (silica fume) by the method of aluminothermy can be used in the manufacture of solar modules.

Claims (1)

CLAIM The method of obtaining metallurgical silicon of high purity from silicon-containing intermediates (quartz fines, silica dust (microsilica)) by the aluminothermy method with batch injection of a mixture consisting of quartz-containing raw materials and aluminum into the pre-melted slag, followed by separation of the slag from silicon, characterized in that the original mixture at a ratio of Cao / 8U ₂ > 1. the amount of aluminum dissolved in silicon is maintained at a level of 5-7%, and the slag is separated from silicon by cooling the mixture.