CN112456499B - Method for preparing high-purity silicon by using silicon cutting waste - Google Patents

Abstract

The invention relates to a method for preparing high-purity silicon by using silicon cutting waste, belonging to the technical field of solid waste resource utilization and material preparation. Mixing silicon cutting waste, a slagging agent and fluorine-free chlorine-free slag, carrying out slagging refining in an inert atmosphere, and separating slag from silicon to obtain massive silicon and fluorine-free chlorine-free slag; taking eutectic Al-Si, Ca-Si or Mg-Si alloy as a refining agent, mixing massive silicon with the refining agent, melting to form hypereutectic Al-Si, Ca-Si or Mg-Si melt, and separating and purifying silicon in the hypereutectic Al-Si, Ca-Si or Mg-Si melt by directional solidification, zone melting or crystal growth method to obtain hypermetallurgical grade silicon and eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities; and (3) performing vacuum directional solidification on the super metallurgical grade silicon to remove impurities such as Al, Mg or Ca and the like to obtain high-purity silicon with the purity of more than 99.999 percent. The invention prepares high-purity silicon by recycling silicon cutting waste, and simultaneously, the generated fluorine-free and chlorine-free residue and eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities can be recycled.

Description

A method for preparing high-purity silicon from silicon cutting waste

technical field

The invention relates to a method for preparing high-purity silicon by utilizing silicon cutting waste, and belongs to the technical field of solid waste resource utilization and material preparation.

Background technique

Due to the massive exploitation and consumption of traditional energy (such as oil, natural gas and coal, etc.), its reserves are nearly exhausted, and energy shortage has become the main problem that restricts the economic and social development of all countries in the world. At present, my country has been the largest energy-consuming country in the world for many years, and the annual energy consumption accounts for 1/5 of the global total. Therefore, the energy problem faced by our country in the future is particularly serious, and it is imminent to find new alternative energy sources. Solar energy is a kind of clean and good new energy. It is widely distributed and has huge reserves. It is generally considered to have bright prospects in future energy use. Solar cells are devices that convert solar energy into electrical energy based on the photovoltaic effect.

The installed capacity of solar cells in my country's photovoltaic industry continues to rank first in the world. High-purity silicon (99.999%) is the raw material for making solar cells and the foundation of the entire photovoltaic industry. The preparation of high-purity silicon solar cells first requires cutting polycrystalline silicon ingots or monocrystalline silicon rods into silicon wafers with a thickness of 0.18-0.19mm. At present, crystalline silicon cutting methods mainly use wire cutting technology and mortar cutting technology. Since the thickness of silicon wafers is approximately equal to that of silicon wafers Due to the slicing gap in the ingot, nearly 35%-40% of the crystalline silicon in the cutting process enters the cutting waste slurry in the form of silicon powder and is lost, causing great waste of resources and serious environmental pollution. 240,000 tons. Since a large amount of impurities will be introduced into the silicon crystal during the cutting process, such as carbon and oxygen elements that will be introduced in the cooling liquid, and aluminum elements will be introduced into the fixed base of the silicon ingot when it is cut, so that the content of silicon in the silicon cutting waste is 60-90%, the total amount of these mixed impurities reaches more than 10% and is difficult to remove.

Therefore, how to efficiently recycle crystalline silicon cut silicon waste is a difficult problem at present. At present, there are several main methods for recycling silicon waste, including phase transfer, electrophoresis and gravity sedimentation, wet pickling, vacuum carbothermic reduction; preparation of high-purity silicon carbide, silicon carbide ceramics, silicon carbide-based composite materials and other silicon-containing materials However, the recycling of silicon waste is hindered by these methods due to different defects. Therefore, it is of greater significance to develop more practical solutions for the recycling of silicon waste.

SUMMARY OF THE INVENTION

Aiming at the problem of battery recycling in the prior art, the present invention provides a method for preparing high-purity silicon by using silicon cutting waste. Ultra-metallurgical grade silicon, and remove impurities such as Al, Mg or Ca through the vacuum directional solidification method to obtain high-purity silicon (99.999%); it can not only recycle industrial solid waste such as silicon cutting waste, but also At the same time, high-purity silicon material that meets solar energy level is obtained. It has obvious economic benefits and industrialization prospects.

A method for preparing high-purity silicon by utilizing silicon cutting waste, the specific steps are as follows:

(1) Mix the silicon cutting waste, the slag-forming agent and the fluorine-free and chlorine-free residue, carry out slag-forming refining in an inert atmosphere, and obtain bulk silicon and fluorine-free and chlorine-free residue after the slag-silicon separation; the fluorine-free and chlorine-free residue passes through After adding a slag-forming agent to adjust the composition, it can be recycled as a fluorine-free and chlorine-free slag in the raw material;

(2) Using eutectic Al-Si, Ca-Si or Mg-Si alloy as refining agent, the bulk silicon in step (1) is mixed with refining agent and melted to form hypereutectic Al-Si, Ca-Si or Mg -Si melt, by directional solidification, zone smelting or crystal growth method to separate and purify silicon in hypereutectic Al-Si, Ca-Si or Mg-Si melt to obtain supermetallurgical grade silicon and cobalt containing trace impurities Crystalline Al-Si, Ca-Si or Mg-Si alloys; eutectic Al-Si, Ca-Si or Mg-Si alloys containing trace impurities can be recycled as refining agents;

(3) removing impurities such as Al, Mg or Ca through the vacuum directional solidification of the supermetallurgical grade silicon in step (2) to obtain high-purity silicon with a purity greater than 99.999%;

The step (1) silicon cutting waste is one or more of diamond wire cutting silicon waste, silicon carbide wire cutting silicon waste, and mortar cutting silicon waste; preferably, the silicon cutting waste is diamond wire cutting silicon waste;

The temperature of described step (1) slagging refining is not lower than 1773K, and the time is 0.5-10h;

In the step (1), the slag-forming agent is one or more of CaO, SiO ₂ , MgO, and Al ₂ O ₃ , and the fluorine-free and chlorine-free slag is an oxide slag that does not contain chloride, fluoride and sodium; Preferably, the fluorine-free and chlorine-free slag is oxide slag with CaO _- SiO as the main component;

The heating temperature of the directional solidification, zone melting or crystal growth method in the step (2) is not lower than the melting point of the corresponding hypereutectic Al-Si, Ca-Si or Mg-Si alloy; The moving speed of the sample is 1-10μm/s, the crystal plane orientation of the seed crystal in the crystal growth method is not limited, and the moving speed of the seed rod in the crystal growth method is 1-5mm/min;

In the step (3), the vacuum directional solidification temperature is not lower than 1723K, the moving speed is 1-10 μm/s, and the vacuum degree is less than 10 ^-3 Pa.

The beneficial effects of the present invention are:

(1) The present invention has obvious removal effect on impurities such as C, O, and Al in the silicon cutting waste, and after refining by slagging, bulk silicon with higher purity is obtained;

(2) the present invention can recycle and reuse the fluorine-free and chlorine-free residue produced after the slag refining, and add an appropriate amount of slag-forming agent to the fluorine-free and chlorine-free residue to readjust the composition and continue to carry out slag refining on the silicon cutting waste; Fluorine-free and chlorine-free slag does not include fluoride, chloride and sodium elements that have an impact on the environment, and has a good environmental protection effect;

(3) The present invention adopts the method of directional solidification, zone smelting or crystal growth to refine bulk silicon to obtain supermetallurgical grade silicon, wherein the refining agent (eutectic Al-Si, Ca-Si or Mg-Si alloy) can be recycled , Although the impurities in silicon enter into the refining agent after silicon refining, but because the impurity content in the refining agent is very low, the obtained eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities can be re-used as Refining agent recycling;

(4) The present invention has no waste gas generation, no carbon emission, low cost, environmental friendliness, and high efficiency.

Description of drawings

Fig. 1 is a schematic flow chart of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the specific embodiments, but the protection scope of the present invention is not limited to the content.

Embodiment 1: a method for preparing high-purity silicon using silicon cutting waste (see Figure 1 ), comprising the following steps:

(1) The diamond wire was cut into silicon waste (the content of Si was 86.9wt%, and the contents of C, O, Al impurities were 0.83wt%, 3.85wt% and 0.87wt%, respectively), slag-forming agent (CaO) and no Fluorine and chlorine-free slag (34wt% CaO and 65wt% SiO ₂ ) was mixed, slag refining was carried out in an inert atmosphere at a temperature of 1773K for 1 hour to remove C, O and Al impurities, and the slag and silicon were separated to obtain a block with a purity of 99.8% Silicon and fluorine-free and chlorine-free residues; the fluorine-free and chlorine-free residues can be recycled as fluorine-free and chlorine-free residues in the raw materials after readjusting the composition by adding a slag-forming agent; the amount of the slag-forming agent CaO accounts for the quality of the fluorine-free and chlorine-free residues 8.3wt%, the ratio of the total slag amount of slag-forming agent and fluorine-free and chlorine-free slag to the amount of diamond wire cutting silicon waste is 1.67:1; the fluorine-free and chlorine-free residue contains 27.5wt% CaO, 67.3wt% _SiO2 and 0.68wt% Al ₂ O ₃ ;

(2) Using the eutectic Al-12.6wt%Si alloy as the refining agent, the bulk silicon in step (1) is mixed with the refining agent eutectic Al-12.6wt%Si alloy, and then heated and melted to form a hypereutectic Al-Si melt , at a smelting temperature of 1273K for 0.5h, and the directional solidification method of electromagnetic induction heating was used to separate and purify the silicon in the hypereutectic Al-Si melt to obtain supermetallurgical grade silicon with a purity of 99.98%. Eutectic Al-Si alloy with trace (0.2wt%) impurities; eutectic Al-Si alloy containing trace (0.2wt%) impurities can be recycled as refining agent; the moving speed of the sample during directional solidification is 10μm/s ;

(3) The supermetallurgical grade silicon with a purity of 99.98% in step (2) (wherein the Al impurity is 150ppmw) is subjected to vacuum directional solidification to remove impurities such as Al to obtain high-purity silicon with a purity of 99.999%; wherein the temperature of the vacuum directional solidification is 1773K , the vacuum degree is 10 ^-3 Pa, the melting time is 1h, and the directional movement speed of the sample is 1μm/s;

After testing, the impurity contents of Al, Fe, Ti, Ca, and Mg in the high-purity silicon of this embodiment are 8 ppmw, 0.3 ppmw, 0.1 ppmw, 1 ppmw, and 0.02 ppmw, respectively.

Embodiment 2: a method for preparing high-purity silicon using silicon cutting waste (see Figure 1), comprising the following steps:

(1) The diamond wire was used to cut silicon waste (the content of Si was 86.9 wt %, and the contents of C, O and Al impurities were 0.83 wt %, 3.85 wt % and 0.87 wt %, respectively), slag-forming agents (CaO and Al ₂ O ₃ ) and fluorine-free and chlorine-free slag (38wt% CaO and 61wt% SiO ₂ ) were mixed, and slag refining was carried out for 1.5h in an inert atmosphere at a temperature of 1873K to remove C, O and Al impurities, and obtained after separation of slag and silicon. Bulk silicon with a purity of 99.7% and fluorine-free and chlorine-free residues; fluorine-free and chlorine-free residues can be recycled as fluorine-free and chlorine-free residues in the raw materials after readjusting the composition by adding a slag-forming agent; among which the slag-forming agents CaO and Al ₂ The amount of _O3 accounted for 3.3wt% and 1wt% of the quality of the fluorine-free and chlorine-free slag, respectively, and the ratio of the total slag amount of the slag-forming agent and the fluorine-free and chlorine-free slag to the amount of diamond wire cutting silicon waste was 1.8:1; The chlorine residue contains 26.5wt% CaO, 68.2wt% SiO ₂ and 1.64wt% Al ₂ O ₃ ;

(2) Using the eutectic Ca-61.4wt%Si alloy as the refining agent, the bulk silicon in step (1) is mixed with the refining agent eutectic Ca-61.4wt%Si alloy, and then heated and melted to form a hypereutectic Ca-Si melt , at a smelting temperature of 1573K for 0.5h, the zone smelting method was used to separate and purify the silicon in the hypereutectic Ca-Si melt to obtain supermetallurgical grade silicon with a purity of 99.98% and a trace amount (0.6wt% of silicon) ) eutectic Ca-Si alloy with impurities; eutectic Ca-Si alloy containing trace (0.6 wt%) impurities can be recycled as a refining agent; the moving speed of the sample during directional solidification is 1 μm/s;

(3) supermetallurgical grade silicon with a purity of 99.99% in step (2) (wherein the Ca impurity is 180ppmw) is subjected to vacuum directional solidification to remove impurities such as Ca to obtain high-purity silicon with a purity of 99.9991%; wherein the temperature of vacuum directional solidification is 1873K , the vacuum degree is 10 ^-4 Pa, the melting time is 1.5h, and the directional movement speed of the sample is 10μm/s;

After testing, the impurity contents of Al, Fe, Ti, Ca, and Mg in the high-purity silicon of this embodiment are 0.3 ppmw, 0.4 ppmw, 0.06 ppmw, 8 ppmw, and 0.05 ppmw, respectively.

Embodiment 3: a method for preparing high-purity silicon using silicon cutting waste (see Figure 1 ), comprising the following steps:

(1) Cutting silicon waste with diamond wire (the content of Si is 86.9wt%, and the content of C, O, Al impurities are 0.83wt%, 3.85wt% and 0.87wt%, respectively), slag-forming agents (CaO and MgO) Mixed with fluorine-free and chlorine-free slag (34wt% CaO and 65wt% SiO ₂ ), in an inert atmosphere at a temperature of 1873K, slag refining was carried out for 2 hours to remove C, O and Al impurities, and the purity was 99.6% after separation of slag and silicon The bulk silicon and fluorine-free and chlorine-free residues; the fluorine-free and chlorine-free residues can be recycled as the fluorine-free and chlorine-free residues in the raw materials after readjusting the composition by adding a slag-forming agent; the consumption of the slag-forming agents CaO and MgO respectively accounts for no 8.3wt% and 1.2wt% of the mass of fluorine-free and chlorine-free slag, the ratio of the total slag amount of slag-forming agent and fluorine-free and chlorine-free slag to the amount of diamond wire cutting silicon waste is 2:1; the fluorine-free and chlorine-free residue contains 28.4wt% %CaO, 67.3 wt% SiO ₂ , 0.63 wt % Al ₂ O ₃ and 1.1 wt % MgO;

(2) Using the eutectic Mg-60.7wt%Si alloy as the refining agent, the bulk silicon in step (1) is mixed with the refining agent eutectic Mg-60.7wt%Si alloy, and then heated and melted to form a hypereutectic Mg-Si melt , and kept for 1 h at a melting temperature of 1373K, using the pulling method to grow single crystal silicon to separate and purify the silicon in the hypereutectic Mg-Si melt to obtain supermetallurgical grade silicon with a purity of 99.99% and containing The eutectic Mg-Si alloy with trace (0.4wt%) impurities; the eutectic Mg-Si alloy containing trace (0.4wt%) impurities can be recycled as a refining agent; the pulling speed of the seed rod is 1mm/min;

(3) supermetallurgical grade silicon with a purity of 99.99% in step (2) (wherein the Mg impurity is 60ppmw) is subjected to vacuum directional solidification to remove impurities such as Mg to obtain high-purity silicon with a purity of 99.9993%; wherein the temperature of vacuum directional solidification is 1773K , the vacuum degree is 10 ^-4 Pa, the melting time is 1h, and the directional movement speed of the sample is 2μm/s;

After testing, the impurity contents of Al, Fe, Ti, Ca, and Mg in the high-purity silicon of this embodiment are 0.1 ppmw, 0.05 ppmw, 0.02 ppmw, 1.2 ppmw, and 5 ppmw, respectively.

The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments, and within the scope of knowledge possessed by those of ordinary skill in the art, various changes can also be made without departing from the purpose of the present invention. .

Claims (5)

1. A method for preparing high-purity silicon by using silicon cutting waste is characterized by comprising the following specific steps:

(1) mixing silicon cutting waste, a slagging agent and fluorine-free chlorine-free slag, carrying out slagging refining in an inert atmosphere, and separating slag from silicon to obtain massive silicon and fluorine-free chlorine-free slag; the slagging agent is CaO or SiO ₂ 、MgO、Al ₂ O ₃ One or more of the fluorine-free and chlorine-free slag is oxide slag without chloride, fluoride and sodium elements, and the fluorine-free and chlorine-free slag is CaO-SiO ₂ Oxide slag as a main component;

(2) taking eutectic Al-Si, Ca-Si or Mg-Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent, melting to form hypereutectic Al-Si, Ca-Si or Mg-Si melt, and separating and purifying silicon in the hypereutectic Al-Si, Ca-Si or Mg-Si melt by directional solidification, zone melting or crystal growth method to obtain super metallurgical grade silicon and the eutectic Al-Si, Ca-Si or Mg-Si alloy;

(3) and (3) performing vacuum directional solidification on the super metallurgical grade silicon obtained in the step (2) to remove impurities to obtain high-purity silicon.

2. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the silicon cutting waste in the step (1) is one or more of diamond wire cutting silicon waste, silicon carbide wire cutting silicon waste and mortar cutting silicon waste.

3. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the temperature of slagging and refining in the step (1) is not lower than 1773K, and the time is 0.5-10 h.

4. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the moving speed of a heater or a sample in the step (2) of directional solidification or zone melting is 1-10 mu m/s, and the moving speed of a seed rod of a crystal growth method is 1-5 mm/min.

5. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the vacuum directional solidification temperature of the step (3) is not lower than 1723K, the moving speed is 1-10 mu m/s, and the vacuum degree< 10 ^-3 Pa。

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