CN104016351B - A kind of efficient except boron slag former, its preparation method and the method except boron slag making - Google Patents

A kind of efficient except boron slag former, its preparation method and the method except boron slag making Download PDF

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CN104016351B
CN104016351B CN201310718123.4A CN201310718123A CN104016351B CN 104016351 B CN104016351 B CN 104016351B CN 201310718123 A CN201310718123 A CN 201310718123A CN 104016351 B CN104016351 B CN 104016351B
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silicon
slag former
boron
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slag
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CN104016351A (en
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谢兴源
杨凤炳
李伟生
龚炳生
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Fujian Shanghang Xingheng silicon products Co.,Ltd.
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FUJIAN XING ZHAOYANG SILICON MATERIALS Co Ltd
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Abstract

The present invention relates to a kind of polycrystalline silicon purifying technical field, particularly relate to a kind of efficient except boron slag former, its preparation method and the method except boron slag making.Described consisting of except boron slag former: nano silicon 40 ~ 60wt%, sodium carbonate 40 ~ 60wt%; Preferred: nano silicon 40 ~ 50wt%, sodium carbonate 50 ~ 60wt%; Wherein the particle diameter of nano silicon is 50 ~ 130nm; Preferably 60 ~ 120nm.Use general silica, the B partition ratio of slag system is 4, and use nano silicon, B partition ratio is increased to 7 ~ 10.Nano-silica surface activity is larger, and except boron partition ratio is high, Be very effective, effectively can reduce the consumption of slag former, shortens the slag making time, greatly reduces cost.

Description

A kind of efficient except boron slag former, its preparation method and the method except boron slag making
Technical field
The present invention relates to a kind of polycrystalline silicon purifying technical field, particularly relate to a kind of efficient except boron slag former, its preparation method and the method except boron slag making.
Background technology
At current energy worsening shortages, under the background that environmental pollution is day by day serious, solar energy power generating, due to features such as technology maturation, resource are never exhausted, environmental pressure is little, becomes 21 century most one of clean energy being hopeful large-scale application, enjoys countries in the world to pay close attention to unique advantage.Polysilicon is described as " blood of modern industry, the foundation stone of microelectronics information industry ", is the basic raw material of development electronics and solar photovoltaic industry and strategic material.
Current polycrystalline silicon purifying mainly contains chemical method and metallurgy method.Chemical method mainly contains improved Siemens, silane thermal decomposition process and fluidized bed process, utilizes chemical method to purify and can obtain the polysilicon of more than purity 9N, but chemical method investment is large, energy consumption is high and seriously polluted.Metallurgy method is produced polysilicon and is referred to metallurgical grade industrial silicon as raw material, when not changing silicon materials physical property, purify to silicon, the purity of Pure Silicon Metal is not less than 99.9999%, Boron contents not higher than 0.3ppm, to be suitable as the requirement of solar cell material.This method most important feature is that production cost is low, and the pollution caused to environment is little, simple to operate, easy scale operation.
In polysilicon, impurity is divided into metallic impurity and nonmetallic impurity.Metallic impurity are because segregation coefficient is much smaller than 1, and available directional solidification method is removed.And nonmetallic impurity B, P segregation coefficient in silicon is 0.8,0.35, far above metallic element, particularly B, close to 1, cannot remove by directional freeze, also cannot as P because saturation steam forces down, and vacuum available melting is removed.At present except the main method of boron has slag making, air blowing, pickling, vacuum, electron beam, plasma body etc.Slagging boron removal is main except boron mode at present, Be very effective and cost is low, is suitable for industrialization and produces.
US Patent No. 5788945 discloses a kind of method by adding slag former in silicon liquid continuously, and slag former composition is 60%CaO and 40%SiO 2, boron drops to 1ppmw from 40ppmw.This continuously with the method for slag former, more owing to wrapping up in silicon in slag, cause silicon to lose large, and in slagging process, the consumption of slag former is relatively too high, causes cost to increase, silicon also can produce certain metallic pollution simultaneously.
Patent CN1926062A discloses a kind of method removing boron from silicon, and this patent is by adding slag former Na in Pure Silicon Metal 2cO 3and SiO 2, form slag, the Boron contents in silicon can be reduced to about 0.3ppmwt by 12ppmwt, but this technique repeats 3 slag making, the quantity of slag is large, and cost is high, and silicon loss is higher, is not suitable for scale operation in industry.
Application 201310337757.5 discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.This slag former, by weight percentage, is mixed by following raw material: Na 2siO 350% ~ 79%, SiO 220% ~ 40% and TiO 21% ~ 15%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value of boron in slag agent and silicon liquid is effectively improve 1 ~ 2 from 2 ~ 4, improve except effect of boron, the Boron contents of silicon material is reduced to below 0.3ppmw.
Application " 201310337930.1 " discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.Slag former, is: Na by weight percentage 2siO 330% ~ 60%, SiO 220% ~ 50%, TiO 21% ~ 15% and Al 2o 31% ~ 5%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value of boron in slag agent and silicon liquid is effectively improve 1 ~ 2 from 2 ~ 4, improve except effect of boron, the Boron contents of silicon material is reduced to below 0.20ppmw.
Application " 201310337756.0 " discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.This slag former, by weight percentage, is mixed by following raw material: Na 2siO 330% ~ 70%, SiO 220% ~ 60%, TiO 21% ~ 15% and FeO1 ~ 5%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value of boron in slag agent and silicon liquid is effectively improve 1 ~ 2 from 2 ~ 4, improve except effect of boron, the Boron contents of silicon material is reduced to below 0.27ppmw.
Slag former and the using method thereof of white residue separation is convenient to when application 201310244836.1 relates to a kind of polycrystalline silicon medium melting.Slag former is mixed by following raw material: SiO 250% ~ 80%, CaO10% ~ 35% and CaCl 25% ~ 15%.Using method is: silicon material joins in plumbago crucible by (1), adopts medium-frequency induction furnace to be heated to silicon material and is all fused into silicon liquid; (2) slag former is joined in mixer mix according to raw material composition; (3) slag former after mixing joins in silicon liquid, and medium melting is carried out in insulation; (4), after medium melting terminates, the old slag produced all is poured out; (5) repeating step (3) ~ (4) 2 ~ 4 times, silicon liquid, through cooled and solidified, measures its Boron contents through ICP-MS.The present invention can improve slag silicon separating effect, reduces the viscosity of slag when slag silicon is separated, improves the rate of recovery, reduce costs.
At present, tradition is except the silicon-dioxide in boron slag former is mainly from high purity quartz ore deposit, and high purity quartz ore resources is limited, streaking, except effect of boron is unstable.
Summary of the invention
Primary goal of the invention of the present invention be to propose a kind of for polysilicon except boron slag former.
Second goal of the invention of the present invention is to propose the preparation method that this removes boron slag former.
3rd goal of the invention of the present invention is to propose use, and this removes the method that boron slag former carries out slagging boron removal.
In order to realize object of the present invention, the technical scheme of employing is:
For polysilicon except a boron slag former, described consisting of except boron slag former: nano silicon 40 ~ 60wt%, sodium carbonate 40 ~ 60wt%; Preferred: nano silicon 40 ~ 50wt%, sodium carbonate 50 ~ 60wt%; Wherein the particle diameter of nano silicon is 50 ~ 130nm; Preferably 60 ~ 120nm.
Wherein the particle diameter of sodium carbonate is the particle diameter of described sodium carbonate is 20 ~ 45 μm; Preferably 25 ~ 40 μm.Described sodium carbonate adopts grinding preparation.
The invention still further relates to a kind of preparation method except boron slag former for polysilicon, comprise the following steps:
(1) combusting rice hull is produced rice hull ash, temperature of combustion is 550 ~ 600 DEG C, and combustion time is 5 ~ 6h;
(2) by rice hull ash and NaOH solution mixing, heated and stirred, has reacted rear filtration, has obtained water glass solution;
(3) water glass solution, hydrochloric acid, oxalic acid added in reactor and heat, Heating temperature is 50 ~ 60 DEG C, and the reaction times is 50min, and in reaction process, the pH value of solution is 8 ~ 8.5, and the pH value of reaction end is 7 ~ 8;
(4) hydrochloric acid is instilled the solution of step (3) gained, regulate pH value to be 4 ~ 4.5;
(5) add Witco 1298 Soft Acid and sodium polyacrylate carries out ageing, Aging Temperature is 90 ~ 100 DEG C, and digestion time 1h separates out white slip;
(6) the white slurry filtration will separated out, with deionized water wash 1 ~ 5 time, by washing with alcohol 1 ~ 3 time, heating volatilization ethanol, dry, pulverize, obtained nano silicon;
(7) above-mentioned obtained nano silicon and sodium carbonate are mixed with obtain removing boron slag former.
First optimal technical scheme of the present invention is: in step (2), and the concentration of NaOH solution is 0.6mol/L, and the ratio of described rice hull ash and NaOH solution is 1kg:15L ~ 18L; Heating temperature is 105 ~ 110 DEG C, and the described reaction times is 4.5 ~ 5h.
Second optimal technical scheme of the present invention is: in step (3), and concentration of hydrochloric acid is 1mol/L, concentration of oxalic acid is 0.1mol/L.
3rd optimal technical scheme of the present invention is: in step (5), and the weight of Witco 1298 Soft Acid is 4 ~ 6wt% of solution; The weight of sodium polyacrylate is 4 ~ 6wt% of solution.
The invention still further relates to a kind of method except boron slag former of polysilicon, comprise the following steps:
(1) metallic silicon power is dropped into heat fused in plumbago crucible, add according to claim 1 except boron slag former after to be melted, be then incubated slag making;
(2) after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Wherein, adopt intermediate frequency induction heating device by metallic silicon power heat fused, described silicon particle size is 60 ~ 200 orders, and the temperature of silicon liquid is 1500 ~ 1700 DEG C;
The mass ratio of metallic silicon power and slag former is 1:0.2 ~ 1:1, preferred 1:0.3 ~ 1:1, more preferably 1:0.4 ~ 1:1;
The slag making time is 15 ~ 20 minutes.
Below technical scheme of the present invention is made further explanation.
The present invention adopts high-temp combustion rice hull ash that organic compound combustion can be made complete, add oxalic acid in precipitin reaction process and make water glass solution more stable dispersion, acidization is conducive to the Impurity removal in silicon-dioxide, in ageing process, two kinds of tensio-active agents adds the formation hindering chemical bond between particle, thus serve the effect of discrete particles, be conducive to the formation of nanoparticle, therefore, the high and narrow particle size distribution of the nano silicon purity prepared of present method.In addition, lower for slagging boron removal partition ratio in slagging process, cause slag former consumption high, cause cost high, the slag making time is long, and it is more owing to wrapping up in silicon in slag, silicon is caused to lose a large difficult problem, the present invention adopts self-control nano silicon, utilize nano silicon to prepare with sodium carbonate and mix slag former, concise by intermediate frequency furnace slag making, effectively boron from industrial silicon content can be reduced to below 0.3ppm, the present invention not only solves rice husk and prepares the not high difficult problem of nano silicon purity, and it is low to solve slagging boron removal partition ratio, slag former consumption is high, cost is high, the difficult problem that the slag making time is long.Use general silica, the B partition ratio of slag system is 4, and use nano silicon, B partition ratio is increased to 7 ~ 10.
The present invention compared with prior art has the following advantages:
Present method can prepare high-purity nano silicon dioxide, has enriched the scope of selecting material of slag former;
Present method slag former adopts nano silicon and sodium carbonate to be mixed with, because nano-silica surface exists the hydroxyl of undersaturated residual bond and different bond styles, surface deviate from stable silica structure because of anoxic, therefore has very strong activity, compared with general silica, surfactivity is larger, can absorb more boron impurities, except boron partition ratio is high, Be very effective, effectively can reduce the consumption of slag former, shorten the slag making time, greatly reduce cost.
The particle diameter of sodium carbonate of the prior art is about 180 μm, because the particle diameter difference of nano level silicon-dioxide and sodium carbonate is excessive, there is the phenomenon being difficult to mix when preparing slag former, thus affect the proportioning of two kinds of compositions in slag former, thus affect the effect of slagging boron removal; And contriver found through experiments, sodium carbonate is processed into the particle that particle diameter is less, can evenly release positively charged ion, thus increase speed of response and reaction efficiency, thus shorten the slag making time.
The specific embodiment of the present invention is only limitted to explain further and the present invention is described, does not limit Composition of contents of the present invention.
Embodiment
Embodiment 1 prepares nano silicon
1. combusting rice hull is produced rice hull ash, temperature of combustion is 550 DEG C, and combustion time is 5h;
2. rice hull ash and 0.6mol/LNaOH solution are added in the reactor of band stirring, and heated and stirred, Heating temperature is 105 DEG C, reaction times is 5h, after question response is complete, is filtered by reaction mass, obtain water glass solution, the ratio of described rice hull ash and NaOH solution is 1kg:15L;
3. above-mentioned water glass solution, 1mol/L hydrochloric acid, 0.1mol/L oxalic acid are added in reactor with the feed rate of metering simultaneously heat, Heating temperature is 60 DEG C, and timing sampling measures the pH value of material, reaction times is 50min, guarantee in reaction process that the pH value of solution is 8 ~ 8.5, the pH value of reaction end is 7 ~ 8;
4. carry out acidifying by the solution of 1mol/L hydrochloric acid instillation step 3 gained, when the pH value of solution is 4 ~ 4.5, stop instillation hydrochloric acid;
5. in the solution after above-mentioned acidifying, add solution 4wt% ten DAADBSA and solution 6wt% sodium polyacrylate carries out ageing, Aging Temperature is 90 ~ 100 DEG C, and digestion time 1h separates out white slip;
6. after ageing has been reacted, by the white slurry filtration of separating out, and with deionized water wash 5 times;
7. by step 6 gained filtrate AG washing with alcohol 2 times, and heating volatilization ethanol, then the filtrate after volatilization is placed the oven drying of 150 DEG C, after to be dried, filtrate is pulverized through simple, obtained nano silicon.The particle diameter of nano silicon is 50 ~ 130nm.
Embodiment 2
1. combusting rice hull is produced rice hull ash, temperature of combustion is 600 DEG C, and combustion time is 6h;
2. rice hull ash and 0.6mol/LNaOH solution are added in the reactor of band stirring, and heated and stirred, Heating temperature is 110 DEG C, reaction times is 4.5h, after question response is complete, is filtered by reaction mass, obtain water glass solution, the ratio of described rice hull ash and NaOH solution is 1kg:18L;
3. above-mentioned water glass solution, 1mol/L hydrochloric acid, 0.1mol/L oxalic acid are added in reactor with the feed rate of metering simultaneously heat, Heating temperature is 50 DEG C, and timing sampling measures the pH value of material, reaction times is 50min, guarantee in reaction process that the pH value of solution is 8 ~ 8.5, the pH value of reaction end is 7 ~ 8;
4. carry out acidifying by the solution of 1mol/L hydrochloric acid instillation step 3 gained, when the pH value of solution is 4 ~ 4.5, stop instillation hydrochloric acid;
5. the 4wt% sodium polyacrylate of 6wt% ten DAADBSA and solution that add solution in the solution after above-mentioned acidifying carries out ageing, and Aging Temperature is 90 ~ 100 DEG C, and digestion time 1h separates out white slip;
6. after ageing has been reacted, by the white slurry filtration of separating out, and with deionized water wash 5 times;
7. by step 6 gained filtrate AG washing with alcohol 1 time, and heating volatilization ethanol, then the filtrate after volatilization is placed the oven drying of 150 DEG C, after to be dried, filtrate is pulverized through simple, obtained nano silicon.The particle diameter of nano silicon is 60 ~ 120nm.
Embodiment 3: prepare sodium carbonate
By milling equipment, it is 325 ~ 700 orders that sodium carbonate is worn into particle diameter, i.e. the powder of 20 ~ 45 microns.
Embodiment 4: prepare sodium carbonate
By milling equipment, it is 375 ~ 500 orders that sodium carbonate is worn into particle diameter, i.e. the powder of 25 ~ 40 microns.
Embodiment 5: slagging boron removal:
1. sodium carbonate prepared by nano silicon and the embodiment 3 that prepared by Example 1 is mixed with except boron slag former, describedly removes in boron slag former, and nano silicon is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, add after to be melted that step 1 prepares except boron slag former 20kg, insulation slag making; Described silicon particle size is 60 ~ 200 orders, and Heating temperature is 1500 DEG C; The slag making time is 15 minutes;
3. after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 6: slagging boron removal
1. sodium carbonate prepared by nano silicon and the embodiment 3 that prepared by Example 1 is mixed with except boron slag former, describedly removes in boron slag former, and nano silicon is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, add after to be melted that step 1 prepares except boron slag former 60kg, insulation slag making; Described silicon particle size is 60 ~ 200 orders, and Heating temperature is 1600 DEG C, and the slag making time is 18 minutes;
3. after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 7: slagging boron removal
1. sodium carbonate prepared by nano silicon and the embodiment 4 that prepared by Example 2 is mixed with except boron slag former, describedly removes in boron slag former, and silicon-dioxide is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, add after to be melted that step 1 prepares except boron slag former 80kg, insulation slag making; Described silicon particle size is 60 ~ 200 orders, and Heating temperature is 1600 DEG C; The slag making time is 20 minutes;
3. after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 8: slagging boron removal
1. sodium carbonate prepared by nano silicon and the embodiment 4 that prepared by Example 2 is mixed with except boron slag former, describedly removes in boron slag former, and nano silicon is 50%, and sodium carbonate is 50%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, add after to be melted that step 1 prepares except boron slag former 100kg, insulation slag making; Described silicon particle size is 60 ~ 200 orders, and Heating temperature is 1700 DEG C; The slag making time is 20 minutes;
3. after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Boron contents measures:
The content of silicon power raw material B in above-described embodiment is denoted as X, the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measured by ICP ~ MS, measuring result is as table 1.
Table 1:
X/ppmw Y/ppmw Test set
Embodiment 5 3.0 0.87 ICP~MS
Embodiment 6 3.0 0.42 ICP~MS
Embodiment 7 3.0 0.25 ICP~MS
Embodiment 8 3.0 0.18 ICP~MS
Comparative example 1 ~ 4:
Get nano silicon and the commercially available common sodium carbonate (particle diameter is 175 ~ 185 μm) of the embodiment of the present invention 1 and embodiment 2 preparation, replace the sodium carbonate in the present invention, slagging boron removal is carried out respectively by the method for embodiment 5 ~ 8, the Pure Silicon Metal that boron-containing quantity is 3.0ppm is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measured by ICP ~ MS, measuring result is as table 2.
Table 2:
X/ppmw Y/ppmw Test set
Comparative example 1 3.0 1.09 ICP~MS
Comparative example 2 3.0 0.65 ICP~MS
Comparative example 3 3.0 0.48 ICP~MS
Comparative example 4 3.0 0.32 ICP~MS
From this comparative example, adopt the sodium carbonate of particle diameter of the present invention can increase speed of response and reaction efficiency, and adopt commercially available common sodium carbonate except effect of boron poor.
Comparative example 5 ~ 8:
Get commercially available general silica (particle diameter is 75 ~ 200 μm) and commercially available common sodium carbonate (particle diameter is 175 ~ 185 μm), slagging boron removal is carried out according to the method for embodiment 5 ~ 8, the Pure Silicon Metal that boron-containing quantity is 3.0ppm is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measured by ICP ~ MS, measuring result is as table 3.
Table 3:
X/ppmw Y/ppmw Test set
Comparative example 5 3.0 1.66 ICP~MS
Comparative example 6 3.0 0.87 ICP~MS
Comparative example 7 3.0 0.56 ICP~MS
Comparative example 8 3.0 0.39 ICP~MS
Comparative example 9 ~ 12
The nano silicon that Example 1 prepares and the sodium carbonate that embodiment 3 prepares, slagging boron removal agent is prepared according to the ratio of table 4, the ratio being 1:1 by metallic silicon power and slag former weight ratio mixes, the Pure Silicon Metal that boron-containing quantity is 3.0ppm is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measured by ICP ~ MS, measuring result is as table 5.
Table 4:
Nano silicon (wt%) Sodium carbonate (wt%)
Comparative example 9 10 90
Comparative example 10 20 80
Comparative example 11 30 70
Comparative example 12 70 30
Comparative example 13 80 20
Comparative example 14 90 10
Table 5:
X/ppmw Y/ppmw Test set
Comparative example 9 3.0 1.12 ICP~MS
Comparative example 10 3.0 0.45 ICP~MS
Comparative example 11 3.0 0.29 ICP~MS
Comparative example 12 3.0 0.35 ICP~MS
Comparative example 13 3.0 0.78 ICP~MS
Comparative example 14 3.0 1.39 ICP~MS
According to above-mentioned simultaneous test, it removes effect of boron the best to adopt ratio of the present invention.And nano silicon is too much or very few, except effect of boron is all poor.

Claims (14)

1. for polysilicon except a boron slag former, it is characterized in that, described consisting of except boron slag former: silicon-dioxide 40 ~ 60wt%, sodium carbonate 40 ~ 60wt%; Wherein the particle diameter of silicon-dioxide is 50 ~ 130nm, and the particle diameter of sodium carbonate is 20 ~ 45 μm.
2. according to claim 1 for polysilicon except boron slag former, it is characterized in that, described consisting of except boron slag former: silicon-dioxide 40 ~ 50wt%, sodium carbonate 50 ~ 60wt%.
3. according to claim 1 for polysilicon except boron slag former, it is characterized in that, the particle diameter of silicon-dioxide is 60 ~ 120nm.
4. according to claim 1 for polysilicon except boron slag former, it is characterized in that, the particle diameter of sodium carbonate is 25 ~ 40 μm.
5. the preparation method except boron slag former for polysilicon according to claim 1, is characterized in that, comprise the following steps:
(1) combusting rice hull is produced rice hull ash, temperature of combustion is 550 ~ 600 DEG C, and combustion time is 5 ~ 6h;
(2) by rice hull ash and NaOH solution mixing, heated and stirred, has reacted rear filtration, has obtained water glass solution;
(3) water glass solution, hydrochloric acid, oxalic acid added in reactor and heat, Heating temperature is 50 ~ 60 DEG C, and the reaction times is 50min, and in reaction process, the pH value of solution is 8 ~ 8.5, and the pH value of reaction end is 7 ~ 8;
(4) hydrochloric acid is instilled the solution of step (3) gained, adjust ph is 4 ~ 4.5;
(5) in the solution of step (4) gained, add Witco 1298 Soft Acid and sodium polyacrylate carries out ageing, Aging Temperature is 90 ~ 100 DEG C, and digestion time 1h separates out white slip;
(6) the white slurry filtration will separated out, with deionized water wash 1 ~ 5 time, by washing with alcohol 1 ~ 3 time, heating volatilization ethanol, dry, pulverize, obtained nano silicon;
(7) above-mentioned obtained nano silicon and sodium carbonate are mixed with obtain removing boron slag former.
6. preparation method according to claim 5, is characterized in that, in step (2), the concentration of described NaOH solution is 0.6mol/L, and the ratio of described rice hull ash and NaOH solution is 1kg:15L ~ 18L; Heating temperature is 105 ~ 110 DEG C, and the described reaction times is 4.5 ~ 5h.
7. preparation method according to claim 5, is characterized in that, in step (3), described concentration of hydrochloric acid is 1mol/L, concentration of oxalic acid is 0.1mol/L.
8. preparation method according to claim 5, is characterized in that, in step (5), the weight of Witco 1298 Soft Acid is 4 ~ 6wt% of solution; The weight of sodium polyacrylate is 4 ~ 6wt% of solution.
9., except the method that boron slag former is purified to polysilicon, it is characterized in that, comprise the following steps:
(1) metallic silicon power is dropped into heat fused in plumbago crucible, add after to be melted described in Claims 1 to 4 any one claim except boron slag former, be then incubated slag making;
(2) after slag making is complete, silicon liquid is injected holding furnace and solidifies, after silicon ingot cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
10. method according to claim 9, is characterized in that, in step (1), adopt intermediate frequency induction heating device by metallic silicon power heat fused, described silicon particle size is 60 ~ 200 orders, and Heating temperature is 1500 ~ 1700 DEG C.
11. methods according to claim 9, is characterized in that, in step (1), the mass ratio of described metallic silicon power and slag former is 1:0.2 ~ 1:1.
12. methods according to claim 11, is characterized in that, in step (1), the mass ratio of described metallic silicon power and slag former is 1:0.3 ~ 1:1.
13. methods according to claim 11, is characterized in that, in step (1), the mass ratio of described metallic silicon power and slag former is 1:0.4 ~ 1:1.
14. methods according to claim 9, is characterized in that, in step (1), the slag making time is 15 ~ 20 minutes.
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