A method for flotation of silicon from silicon slag

Abstract

The present application belongs to the technical field of silicon slag recovery and treatment, and specifically is a method for flotation of silicon from silicon slag, comprising: (1) crushing the silicon slag; (2) washing the crushed silicon slag with water for desliming, filtering and standby use; (3) immersing the washed silicon slag in a NaOH solution; (4) surface treating the immersion silicon slag; (5) placing the surface-treated silicon slag in a flotation tank for flotation, and when the foam is full, turning on the scraper switch to collect the foam and the tailings sinking in the flotation tank; (6) adding a strong acid solution to the tailings under stirring until the tailings no longer dissolve, and filtering to obtain a filtrate; (7) mixing the immersion solution and the filtrate, stirring the mixed solution until no precipitation is generated, and filtering to obtain a filter residue and a filtrate; (8) washing, filtering, drying, weighing, testing and calculating the recovery rate of silicon in the silicon slag.

Description

Technical Field

[0001] The present application belongs to the technical field of silicon slag recovery and treatment, and specifically relates to a method for floating silicon from silicon slag. Background Art

[0002] With the rapid development of solar cells, the demand for industrial silicon is increasing. The production of industrial silicon is mainly obtained through the smelting of silica, which consumes a lot of electricity and energy, causing the production cost to gradually increase. In addition, the suspension of production of some high-pollution, high-energy-consuming small and medium-sized enterprises has exacerbated the contradiction between supply and demand.

[0003] In the process of smelting silica, a large amount of industrial silicon slag is inevitably produced. Silicon slag contains not only Si resources, but also metal impurities such as Mg, Fe, and Al. The silicon metal in the silicon-containing silicon slag of silicon and silicon alloy smelting production enterprises cannot be effectively recycled. Enterprises either sell it cheaply at a price of tens of yuan per ton, or use it for paving roads or as waste slag storage. If the metal silicon in the silicon slag can be recycled by a certain method, it can not only greatly improve the economic benefits of the enterprise, but also have far-reaching and significant practical significance for building a resource-saving and environmentally friendly enterprise.

[0004] In the contradiction between supply and demand, people began to actively explore various methods of producing silicon. At present, in addition to smelting and producing metallic silicon, people have also begun to actively explore the silicon in the silicon slag produced in the process of producing industrial silicon. The existing silicon slag recovery system generally uses a suspension to float the silicon slag. It is generally composed of an independent suspension supply system, a silicon slag delivery system and a stirring system. The matching degree between the systems is not high. If a system has a problem, it is easy to cause the entire system to collapse and a serious accident to occur. Not only is the silicon recovery rate low, but other metal ions in the silicon slag cannot be recovered. Summary of the invention

[0005] In order to solve the above technical problems, the present application discloses a method for flotation of silicon from silicon slag, which is achieved by the following scheme:

[0006] A method for flotation of silicon from silicon slag, characterized in that the steps are as follows: (1) crushing the silicon slag to 0.08-0.5 mm by roller crushing; (2) desludging and washing the crushed silicon slag with water, filtering and setting aside; (3) placing the washed silicon slag in a NaOH solution, and immersing it for 1-2 hours under stirring, with the immersion temperature being 0-30°C; (4) taking out the immersed silicon slag, and rinsing it with clean water, and then placing the silicon slag in a 0.1-5 mol·L -1The surface treatment is carried out in hydrofluoric acid for 1-20 minutes; (5) the surface treated silicon slag is placed in a flotation tank, a non-ionic collector is added, the pH of the flotation solution is adjusted to 7, and the mixture is stirred at 20-30 r / min for 5 minutes, and then the rotation speed is adjusted to 1700 r / min, and the bubbling switch is turned on to start flotation. When the foam is full, the scraper switch is turned on to collect the foam and the tailings sinking in the flotation tank; (6) a strong acid solution is added to the tailings under stirring until the tailings are no longer dissolved, and a filtrate is obtained by filtering; (7) the mixture of step (3) The impregnation liquid and the filtrate obtained in step (6) are mixed, the mixed solution is stirred until no precipitate is generated, filtered to obtain filter residue 1 and filtrate 1, the pH of filtrate 1 is adjusted to 2-4, and filtered to obtain filter residue 2 and filtrate 2 under stirring, the pH of filtrate 2 is adjusted to 10-13, and filtered to obtain filter residue 3 and filtrate 3 under stirring, the filter residue 1, filter residue 2 and filter residue 3 are washed with water once and dried respectively; (8) the concentrate collected in the foam is washed, filtered, dried, weighed, tested and the recovery rate of silicon in the silicon slag is calculated.

[0007] Preferably, in step (1), the silicon slag is crushed to 0.091-0.105 mm.

[0008] More preferably, the concentration of sodium hydroxide in step (3) is 0.1-2 mol·L -1 ;

[0009] By placing the silicon slag in a NaOH solution, the aluminum element in the silicon slag can be dissolved in the sodium hydroxide solution, reducing the impurities in the silicon slag and preparing for subsequent flotation.

[0010] More preferably, the concentration of the hydrofluoric acid in step (4) is 1.2-1.4 mol·L -1 , the processing time is 5min;

[0011] By surface treating the silicon slag, the contact angle of the silicon phase is increased, the hydrophobic property of the silicon phase is increased, and the flotation effect is increased. After the surface treatment of the silicon slag, the contact angle of the slag phase remains basically unchanged and the hydrophilic property is still maintained.

[0012] More preferably, in step (5), sulfuric acid is used to adjust the pH of the flotation solution to 7, and the flotation solution is water or a salt solution.

[0013] More preferably, the salt solution is a sodium chloride solution, and the concentration of the sodium chloride solution is 0.5 mol·L -1 .

[0014] More preferably, the nonionic collector in step (5) is polyoxyethylene ether, and the concentration of the nonionic collector in the flotation solution is 0.1-20.1-2 g·L-1 .

[0015] More preferably, the strong acid solution in step (6) is hydrochloric acid or sulfuric acid, and the concentration of the strong acid solution is 0.1-1 mol·L -1 .

[0016] The beneficial effects are: (1) the silicon slag is first treated with hydrofluoric acid, filtered and then flotated, which greatly reduces the amount of hydrofluoric acid used and the amount of wastewater;

[0017] (2) No flotation agent is added during the entire process, and hydrofluoric acid can be recycled;

[0018] (3) After being treated with hydrofluoric acid, the contact angle of the silicon phase is increased, and the hydrophobic property of the silicon phase is increased, while the contact angle of the slag phase remains basically unchanged, and the hydrophilic property is still maintained, thereby increasing the flotation effect;

[0019] (4) dissolving the aluminum element in the silicon slag in a sodium hydroxide solution, mixing the sodium hydroxide solution with the filtrate, obtaining a filter residue 1 which is aluminum hydroxide, adjusting the pH of the filtrate 1 to 2-4, obtaining a filter residue 2 which is iron hydroxide, adjusting the pH of the filtrate 2 to 10-13, obtaining a filter residue 3 which is magnesium hydroxide;

[0020] (5) The present application is reasonably designed and has a simple process flow, and does not require scavenging, roughing and other processes. On the basis of achieving efficient recovery of silicon in silicon slag, other metal elements in the silicon slag are recovered. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for the description of the embodiments are briefly introduced below. Obviously, the drawings described below are only some of the preferred embodiments of the present application, not all of the embodiments. For the preferred embodiments in the present application, for ordinary technicians in this field, other embodiments and drawings can be obtained based on these embodiments and drawings without creative work, and they all belong to the protection scope of the present application.

[0022] Figure 1 This is a schematic diagram showing the effect of hydrofluoric acid concentration on flotation results in Example 2;

[0023] Figure 2 This is a schematic diagram showing the effect of the hydrofluoric acid treatment time on the flotation effect of silicon slag in Example 3;

[0024] Figure 3 This is a schematic diagram showing the effect of silicon slag crushing method on silicon slag flotation effect in Example 4;

[0025] Figure 4 The effect of silicon slag particle size on silicon slag flotation effect in Example 5 is shown in FIG. Figure 1 ;

[0026] Figure 5 The effect of silicon slag particle size on silicon slag flotation effect in Example 5 is shown in FIG. Figure 2 ;

[0027] Figure 6 The effect of silicon slag particle size on silicon slag flotation effect in Example 5 is shown in FIG. Figure 3 ;

[0028] Figure 7 The effect of silicon slag particle size on silicon slag flotation effect in Example 5 is shown in FIG. Figure 4 ;

[0029] Figure 8 The effect of collector type on the flotation effect of silicon slag powder in Example 6 is shown in FIG. Figure 1 ;

[0030] Fig. 9 The effect of collector type on the flotation effect of silicon slag powder in Example 6 is shown in FIG. Figure 2 ;

[0031] Fig.10 The effect of collector type on the flotation effect of silicon slag powder in Example 6 is shown in FIG. Figure 3 ;

[0032] Fig.11 This is a schematic diagram of the effect of collector concentration on the flotation effect of silicon slag powder in Example 7. DETAILED DESCRIPTION

[0033] Example 1

[0034] A method for flotation of silicon from silicon slag, characterized in that the steps are as follows: (1) crushing the silicon slag to 0.091-0.105 mm by roller crushing; (2) desludging and washing the crushed silicon slag with water, filtering and setting aside; (3) placing the washed silicon slag in a NaOH solution, and immersing it for 1.5 h under stirring, the immersion temperature being 15° C.; (4) removing the immersed silicon slag, and rinsing it with clean water, and then placing the silicon slag in a 1.2 mol·L -1The surface treatment is carried out in hydrofluoric acid for 5 minutes; (5) the surface treated silicon slag is placed in a flotation tank, polyoxyethylene ether is added as a collector, the pH of the flotation solution is adjusted to 7, and the mixture is stirred at 20-30 r / min for 5 minutes, and then the rotation speed is adjusted to 1700 r / min, and the bubbling switch is turned on to start flotation. When the foam is full, the scraper switch is turned on to collect the foam and the tailings sinking in the flotation tank; (6) a strong acid solution is added to the tailings under stirring until the tailings are no longer dissolved, and a filtrate is obtained by filtering; (7) the mixture obtained in step ( 3) The impregnation liquid and the filtrate obtained in step (6) are mixed, the mixed solution is stirred until no precipitation is generated, and the filter residue 1 and the filtrate 1 are obtained by filtering, the pH value of the filtrate 1 is adjusted to 2-4, and no precipitation is generated under stirring, and the filter residue 2 and the filtrate 2 are obtained by filtering, the pH value of the filtrate 2 is adjusted to 10-13, and no precipitation is generated under stirring, and the filter residue 3 and the filtrate 3 are obtained, and the filter residue 1, the filter residue 2 and the filter residue 3 are washed with water once and dried respectively; (8) The concentrate collected in the foam is washed, filtered, dried, weighed, tested and the recovery rate of silicon in the silicon slag is calculated;

[0035] More preferably, the concentration of sodium hydroxide in step (3) is 0.5 mol·L -1 ;

[0036] More preferably, the concentration of the collector in the flotation solution is 0.1-2 g·L -1 .

[0037] More preferably, in step (5), sulfuric acid is used to adjust the pH of the flotation solution to 7, and the flotation solution is a sodium chloride solution with a concentration of 0.5 mol·L -1 ;

[0038] More preferably, the strong acid solution in step (6) is hydrochloric acid, and the concentration of the hydrochloric acid solution is 0.2 mol·L -1 ;

[0039] The flotation recovery rate was 92.9%, and the silicon content was 99.01%.

[0040] Example 2

[0041] Experiment on the effect of hydrofluoric acid concentration on flotation results: The concentrations of hydrofluoric acid in step (4) are 0, 0.2, 0.6, 0.8, 1.0, 1.4, 1.6, 1.8, and 2.0 mol·-1, respectively. The other conditions are the same as those in Example 1. The recovery rate of silicon in silicon slag is as follows: Figure 1 .

[0042] Depend on Figure 1 It can be seen that the silicon recovery rate increases rapidly with the increase of HF concentration. When the HF concentration reaches 1.2 mol·L -1When HF is added, the recovery rate reaches 92.9% and tends to equilibrium. Continuing to increase HF, the silicon recovery rate increases slightly, and the maximum recovery rate can reach 93.7%. The trend of the recovery rate gradually increasing and then tending to equilibrium is mainly because with the increase of HF concentration, the hydrophobicity of the silicon surface in the silicon slag powder becomes stronger and stronger, and it becomes easier to combine with foam. When the HF concentration increases to a certain level, the hydrophobicity of the silicon surface reaches the maximum, so the recovery rate tends to equilibrium.

[0043] As the HF concentration increases, the silicon content increases first and then decreases. When the HF concentration is 1.4 mol·L-1, the silicon content reaches a maximum value of 99.03%.

[0044] Example 3

[0045] Experiment on the effect of hydrofluoric acid treatment time on silicon slag flotation effect: The surface treatment time in step (4) is 1, 3, 7, 9, 11, 13, and 15 minutes respectively, and the other aspects are the same as in Example 1. The recovery rate of silicon in silicon slag is as follows: Figure 2 .

[0046] Depend on Figure 2 It can be seen that when other conditions are fixed, the silicon recovery rate increases rapidly with the increase of surface treatment time. When the treatment time is 5 minutes, the recovery rate tends to balance, and the silicon recovery rate does not change significantly after 5 minutes. However, the silicon percentage does not change significantly with the extension of treatment time, indicating that the silicon percentage is not greatly affected by the treatment time. The reason for this situation is that the treatment time is too short, the surface treatment agent HF does not fully react with the silicon phase, the hydrophobic properties of the silicon powder surface vary in strength, and the silicon particles with stronger hydrophobic properties combine well with the bubbles, while some silicon particles with weaker hydrophobicity cannot combine well with the bubbles and cannot float, resulting in a low recovery rate. As the treatment time increases, the silicon particles can fully react with the surface treatment agent, thereby producing better hydrophobicity, and then be captured by the bubbles to form a silicon-rich phase. The reason why the silicon percentage is not greatly affected is that only the silicon particles produce hydrophobicity, so the silicon percentage is not greatly affected by the treatment time when other conditions are fixed.

[0047] Example 4

[0048] Experiment on the effect of silicon slag crushing method on silicon slag flotation effect: The crushing method and crushing particle size of silicon slag in step (1) are as shown in the following table. Others are the same as in Example 1. The recovery rate of silicon in silicon slag is as follows: Figure 3 ;

[0049]

[0050] Depend on Figure 3It can be seen that the silicon content of roller milled silicon slag and ball milled silicon slag has roughly the same trend and little difference, but the recovery rate of roller milled silicon slag has obvious advantages over ball milled silicon slag. This shows that the silicon slag particles crushed by roller milling have a rough surface, which can promote the hydrophobic silicon particles to better adhere to the bubbles, which is beneficial to improve the effect of flotation separation of silicon in silicon slag.

[0051] Example 5

[0052] Experiment on the effect of silicon slag particle size on silicon slag flotation effect: The particle size of silicon slag in step (1) and the concentration of hydrofluoric acid in step (4) are as shown in the following table. Other aspects are the same as in Example 1. The recovery rate of silicon in silicon slag is as follows: Figure 4-7 ,

[0053]

[0054] Depend on Figure 4-7 It can be seen that when the particle size is 0.200-0.355mm, the silicon recovery rate is about 35%, and it does not change much with the increase of HF concentration. The silicon percentage increases slightly with the increase of HF concentration. When the silicon slag powder particle size decreases to 0.135-0.200mm, the silicon recovery rate increases rapidly with the increase of HF concentration until equilibrium, and the silicon percentage of the concentrate also increases slightly. When the particle size is 0.091-0.105mm, at the HF concentration of 1.2mol·L -1 The best effect was obtained, indicating that the dissociation degree between silicon phase and slag phase was high within this particle size range.

[0055] Example 6

[0056] Experiment on the effect of different collector types on the flotation effect of silicon slag powder: The amount of collector added in step (5) is 1 g·L -1 The collector described in step (5) and the pH value of the flotation solution are specifically as follows: Others are the same as in Example 1. The recovery rate of silicon in silicon slag is as follows: Figure 8-10 ,

[0057]

[0058] Depend on Figure 8-10 It can be seen that different types of collectors have different abilities to capture metallic silicon. The cationic collector hexadecyltrimethylammonium bromide has a high recovery rate for silicon capture under acidic conditions. As the alkalinity becomes stronger, the recovery rate decreases rapidly, while the proportion of silicon has a downward trend. The main reason is that the amino groups in the amine collectors have good adsorption properties for both the residual oxides on the surface of the silicon phase and the oxides on the surface of the slag phase, so the selectivity is poor. During flotation, the slag phase and the silicon phase will be floated together, resulting in the inability to separate the silicon phase from the slag phase well.

[0059] The non-ionic collector Brij 58 will not ionize, will not affect the charge on the surface of silicon slag, and can produce abundant and dense bubbles with strong carrying capacity, which can adhere well to hydrophobic silicon phase particles, but not to hydrophilic slag phase particles. The recovery rate of silicon capture has a certain capture effect under both acidic and alkaline conditions, but the capture effect is best under neutral conditions, with a recovery rate of up to 92.9%. At the same time, the silicon proportion also has a peak area under neutral conditions, up to 99.01%.

[0060] The bubbles produced by the anionic collector SDBS have poor stability and cannot carry hydrophobic particles, so the silicon recovery rate has basically no collection effect under acidic and alkaline conditions, indicating that the anionic collector cannot separate and recover silicon from silicon slag.

[0061] In summary, the most suitable collector type for silicon flotation is non-ionic collector. In this exploratory experiment, the collector used was polyoxyethylene ether (Brij 58). The best flotation effect was when the pH of the flotation solution was around 7, the recovery rate was 92.9%, and the silicon accounted for 99.01%.

[0062] Example 7

[0063] Experiment on the effect of collector concentration on the flotation effect of silicon slag powder: The collector described in step (5) is polyoxyethylene ether, and the addition amount of the collector is 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, and 1.6 g / L flotation solution, respectively. The other aspects are the same as in Example 1. The recovery rate of silicon in silicon slag is as follows: Fig.11 .

[0064] Depend on Fig.11 It can be seen that the recovery rate of flotation silicon increases with the increase of collector concentration. When the collector concentration is 1.0g / L, the change trend is no longer obvious. The recovery rate no longer increases with the increase of collector concentration. The silicon percentage does not change with the increase of collector concentration, indicating that the flotation silicon percentage is not affected by the collector concentration. As the collector concentration increases, more foam will be generated, and at the same time, the flotation time will increase.

Claims

1. A method for flotation of silicon from silicon slag, characterized in that: The steps are as follows: (1) crushing the silicon slag to 0.08-0.5 mm by roller crushing; (2) desludging and washing the crushed silicon slag with water, filtering and setting aside; (3) placing the washed silicon slag in a NaOH solution, immersing it for 1-2 h under stirring, and the immersion temperature is 0-30°C; (4) taking out the immersed silicon slag, rinsing it with clean water, and then placing the silicon slag in a 0.1-5 mol·L -1 Surface treatment is performed in hydrofluoric acid for 1-20 min; (5) placing the surface treated silicon slag in a flotation tank, adding a non-ionic collector, adjusting the pH of the flotation solution to 7, stirring at 20-30 r / min for 5 min, then adjusting the speed to 1700 r / min, and turning on the bubbling switch to start flotation. When the foam is full, turning on the scraper switch to collect the foam and the tailings sinking in the flotation tank; (6) adding a strong acid solution to the tailings under stirring until the tailings no longer dissolve, and filtering to obtain a filtrate; (7) 3) The impregnation liquid and the filtrate obtained in step (6) are mixed, the mixed solution is stirred until no precipitate is generated, and the filter residue 1 and the filtrate 1 are obtained by filtering, the pH value of the filtrate 1 is adjusted to 2-4, and the filtrate 2 and the filter residue 2 are obtained by filtering under stirring until no precipitate is generated, the pH value of the filtrate 2 is adjusted to 10-13, and the filtrate 3 and the filter residue 3 are obtained by filtering under stirring until no precipitate is generated, and the filter residue 1, the filter residue 2 and the filter residue 3 are washed with water once and dried respectively; (8) The concentrate collected in the foam is washed, filtered, dried, weighed, tested and the recovery rate of silicon in the silicon slag is calculated.

2. A method for flotation of silicon from silicon slag according to claim 1, characterized in that: In the step (1), the silicon slag is crushed to 0.091-0.105 mm.

3. A method for flotation of silicon from silicon slag according to claim 1, characterized in that: The concentration of sodium hydroxide in step (3) is 0.1-2 mol·L -1 .

4. A method for flotation of silicon from silicon slag according to claim 1, characterized in that: The concentration of hydrofluoric acid in step (4) is 1.2-1.4 mol·L -1 , the processing time is 5min.

5. The method for flotation of silicon from silicon slag according to claim 1, characterized in that: In the step (5), sulfuric acid is used to adjust the pH of the flotation solution to 7, and the flotation solution is water or a salt solution.

6. A method for flotation of silicon from silicon slag according to claim 5, characterized in that: The salt solution is a sodium chloride solution, and the concentration of the sodium chloride solution is 0.5 mol·L -1 .

7. The method for flotation of silicon from silicon slag according to claim 1, characterized in that: The nonionic collector described in step (5) is polyoxyethylene ether, and the concentration of the nonionic collector in the flotation liquid is 0.1-2 g·L -1 .

8. A method for flotation of silicon from silicon slag according to claim 2, characterized in that: The strong acid solution in step (6) is hydrochloric acid or sulfuric acid, and the concentration of the strong acid solution is 0.1-1 mol·L -1 .

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