Pollution-free purification method of coal for industrial silicon smelting

Abstract

The invention relates to a pollution-free purification method of coal for industrial silicon smelting, and belongs to the technical field of industrial silicon smelting. In order to solve the problems that an existing industrial silicon coal production process is poor in universality and depends on the characteristics of raw coal, coal particles are added into water to be mechanically ground and activated, and activated coal particles are obtained through solid-liquid separation; adding the activated coal particles into a sulfuric acid-hydrogen peroxide mixed solution, then adding an iron salt catalyst for soaking and impurity removal, carrying out solid-liquid separation to obtain coarse purified coal particles and a first-stage leaching solution, and regenerating and returning the first-stage leaching solution to replace the sulfuric acid-hydrogen peroxide mixed solution; the additive fluorite is dissolved in a hydrochloric acid solution at the temperature of 50-80 DEG C to obtain an additive solution, the coarsely purified coal particles are added into the additive solution to be soaked to remove impurities, solid-liquid separation is conducted to obtain clean coal and a second-stage leaching solution, and the second-stage leaching solution is regenerated and returned to replace the hydrochloric acid solution. The method provided by the invention can effectively remove iron, aluminum, calcium, titanium, phosphorus, boron and other impurities affecting the quality of industrial silicon in coal, and the waste liquid is cyclically regenerated to realize pollution-free purification.

Description

Technical Field

[0001] The invention relates to a pollution-free purification method for coal used in industrial silicon smelting, belonging to the technical field of industrial silicon smelting. Background Art

[0002] Industrial silicon is obtained by smelting silica and carbonaceous reducing agents in a submerged arc furnace. The levels of impurities such as iron, aluminum, calcium, titanium, boron, and phosphorus are important criteria for evaluating the quality of industrial silicon. Impurities in industrial silicon come from smelting raw materials such as silica and carbonaceous reducing agents, among which the impurities in carbonaceous reducing agents are the most complex and variable and have the greatest impact. Nowadays, with the large-scale application of large submerged arc furnaces, the considerable reserves of coal, low cost and suitable reactivity have gradually increased its proportion in the mixed reducing agent. The full coal process for industrial silicon smelting has entered commercial application, and coal has become the main reducing agent for industrial silicon smelting. Coal is a natural ore, and it is inevitable to bring in mineral impurities during the molding, mining and transportation process. Under natural conditions, iron in coal exists in the form of hematite, magnetite, pyrite, siderite, and goethite; aluminum mainly exists in the form of silicates such as kaolinite, mica, feldspar, illite, and montmorillonite; calcium exists in the form of calcite, dolomite, and gypsum; titanium mainly exists in the form of rutile; boron exists in the form of borax and organic boron; phosphorus usually exists in the form of apatite and organic phosphorus. In actual production, impurities in coal partially enter industrial silicon products along with the carbon thermal reduction reaction in the electric furnace, and oxidative refining cannot remove iron, titanium, boron, and phosphorus impurities in industrial silicon. Therefore, the use of low-impurity high-quality coal for smelting has become the key to controlling the quality of industrial silicon products. With the continuous reduction of low-impurity high-quality coal reserves, the production of high-quality industrial silicon has been greatly restricted. The industry urgently needs to develop a highly universal industrial smelting coal production technology to achieve stable production and supply of high-quality coal.

[0003] The clean coal production process used on a large scale is the physical washing method, that is, after the raw coal is mined, it is separated from the impurities by jigging, heavy medium separation, magnetic separation, electrostatic separation and other methods alone or in combination. In practical applications, the jigging method can only separate impurity minerals with large particle sizes, and the removal effect of associated tiny impurities is poor. The heavy medium separation process introduces a suspension medium, which is easy to cause secondary impurities. The magnetic separation method can only remove some iron impurities with magnetism, and cannot remove other types of impurities, and its scope of application is limited. The electrostatic separation method has strict range requirements for the particle size of coal. Too coarse or too fine will result in ineffective separation. Therefore, the separation effect of the physical method depends on the characteristics of the raw coal itself. In summary, in the field of purification of coal for industrial silicon smelting, there is currently no method that can be generally applied to the removal of complex mineral impurities. Summary of the invention

[0004] In view of the poor universality of the existing coal production process for silicon smelting and the reliance on the characteristics of the coal itself, the present invention proposes a pollution-free purification method for industrial silicon smelting coal, which comprises mechanically activating the coal to reduce the reaction activation energy and fully exposing internal impurities to obtain activated coal particles; the activated coal particles are subjected to primary impurity removal, during which an iron salt catalyst is introduced to enhance the removal of iron, boron and phosphorus, and solid-liquid separation is performed to obtain roughly purified coal particles and a primary leaching solution; the crudely purified coal particles are subjected to secondary impurity removal, during which a fluorite solvent is introduced to deeply remove aluminum, calcium and titanium, and solid-liquid separation is performed to obtain clean coal for industrial silicon smelting and a secondary leaching solution; the pH of the leaching solution is adjusted by adding a precipitant to remove impurities, and the pH of the filtrate is adjusted by solid-liquid separation to obtain a two-stage regeneration liquid, which is recycled to the two-stage impurity removal process.

[0005] A pollution-free purification method for coal used in industrial silicon smelting, the specific steps are as follows:

[0006] (1) crushing and screening the reducing agent coal for industrial silicon smelting to obtain coal particles;

[0007] (2) adding coal particles into water for mechanical grinding and activation, and then separating the solid and liquid to obtain activated coal particles;

[0008] (3) The activated coal particles are added to a sulfuric acid-hydrogen peroxide mixed solution, and then an iron salt catalyst is added to soak and remove impurities (remove iron, boron and phosphorus), and solid-liquid separation is performed to obtain roughly purified coal particles and a primary leaching solution; the acidic environment improves the oxidation ability of hydrogen peroxide, promotes the oxidation and decomposition of sulfide ore, and strengthens the removal of impurities; the iron salt catalyzes hydrogen peroxide to produce highly active hydroxyl radicals, so that organic impurities are oxidized and removed; the impurities in the activated coal particles are less than 0.15wt.%, boron less than 0.005wt.%, and phosphorus less than 0.15wt.%.

[0009] <0.0015wt.%; (4) adding a precipitant to the primary leachate to adjust the pH value to 6-8 and allowing to settle, separating the solid and liquid, adjusting the liquid pH to 0-2 to obtain a primary regeneration liquid, and returning the primary regeneration liquid to step (3) to replace the sulfuric acid-hydrogen peroxide mixed solution;

[0010] (5) dissolving the additive fluorite in a hydrochloric acid solution at a temperature of 50 to 80° C. to obtain an additive solution, adding the crude purified coal particles into the additive solution for soaking and impurity removal, and performing solid-liquid separation to obtain clean coal and a secondary leachate; the impurity content of the clean coal is iron <0.1wt.%, aluminum <0.2wt.%, calcium <0.2wt.%, titanium <0.01wt.%, boron <0.005wt.%, and phosphorus <0.001wt.%;

[0011] (6) Add a precipitant to the secondary leaching solution to adjust the pH value to 6-8 and allow to settle, separate the solid and liquid, and adjust the pH value of the liquid to 0-2 to obtain a secondary regeneration liquid. The secondary regeneration liquid is returned to step (5) to replace the hydrochloric acid solution.

[0012] Preferably, the particle size of the coal particles in step (1) is 2 to 3 cm, the total amount of metal impurities in the coal particles is 0.8 to 8 wt.%, and the total amount of non-metallic impurities is 0.01 to 0.05 wt.%.

[0013] The metal impurity elements in step (1) include one or more of iron, aluminum, calcium, and titanium, and the non-metallic impurity elements include boron and / or phosphorus.

[0014] Preferably, in step (2), the liquid-solid ratio of water to coal particles is 2 to 10:1 in mL:g, the mechanical stirring rate is 2 to 5 rpm, and the activation time is 0.5 to 1.5 h. Under the action of mechanical force, a large number of cracks and pores are generated on the surface of the coal, so that the internal impurities are fully exposed, reducing the activation energy of impurity removal; the rotation speed should not be too high, and the activation time should not be too long, so as to avoid the coal particles being too fine to meet the requirements of industrial silicon production.

[0015] Preferably, in the sulfuric acid-hydrogen peroxide mixed solution in step (3), the mass concentration of sulfuric acid is 15-25%, and the mass concentration of hydrogen peroxide is 5-15%.

[0016] Preferably, in step (3), the liquid-solid ratio of the sulfuric acid-hydrogen peroxide mixed solution to the activated coal particles is 1 to 5:1 in mL:g, the amount of the iron salt catalyst added is 0.5 to 3 wt.%, and the soaking and impurity removal temperature is 15 to 50° C., and the time is 4 to 8 hours.

[0017] Preferably, the iron salt additive in step (3) is ferric chloride, ferric sulfate, ferric nitrate, ferric acetate or ferric citrate.

[0018] Preferably, the calcium fluoride content in the additive fluorite in step (5) is greater than 80%, and the mass ratio of fluorite to crude purified coal particles is 1:20-10.

[0019] Preferably, the mass concentration of the hydrochloric acid solution is 25-35%, the liquid-solid ratio of the additive solution to the crude purified coal particles is 5-10:1 in mL:g, the soaking and impurity removal temperature is 15-50°C, and the time is 4-8h.

[0020] Preferably, the precipitating agent in step (4) and step (6) is one or more of calcium oxide, calcium hydroxide and calcium carbonate.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention can effectively remove impurities such as iron, aluminum, calcium, titanium, phosphorus, and boron in coal that affect the quality of industrial silicon, and has good selectivity and universality for a variety of complex minerals;

[0023] (2) For organic impurities that are difficult to remove, the present invention adds iron salt to hydrogen peroxide to produce a Fenton-like effect, catalyzing the generation of highly active hydroxyl radicals, which can effectively remove organic impurities in coal;

[0024] (3) The present invention adopts a fully wet process and realizes the recycling of waste liquid. The reaction conditions are mild and the process is simple. It has the advantages of easy realization of production automation, mechanization and scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0027] In the embodiment of the present invention, the impurity content in the coal is determined by pretreatment according to GB / T30732-2014 and analysis by ICP-OES.

[0028] Example 1: The impurity contents of the reducing agent coal for industrial silicon smelting in this example are 1.48wt.% iron, 3.76wt.% aluminum, 0.62wt.% calcium, 0.14wt.% titanium, 0.023wt.% boron, and 0.0074wt.% phosphorus; a pollution-free purification method for industrial silicon smelting coal, the specific steps are as follows:

[0029] (1) crushing and screening the reducing agent coal for industrial silicon smelting to obtain coal particles with a particle size of 2 to 3 cm;

[0030] (2) adding coal particles to water, mechanically grinding and activating the particles for 0.5 h at a stirring rate of 5 rpm, and performing solid-liquid separation to obtain activated coal particles with a particle size of 0.5 to 1.5 cm; the liquid-to-solid ratio of water to coal particles is 10:1 in mL:g;

[0031] (3) The activated coal particles are added to a sulfuric acid-hydrogen peroxide mixed solution, and then an iron salt catalyst (ferric sulfate) is added, and the mixture is soaked at a temperature of 15° C. for 6 hours to remove impurities (to remove iron, boron and phosphorus), and solid-liquid separation is performed to obtain crude purified coal particles and a primary leachate; the sulfuric acid mass concentration in the sulfuric acid-hydrogen peroxide mixed solution is 15%, and the hydrogen peroxide mass concentration is 10%; the liquid-solid ratio of the sulfuric acid-hydrogen peroxide mixed solution to the activated coal particles is 3:1, and the amount of the iron salt catalyst (ferric sulfate) added is 1.5wt.%; the impurities in the crude purified coal particles are 0.095wt.% iron, 0.0026wt.% boron, and 0.0011wt.% phosphorus;

[0032] (4) adding a precipitant (calcium carbonate) to the primary leachate to adjust the pH value to 7 and allowing the solution to settle, separating the solid and the liquid, and adjusting the pH value of the solution to 1 with sulfuric acid to obtain a primary regeneration solution, which is returned to step (3) to replace the sulfuric acid-hydrogen peroxide mixed solution;

[0033] (5) at a temperature of 80° C., an additive fluorite (the calcium fluoride content in the fluorite is 95 wt.%, and the mass ratio of fluorite to crude purified coal particles is 1:10) is dissolved in a hydrochloric acid solution with a mass concentration of 30% to obtain an additive solution, and the crude purified coal particles are added to the additive solution, soaked at a temperature of 50° C. for 8 hours to remove impurities, and solid-liquid separation is performed to obtain clean coal and a secondary leachate; the liquid-solid ratio of the additive solution to the crude purified coal particles is 8:1 in mL:g;

[0034] (6) adding a precipitant (calcium carbonate) to the secondary leachate to adjust the pH value to 7 and allowing the solution to settle, separating the solid from the liquid, adjusting the pH value of the solution to 1 with hydrochloric acid to obtain a secondary regeneration solution, and returning the secondary regeneration solution to step (5) to replace the hydrochloric acid solution;

[0035] After testing, the impurity contents in the clean coal of this embodiment are: iron 0.074wt.%, aluminum 0.12wt.%, calcium 0.025wt.%, titanium 0.0064wt.%, boron 0.0019wt.%, and phosphorus 0.00081wt.%.

[0036] Example 2: The impurity contents of the reducing agent coal for industrial silicon smelting in this example are 1.73wt.% iron, 4.16wt.% aluminum, 0.72wt.% calcium, 0.081wt.% titanium, 0.024wt.% boron, and 0.016wt.% phosphorus;

[0037] A pollution-free purification method for coal used in industrial silicon smelting, the specific steps are as follows:

[0038] (1) crushing and screening the reducing agent coal for industrial silicon smelting to obtain coal particles with a particle size of 2 to 3 cm;

[0039] (2) adding coal particles to water, mechanically grinding and activating the particles for 1 hour at a stirring rate of 3 rpm, and performing solid-liquid separation to obtain activated coal particles with a particle size of 0.5 to 1.5 cm; the liquid-to-solid ratio of water to coal particles is 6:1 in mL:g;

[0040] (3) The activated coal particles are added to a sulfuric acid-hydrogen peroxide mixed solution, and then an iron salt catalyst (ferric acetate) is added, and the mixture is soaked at a temperature of 30° C. for 8 hours to remove impurities (to remove iron, boron and phosphorus), and solid-liquid separation is performed to obtain crude purified coal particles and a primary leaching solution;

[0041] The sulfuric acid mass concentration in the sulfuric acid-hydrogen peroxide mixed solution is 20%, and the hydrogen peroxide mass concentration is 15%; the liquid-solid ratio of the sulfuric acid-hydrogen peroxide mixed solution to the activated coal particles is 1:1, and the amount of the iron salt catalyst (ferric acetate) added is 3wt.%; the impurities in the crude purified coal particles are 0.073wt.% iron, 0.0046wt.% boron, and 0.00081wt.% phosphorus;

[0042] (4) adding a precipitant (calcium hydroxide) to the primary leachate to adjust the pH value to 8 and allowing the solution to settle, separating the solid from the liquid, and adjusting the pH value of the solution to 2 with sulfuric acid to obtain a primary regeneration solution, which is returned to step (3) to replace the sulfuric acid-hydrogen peroxide mixed solution;

[0043] (5) at a temperature of 70° C., an additive fluorite (the calcium fluoride content in the fluorite is 90 wt.%, and the mass ratio of fluorite to crude purified coal particles is 1:20) is dissolved in a hydrochloric acid solution with a mass concentration of 35% to obtain an additive solution, and the crude purified coal particles are added to the additive solution, soaked at a temperature of 30° C. for 6 hours to remove impurities, and solid-liquid separation is performed to obtain clean coal and a secondary leachate; the liquid-solid ratio of the additive solution to the crude purified coal particles is 10:1 in mL:g;

[0044] (6) adding a precipitant (calcium hydroxide) to the secondary leachate to adjust the pH value to 8 and allowing the solution to settle, separating the solid from the liquid, adjusting the pH value of the solution to 2 with hydrochloric acid to obtain a secondary regeneration solution, and returning the secondary regeneration solution to step (5) to replace the hydrochloric acid solution;

[0045] After testing, the impurity contents in the clean coal of this embodiment are: iron 0.058wt.%, aluminum 0.19wt.%, calcium 0.042wt.%, titanium 0.0081wt.%, boron 0.0037wt.%, and phosphorus 0.00079wt.%.

[0046] Example 3: The impurity contents of the reducing agent coal for industrial silicon smelting in this example are 0.87wt.% iron, 2.16wt.% aluminum, 0.34wt.% calcium, 0.12wt.% titanium, 0.019wt.% boron, and 0.0057wt.% phosphorus;

[0047] A pollution-free purification method for coal used in industrial silicon smelting, the specific steps are as follows:

[0048] (1) crushing and screening the reducing agent coal for industrial silicon smelting to obtain coal particles with a particle size of 2 to 3 cm;

[0049] (2) adding coal particles to water, mechanically grinding and activating the particles for 1.5 h at a stirring rate of 2 rpm, and performing solid-liquid separation to obtain activated coal particles with a particle size of 0.5 to 1.5 cm; the liquid-solid ratio of water to coal particles is 2:1 in mL:g;

[0050] (3) The activated coal particles are added to a sulfuric acid-hydrogen peroxide mixed solution, and then an iron salt catalyst (ferric chloride) is added, and the mixture is soaked and removed at a temperature of 50° C. for 4 hours (to remove aluminum, calcium and titanium), and solid-liquid separation is performed to obtain crude purified coal particles and a primary leachate; the mass concentration of sulfuric acid in the sulfuric acid-hydrogen peroxide mixed solution is 25%, and the mass concentration of hydrogen peroxide is 5%; the liquid-solid ratio of the sulfuric acid-hydrogen peroxide mixed solution to the activated coal particles is 5:1, and the amount of the iron salt catalyst (ferric chloride) added is 0.5wt.%; the impurities in the crude purified coal particles are 0.069wt.% iron, 0.0021wt.% boron, and 0.00092wt.% phosphorus;

[0051] (4) adding a precipitant (calcium oxide) to the primary leachate to adjust the pH value to 6 and allowing the solution to settle, separating the solid and the liquid, adjusting the pH value of the solution to 0 with sulfuric acid to obtain a primary regeneration solution, and returning the primary regeneration solution to step (3) to replace the sulfuric acid-hydrogen peroxide mixed solution;

[0052] (5) at a temperature of 50° C., an additive fluorite (the calcium fluoride content in the fluorite is 80 wt.%, and the mass ratio of fluorite to crude purified coal particles is 1:15) is dissolved in a hydrochloric acid solution with a mass concentration of 25% to obtain an additive solution, and the crude purified coal particles are added to the additive solution, soaked at a temperature of 15° C. for 4 hours to remove impurities, and solid-liquid separation is performed to obtain clean coal and a secondary leachate; the liquid-solid ratio of the additive solution to the crude purified coal particles is 5:1 in mL:g;

[0053] (6) adding a precipitant (calcium oxide) to the secondary leaching solution to adjust the pH value to 6 and allowing the solution to settle, separating the solid from the liquid, and adjusting the pH value of the solution to 0 with hydrochloric acid to obtain a secondary regeneration solution, which is returned to step (5) to replace the hydrochloric acid solution;

[0054] After testing, the impurity contents in the clean coal of this embodiment are: iron 0.044wt.%, aluminum 0.17wt.%, calcium 0.049wt.%, titanium 0.0094wt.%, boron 0.0024wt.%, and phosphorus 0.00089wt.%.

[0055] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A pollution-free purification method for coal used in industrial silicon smelting, characterized in that: The specific steps are as follows: (1) crushing and screening the reducing agent coal for industrial silicon smelting to obtain coal particles; (2) adding coal particles into water for mechanical grinding and activation, and then separating the solid and liquid to obtain activated coal particles; (3) adding the activated coal particles into a sulfuric acid-hydrogen peroxide mixed solution, then adding an iron salt catalyst for soaking and impurity removal, and performing solid-liquid separation to obtain crude purified coal particles and a primary leaching solution; (4) adding a precipitant to the primary leachate to adjust the pH value to 6-8 and allowing the solution to settle, separating the solid from the liquid, and adjusting the pH value of the solution to 0-2 to obtain a primary regeneration solution, which is returned to step (3) to replace the sulfuric acid-hydrogen peroxide mixed solution; (5) dissolving the additive fluorite in a hydrochloric acid solution at a temperature of 50 to 80° C. to obtain an additive solution, adding the crude purified coal particles into the additive solution for soaking and impurity removal, and performing solid-liquid separation to obtain clean coal and a secondary leachate; (6) Add a precipitant to the secondary leaching solution to adjust the pH value to 6-8 and allow to settle, separate the solid and liquid, and adjust the pH value of the liquid to 0-2 to obtain a secondary regeneration liquid. The secondary regeneration liquid is returned to step (5) to replace the hydrochloric acid solution.

2. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: The particle size of the coal particles in step (1) is 2 to 3 cm, the total amount of metal impurities in the coal particles is 0.8 to 8 wt.%, and the total amount of non-metallic impurities is 0.01 to 0.05 wt.%.

3. The pollution-free purification method for industrial silicon smelting coal according to claim 2, characterized in that: The metal impurity elements in step (1) include one or more of iron, aluminum, calcium, and titanium, and the non-metal impurity elements include boron and / or phosphorus.

4. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: In step (2), the liquid-to-solid ratio of water to coal particles is 2 to 10:1 in mL:g, the mechanical stirring rate is 2 to 5 rpm, and the activation time is 0.5 to 1.5 h.

5. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: In step (3), the sulfuric acid-hydrogen peroxide mixed solution has a sulfuric acid mass concentration of 15-25%, and a hydrogen peroxide mass concentration of 5-15%.

6. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: In step (3), the liquid-solid ratio of the sulfuric acid-hydrogen peroxide mixed solution to the activated coal particles is 1 to 5:1 in mL:g, and the amount of the iron salt catalyst added is 0.5 to 3 wt.%; the soaking and impurity removal temperature is 15 to 50° C., and the time is 4 to 8 hours.

7. The pollution-free purification method for industrial silicon smelting coal according to claim 1 or 6, characterized in that: The iron salt additive in step (3) is ferric chloride, ferric sulfate, ferric nitrate, ferric acetate or ferric citrate.

8. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: In step (5), the calcium fluoride content in the additive fluorite is greater than 80%, and the mass ratio of fluorite to the roughly purified coal particles is 1:20-10.

9. The pollution-free purification method for industrial silicon smelting coal according to claim 1 or 8, characterized in that: The mass concentration of the hydrochloric acid solution is 25-35%, the liquid-solid ratio of the additive solution to the crude purified coal particles is 5-10:1 in mL:g, the soaking and impurity removal temperature is 15-50°C, and the time is 4-8h.

10. The pollution-free purification method for industrial silicon smelting coal according to claim 1, characterized in that: The precipitating agent in step (4) and step (6) is one or more of calcium oxide, calcium hydroxide and calcium carbonate.

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