A comprehensive utilization method of by-product silicon slag in a hydrogen fluoride production process from fluosilicic acid

Abstract

The present application relates to a method for comprehensive utilization of by-product silicon slag in hydrogen fluoride production process from fluosilicic acid, specifically, the by-product silicon slag in hydrogen fluoride production process is used as raw material, and under the action of dispersant and additive, selective dispersion and sedimentation are carried out, centrifugal drying is carried out on the emulsion formed by dispersing silicon dioxide, SiO2 in the silicon slag is recovered as white carbon black product, and the filtrate can be used as dispersant after concentration and recovery, the recovery rate of effective components in the silicon slag in the present application is greater than 90%, the operation process is simple, the solid waste emission in the production process is effectively reduced, waste is turned into treasure, and the present application is green and environment-friendly.

Description

Technical Field

[0001] This invention belongs to the technical field of comprehensive utilization of solid waste in inorganic chemical production processes, specifically relating to a method for selectively recovering SiO2 from by-product silicon slag in the production of hydrogen fluoride from fluorosilicic acid, a by-product of the phosphate fertilizer industry, through dispersion and sedimentation, as precipitated silica. Background Technology

[0002] Phosphate fertilizer production generates a large amount of 15-20% fluorosilicic acid as a byproduct. Currently, only 30% of this is utilized domestically for high-value conversion into HF. However, in the existing mature process of producing hydrogen fluoride from fluorosilicic acid, only the fluorine (F) element in the fluorosilicic acid is effectively utilized. The silicon element, on the other hand, settles as SiO2 during the production process. During this settling process, it is mixed with fluorosilicic acid, mechanical residues, and a small amount of divalent metal ions (mainly calcium and magnesium ions), making it difficult to handle. Currently, it is mainly discharged upstream as silicon slag to the phosphate plant and finally discharged to the slag yard as slag paste, resulting in a waste of silicon resources.

[0003] Patent CN102674367A describes a process where ammonium fluoride and fluorosilicic acid are mixed in a molar ratio of 9-15 to produce hydrogen fluoride from silicon slag. The mixture is then dissolved at 90-108°C and 15-0 kPa. The undissolved SiO2 and mechanical impurities are removed by hot filtration, and the filtrate is then subjected to gradient cooling and crystallization to obtain ammonium fluorosilicate. However, this process only recovers the trace amounts of fluorosilicic acid contained in the silicon slag, without properly recovering the majority of the SiO2.

[0004] CN103663474B uses an alkaline solution to react with silicon slag, a byproduct of hydrogen fluoride production from fluorosilicic acid, at 40-80℃ to obtain a mixed aqueous solution of SiO2 and fluoride salts. Then, solid-liquid separation is performed to obtain fluoride salts and silica separately. However, in actual production, due to the low solubility of fluoride salts, some fluoride salts are mixed into the SiO2 precipitate. In addition, SiO2 is not uniformly dispersed in the system in this method, and the particles are relatively large. Therefore, the recovered silica product inevitably contains a small amount of fluoride salts, and the particles are large with a small specific surface area, resulting in poor silica quality.

[0005] In summary, the silicon slag produced as a byproduct in the current fluorosilicic acid to hydrogen fluoride production process is mostly treated as solid waste, failing to effectively utilize silicon resources. Furthermore, existing literature indicates that only partial recycling is possible, or that process defects result in poor-quality recovered silica. Therefore, there is an urgent need to develop a method for the rational utilization of silicon slag, improving the quality of silica and reducing solid waste emissions. Summary of the Invention

[0006] This invention addresses the aforementioned shortcomings of existing technologies by providing a method for the comprehensive utilization of silicon slag, a byproduct of the hydrogen fluoride production process from fluorosilicic acid. Using silicon slag as a raw material, the method involves reacting it with an aqueous solution containing an aqueous dispersant to form a slurry. Under the action of the dispersant, the SiO2 in the silicon slag is highly dispersed, forming a stable SiO2 dispersion emulsion. Solid impurities such as dihydrate fluorosilicic acid crystals trapped in the silicon slag are not dispersed during the aging process and settle. Metal ions such as calcium and magnesium in the silicon slag are removed by forming aqueous chelates with the additives, thus avoiding impurities and achieving the goal of selectively recovering high-quality silica from the silicon slag through dispersion. This invention solves the problems of unutilized silicon slag in existing production technologies, low utilization rates reported in literature, and poor quality of recovered silica.

[0007] The technical solution of this invention is as follows:

[0008] A method for the comprehensive utilization of silicon slag, a byproduct of the production of hydrogen fluoride from fluorosilicic acid, includes the following steps: silicon slag is mixed with water containing dispersants and additives in a silicon slag dissolving kettle to form a slurry; the slurry is discharged into a settling tank for aging; after aging, the upper flowing emulsion is centrifuged, sprayed, washed, and dried to obtain silica. The filtrate can be concentrated and reused as an aqueous dispersant solution.

[0009] In this invention, the mass ratio of the silicon slag to the dispersant, additives, and water is 1:0.03-0.15:0.001-0.01:1-3;

[0010] Furthermore, the dispersant is an aqueous dispersant, preferably a hydrophilic polymeric compound with ester bond segments, and the commercially available brands involved are BYK190, BYK191, BYK192, and BYK194.

[0011] The aforementioned additives are water-soluble chelating agents, mainly sodium diacetate salts, etc., and the commercially available brands involved are: GLDA (tetrasodium glutamate diacetate), ASDA (tetrasodium aspartate diacetate), MGDA (trisodium methylglycine diacetate), PASP-Na (sodium polyaspartate), with GLDA and MGDA being preferred.

[0012] In this invention, the operating conditions of the dissolving vessel are as follows: temperature 20-80℃, preferably 20-40℃; stirring speed 500-1500rpm, preferably 1000-1500rpm; stirring time 10-80min, preferably 20-50min; and the type of stirring paddle for the dissolving vessel is double-blade, triple-blade, oblique-blade, frame type, turbine type, anchor type, or spiral type, preferably frame type.

[0013] Furthermore, the operating conditions of the settling tank are as follows: aging time of 10-20 hours, preferably 10-15 hours; aging temperature of 10-50℃, preferably 10-30℃.

[0014] Furthermore, the centrifuge used for centrifugation can be a three-legged, flat-plate, benchtop, horizontal, butterfly, or tubular type, with a benchtop type being preferred; the rotation speed is 6000-10000 rpm; and the operating temperature is 10-30℃.

[0015] Furthermore, the spray washing is performed 2-3 times, the detergent is water, and the amount of detergent used each time is 40-200% of the mass of silicon slag added to the dissolving kettle, preferably 40-100%; the washing operation temperature is 10-30℃.

[0016] Furthermore, the drying conditions for the filter cake after spray washing are: operating temperature 80-120℃, operating pressure 30-90KPa, and drying time 1-15h, preferably 3-10h.

[0017] Furthermore, the centrifuged filtrate and the washing filtrate are combined and concentrated using a falling film evaporator at a temperature of 70-100℃ and a pressure of 40-70 kPa. The concentration of the dispersant after concentration is 1.5-5.5%.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1) Additives are used to specifically remove divalent metal ions (mainly calcium and magnesium ions) from silicon slag to form water-soluble chelates; dispersants change the surface tension of the aqueous solution, allowing SiO2 to be highly dispersed in water. At the same time, the chelates and dispersants work synergistically to ensure the formation of a stable SiO2 emulsion without sedimentation, while effectively controlling the metal ion content in SiO2.

[0020] 2) Due to the large molecular weight difference between fluorosilicic acid dihydrate and SiO2, and the low proportion of hydrophilic dispersed O atoms, fluorosilicic acid crystals cannot be dispersed to form a stable emulsion and are slowly removed by sedimentation during the aging process.

[0021] 3) This invention is simple to operate. The filtrate after centrifugation contains a dispersant, which can be concentrated and returned to the silicon slag dissolving kettle for reuse, resulting in high production efficiency. Detailed Implementation

[0022] The present invention will be further described in detail with reference to specific embodiments, but the scope of the present invention is not limited to these embodiments.

[0023] Thermogravimetric analysis: using a Mettler surface area analyzer (Swiss).

[0024] Moisture analysis: A Swiss Metrohm moisture analyzer was used.

[0025] Example 1

[0026] Dissolve 150g of BYK190 dispersant and 7.3g of MGDA in 2800g of water. At 35℃, using a frame-type stirring paddle, add 1200g of silicon slag (SiO2) at 1200rpm. 82%, 7% dihydrate fluorosilicic acid, 0.5% mechanical residue, 10.4% water, and 0.1% divalent metal ions were added and stirred and dispersed for 40 minutes. Then, stirring was stopped, and the slurry was discharged into a settling tank and cooled to 25°C for aging and settling for 15 hours. After 15 hours, 3989.4g of the upper emulsion was poured into a benchtop centrifuge and centrifuged at 25°C and 9000rpm to obtain 2523.4g of filtrate. The filter cake was washed and centrifuged three times with water spray at 25°C and 9000rpm, with 800g of water used each time, resulting in a filter cake mass of 1357.3g and a three-wash filtrate mass of 2508.6g. The four filtrates were combined to obtain 5031.9g.

[0027] 1357.3g of filter cake was dried at 110℃, operating pressure 85KPa, and drying time for 5 hours to obtain 976.2g of silica product (purity 96.5%). The specific surface area, measured by a surface area analyzer, was 386m². 2 / g, the SiO2 recovery rate in silicon slag is 95.7%.

[0028] The combined filtrate of 5031.9g was concentrated using a falling film evaporator at a temperature of 90℃ and a pressure of 60KPa. After concentration, 2941g of dispersant aqueous solution was obtained, with a dispersant concentration of 5.02%.

[0029] The recovered 2941g of dispersant aqueous solution and 7.3g of MGDA were mixed with 1200g of the same silica slag, and 973.6g of silica product with a purity of 96.4% was obtained by following the above operation. The specific surface area was measured to be 375m². 2 / g, ICP analysis showed that the content of divalent metal ions in the silica was <5ppm, and the recovery rate of SiO2 in the silica slag was 95.4%.

[0030] Example 2

[0031] Dissolve 100g of BYK192 dispersant and 5.4g of GLDA in 2000g of water. At 24℃, using a frame-type stirring paddle, add 1200g of silicon slag (SiO2) at 600rpm. 74.3%, fluorosilicic acid dihydrate 10.2%, mechanical residue 0.8%, water 14.65%, divalent metal ions 0.05%), were added and stirred and dispersed for 50 minutes. Then, stirring was stopped, and the slurry was discharged into a settling tank and cooled to 25°C for aging and settling for 13 hours. After 13 hours, 3106.8g of the upper emulsion was poured into a benchtop centrifuge and centrifuged at 25°C and 6000rpm to obtain 1785.6g of filtrate. The filter cake was washed and centrifuged three times with water spray at 25°C and 6000rpm, with 500g of water used each time, to obtain a filter cake mass of 1223.3g. The mass of the three washing filtrates was 1598.3g. The four filtrates were combined to obtain 3383.9g.

[0032] 1223.3g of filter cake was dried at 90℃, operating pressure 50KPa, and time 8h to obtain 867.3g of silica product (purity 97.3%). The specific surface area was measured to be 392m² using a specific surface meter. 2 / g, the SiO2 recovery rate in silicon slag is 94.6%.

[0033] The combined filtrate of 3383.9g was concentrated using a falling film evaporator at a temperature of 95℃ and a pressure of 68KPa, yielding a dispersant aqueous solution of 2177.8g with a dispersant concentration of 4.5%.

[0034] The recovered 2177.8g of dispersant aqueous solution and 5.3g of GLDA were mixed with 1200g of the same silica slag, and 869.8g of silica product with a purity of 97.1% was obtained by following the above operation. The specific surface area was measured to be 387m². 2 / g, ICP analysis showed that the content of divalent metal ions in the silica was <3ppm, and the recovery rate of SiO2 in the silica slag was 94.7%.

[0035] Example 3

[0036] Dissolve 50g of BYK192 dispersant and 10.8g of MGDA in 1500g of water. At 31℃, using a frame-type stirring paddle, add 1200g of silicon slag (SiO2) at 900rpm. 82%, 7% dihydrate fluorosilicic acid, 0.5% mechanical residue, 10.3% water, and 0.2% divalent metal ions were added and stirred and dispersed for 25 minutes. Then, stirring was stopped, and the slurry was discharged into a settling tank and cooled to 25°C for aging and settling for 10 hours. After 10 hours, 2514.8g of the upper emulsion was poured into a benchtop centrifuge and centrifuged at 20°C and 7500rpm to obtain 1123.6g of filtrate. The filter cake was washed and centrifuged three times with water spray at 20°C and 7500rpm, with 650g of water used each time, resulting in a filter cake mass of 1287.4g and a three-wash filtrate mass of 2053.8g. The four filtrates were combined to obtain a total of 3177.4g.

[0037] 1287.4g of filter cake was dried at 80℃, operating pressure 30KPa, and drying time 6h to obtain 928.0g of silica product (purity 96.8%), with a specific surface area of ​​369m² as measured by a surface area analyzer. 2 / g, the SiO2 recovery rate in silicon slag is 91.3%.

[0038] The combined filtrate of 3177.4g was concentrated using a falling film evaporator at a temperature of 95℃ and a pressure of 68KPa. After concentration, 1436.2g of dispersant aqueous solution was obtained, with a dispersant concentration of 3.4%.

[0039] The recovered 1436.2g of dispersant aqueous solution and 10.3g of MGDA were mixed with 1200g of the same silica slag, and 938.4g of silica product with a purity of 96.3% was obtained by following the above operation. The specific surface area was measured to be 358m². 2 / g, ICP analysis showed that the content of divalent metal ions in the silica was <5ppm, and the recovery rate of SiO2 in the silica slag was 91.8%.

[0040] Comparative Example 1

[0041] Following the procedures and dosages in Example 1, without adding a dispersant, 943g of silica product was obtained with a purity of 91.2% and a specific surface area of ​​65m² as measured by a surface area analyzer. 2 / g, the metal ion content in the silica was 437ppm according to ICP analysis, and the recovery rate of SiO2 in the silica slag was 87.4%.

[0042] Comparative Example 2

[0043] Following the procedures and dosages in Example 1, without adding any additives, 960.2 g of silica product was obtained with a purity of 90.8%, and the specific surface area was measured to be 87 m².2 / g, the metal ion content in the silica was 892ppm according to ICP analysis, and the recovery rate of SiO2 in the silica slag was 88.6%.

Claims

1. A method for comprehensive utilization of silicon slag, a byproduct of the production process of hydrogen fluoride from fluorosilicic acid, comprising the following steps: Silica is prepared by mixing silica slag with water containing dispersants and additives. The slurry is aged, and the upper emulsion is centrifuged, washed, and dried after aging to obtain silica. The dispersant is BYK190, BYK191, BYK192 or BYK194, and the adjuvant is tetrasodium glutamate diacetate, tetrasodium aspartate diacetate or trisodium methylglycine diacetate. The mass ratio of the silicon slag to the dispersant, additives, and water is 1:0.03-0.15:0.001-0.01:1-3. The operating conditions for preparing the slurry are as follows: temperature 20-80℃; stirring speed 500-1500rpm; stirring time 10-80min. The aging conditions are as follows: aging time 10-20 hours, aging temperature 10-50℃.

2. The method according to claim 1, wherein, The operating conditions for preparing the slurry are: temperature 20-40℃.

3. The method according to claim 1, wherein, The centrifuge speed is 6000-10000 rpm; the operating temperature is 10-30℃.

4. The method according to claim 1, wherein, The washing is performed 2-3 times, with water as the detergent. The amount of detergent used each time is 40-200% of the mass of the silicon slag. The washing temperature is 10-30℃.

5. The method according to claim 1, wherein, The drying conditions for the washed filter cake are: drying temperature 80-120℃, drying pressure 30-90KPa, and drying time 1-15h.

6. The method according to claim 1, wherein, The centrifuged filtrate and the washing filtrate are combined and concentrated at a temperature of 70-100℃ and a pressure of 40-70 kPa. The concentration of the dispersant after concentration is 1.5-5.5%.