Preparation method of fluosilicate

Abstract

The invention relates to a method for preparing high-purity fluosilicate by taking industrial fluorine-containing sludge as a raw material. Comprising the following steps: slurrying calcium fluoride sludge, acidifying with inorganic acid, adding an adsorbent, and filtering; adding soluble salt into the filtrate to carry out crystallization reaction and adjusting the pH value; and cooling, filtering, washing and drying to obtain a target product. Solid waste resource utilization is achieved, the product purity is larger than or equal to 98%, and energy consumption is reduced by 60% or above compared with a traditional process.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic chemical industry, and particularly relates to a green process for preparing fluorosilicate by utilizing industrial fluorine-containing sludge. Background Art

[0002] Fluorosilicates are important fluorine chemical raw materials, widely used in the building materials, metallurgy, electronics and other industries. The traditional production process mainly uses fluorspar (CaF2) and quartz sand to be roasted at 500-800℃, followed by sulfuric acid leaching and salting out (CN102190344A). This process has three major drawbacks: 1. High energy consumption: more than 0.8 tons of standard coal are consumed per ton of product; 2. Limited raw materials: Fluorite prices continue to rise; 3. Heavy pollution: produces fluorine-containing waste gas (HF) and acidic wastewater.

[0003] In recent years, patent CN107500369A proposed to prepare ammonium fluorosilicate by reacting ammonium fluoride wastewater with silica gel, but the raw material cost is high; patent CN109231264A adopts the neutralization method of fluorosilicic acid and alkali, which relies on phosphate fertilizer by-products and the raw material source is unstable.

[0004] Wastewater treatment in the semiconductor and photovoltaic industries generates large amounts of calcium fluoride sludge (CaF2 content 30-80%), which is currently primarily disposed of in landfills. This innovative method uses this waste as a raw material to directly synthesize fluorosilicates at low temperatures. This solves the problem of fluorine-containing waste disposal while reducing production costs, creating a "waste-to-waste" circular economy model. Summary of the Invention

[0005] The present invention provides a low-temperature, low-energy-consumption method for preparing fluorosilicates, the core of which is: 1. Convert CaF2 in sludge into H2SiF6 through wide range acidification control; 2. Preparation of different fluorosilicates by multiple salting-out crystallization mechanisms; 3. Flexible process parameters adapt to the characteristics of various industrial sludges. DETAILED DESCRIPTION

[0006] The following examples are used in the following raw materials: - Calcium fluoride sludge: Wastewater treatment sludge from a photovoltaic company, CaF2 65%, SiO2 12%, Al2O3 5% - Comparative example: Fluorosilicic acid (H2SiF6 20%) produced as a by-product of a phosphate fertilizer plant Example 1 (Basic Process) Take 1 kg of sludge and add water to a solid-liquid ratio of 1:5 to form a slurry. Add 150 g of 98% sulfuric acid (pH = 1.5), stir at 60°C for 1 hour, and then add activated carbon. After filtering, add 120 g of sodium chloride (2x molar ratio) to the filtrate (containing 0.8 mol of Si) and crystallize at 60°C for 1 hour. Cool at 3°C / min to 5°C, hold for 0.5 hour, and filter. Wash the solid twice with 15% ethanol and three times with deionized water, then dry at 100°C to obtain 296 g of sodium fluorosilicate (98.2% purity, 95% yield).

[0007] Example 2-6 (Influence of Acid Type) According to the process of Example 1, the acid was replaced by: - Example 2: 150g hydrochloric acid (pH=1.8) → purity 97.8% - Example 3: 130g nitric acid (pH=2.0) → purity 97.5% - Example 4: 100g hydrofluoric acid + 100g hydrochloric acid (pH = 1.0) → purity 98.0% - Example 5: 200g phosphoric acid (pH=1.2) → purity 96.8% - Example 6: Sulfuric acid / nitric acid mixture (1:1) → purity 97.5% Examples 7-12 (Salt Type Optimization) Fixed sulfuric acid acidification, add: - Example 7: Sodium sulfate → purity 98.5% - Example 8: Potassium carbonate → potassium fluorosilicate (purity 97.9%) - Example 9: Ammonium acetate → ammonium fluorosilicate (purity 97.5%) - Example 10: Lithium bromide → lithium fluorosilicate (purity 96.2%) - Example 11: Calcium formate → calcium fluorosilicate (purity 97.1%) - Example 12: Sodium iodide → purity 96.8% Examples 13-17 (Wide Range Parameters) Adjustments based on Example 1: - Example 13: Slurry solid-liquid ratio 0.05 (high concentration slurry) → yield 92% - Example 14: Slurry solid-liquid ratio 1.8 (low concentration slurry) → purity 97.5% - Example 15: Crystallization temperature 25°C (room temperature crystallization) → Yield 89% - Example 16: Crystallization temperature 85°C (high temperature crystallization) → yield 98.3% - Example 17: Cooling end point -5°C (deep cooling) → purity 98.7% Examples 18-22 (Sludge from Different Industries) - Example 18: Semiconductor etching sludge (CaF2 52%) → purity 97.5% - Example 19: Glass grinding sludge (CaF2 40%) → purity 96.8% - Example 20: Metallurgical pickling sludge (CaF2 35%) → purity 95.2% - Example 21: Chemical fluorine-containing sludge (CaF2 28%) → purity 94.5% - Example 22: Mixed industrial sludge (CaF2 45%) → purity 97.0% Examples 23-26 (Special Anionic Salts) - Example 23: Sodium formate → purity 97.8% - Example 24: Potassium bicarbonate → Potassium fluorosilicate (purity 96.9%) - Example 25: Calcium nitrate → calcium fluorosilicate (purity 97.2%) - Example 26: Ammonium chloride + sodium sulfate mixed salt → double salt purity 97.5% Examples 27-30 (boundary parameters) - Example 27: pH = 0.6 (strong acidity) → yield 93% - Example 28: pH = 4.8 (weakly acidic) → yield 88% - Example 29: Salt addition 0.2 times (low salt content) → yield 75% - Example 30: 12-fold salt addition (high salt content) → 96.5% purity Examples 31-35 (Drying and Washing) - Example 31: Methanol washing → purity 97.8% - Example 32: Acetone washing → purity 97.5% - Example 33: Low temperature drying at 60°C → good product fluidity - Example 34: 140°C high temperature drying → low moisture content - Example 35: Water-ethanol gradient washing → purity 98.2% Wide adaptability of raw materials: can process various industrial fluorine-containing sludges with CaF2 content above 25%;

[0008] 2. High process flexibility: wide range of key parameters to adapt to different production conditions; 3. Product diversification: various fluorosilicates such as sodium, potassium, lithium, calcium, and ammonium can be produced; 4. High economic benefits: Reduce production costs by more than 40% compared with traditional processes.

Claims

1. A method for preparing fluorosilicate, characterized in that: The method comprises the following steps: (a) mixing fluorine-calcium compound sludge with water to form a slurry; (b) adding acid to the slurry to adjust the system to an acidic condition, and then adding an adsorbent to separate the solid and liquid; (c) introducing a cation donor into the separated liquid, adjusting the pH to a weakly acidic state, and heating to promote crystallization; (d) cooling the crystallization system and separating the solid and the liquid; (e) washing and drying the separated solid to obtain a fluorosilicate product.

2. The method according to claim 1, wherein: The fluorine-containing calcium compound sludge comes from the industrial fluorine-containing wastewater treatment process, including fluorine-containing sludge generated by the semiconductor, photovoltaic, glass manufacturing, metallurgy or chemical industries.

3. The method according to claim 1, wherein: The acid solution is selected from inorganic acid, organic acid or a combination thereof, and is used to adjust the pH of the system to ≤5.

4. The method according to claim 1, wherein: The adsorbent is at least one of activated carbon, diatomaceous earth or activated alumina.

5. The method according to claim 1, wherein: The cation donor is an alkali metal compound, an alkaline earth metal compound, an ammonium compound or a combination thereof.

6. The method according to claim 1, wherein: In step (c), the pH is adjusted to 4-7 and the crystallization temperature is 40-100°C.

7. The method according to claim 1, wherein: In step (d), the cooling rate is 3-25°C / min, and the terminal temperature is 5-30°C.

8. The method according to claim 1, wherein: The washing liquid in step (e) is water, an organic solvent or a mixed solution thereof.

9. The method according to claim 1, wherein: The fluorosilicate product includes sodium fluorosilicate, potassium fluorosilicate, ammonium fluorosilicate, calcium fluorosilicate or magnesium fluorosilicate.

10. The method according to claim 1, wherein: The solid residue after separation in step (b) and the mother liquor after separation in step (d) can be recycled to step (a) or (c) for reuse.