Method for preparing high-molecule-ratio cryolite by using phosphoric acid industrial fluorine-containing waste gas

A technology of cryolite and waste gas, applied in the direction of aluminum fluoride and aluminum halide, etc., can solve the problems of lack of green fluorine-containing waste gas, not put into use, high energy consumption, etc., achieve the effect of non-toxic raw materials, avoid pollution, and reduce consumption

Inactive Publication Date: 2012-05-23
WUHAN UNIV OF SCI & TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

This method consumes a lot of energy and often requires heating the superheated steam to a temperature above 1400°C
Another method is melting defluorination, that is, melting phosphate rock and silicon dioxide, converting the phosphate rock into calcium phosphate and calcium silicate, and the fluorine in the phosphate rock reacts with silicon dioxide to form SiF 4 gas, SiF 4 After the gas is absorbed by water, ammonia water or sodium hydroxide is added to precipitate the silicon in the form of silicon dioxide, and the fluorine is converted into sodium fluoride or ammonium fluoride, and then reacted with sodiu

Method used

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  • Method for preparing high-molecule-ratio cryolite by using phosphoric acid industrial fluorine-containing waste gas
  • Method for preparing high-molecule-ratio cryolite by using phosphoric acid industrial fluorine-containing waste gas
  • Method for preparing high-molecule-ratio cryolite by using phosphoric acid industrial fluorine-containing waste gas

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0046] Will be composed of 2.5% (volume ratio) HF and 1.7% (volume ratio) SiF 4 The fluorine-containing waste gas composed of air and ceramic Raschig ring packed tower is absorbed with 5% sodium bicarbonate solution. Control the reflux ratio = 5, make the pH of the absorption solution = 7.5, and the tail gas contains 0.023% HF and SiF after detection 4 0.028%, that is, the absorption rate of HF has reached 99.1%, and the absorption rate of SiF 4 The absorption rate reached 98.4%. Raise the temperature of the absorption solution to 90°C, add polyacrylamide with a total amount of 0.05% of the precipitate into the solution as a flocculant, keep it warm for 2 hours, cool to 30°C at a cooling rate of 15°C / h and filter, and wash the filter residue twice with water , then dried at 110°C for 2h, and calcined at 250°C for 3h to obtain a specific surface area of ​​147m 2 / g of white carbon black. Then the theoretical amount of 95% aluminum hydroxide is reacted with 20% sodium hydro...

Embodiment 2

[0056] The ceramic Raschig ring in the absorption tower packing in the embodiment 1 is replaced by the plastic Pall ring, adopts 8% NaHCO 3 The solution absorbs. Control the reflux ratio = 6, make the pH of the absorption solution = 7.8, and the tail gas contains 0.014% HF and SiF after detection 4 0.013%, that is, the absorption rate of HF reaches 99.4%, and the absorption rate of SiF 4 The absorption rate reached 99.2%. Raise the temperature of the absorption solution to 90°C, add polyacrylamide with a total amount of 0.08% of the precipitate into the solution as a flocculant, keep it warm for 2 hours, cool to 40°C at a cooling rate of 10°C / h and filter, and wash the filter residue with water 4 times , then dried at 120°C for 2h, and calcined at 300°C for 2h to obtain a specific surface area of ​​172m 2 / g of white carbon black. Then react the theoretical amount of 98% aluminum hydroxide with 20% sodium hydroxide solution to obtain ~29% sodium metaaluminate solution, th...

Embodiment 3

[0066] The gas composition is still the same as that of the above-mentioned embodiment, and the packing of the absorption tower adopts a plastic Pall ring, and adopts 10% NaHCO 3 The solution absorbs. Control the reflux ratio = 6, make the pH of the absorption solution = 8.0, and the tail gas contains 0.012% HF and SiF after detection 4 0.011%, that is, the absorption rate of HF has reached 99.5%, and the absorption rate of SiF 4 The absorption rate reached 99.4%. Raise the temperature of the absorption solution to 90°C, add polyacrylamide with a solid content of 0.1% in the solution as a flocculant, keep it warm for 3 hours, cool to 40°C at a cooling rate of 10°C / h and filter, wash the filter residue 4 times with water, and then Dry at 120°C for 1 hour, then calcinate at 300°C for 2 hours to obtain a specific surface area of ​​196m 2 / g of white carbon black. Then react the theoretical amount of 95% aluminum hydroxide with 20% sodium hydroxide solution to obtain 28% sodiu...

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Abstract

The invention relates to a method for preparing high-molecule-ratio cryolite by using phosphoric acid industrial fluorine-containing waste gas, belonging to the field of inorganic chemical engineering. Fluorine-containing waste gas is absorbed by adopting circulation of a sodium bicarbonate solution, so that the problems of secondary pollution and high processing cost in a process of treating the fluorine-containing waste gas are solved, and chemical products such as cryolite, white carbon black, and the like with high additional value are prepared at low cost by using the fluorine-containing waste gas. The principle is as follows: HF and SiF4 in the fluorine-containing waste gas are absorbed by using sodium bicarbonate so as to generate NaF and SiO2.H2O; by using the characteristic that the NaF is slightly dissolved in water and SiO2.H2O is not dissolved in a NaHCO3 solution, the SiO2.H2O is removed through filtering and further processed into white carbon black; and the white carbon black with high specific surface area can be prepared through changing the pH of an absorption solution. The filtered NaF solution reacts with NaAlO2, and CO2 is blown, so that the cryolite can be prepared; and the cryolite with molecule ratio of more than 2.90 can be prepared through controlling excessive percentage of the NaF. The invention can be used in treatment of the fluorine-containing waste gas in phosphoric acid and phosphatic fertilizer industries.

Description

Technical field: [0001] The invention relates to a production method for comprehensively utilizing fluorine-containing waste gas in the production process of phosphoric acid to prepare cryolite with a high molecular ratio and by-product white carbon black, which belongs to the field of inorganic chemical industry. Background technique: [0002] Phosphoric acid is obtained by metathesis reaction of phosphate rock with strong inorganic acids (such as sulfuric acid and hydrochloric acid). The main component of phosphate rock is fluorapatite (Ca 5 F(PO 4 ) 3 ), the fluorine element in the phosphate rock will be released in the form of HF gas during the acidolysis process, and another part will be dissolved in the liquid phase, and the HF dissolved in the liquid phase and the SiO in the phosphate rock 2 SiF 4 , SiF 4 It will also be digested in the form of gas during the subsequent concentration of phosphoric acid. Therefore, a large amount of HF and SiF will be produced in...

Claims

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Application Information

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IPC IPC(8): C01F7/54
Inventor 范宝安
Owner WUHAN UNIV OF SCI & TECH
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