Process for preparing calcium fluoride from fluosilicic acid

A technology of fluorosilicic acid and calcium fluoride, applied in chemical instruments and methods, silicon compounds, chemical methods for reacting liquids and gaseous media, etc., can solve the huge loss of fluorine and ammonia, long reaction time, and difficulty in ammonia recovery And other issues

Active Publication Date: 2018-05-11
OCP
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  • Summary
  • Abstract
  • Description
  • Claims
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Problems solved by technology

Furthermore, there is a disadvantage in the fact that a relatively long reaction time of about 30 minutes to 2 hours is required
Furthermore, a considerable disadvantage of the above two methods lies in the fact that only very dilute fluosilicic acid can be used (maximum concentration 4% to 6%)
[0026] However, since calcium hydroxide is used to precipitate calcium fluoride, the chemistry and kinetics of the reaction are less favorable to easily obtain calcium fluoride with the desired purity and size fraction for the acid fluorspar market
In addition, the loss of fluorine and ammonia during the separation of CaF2 is enormous due to the formation and shape of CaF2 crystals
In addition, the ammonium hydroxide filtrate is mainly concentrated in NH 3 , which makes ammonia recovery very difficult and costly

Method used

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  • Process for preparing calcium fluoride from fluosilicic acid

Examples

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Comparison scheme
Effect test

Embodiment 1

[0108] 252 grams of a solution of fluorosilicic acid at a concentration of 32% by weight, which is commercial fluorosilicic acid, was fed into a 1 liter stirred reaction vessel. The solution in the reaction vessel was stirred at a speed of 250 rpm. During stirring, will be like NH 3 A solution of 380 g of ammonium hydroxide having a concentration of 25% by weight is injected just below the liquid surface. The residence time of the reaction mixture was about 60 minutes, the final pH was about 8.3, and the temperature dropped from 61°C to 28°C. The reaction mixture was then filtered, and the resulting filter cake was washed with distilled water and dried at 110°C. Under these conditions, the neutralization yield of fluorine was 81.24%. Chemical analysis and X-ray diffraction measurements of the dried cake indicated that ammonium fluorosilicide was produced instead of reactive silica.

Embodiment 2

[0112] 80 g of ammonium fluoride having a concentration of 8.47% by weight recovered from the fluorosilicic acid neutralization step was supplied to a reaction vessel provided with a stirrer. The solution in the reaction vessel was stirred at a speed of 250 rpm. During stirring, 71.4 g of calcium hydroxide (concentration of 74.16% by weight) suspension (19.5% by weight) was supplied to make the NH 4 The F / CaO weight ratio is equal to 2.1. The residence time of the reaction mixture was about 30 minutes, the final pH was about 10, and the temperature dropped from 21°C to 16°C. The reaction mixture was then filtered, and the resulting filter cake was washed with distilled water and dried at 110°C. Under these conditions, the precipitation yield of fluorine was 87.62%. Chemical analysis and X-ray diffraction measurements of the dried cake indicated that calcium fluoride was obtained.

Embodiment 3

[0118] 200 g of a fluorosilicic acid solution having a concentration of 23% by weight, prepared by diluting 32% by weight of commercially available fluorosilicic acid, was supplied to a 1-liter reaction vessel equipped with a stirrer. The solution in the reaction vessel was stirred at a speed of 250 rpm. During stirring, will be like NH 3 A solution of 308 grams of ammonium hydroxide having a concentration of 25% by weight was injected just below the surface layer of the liquid surface. The residence time of the reaction mixture was about 60 minutes, the final pH was about 9.6, and the temperature was decreased from 54°C to 20°C. The reaction mixture was then filtered, and the resulting filter cake was washed with distilled water and dried at 110°C. Under these conditions, depending on the silica morphology and filtration parameters of the method, the maximum neutralization yield of fluorine was 98.22%. Chemical analysis showed that the active silica obtained had a high sil...

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Abstract

The invention relates to a process for preparing synthetic calcium fluoride (CaF2) (min 90 wt% CaF2) from fluosilicic acid. Said process includes the following steps: (a) reacting fluosilicic acid (H2SiFe) with ammonium hydroxide or ammonia in a first reactor (1) so as to obtain a first thick suspension, filtering said first suspension so as to obtain a filtrate containing an ammonium fluoride solution, (b) precipitating the ammonium fluoride solution, obtained in the form of a filtrate in step (a), with calcium carbonate in dry form or in the form of a suspension having a concentration of between 10 and 80 wt%, in a second reactor (3) so as to produce a second suspension containing the calcium fluoride and the ammonium carbonate, filtering said second suspension so as to obtain a filter cake containing calcium fluoride, and a filtrate containing an ammonia carbonate solution, washing and drying said filter cake so as to obtain calcium fluoride and a washing filter cake containing an ammonium hydroxide solution, wherein a portion of the second suspension, of from 10 to 70 wt%, is recycled to the second reactor (3) so as to enhance the crystallization of the calcium fluoride, changein most of the ammonia from the second reactor in step (b) due to partial decomposition of the ammonium carbonate under reactor conditions, then washing and sending said ammonia back into the first reactor, and collecting and treating, by means of distillation and condensation, the ammonium carbonate solutions obtained as filtrate and washing filter cake in step (b), so as to recover the liquid ammonia which is recycled to the first reactor (1).

Description

technical field [0001] The present invention relates to by fluosilicic acid (H 2 SiF 6 ) to prepare synthetic calcium fluoride (CaF 2 ) and activated silica methods. Background technique [0002] Phosphate rock contains 2% to 4% fluorine. [0003] A part of the fluorine from the phosphate rock is precipitated by gypsum, another part is leached with the phosphoric acid product, and the remaining part, accounting for about 70% of the total fluorine, is evaporated in the reactor and evaporator. [0004] As environmental regulations continue to reduce chemical processing emissions, phosphate plant operators will eventually be required to neutralize fluoride waste. [0005] Most phosphate plants currently use direct contact barometric condensers with recirculating cooling pond water saturated with fluoride salts. [0006] Most of this fluoride precipitates as the circulating water in the large cooling pond system cools. [0007] When treatment of fluoride-contaminated water...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C01F11/22C01B33/12
CPCC01B33/186C01C1/026C01C1/26C01F11/22C01P2004/61C01P2006/12C01P2006/80B01J10/00
Inventor K·萨姆拉尼A·科西勒
Owner OCP
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