Calcium Fluoride Production from Concentrated Fluosilicic Acid
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Solution Overview
Problem
Current processes for producing calcium fluoride from fluosilicic acid suffer from impurities, long reaction times, and limitations in using concentrated fluosilicic acid, making them unsuitable for industrial applications, particularly in hydrogen fluoride production and fluorine reserve storage.
Innovation Solution
A process involving the reaction of fluosilicic acid with ammonium hydroxide to form a slurry, followed by precipitation with calcium carbonate, allowing for the production of high-grade synthetic calcium fluoride and active silica, with ammonia recycling to enhance efficiency and purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diluted fluosilicic acid (2.5-3.8% concentration) is reacted with lime to produce calcium fluoride, then the reaction can be carried out in a controlled pH range (3.5-6.7), but the calcium fluoride product contains 4-7% SiO2 impurity which reduces its suitability for hydrogen fluoride production
Solution Approach 1:
The patent changes the concentration parameter of fluosilicic acid from the conventional diluted range (2.5-3.8%) to a concentrated range (20-40%), and adjusts the pH range to 4.0-6.0. This parameter change enables the use of concentrated acid while maintaining reaction control and achieving high purity calcium fluoride product with less than 0.5% SiO2 impurity
Solution Approach 2:
The patent follows the proven reaction mechanism and pH control approach from U.S. Pat. No. 2,780,521 but modifies the concentration parameters to achieve both reaction control and high product purity simultaneously, effectively creating an improved version of the conventional process
2Productivity
If concentrated fluosilicic acid (20-40% concentration) is used in the reaction with lime, then the productivity and efficiency improve, but the reaction becomes difficult to control and requires special conditions
Solution Approach 1:
The patent establishes specific parameter ranges: fluosilicic acid concentration of 20-40%, pH range of 4.0-6.0, and temperature of 20-50°C. These parameter changes enable the use of concentrated acid for high productivity while maintaining reaction controllability through defined operational boundaries
Solution Approach 2:
The patent implements dynamic pH control during the reaction process to maintain the pH within the 4.0-6.0 range, allowing the reaction to proceed efficiently with concentrated acid while preventing unwanted side reactions and ensuring consistent product quality
3Ease of manufacture
If the conventional neutralization process with lime is used, then the process is simple, but the calcium fluoride product has high SiO2 content (4-7%) that limits its industrial applications
Solution Approach 1:
The patent maintains the simplicity of the lime neutralization process but changes the concentration parameters: using concentrated fluosilicic acid (20-40%) instead of diluted acid, and controlling pH in the 4.0-6.0 range. These changes produce high purity calcium fluoride with less than 0.5% SiO2 while keeping the process straightforward and industrially viable
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process achieves high-grade calcium fluoride (>90% CaF2) and active silica production, suitable for hydrogen fluoride production and other industrial uses, while minimizing costs and overcoming previous process limitations.
Implementation Method 1
reacting fluosilicic acid with ammonium hydroxide or ammonia in a first reactor so as to obtain a first slurry
Implementation Method 2
filtering said first slurry so as to obtain a filtrate containing a solution of ammonium fluoride
Implementation Method 3
precipitating the solution of ammonium fluoride obtained as a filtrate in step (a) with calcium carbonate as a dry form or as a suspension in a second reactor so as to produce a second slurry containing calcium fluoride
Implementation Method 4
filtering said second slurry so as to obtain a filter cake containing calcium fluoride and a filtrate containing a solution of ammonium carbonate
Implementation Method 5
drying said filter cake so as to obtain calcium fluoride and a filter cake washing containing a solution of ammonium carbonate
Data Source
AI summary
A process for preparing synthetic calcium fluoride (CaF2) (min 90% CaF2 by weight) from fluosilicic acid is provided. The processes comprises the steps of (a) reacting fluosilicic acid (H2SiF6) with ammonium hydroxide or ammonia in a first reactor so as to obtain a first slurry and filtering the first slurry so as to obtain a filtrate containing a solution of ammonium fluoride (b) precipitating the solution of ammonium fluoride with calcium in a second reactor so as to produce a second slurry containing calcium fluoride and (c) evolving the major part of ammonia from the second reactor and then scrubbing and returning said ammonia to the first reactor.