Phosphoric Acid Dihydrate-Hemihydrate Process Fluorine Crystallization
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Solution Overview
Problem
The production of phosphoric acid from phosphated rock with high impurity content, particularly those with a Minor Element Ratio (MER) above 10, faces challenges in crystallization and filtration due to impurity influence, leading to poor quality crystallization and high sulfuric acid pollution, which limits extraction yield and product quality.
Innovation Solution
A method involving the attack of phosphated rock with sulfuric acid at 70-90°C to form a dihydrate slurry with high P2O5 content, followed by heating to solubilize and recrystallize calcium sulfate as hemihydrate, with the addition of a fluorine source to improve crystallization and reduce acidity requirements, allowing for efficient separation of phosphoric acid with low free SO3 content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphated rock with high impurity content (MER>10) is attacked with sulfuric acid under standard conditions to form gypsum slurry, then phosphoric acid can be produced, but the impurities interfere with crystallization and filtration, reducing product quality and extraction yield
Solution Approach 1:
The invention changes the physical-chemical parameters of the system by adding fluorine sources (HF, CaF2, NaF) to modify the crystallization behavior of calcium sulfate. The fluorine adds 0.1-5 g/L to the slurry, which alters the crystal lattice formation and improves the crystallization quality even in the presence of high impurity content (MER>10), thereby resolving the contradiction between maintaining high extraction yield and ensuring good crystallization quality
Solution Approach 2:
Fluorine acts as an intermediary substance that mediates between the impure phosphated rock and the sulfuric acid attack process. It interferes with the harmful effect of impurities (Al2O3, Fe2O3, MgO) on crystallization by incorporating into the calcium sulfate crystal structure, thus protecting the crystallization process from impurity interference while maintaining high P2O5 extraction efficiency
2Productivity
If gypsum is converted to hemihydrate by mixing with concentrated sulfuric acid and heating to improve P2O5 extraction yield, then extraction yield increases, but the installation becomes congested due to requiring two filtrations
Solution Approach 1:
The invention extracts the beneficial effect of fluorine addition from the complex two-stage conversion process. By adding fluorine during the initial sulfuric acid attack, the system achieves both high P2O5 extraction yield and good filterability in a single filtration step, eliminating the need for the second conversion and filtration stage that causes installation congestion
Solution Approach 2:
The invention segments the fluorine addition step from the subsequent conversion operations. Fluorine is added during the attack phase, and its effects persist through to filtration, allowing the process to be simplified while maintaining the benefits of improved crystallization and high extraction yield without requiring additional filtration equipment
3Ease of operation
If gypsum slurry is directly mixed with sulfuric acid to form hemihydrate without prior phosphoric acid separation, then filtration is simplified, but the filtrate contains mixed phosphoric and sulfuric acid requiring desulfation
Solution Approach 1:
The invention performs preliminary action by adding fluorine during the sulfuric acid attack phase before any conversion operations. This preliminary fluorine addition ensures that when the slurry is later mixed with sulfuric acid for hemihydrate formation, the crystallization quality is already optimized, allowing direct filtration without desulfation while maintaining操作简单性
4Adaptability or versatility
If phosphated rock with low P2O5 content (≤30%) is processed to exploit depleted high-grade deposits, then resource utilization improves, but extraction yield and product quality decrease due to high impurity content
Solution Approach 1:
The invention changes the chemical parameters of the attack process by introducing fluorine sources that specifically enhance the reactivity and crystallization behavior for low-grade ores. The fluorine concentration (0.1-5 g/L) is optimized for MER>10 ores, enabling high P2O5 extraction yields (≥85%) from phosphated rock with P2O5 content as low as 20-30%, thus resolving the contradiction between ore grade adaptability and extraction productivity
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 method achieves high P2O5 extraction yield and quality phosphoric acid production with low free SO3 content, even with high impurity levels, and simplifies the conversion process, avoiding filtration congestion and desulfation steps, while maintaining industrial applicability in existing installations.
Implementation Method 1
attack in an aqueous medium of phosphated rock with sulfuric acid at a first temperature comprised between 70 and 90° C. with formation of a first slurry of calcium sulfate dihydrate crystals
Implementation Method 2
conversion of this first slurry by heating to a temperature above 90° C., with solubilization of the calcium sulfate dihydrate crystals and recrystallization of the solubilized calcium sulfate giving rise to a second slurry formed with calcium hemihydrate crystals
Implementation Method 3
with the addition of a fluorine source to improve crystallization and reduce acidity requirements
Data Source
AI summary
A method for producing phosphoric acid, comprising attack in an aqueous medium of phosphated rock with sulfuric acid, with formation of a first dihydrate slurry suspended in an aqueous phase having a free P2O5 content between 38 and 50% and a free SO3 content of less than 0.5%, conversion of this first slurry by heating with recrystallization of the solubilized calcium sulfate giving rise to a second hemihydrate slurry, and separation in the second slurry between a production phosphoric acid and a hemihydrate cake, characterized in that it comprises during the attack, addition of a fluorine source in the first slurry in a content from 1% to 5% by weight of F relatively to the P2O5 contained in the phosphated rock.