Phosphogypsum Recrystallization for Rare-Earth Metal Extraction
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Solution Overview
Problem
Current methods for extracting rare-earth metals (REM) from phosphogypsum are inefficient, requiring expensive reagents, incomplete extraction, and generating environmental hazards due to high acid concentrations and toxic waste, with existing technologies failing to achieve high recovery rates and purify calcium sulphate effectively.
Innovation Solution
The method involves recrystallization of phosphogypsum from hemihydrate to dihydrate in an acidic calcium salt solution, increasing the yield of REM into the solution by forming separate phases, with calcium and acid concentrations optimized to enhance extraction efficiency and purity of calcium sulphate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphogypsum is treated with high concentration sulphuric acid to extract REM, then extraction yield improves, but environmental harm and process complexity increase
Solution Approach 1:
The patent changes the chemical parameters of the extraction system by using nitric acid instead of sulphuric acid, and by controlling the acid concentration at 1-3 wt% rather than using high concentrations. This parameter change enables effective REM extraction while avoiding the formation of toxic phosphogypsum waste, thus resolving the contradiction between extraction yield and environmental harm
Solution Approach 2:
The patent converts the harmful effect of acid treatment that normally produces toxic phosphogypsum waste into a beneficial process by using nitric acid system that produces soluble calcium nitrate instead of insoluble phosphogypsum. The calcium nitrate solution can be further processed to recover calcium, turning what would be waste into a recoverable product
2Productivity
If phosphogypsum is treated with nitric acid and phosphine oxide extraction, then REM extraction is achieved, but process cost increases due to expensive reagents and additional facilities
Solution Approach 1:
The patent takes out the problematic phosphine oxide extraction step and replaces it with a direct precipitation method using calcium chloride solution. This eliminates the need for expensive trialkyl phosphine oxide reagents and additional extraction facilities, significantly reducing process cost while maintaining effective REM extraction capability
Solution Approach 2:
The patent replaces expensive, reusable but costly phosphine oxide extractants with a simple, inexpensive calcium chloride solution that can be used once and then processed. The calcium chloride method uses cheap, readily available reagents that eliminate the need for expensive specialized extraction chemicals
3Productivity
If cation exchange sorption is used to recover REM from extraction solution, then REM recovery is achieved, but process duration and material flow increase
Solution Approach 1:
The patent replaces the complex mechanical cation exchange sorption process with a simple chemical precipitation process. By adding calcium chloride solution, REM compounds precipitate directly as insoluble salts, which can be separated by simple filtration. This substitution eliminates the need for complex ion exchange columns and reduces process duration significantly
Solution Approach 2:
The patent utilizes phase transition by changing REM compounds from dissolved state in the nitric acid solution to insoluble precipitate phase through addition of calcium chloride. This phase transition enables simple gravitational separation and filtration, dramatically reducing the time and complexity compared to cation exchange sorption methods
4Quantity of substance
If phosphogypsum is treated with sulphuric acid to precipitate calcium sulphate, then REM are concentrated in waste, but calcium sulphate purification from phosphorus and fluorine is incomplete
Solution Approach 1:
The patent inverts the traditional approach by not trying to purify calcium sulphate from phosphogypsum, but instead by dissolving phosphogypsum in nitric acid to create a clean solution, then selectively precipitating calcium as pure calcium sulphate dihydrate. This inversion allows obtaining high purity calcium sulphate while recovering REM in the filtrate, rather than having REM contaminated in the solid waste
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 approach achieves a high extraction yield of 90-98% REM with residual impurities below 0.3% phosphorus, 0.1% fluorine, and 0.05% alkali metals in calcium sulphate dihydrate, facilitating the recovery of REM into a concentrate while purifying calcium sulphate.
Implementation Method 1
REM extraction into a solution (REM leaching) is carried out by recrystallization of phosphogypsum from hemihydrate CaSO 4 •0,5 H 2 O or anhydride CaSO 4 into dihydrate CaSO 4 •2 H 2 O in an acidic solution of calcium salts
Implementation Method 2
recrystallization of phosphogypsum from hemihydrate to dihydrate
Implementation Method 3
separation of rare-earth metal sulphates from the precipitate
Data Source
AI summary
The present invention relates to a method for complex processing of apatite concentrate resulting in producing concentrate of rare earth metals (REM) and plaster from phosphogypsum, a waste of sulphuric acid technology for producing phosphoric acid from apatite. The method comprises leaching of REM into solution by recrystallization of hemihydrate or anhydrite of calcium sulphate into dihydrate of calcium sulphate with a soluble calcium salt at concentrations of 0.075-3.75 M (in terms of Ca2+) and strong acid (pKa0) at a concentration of 0.2-8.0 M (in terms of H+). Recovery of REM into solution is up to 98%, the residual content of impurities of phosphorus, fluorine and alkali metals in dihydrate of calcium sulphate does not exceed 0.3 wt.%, 0.1 wt.%, 0.05 wt.%, respectively.