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, high acid concentrations, and incomplete extraction, leading to environmental concerns due to toxic waste accumulation.
Innovation Solution
The method involves recrystallization of phosphogypsum from hemihydrate to dihydrate in a neutral or subacidic calcium salt solution, allowing REM extraction into a separate solid phase, followed by acid treatment to dissolve impurities, achieving up to 95% REM extraction with reduced residual impurities in calcium sulphate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphogypsum is treated with high concentration sulphuric acid to extract rare-earth metals, then extraction efficiency improves, but residual impurities (phosphorus, fluorine, alkali metals) in calcium sulphate increase
Solution Approach 1:
The extraction process is divided into two separate stages: first treating phosphogypsum with neutral/subacidic calcium salt solution to extract REM, then treating the resulting calcium sulphate with acid to remove residual impurities. This segmentation allows optimization of each stage for its specific purpose without compromising the other.
Solution Approach 2:
The patent applies preliminary action by first extracting REM with neutral/subacidic solution before applying acid treatment. This sequence prevents excessive acid from being in contact with the original phosphogypsum, thereby reducing impurity incorporation into calcium sulphate while still achieving high REM extraction.
2Manufacturing precision
If phosphogypsum is treated with neutral or subacidic calcium salt solution for REM extraction, then residual impurities in calcium sulphate decrease, but extraction efficiency of rare-earth metals reduces
Solution Approach 1:
The process separates REM extraction from impurity removal into two distinct operations performed in sequence, allowing the first stage to focus on maximum REM extraction with gentle conditions, while the second stage handles purification without compromising extraction efficiency.
Solution Approach 2:
The patent changes the chemical parameters of the treatment solution between stages: using neutral/subacidic calcium salt solution for extraction, then switching to acid solution for impurity removal. This parameter change optimizes each stage for its specific function.
3Productivity
If conventional acid extraction methods are used, then rare-earth metals are extracted into solution, but the process requires expensive reagents and high acid concentrations
Solution Approach 1:
The patent replaces expensive conventional reagents (such as trialkyl phosphine oxide) with inexpensive, readily available calcium salt solutions for the extraction stage, and uses acid only in the subsequent impurity removal stage, significantly reducing overall reagent consumption and cost.
Solution Approach 2:
The patent extracts REM into the solid phase rather than keeping them in solution, which allows for easier separation and reduces the need for large volumes of expensive extracting reagents. The REM are incorporated into the calcium sulphate solid structure during crystallization.
4Productivity
If phosphogypsum is processed to extract REM, then valuable rare-earth metals are recovered, but toxic waste accumulates in the environment
Solution Approach 1:
The patent converts the harmful toxic components (phosphorus, fluorine, alkali metals) that were previously wasted into removable impurities that can be systematically eliminated through the two-stage process. The first stage recovers valuable REM, and the second stage removes toxic impurities, transforming waste into separable byproducts.
Solution Approach 2:
The process discards toxic impurities from the final calcium sulphate product through acid treatment and washing, while recovering valuable rare-earth metals in the first stage. This selective discarding and recovering approach eliminates environmental hazards while preserving valuable materials.
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 effectively recovers REM with high efficiency, minimizing residual phosphorus, fluorine, and alkali metal impurities in calcium sulphate, enabling the production of a REM concentrate while addressing environmental concerns.
Implementation Method 1
recrystallization of phosphogypsum from hemihydrate to dihydrate in a neutral or subacidic calcium salt solution, allowing REM extraction into a separate solid phase
Implementation Method 2
followed by acid treatment to dissolve impurities, achieving up to 95% REM extraction with reduced residual impurities in calcium sulphate
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 recrystallization of hemihydrate or anhydrite of calcium sulphate into dihydrate of calcium sulphate in the presence of a soluble calcium salt at concentrations of 0.075-3.75 M (in terms of Ca2+) at subacidic conditions (pH>1), and dissolution with strong acid (pKa<0) at a concentration of 0.2-8.0 M (in terms of H+). Recovery of REM into solution is up to 95%, 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.