Apatite Rare Earth Recovery via Phosphate Extraction and pH Precipitation
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Solution Overview
Problem
Conventional methods for processing apatite minerals to recover rare earth elements are economically unviable due to high transportation costs of nitric acid, corrosion issues with hydrochloric acid, and inefficient water-balance in hydrochloric acid routes, leading to costly gypsum disposal and low recovery of valuable products.
Innovation Solution
A method involving the dissolution of apatite in hydrochloric acid with controlled liquid-to-solid ratios, followed by solvent extraction using tributyl phosphate, and gypsum precipitation in dihydrate form to maintain a balanced water-balance, producing high-quality gypsum and recover rare earth elements effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional sulfuric acid digestion is used for apatite processing, then phosphoric acid production is enabled with easy calcium separation, but the residual gypsum is of low quality requiring costly disposal and rare earth elements are lost in the gypsum lattice
Solution Approach 1:
The patent extracts rare earth elements from the apatite digestion process by using a water-soluble chelating agent that selectively binds rare earth elements and allows their separation from the gypsum phase. This enables recovery of rare earth elements while maintaining efficient calcium separation through conventional gypsum precipitation.
Solution Approach 2:
The patent introduces a water-soluble chelating agent as an intermediary substance that mediates between the phosphoric acid digestion process and rare earth element recovery. This chelating agent forms soluble complexes with rare earth elements, enabling their extraction from the digestion mixture without interfering with the calcium-gypsum separation process.
2Ease of manufacture
If nitric acid is used for apatite digestion to enable calcium nitrate production, then calcium removal is achieved, but transportation costs increase significantly due to nitric acid being delivered at maximum 60% concentration
Solution Approach 1:
The patent changes the concentration parameter of the acid used for apatite digestion from 60% nitric acid to concentrated sulfuric acid (96-98%). This parameter change reduces transportation volume significantly while maintaining effective calcium removal through gypsum precipitation, and enables rare earth element recovery through chelation.
3Productivity
If hydrochloric acid is used for apatite dissolution to enable rare earth element recovery, then dissolution efficiency is improved, but corrosion issues arise and water-balance becomes unbalanced leading to costly gypsum disposal
Solution Approach 1:
The patent replaces expensive and corrosive concentrated hydrochloric acid with cheaper and less corrosive sulfuric acid for the dissolution step. While sulfuric acid has its own challenges, the patent mitigates these by using a chelating agent system that enables rare earth element recovery and gypsum valorization, making the process economically viable without requiring expensive corrosion-resistant materials throughout the entire process.
4Productivity
If sulfuric acid digestion is used to produce phosphoric acid, then phosphorus recovery is achieved, but residual water must be removed by evaporation increasing energy consumption
Solution Approach 1:
The patent changes the acid system from sulfuric acid to hydrochloric acid for apatite dissolution. This parameter change produces phosphoric acid in a chloride medium that does not require extensive evaporation for water removal, thereby reducing energy consumption while maintaining effective phosphorus recovery and enabling rare earth element solubilization.
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 enables the production of high-value phosphoric acid and ammonium phosphates, reduces gypsum disposal, and recovers rare earth elements efficiently, improving the economic viability and environmental sustainability of the process.
Implementation Method 1
dissolving of apatite in hydrochloric acid with controlled liquid-to-solid ratios, followed by solvent extraction
Implementation Method 2
solvent extraction using tributyl phosphate
Implementation Method 3
gypsum precipitation in dihydrate form to maintain a balanced water-balance
Data Source
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Figure 2~4
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AI summary
A method for recovery of rare earth elements from apatite mineral comprises dissolving (S10) of apatite mineral of magmatic origin in an acid comprising hydrochloric acid. The dissolving results in a first liquid solution comprising phosphate, calcium and chloride ions, rare earth elements, arsenic and iron. The arsenic and any ferric iron are removed. The first liquid solution is treated (S20) into a second liquid solution by extracting (S22) of a major part of the phosphate ions with an organic solvent. The treating of the first liquid solution into the second liquid solution further comprises partially neutralizing (S75) a raffinate resulting from the extracting of a major part of the phosphate to a pH > 1.5, causing precipitation of phosphates of rare earth elements, and filtering (S76) the precipitated phosphates of rare earth elements from the raffinate.