Supercritical Fluid Extraction of Rare Earth Elements from Coal Fly Ash
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Solution Overview
Problem
Current methods for extracting rare earth elements (REEs) from coal fly ash are energy-intensive, use toxic solvents, and result in low purity due to high impurity concentrations, making them environmentally unsustainable and inefficient.
Innovation Solution
A process using supercritical fluids (SCFs) like CO2, N2, and air to selectively extract REEs from coal-based resources with a tributyl phosphate-nitric acid complex, achieving high extraction efficiencies and purities by altering the reactivity of the extractant and separating REEs from impurities through a multistage stripping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional high temperature alkaline roasting and acid leaching processes are used to extract REEs from coal fly ash, then REE extraction can be achieved, but energy consumption and chemical demands increase significantly
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional high temperature alkaline roasting and acid leaching to supercritical fluid extraction. This involves changing the physical state parameters (temperature, pressure) and chemical environment to achieve REE extraction without high energy consumption. The supercritical fluid extraction operates under milder conditions while maintaining effective extraction, directly resolving the contradiction between extraction efficiency and energy consumption.
2Quantity of substance
If conventional organic solvent extraction is used to extract REEs from leachate, then REE separation can be achieved, but toxic solvents are consumed and environmental harm increases
Solution Approach 1:
The patent extracts the harmful organic solvent component from the extraction system and replaces it with supercritical fluids (CO2, N2, or air). This 'taking out' of the toxic element while retaining the extraction function directly addresses the contradiction between separation efficiency and environmental harm. The supercritical fluids provide effective REE separation without the toxic byproducts of conventional organic solvents.
3Quantity of substance
If conventional extraction methods are used on low grade REE sources like coal fly ash, then REE recovery is possible, but the process becomes excessively complex and costly
Solution Approach 1:
The patent segments the complex conventional process (roasting, leaching, solvent extraction, multiple purification steps) into a single integrated supercritical fluid extraction step. This segmentation consolidates multiple operations into one process, dramatically reducing complexity while maintaining recovery efficiency from low grade sources like coal fly ash.
4Productivity
If high concentration impurities are present in the extracted REE solution, then REE extraction yield is maintained, but product purity decreases
Solution Approach 1:
The patent introduces supercritical fluids as an intermediary medium that selectively complexes with REEs while leaving impurities behind. This intermediary action enables simultaneous achievement of high extraction yield and high product purity, as the supercritical fluid selectively binds to REEs and facilitates their separation from impurity-containing matrices through controlled phase changes.
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 REE extraction efficiencies (66-79%) and purities (up to 6.5%), reducing energy and chemical demands while minimizing organic waste and environmental impact, effectively addressing the challenges of existing methods.
Implementation Method 1
extracting the rare earth element from the mixture in the presence of a supercritical fluid
Implementation Method 2
facilitates mass transfer, and has high selectivity
Implementation Method 3
recovering the rare earth element in at least one stripping stage
Data Source
AI summary
Abstract: Described herein is a process for obtaining rare earth elements from coal-based resources. Advantages of this process include low energy demands, application of environmentally-friendly solvents, and high purities of obtained rare earth elements.