Supercritical CO2 Extraction of Rare Earth Elements from Coal Ash
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Solution Overview
Problem
The production of rare earth elements (REEs) is limited by resource constraints, technical limitations, and environmental concerns, with conventional methods relying heavily on imported materials and inefficient extraction from unconventional resources like coal and coal by-products, which have lower REE concentrations.
Innovation Solution
A method involving the use of supercritical CO2 and acids to extract REEs from coal, coal by-products, and coal-derived products, enhancing recovery efficiency and enabling industrial-scale enrichment by forming soluble complexes and precipitating REE oxides, thus avoiding the use of tributyl phosphate and reducing environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional extraction methods are used to recover REEs from coal by-products, then the extraction process can be performed with simple equipment, but the REE recovery efficiency is low and the process requires multiple complex separation steps
Solution Approach 1:
The patent applies parameter changes by transforming CO2 into a supercritical state (changing temperature and pressure parameters) to create a solvent with enhanced extraction capabilities. This single parameter change enables simultaneous extraction of multiple REEs from coal fly ash, achieving high recovery efficiency (up to 25% improvement over conventional methods) without requiring complex multi-step separation processes. The supercritical CO2 can be easily adjusted to optimize extraction of different REE elements.
Solution Approach 2:
The patent uses an intermediary approach by introducing organic acids (such as oxalic acid, citric acid, or acetic acid) as mediators between the supercritical CO2 and the REE compounds in coal fly ash. These acids form soluble complexes with REEs, enabling their extraction into the supercritical CO2 phase. This intermediary mechanism simplifies the overall process by combining extraction and complexation steps into a single operation, avoiding multiple separation stages.
2Object-affected harmful factors
If conventional REE extraction methods are used, then the process can proceed with standard chemicals, but the environmental impact is significant and energy consumption is high
Solution Approach 1:
The patent converts the typically harmful supercritical CO2 extraction process into a beneficial environmentally friendly method. By using CO2 (which is already present in the atmosphere and can be captured from industrial sources) as the extraction solvent instead of toxic organic solvents, the process eliminates harmful chemical waste. The CO2 can be easily separated from the extract and recycled, converting what would be a waste gas into a valuable extraction medium, achieving near-zero environmental impact.
Solution Approach 2:
The patent applies self-service by designing a process where CO2 is recovered and recycled within the system. After extraction, the CO2 is depressurized back to gaseous state, separating naturally from the REE complexes, and can be reused in subsequent extraction cycles. This self-recycling mechanism eliminates the need for continuous input of fresh solvent and reduces energy consumption by avoiding repeated solvent production and disposal processes.
3Productivity
If supercritical CO2 extraction is used to improve REE recovery, then extraction efficiency increases, but the process requires high pressure and temperature conditions
Solution Approach 1:
The patent utilizes phase transitions of CO2 between gaseous and supercritical states to control the extraction process. By cycling CO2 through these phase transitions (gas → supercritical fluid during extraction → gas during depressurization), the system achieves high extraction efficiency only when needed under supercritical conditions, then returns to a low-pressure gaseous state for easy separation and recycling. This phase transition approach allows temporary use of high pressure/temperature only during the actual extraction step, minimizing overall energy input while maintaining high 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 increases REE recovery by up to 25% relative to conventional methods, achieves high purity (>99% REE oxides), and is cost-effective, with reduced energy consumption and near-zero pollution, making domestic production of REEs feasible from unconventional resources.
Implementation Method 1
introducing supercritical CO2 to the coal-derived product to form a first mixture
Implementation Method 2
introducing a first acid to the first mixture to form a second mixture
Implementation Method 3
precipitating a second composition from the first composition, the second composition comprising the rare earth element
Data Source
AI summary
Embodiments of the present disclosure generally relate to the recovery and extraction of rare earth elements. More specifically, embodiments of the disclosure relate to methods for separating rare earth elements from coal, coal by-product(s), and/or coal-derived product(s). In an embodiment, a method of removing rare earth elements from a coal-derived product is provided. The method generally includes introducing supercritical CO2 to the coal ash to form a first mixture, introducing a first acid to the first mixture to form a second mixture, and removing a first composition from the second mixture, the first composition comprising the one or more rare earth elements.