Supercritical CO2 Extraction of Rare Earth Elements
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Solution Overview
Problem
Current methods for recycling rare earth elements (REEs) from waste electrical and electronic equipment face challenges such as low recovery rates, high energy consumption, and environmental hazards due to the use of pyrometallurgy and hydrometallurgy, which are inefficient and unsustainable.
Innovation Solution
The development of a supercritical fluid extraction (SCFE) process using CO2 as a solvent and chelating agents like TBP-HNO3 to extract REEs from sources like NiMH batteries, permanent magnets, and phosphors, which operates at lower temperatures, reduces waste, and enhances extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pyrometallurgy and hydrometallurgy are used for REE recycling, then extraction capability is achieved, but energy consumption increases and environmental hazards occur
Solution Approach 1:
The patent applies parameter changes by transitioning from traditional high-temperature pyrometallurgy and chemical-intensive hydrometallurgy to supercritical fluid extraction operating at moderate temperatures and pressures. The supercritical state of CO2 (achieved at 31.1°C and 7.38 MPa) provides unique solvation properties that enable effective REE extraction without the high energy input required by conventional methods, directly resolving the contradiction between extraction capability and energy consumption
Solution Approach 2:
The patent replaces the thermal and chemical systems of pyrometallurgy and hydrometallurgy with a supercritical fluid system. Instead of using high-temperature heating and strong chemical reagents, the invention uses supercritical CO2 with chelating agents under controlled pressure and temperature conditions, substituting a mechanical/physical supercritical state system for the thermal-chemical systems, thereby reducing energy consumption while maintaining extraction effectiveness
2Productivity
If pyrometallurgy and hydrometallurgy are used for REE recycling, then extraction capability is achieved, but environmental hazards increase
Solution Approach 1:
The patent converts the typically harmful high-temperature and strong-chemical processes of conventional metallurgy into a beneficial low-temperature supercritical fluid process. The CO2, which can be harmful as a greenhouse gas, is utilized in a controlled supercritical state where it provides excellent solvation properties, and after extraction, it simply depressurizes and returns to gaseous state without leaving harmful residues, thus converting a potential harm into a benefit
Solution Approach 2:
The patent employs supercritical CO2 as an inert solvent that creates a safe extraction environment. Unlike hydrometallurgy which uses strong acids and bases, or pyrometallurgy which involves high-temperature oxidation, the supercritical CO2 system is chemically inert and non-flammable, eliminating environmental hazards associated with harmful chemicals and high-temperature emissions while maintaining effective REE extraction through chelating agents
3Use of energy by moving object
If supercritical fluid extraction is used, then energy consumption is reduced and environmental safety is improved, but extraction efficiency must be enhanced
Solution Approach 1:
The patent introduces chelating agents as intermediaries between the supercritical CO2 solvent and the REE target materials. These chelating agents form stable complexes with REE ions, enhancing the solubility and extractability of REEs in the supercritical fluid phase. This intermediary mechanism allows the system to achieve high extraction efficiency without requiring high energy input, as the chelating agents facilitate selective complexation and transfer of REEs under mild supercritical conditions
Solution Approach 2:
The patent optimizes extraction efficiency through precise parameter control of the supercritical system. By adjusting temperature, pressure, and CO2 flow rate within specific ranges, the system achieves optimal solvation and mass transfer conditions. The moderate temperature (31.1°C critical point) and pressure (7.38 MPa critical point) parameters provide sufficient energy for extraction while consuming significantly less energy than conventional methods, and the parameters can be fine-tuned to maximize extraction efficiency for different REE sources
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
The SCFE process achieves high REE recovery rates (up to 90% for NiMH batteries and 94% for NdFeB magnets) with minimal hazardous waste and lower energy consumption, making it a more sustainable and efficient method for urban mining of REEs.
Implementation Method 1
supercritical fluid extraction (SCFE) process using CO2 as a solvent
Implementation Method 2
SCFs have a low viscosity and a high diffusivity (gas-like properties), and the ability to dissolve materials like a liquid. These properties enable them to penetrate and transport solutes from different matrices at a higher rate
Implementation Method 3
Because sc-CO2 is a non-polar solvent, there is a significant polarity difference between the solute and solvent when extracting metal ions and organometallic compounds. In such cases, it is therefore necessary to utilize complexing (chelating) agents to satisfy the charge neutrality and improving solvent-solute interactions.
Data Source
AI summary
A method for supercritical fluid extraction of metal from a source, the method comprising: providing a reactor chamber; providing a source comprising a target metal; optionally, providing a chelating agent; providing a solvent; adding the source comprising the target metal, the chelating agent and the solvent into the reactor chamber; adjusting the temperature and pressure in the reactor chamber so that the solvent is heated and compressed above its critical temperature and pressure; optionally, providing mechanical agitation to the reactor chamber; recovering a chelate comprising the target metal.