Step-Leaching Rare Earth Elements from Ash Using Mild Acids
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Solution Overview
Problem
Current methods for extracting rare earth elements (REEs) from ash materials are inefficient, costly, and environmentally hazardous, often requiring strong acids, high temperatures, and resulting in the co-extraction of undesirable elements and radioactive thorium.
Innovation Solution
A method using mild acids in smaller amounts and low concentrations to selectively leach REEs from ash materials in ambient conditions, reducing chemical consumption and waste production by targeting specific phases of the ash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If strong acids and high temperatures are used to extract REEs from ash materials, then the extractability of REEs is improved, but the environmental hazards and chemical consumption increase
Solution Approach 1:
The patent changes the parameters of the leaching process by using mild acids (such as acetic acid, citric acid, or malic acid) instead of strong acids, and conducting the process at ambient temperature (20-25°C) instead of high temperatures (90-400°C). This parameter change maintains high REE extractability (80-95%) while significantly reducing environmental hazards and chemical consumption.
Solution Approach 2:
The patent applies selective leaching where mild acids target specific calcium phases (such as calcite, aragonite, or CA-S phases) in the ash material that contain REEs, while leaving other phases intact. This localized action on specific phases achieves high REE extraction without the need for strong acids that would attack all phases non-selectively.
2Productivity
If strong acids are used to leach REEs from ash, then the extraction efficiency is improved, but the co-extraction of undesirable elements and radioactive thorium increases
Solution Approach 1:
The mild acid selectively attacks calcium phases containing REEs while leaving phases with undesirable elements (Al, Fe, Si) and radioactive thorium intact. This selective action on specific local phases achieves high REE extraction efficiency (80-95%) while minimizing co-extraction of contaminants, producing a cleaner leachate that requires less purification.
Solution Approach 2:
The patent uses mild, biodegradable organic acids (acetic, citric, malic acid) instead of persistent strong mineral acids. These mild acids are consumed in the process but decompose harmlessly, reducing the persistence and accumulation of harmful substances in the environment while maintaining effective REE extraction.
3Productivity
If high temperatures are applied to the ore, then the REE extraction rate is improved, but the energy consumption and capital costs increase
Solution Approach 1:
The patent fundamentally changes the temperature parameter from high temperature (90-400°C) to ambient temperature (20-25°C). This parameter change eliminates the need for heating fuel while maintaining high REE extraction rates (80-95%), directly reducing energy consumption and capital costs for heating equipment.
Solution Approach 2:
The mild acid leaching process works effectively at ambient temperature using the natural reactivity of the acid with calcium phases, without requiring external heating energy input. The system serves itself by utilizing ambient conditions, eliminating the need for energy-intensive heating infrastructure.
4Productivity
If strong acids and extended processing are used, then the REE extraction is improved, but the unit costs for REEs increase
Solution Approach 1:
The patent uses mild acids at ambient temperature with controlled pH (3-6) to achieve high REE extraction in a simplified process. This parameter change reduces the need for complex multi-step processing, extensive infrastructure, and multiple purification cycles, thereby reducing unit costs while maintaining high extraction efficiency.
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 achieves high extractability of REEs with reduced acid consumption and waste generation, making it economically viable and environmentally benign, while also eliminating the need for pre-treatment and high-temperature processing.
Implementation Method 1
uses mild inorganic acids to selectively dissolve certain phases in the ash, thereby leaching the REEs
Data Source
AI summary
The invention provides a method for extracting REEs from ash having the steps of contacting ash with a first acid solution to generate leachate having a pH between approximately 5.0 and approximately 5.5; contacting the ash with a second acid solution to generate leachate having a pH between approximately 2.8 and approximately 3.5; and contacting the ash with a third acid solution to generate leachate having a pH between approximately −0.6 and approximately 0.5. The invention also provides a method for leaching REEs from ash having the steps of: contacting ash with a first amount of acid sufficient to leach Ca and Al from the ash without leaching REEs; contacting the ash with a second amount of acid sufficient to leach REEs from the ash without leaching Fe and Sc; and contacting ash with a third amount of acid sufficient to leach Fe and Sc from the ash.