High-Pressure Caustic Leaching for Scandium Recovery From Silicates
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Solution Overview
Problem
Current methods are ineffective in efficiently recovering scandium and rare-earth elements from hard-rock type scandium-bearing silicates, such as pyroxenes and amphiboles, due to their chemical similarity and reactivity, leading to low recovery rates and limited commercial applications.
Innovation Solution
A high-pressure caustic leaching process using an alkali solution at elevated temperatures and pressures to break down the silicate matrix, followed by mineral acid leaching to extract scandium and rare-earth elements, with subsequent purification steps to achieve high purity products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional acid leaching methods are used to extract scandium from hard-rock type scandium-bearing silicates, then the process is simple and cost-effective, but the recovery rate is low because scandium cannot be effectively liberated from the silicate matrix
Solution Approach 1:
The leaching process is divided into two distinct stages: (1) a high-pressure caustic leaching stage to break down the silicate matrix and liberate scandium, and (2) an acid leaching stage to extract the liberated scandium from the solution. This segmentation allows each stage to be optimized for its specific function, with the caustic stage handling matrix breakdown and the acid stage handling metal extraction, thereby achieving high recovery rates while maintaining process manageability
Solution Approach 2:
The high-pressure caustic leaching is performed as a preliminary action before acid leaching. The caustic treatment pre-breaks down the resistant silicate matrix and liberates scandium compounds, making them more accessible to the subsequent acid leaching process. This preliminary breakdown of the matrix structure is essential for enabling effective scandium extraction in the second stage
2Productivity
If high-pressure caustic leaching is used to break down the silicate matrix, then scandium liberation is significantly improved, but the process requires elevated temperatures and pressures increasing energy consumption
Solution Approach 1:
The process utilizes parameter changes by conducting the caustic leaching at elevated temperatures (typically 100-200°C) and pressures (typically 1-10 atm) to enhance the breakdown of the silicate matrix. These parameter changes increase the reaction rate and effectiveness of the caustic treatment, enabling complete matrix breakdown and scandium liberation. The subsequent acid leaching is performed at lower temperatures and pressures, optimizing energy efficiency while maintaining high extraction rates
3Productivity
If conventional leaching methods are used, then the process is cost-effective, but scandium remains trapped in the silicate matrix resulting in low recovery rates
Solution Approach 1:
The high-pressure caustic solution acts as an intermediary agent between the scandium-bearing silicate matrix and the subsequent acid leaching process. The caustic treatment intermediates the matrix breakdown and scandium liberation, creating a form of scandium that is then easily extracted by the acid. This intermediary caustic treatment step is essential for making the scandium accessible to the extraction process while maintaining overall process feasibility
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 method effectively liberates scandium and rare-earth elements from silicate minerals, achieving high recovery rates and purity levels, addressing the limitations of existing technologies and enabling broader commercial utilization.
Implementation Method 1
leaching the ore, the REE and/or scandium bearing feedstock and/or the scandium/REE bearing mineral concentrate in an alkali solution at a first temperature for a target duration and at a given pressure to produce a leachate slurry
Implementation Method 2
leaching of the solid residue in a mineral acid to form a primary leach solution
Data Source
AI summary
Despite the abundance of scandium, its commercial applications continue to be limited by the absence of reliable, secure, stable and long-term production. The subject-matter disclosed herein provides for a method for extracting Rare Earth Elements (REE), scandium and/or Rare-Earth Oxides (REO) from ore and mineral concentrates, the method comprising: providing Rare Earth Elements (REE) and/or scandium bearing feedstock; a high-pressure caustic (HPC) leaching step, comprising leaching the feedstock in an alkali solution at a first temperature for a target period of time and at a given pressure to produce a leachate slurry; extracting a solid residue from the leachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution; extracting scandium and/or REE from the primary leach solution; and/or precipitating REE remaining in the raffinate to form a mixed REE-carbonate to thereby facilitate the extraction of REO.