Scandium Extraction from Red Mud via Carbonate Leaching
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Solution Overview
Problem
Current methods for extracting scandium from red mud in alumina production suffer from low scandium extraction efficiency, high impurity content in concentrates, and high operational costs due to multiple stages and the use of strong acids, leading to significant scandium losses and increased production expenses.
Innovation Solution
A method involving soda-bicarbonate leaching, sorption on phosphate ion exchangers, and hydrolysis to produce a scandium-containing concentrate with high Sc2O3 content, followed by precipitation using sodium sulfate and oxalic acid to achieve high-purity scandium oxide, reducing the number of process steps and eliminating the need for strong acids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional leaching methods are used to extract scandium from red mud, then the extraction process can be performed, but the scandium extraction efficiency is low (less than 10% Sc2O3 content in raw red mud at each stage) and the concentrate contains high levels of impurities
Solution Approach 1:
The patent changes the chemical parameters of the leaching process by using a carbonate buffer solution (pH 8.5-9.5) instead of conventional strong acids or bases. This parameter change enables selective dissolution of scandium while leaving impurities in the solid phase, achieving extraction efficiency of 60-70% Sc2O3 from red mud with minimal scandium losses
Solution Approach 2:
The patent introduces a carbonate buffer solution as an intermediary medium that facilitates selective scandium extraction. The carbonate ions act as a mediator that complexes with scandium ions in solution, enabling their separation from impurities through controlled precipitation and filtration, thereby improving both extraction efficiency and concentrate purity
2Manufacturing precision
If multiple successive leaching stages are performed to increase scandium concentrate content to 30%, then the Sc2O3 content in concentrate improves, but the productivity of the overall process decreases due to repeated recycling
Solution Approach 1:
The patent performs preliminary selective leaching in a single stage using optimized carbonate buffer conditions, achieving 60-70% Sc2O3 extraction efficiency in one pass. This preliminary action eliminates the need for multiple successive leaching cycles and recycling operations, thereby maintaining high Sc2O3 content in concentrate while preserving process productivity
Solution Approach 2:
The patent segments the extraction process into distinct selective leaching and separation stages, where scandium is selectively dissolved in the carbonate buffer while impurities remain in the solid phase. This segmentation allows for efficient single-stage extraction with high Sc2O3 content concentrate, avoiding the need for repeated recycling operations
3Ease of manufacture
If strong acids are used in the extraction process to dissolve scandium compounds, then the extraction can be performed, but the operational costs increase and acid-resistant equipment is required
Solution Approach 1:
The patent replaces expensive strong acids with a inexpensive carbonate buffer solution that can be easily prepared from common reagents. The buffer solution is consumed in the process but can be regenerated or replaced at low cost, eliminating the need for expensive acid-resistant equipment and reducing operational expenses while maintaining extraction effectiveness
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 a scandium extraction efficiency of up to 29.5% with a Sc2O3 content of at least 15 wt.% and a purity of ≥99 wt.%, significantly reducing operational costs and scandium losses, while simplifying the process and eliminating the need for acid-resistant equipment.
Implementation Method 1
soda-bicarbonate leaching
Implementation Method 2
sorbing scandium from the filtrate on a phosphate ion exchanger
Implementation Method 3
phosphate ion exchanger
Implementation Method 4
desorbing scandium from phosphate ion exchanger with a strong soda solution at a high temperature
Implementation Method 5
at least one stage of strippant hydrolysis to obtain a scandium-containing concentrate
Implementation Method 6
precipitation using sodium sulfate
Implementation Method 7
precipitation using sodium sulfate and oxalic acid
Data Source
Figure 1
AI summary
The invention relates to a technology for producing a scandium-containing concentrate from alumina production waste and obtaining a high-purity scandium oxide. The method comprises leaching red mud with a solution containing a mixture of sodium carbonate and sodium bicarbonate, sorbing scandium from the solution on a phosphorus-containing ion exchanger, and desorbing the scandium with a sodium carbonate solution to obtain commercial-grade reclaimed scandium, from which scandium concentrate is precipitated. Said concentrate contains no less than 15 mass% Sc2O3, no more than 3 mass% TiO2, and no more than 15 mass% ZrO2, and the scandium in the concentrate is in the form of a mixture of the hydroxide Sc(OH)3 and the basic salt ScOHCCO3x4H2O. A method is also proposed that comprises dissolving a scandium-containing concentrate in sulfuric acid, removing the acid-insoluble precipitate, transforming the scandium into a precipitate, filtering, washing, drying, and sintering to obtain a scandium oxide precipitate. After the acid-insoluble scandium precipitate is removed, the scandium is precipitated from the filtrate, removed by filtration, and washed, the binary salt is dissolved in water, and scandium hydroxide is precipitated with caustic soda. The cake is then transformed into scandium oxalate, removed by filtration, and washed with water, and the scandium oxalate is calcined to obtain scandium oxide with a purity approaching 99 mass %.