Lithium Salt Separation with Bipolar Membrane Efficiency Control
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Solution Overview
Problem
Existing lithium salt separation methods using bipolar membranes suffer from reduced current efficiency and increased impurity generation due to ion diffusion and sulfur impurity migration, particularly at higher concentrations.
Innovation Solution
A method involving a bipolar electrodialysis device with controlled concentration and pH of discharged solutions, using a bipolar membrane, anion exchange membrane, and cation exchange membrane, to improve current efficiency and minimize impurities by controlling ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lithium salt aqueous solution is processed at higher concentrations, then productivity increases, but current efficiency decreases due to back-contamination and ion diffusion
Solution Approach 1:
A bipolar membrane is introduced as an intermediary component between the acid and base compartments. This membrane performs water electrolysis to generate H+ and OH- ions in situ, replacing the need for external acid and base solutions. The bipolar membrane acts as a mediator that prevents back-contamination by generating fresh ions at the interface, thereby maintaining current efficiency even at higher processing concentrations of lithium salt.
Solution Approach 2:
The invention changes the chemical parameters of the acid and base compartments by using a bipolar membrane that dynamically generates H+ and OH- ions through water electrolysis. This parameter change allows the system to operate at higher lithium salt concentrations without the degradation of current efficiency that occurs in conventional systems with fixed acid and base solutions.
2Productivity
If higher concentrations are used in acid and base compartments, then productivity improves, but impurity generation increases due to ion diffusion
Solution Approach 1:
The bipolar membrane serves as an intermediary that generates H+ and OH- ions through water electrolysis at its internal interface. This eliminates the need for high-concentration external acid and base solutions that cause impurity generation through ion diffusion. The membrane mediates the chemical reactions to produce the necessary ions in situ, preventing contamination while maintaining productivity.
Solution Approach 2:
The invention extracts the source of impurities by removing the need for high-concentration acid and base solutions from the system. Instead of using external acid and base reservoirs that can diffuse ions and create contaminants, the system uses a bipolar membrane to generate the necessary ions through water electrolysis, thereby taking out the harmful element (external high-concentration solutions) while maintaining the desired function.
3Device complexity
If conventional ion exchange membranes are used, then device complexity is reduced, but current efficiency decreases due to back-contamination
Solution Approach 1:
The invention uses a composite membrane structure - a bipolar membrane that combines a cation-exchange layer and an anion-exchange layer in a single integrated component. This composite material performs multiple functions: it separates ions, conducts electricity, and generates H+ and OH- ions through water electrolysis. The composite nature of the bipolar membrane provides enhanced performance compared to conventional single-function ion exchange membranes, improving current efficiency while maintaining reasonable device complexity.
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
Enhances current efficiency and reduces impurity generation by optimizing the concentration and pH of discharged solutions, achieving economic viability and improved product purity.
Implementation Method 1
a bipolar membrane that performs water electrolysis to generate H + and OH -
Implementation Method 2
introducing a lithium salt aqueous solution into a salt compartment located between an adjacent anion exchange membrane and a cation exchange membrane
Implementation Method 3
introducing water into an acid compartment located between an adjacent bipolar membrane and an anion exchange membrane
Implementation Method 4
applying an electric current to the bipolar electrodialysis device to obtain an aqueous lithium hydroxide solution from the base compartment
Data Source
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AI summary
The present embodiments provide a method for separating a lithium salt using a bipolar membrane, the method comprising: introducing a lithium salt aqueous solution into a salt compartment located between an adjacent anion exchange membrane and a cation exchange membrane of a bipolar electrodialysis device; introducing water into an acid compartment located between an adjacent bipolar membrane and an anion exchange membrane; introducing water into a base compartment located between an adjacent bipolar membrane and a cation exchange membrane; and applying an electric current to the bipolar electrodialysis device to obtain an aqueous lithium hydroxide solution from the base compartment and, simultaneously, to obtain an acid aqueous solution as a byproduct from the acid compartment, wherein the method comprises controlling the concentration of the aqueous lithium hydroxide solution discharged from the base compartment or the concentration of the acid aqueous solution discharged from the acid compartment, so as to improve the current efficiency of the entire process.