Lithium Recovery via Phosphate Precipitation and Acid Digestion
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Solution Overview
Problem
Current processes for recovering lithium salts from lithium-bearing solutions, such as brines or pregnant process liquors, face challenges due to the presence of alkali metal and alkaline earth metal cations, which complicate separation and require energy-intensive multi-stage processes to concentrate lithium carbonate and lithium hydroxide beyond their solubility limits, especially when lithium grades are low.
Innovation Solution
A process involving the addition of phosphate to a lithium-bearing solution to produce a lithium phosphate precipitate, followed by digestion in sulfuric acid to precipitate lithium sulfate, with recycling of alkali metal phosphate to enhance phosphate availability and reduce impurities, allowing for the recovery of lithium phosphate and lithium sulfate while minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional evaporation processes are used to concentrate lithium salts beyond solubility limits, then lithium carbonate and lithium hydroxide can be recovered as solids, but energy consumption and capital intensity increase significantly
Solution Approach 1:
The patent changes the chemical parameters of the system by introducing phosphate ions that react with lithium to form insol lithium phosphate precipitate. This chemical transformation allows lithium recovery without requiring evaporation to exceed solubility limits, thereby reducing energy consumption while maintaining effective lithium salt recovery
Solution Approach 2:
The patent utilizes precipitation as a phase transition mechanism where lithium phosphate forms as a solid precipitate from the aqueous solution through chemical reaction with phosphate. This phase change enables lithium separation and recovery without the need for thermal evaporation, significantly reducing energy requirements compared to conventional methods
2Manufacturing precision
If multi-stage processes are implemented to separate lithium from mixed metal solutions containing alkali and alkaline earth metals, then lithium purity can be achieved, but process complexity increases
Solution Approach 1:
The patent extracts lithium from the mixed metal solution by selective precipitation as lithium phosphate. The phosphate addition causes lithium to precipitate separately from other alkali and alkaline earth metals, which remain in solution. This selective extraction achieves lithium purification in a single step rather than requiring multiple separation stages
Solution Approach 2:
Phosphate acts as an intermediary reagent that facilitates the separation of lithium from other metals. By introducing phosphate ions, lithium is selectively precipitated as lithium phosphate while other metals remain dissolved, enabling efficient purification without complex multi-stage processing
3Quantity of substance
If phosphate is added in stoichiometric excess to reduce soluble lithium in solution, then lithium recovery efficiency improves, but residual phosphate in solution increases
Solution Approach 1:
The patent recovers the residual phosphate from the solution by reacting it with alkali metal hydroxide to regenerate alkali metal phosphate. This regenerated phosphate is then recycled back to the precipitation step, reducing waste and minimizing the net loss of phosphate while maintaining high lithium recovery efficiency through continued excess phosphate addition
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 process effectively reduces impurities by an order of magnitude, achieves efficient recovery of lithium salts, and recycles alkali metal phosphate, thereby reducing operational costs and energy requirements, making it economically beneficial.
Implementation Method 1
adding phosphate to the lithium-bearing solution to produce a lithium phosphate precipitate
Implementation Method 2
digesting the separated lithium phosphate precipitate in sulfuric acid to precipitate lithium sulfate
Implementation Method 3
adding alkali metal hydroxide to the separated digestion mixture from step c) to produce an alkali metal phosphate solution
Data Source
AI summary
A process for recovering lithium phosphate and lithium sulfate from a lithium-bearing solution, such as a brine or pregnant process liquor is described. The process includes adding phosphate to the lithium-bearing solution to precipitate lithium phosphate and then separating the resulting lithium phosphate precipitate from the solution. The separated lithium phosphate precipitate is then digested in sulphuric acid to produce a digestion mixture from which a lithium sulfate precipitate is separated. An alkali metal hydroxide is added to the separated solution to produce an alkali metal phosphate solution and this is recycled for use as phosphate in the first step of the process.