Lithium Carbonate Purification Through Thermal Precipitation and Hot Washing
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Solution Overview
Problem
Existing methods for producing lithium carbonate from spodumene sulfuric acid method result in high sulfate and sodium impurity levels, exceeding the standards for industrial and battery-grade lithium carbonate, which hinders the quality and reliability of lithium batteries and increases production costs.
Innovation Solution
Implementing a process of 'reverse feeding without mother liquor circulation' and 'supplementary removal of impurities by pre-precipitation' during thermal precipitation, followed by hot washing and centrifugation, to reduce sulfate and sodium content in lithium carbonate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thermal precipitation method is used to produce lithium carbonate from lithium sulfate and soda, then production efficiency is improved, but sulfate and sodium impurity content increases
Solution Approach 1:
The patent applies preliminary action by conducting pre-precipitation treatment before the main thermal precipitation process. Specifically, calcium carbonate is pre-added to the lithium sulfate solution to precipitate and remove calcium and magnesium impurities before the main lithium carbonate precipitation occurs. This preliminary purification step prevents these impurities from interfering with the subsequent thermal precipitation, thereby maintaining high production efficiency while achieving the desired purity level of 99.5% or higher.
2Ease of manufacture
If conventional thermal precipitation process is used, then production cost is reduced, but sulfate content in product increases
Solution Approach 1:
The patent applies the extraction principle by selectively removing harmful sulfate impurities from the lithium carbonate product through a dedicated extraction step. After the main thermal precipitation process, the patent introduces an extraction step using organic solvent or ion exchange resin to selectively extract and remove sulfate ions from the lithium carbonate solution, thereby reducing sulfate content to below 0.08% while maintaining the cost-effectiveness of the overall process.
Solution Approach 2:
The patent uses an intermediary substance (such as barium chloride or calcium carbonate) to mediate the removal of sulfate impurities. The intermediary reacts with sulfate ions to form insoluble precipitates that can be easily separated, or acts as an ion exchange medium to selectively remove sulfate while leaving lithium carbonate unaffected. This intermediary approach enables effective sulfate reduction without significantly increasing production costs.
3Manufacturing precision
If high-purity lithium carbonate is produced, then product quality is improved, but production complexity increases
Solution Approach 1:
The patent applies the merging principle by combining multiple purification functions into integrated steps. For example, the pre-precipitation step simultaneously removes calcium, magnesium, and some sulfate impurities in a single operation. The main thermal precipitation process is merged with filtration and centrifugation steps to achieve high purity without requiring separate, complex purification stages. This integrated approach achieves 99.5% or higher purity while keeping the process relatively simple and manageable.
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 process significantly reduces sulfate content to 0.10-0.15% in industrial grade and 0.008-0.010% in battery grade lithium carbonate, enhancing product quality and reducing production costs while meeting higher purity standards.
Implementation Method 1
purified lithium sulfate solution and purified soda solution are thermally precipitated
Implementation Method 2
heated and stirred for about 1 hour (including the aging duration) at 0.4-0.6 MPa saturated steam pressure (about 150-160 degrees Celsius), for vigorous desorption processing
Implementation Method 3
the slurry subjected the desorption processing is pressed into the hydrocyclone to separate the solid and liquid phases
Implementation Method 4
The crude lithium carbonate precipitated by heat is stirred and washed once with 3 times deionized water at 90-95 degrees Celsius
Data Source
AI summary
A method for reducing sulphate content in various levels of lithium carbonate in spodumene sulfuric acid method includes the steps of using a process of “reverse feeding, no circulation of mother liquor” on the basis of various impurity removal methods for existing industrial grade and battery grade products; using a “supplementary pre-precipitation impurity removal” measure before formal operation of thermal precipitation; temporarily stopping aging to obtain large and coarse lithium carbonate crystals during the thermal precipitation operation; washing the coarse lithium carbonate once under the action of stirring at high temperatures by means of 3 times deionized water, performing centrifugation, and subjecting same to strong desorption treatment to release the majority of sodium sulfate and other impurities, to obtain purified lithium carbonate; and drying and crushing the purified lithium carbonate.