Magnesium Removal via Multi-Step Crystallization
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Solution Overview
Problem
Current methods for purifying lithium are inefficient in removing magnesium impurities, which are abundant and costly to process, often resulting in significant waste and product losses due to undesired salt formation during crystallization.
Innovation Solution
A multi-step process involving forced circulation and draft tube crystallization, followed by chemical precipitation, to effectively remove magnesium as magnesium sulfate hydrate, reducing waste and optimizing lithium recovery by predicting caustic material needs and recycling brine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If chemical precipitation with quicklime is used to remove magnesium, then magnesium removal is achieved, but operational cost increases and large amounts of waste cake are generated
Solution Approach 1:
The patent extracts magnesium from the lithium-containing solution through selective crystallization, separating it as magnesium sulfate hydrate crystals. This extraction approach removes the harmful impurity (magnesium) while preserving the valuable lithium in solution, avoiding the need for costly chemical precipitation and reducing waste generation.
Solution Approach 2:
The patent employs temperature and concentration parameter changes to control selective crystallization. By adjusting these parameters, magnesium sulfate hydrate crystallizes preferentially while lithium remains in solution, enabling efficient magnesium removal without requiring additional chemical reagents and reducing operational costs.
2Loss of substance
If chemical precipitation with quicklime is used, then magnesium is removed, but a large amount of filter cake is generated that must be stored as waste
Solution Approach 1:
The patent extracts magnesium through selective crystallization as magnesium sulfate hydrate, which can be easily separated by filtration. This method removes magnesium efficiently while generating minimal waste compared to chemical precipitation, as the crystallized magnesium can be directly removed without forming large volumes of insoluble hydroxide sludge.
Solution Approach 2:
The patent utilizes phase transition from dissolved magnesium sulfate to solid magnesium sulfate hydrate crystals through controlled crystallization. This phase change enables easy separation of magnesium from the lithium-containing solution and produces a manageable solid product rather than voluminous waste sludge.
3Loss of substance
If typical crystallization methods are used, then magnesium is removed, but undesired lithium containing salt formation occurs and product losses increase
Solution Approach 1:
The patent applies local quality by controlling crystallization conditions to favor magnesium sulfate hydrate formation specifically, while keeping lithium in solution. By localizing the crystallization process to target magnesium selectively under controlled temperature and concentration conditions, the method achieves high magnesium removal without co-precipitation of lithium salts, maintaining product purity.
Solution Approach 2:
The patent uses precise parameter changes in temperature and concentration to control the selective crystallization of magnesium sulfate hydrate. By adjusting these parameters within specific ranges, the process achieves selective magnesium removal while preventing lithium salt formation, ensuring high product purity and minimizing lithium losses.
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 significantly reduces magnesium content, minimizes waste generation, and enhances lithium recovery by efficiently washing and concentrating the product, thereby lowering operational costs and maintaining high purity.
Implementation Method 1
a first crystallization step in a forced circulation crystallizer
Implementation Method 2
concentrating the neutralized filtrate by Mechanical Vapor Recompression heated falling film evaporators
Implementation Method 3
crystallizing impurities from the neutralized filtrate in a second crystallization step in a first draft tube crystallizing step
Implementation Method 4
crystallizing impurities from the neutralized filtrate in a third crystallization step in a second draft tube crystallizing step
Implementation Method 5
precipitating remaining impurities via addition of a caustic material
Implementation Method 6
concentrating the neutralized filtrate by Mechanical Vapor Recompression heated falling film evaporators
Implementation Method 7
concentrating the neutralized filtrate by Mechanical Vapor Recompression heated falling film evaporators
Data Source
AI summary
A method for removing alkali earth metals from a filtrate including a first crystallization step and a second crystallization step, wherein the first crystallization step is a forced circulation crystallizer, and wherein the second crystallization step is a draft tube crystallizer. Also included is a method for reducing magnesium in a chemical liquor including crystallizing magnesium into a magnesium sulfate hydrate in a first crystallization step and precipitating magnesium via addition of a caustic material in a chemical precipitation step.