Fluoride Adsorption in High-pH Hydroxide Solutions
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Solution Overview
Problem
Existing methods are ineffective in efficiently removing fluoride from aqueous alkaline solutions of high pH, such as those resulting from lithium-containing materials like spent lithium ion batteries, due to high concentrations of hydroxyl ions that displace fluoride from adsorbents, limiting the effectiveness of conventional adsorbents at pH values above 12.
Innovation Solution
The process involves contacting the alkaline solution with solid phase adsorbents like alkaline earth salts (e.g., calcium phosphates, magnesium carbonate) and cation binding resins loaded with 3-valent cations (e.g., aluminum, lanthanum) in a polar solvent, allowing for effective fluoride removal from solutions with high alkaline hydroxide concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional adsorbents are used for fluoride removal, then fluoride adsorption capacity is improved, but effectiveness deteriorates at pH values above 12 due to hydroxyl ion displacement
Solution Approach 1:
The invention changes the chemical parameters of the adsorbent by selecting specific materials (calcium phosphates, magnesium carbonate, hydroxyapatite, tricalcium phosphate) that maintain their fluoride adsorption capability at high pH values. These materials have chemical compositions and surface properties that resist hydroxyl ion displacement, allowing effective fluoride removal even when pH > 12
Solution Approach 2:
The invention employs composite or mixed-phase adsorbent materials that combine different calcium phosphates, magnesium carbonates, or other alkaline earth salts. These composite materials exhibit enhanced stability and fluoride binding affinity at high pH conditions, overcoming the limitations of single-component adsorbents
2Manufacturing precision
If ion exchange is used for defluorination at neutral pH, then fluoride removal is effective, but the method becomes ineffective at high pH due to hydroxyl ion interference
Solution Approach 1:
The invention extends the operational pH range of fluoride removal by selecting adsorbents with isoelectric points and surface charge characteristics that remain favorable for fluoride binding even at pH > 12. The chosen materials maintain positive or neutral surface charges at high pH, enabling continued electrostatic attraction of fluoride ions despite the presence of hydroxyl ions
3Stability of the object's composition
If high concentrations of hydroxyl ions are present, then alkaline solution properties are maintained, but fluoride adsorption is inhibited due to displacement from bonding sites
Solution Approach 1:
The invention converts the harmful effect of high hydroxyl ion concentration into a beneficial condition by selecting adsorbents that are specifically activated or stabilized under highly alkaline conditions. The high pH environment, which normally competes for bonding sites, actually enhances the surface properties and fluoride affinity of the chosen adsorbent materials
Solution Approach 2:
The invention introduces specific adsorbent materials as intermediaries that mediate between the high hydroxyl ion concentration and fluoride ions. These materials have selective binding sites that preferentially interact with fluoride over hydroxyl ions, allowing fluoride removal to proceed despite the high alkaline environment
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 approach significantly enhances fluoride removal efficiency from high pH solutions, achieving effective adsorption even at high concentrations of alkaline hydroxide, thereby purifying lithium hydroxide and reducing fluoride impurities, which is crucial for recycling lithium from battery waste and other lithium-containing resources.
Implementation Method 1
the alkaline solution is contacted with a solid phase adsorbent chosen from alkaline earth salts comprising carbonate anions, oxo anions, sulphate anions, phosphate anions, or mixtures of such anions or mixtures of such anions with hydroxyl anions
Data Source
AI summary
A process for extracting fluoride from a solution of high pH comprising more than 0.1 mol of alkaline hydroxide and/or alcoholate per liter dissolved in a polar solvent is described. The polar solvent is chosen from water, lower alcohols, and mixtures thereof. The process is characterized in that the solution liquid is contacted with a solid phase adsorbent chosen from a) alkaline earth salts comprising carbonate anions, oxo anions, sulphate anions, or phosphate anions, and alkaline earth salts comprising a mixture of such anions or a mixture of such anions with hydroxyl anions, and b) cation binding resins loaded with one or more 3-valent cations, chosen from 3-valent cations of Al, Ga, In, Fe, Cr, Sc, Y, La and lanthanoides.