We have a plant for liquefaction of sodium hydroxide (NaOH) in the form of flakes to concentration of about 50%, but there is unfavorable NaCl content about 200 ppm, we need to reduce the concentration of NaCl to under 50ppm. Is there any cost-effective and economical solution for such problem?
To reduce the NaCl content in a liquid NaOH solution, you can consider the following methods:
1. Ion Exchange: Using a cation exchange resin can selectively remove sodium ions (Na⁺) associated with chloride ions (Cl⁻), effectively reducing NaCl levels. This method is widely used for purification and can be economical if the resin is regenerated properly.
2. Membrane Filtration (Electrodialysis): Electrodialysis is an efficient method to separate ions from solutions. It uses selective membranes to remove chloride ions, but the cost and energy requirements need to be assessed for large-scale operations.
3. Crystallization: Carefully controlling the cooling and evaporation processes during NaOH concentration can help crystallize and remove NaCl, as it has a lower solubility compared to NaOH.
4. Chemical Additives: Specific reagents, such as barium hydroxide or silver nitrate, can precipitate chloride ions as insoluble salts (e.g., BaCl₂ or AgCl). However, these methods may introduce new impurities and require post-treatment.
5. Multi-Stage Evaporation: Fine-tuning the evaporation process can selectively remove NaCl during liquefaction, ensuring lower contamination levels in the final product.
Among these, ion exchange and crystallization are often the most cost-effective for reducing NaCl levels to under 50 ppm, but the choice depends on your plant’s capacity, cost constraints, and available infrastructure.
Thanks for your answer. However, I have a few more questions regarding ion exchange and chemical additives.
Hasan Altawil, regarding the chemical additives, I would like to know if there is a specific ratio for the amount of barium hydroxide and silver nitrate to the total volume of the NaOH solution.
Also, how should the additive be added to the solution? I need to know if the solution should be added gradually, drop by drop, or it is being poured all at once?
Additionally, what kind of filter should we use for the filtration of precipitated BaCl2 or AgCl?
Lastly, I want to know the effects of additives on the color, pH, and concentration of the final NaOH solution."
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