Why is it necessary to add an alkaline solution for neutralization when removing ammonia nitrogen from stripped acidic water? ?
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I would like to ask the experts here: The ammonia nitrogen level in the company’s 60 m3/h acidic water stripping unit cannot be reduced. Moreover, after adding alkali solution for neutralization, the levels drop significantly. Does the alkali solution work by undergoing a chemical reaction with organic nitrogen to cause this reduction?
It’s acid-base neutralization; the pH value of acidic water is less than 7, and alkali must be added to adjust the pH to 7 before it can be discharged.
Under alkaline conditions, ammonia nitrogen is dissolved in water mainly in the form of free NH3, and is easily distilled off.
The stripping unit involves three types of equilibrium reactions occurring simultaneously; you can take a look at the principle behind the stripping reaction to understand what’s going on
In water, there are anions such as sulfate ions and chloride ions, which combine with ammonia to form salts that are difficult to strip off. By adding alkali, the ammonium ions are replaced by sodium ions, allowing ammonia to be stripped away
Ammonia ionizes in water to form NH4+ and OH-. Adding alkali to the stripping tower increases the concentration of OH- in the solution, causing the equilibrium to shift to the left, which facilitates the stripping of ammonia along with the acidic gases. However, an excessive amount of alkali causes the H+ ions produced by the ionization of H2S to combine with OH-, pushing the ionization of H2S to the right; as a result, HS- accumulates in large quantities in the solution, leading to a sharp drop in ammonia nitrogen levels in the purified water while sulfur compound levels rise. Therefore, alkali should be added in an appropriate amount based on the quality of the purified water