Sulfur Daily Question, May 22------3 points for participation, 10 points for a correct answer

NH3 as well as ammonium salts such as (NH4)2CO3 and NH4HCO3

In acidic water, substances such as ammonia, hydrogen sulfide, and carbon dioxide exist primarily in the forms of NH4HS, NH4HCO3, etc., resulting in a solution that is a salt of weak acids and weak bases. H2S, NH3, and CO2 in the liquid phase are volatile components; according to Henry’s law, reducing the partial pressure of these components using steam allows H2S, NH3, and CO2 to be transferred from the solution into the gas phase. This is the basic principle behind acid water stripping. The stripping process of the H2S─NH3─CO2─H2O quaternary system can be represented by the following reaction: NH4+ + HS- ⇌ (NH4HS)? ⇌ (NH3 + H2S + H2O)liquid ⇌ (NH3 + H2S + H2O)gas. Increasing the amount of stripping steam and the number of trays in the stripping tower can reduce the ammonia nitrogen content in the purified water; however, the reduction in ammonia nitrogen is limited, and even with a large amount of steam used, it is not possible to reduce the mass concentration of ammonia nitrogen in the purified water to below 50 mg/L. Through the analysis of the form of this portion of ammonia nitrogen that cannot be removed by conventional stripping processes, it is believed that the following reaction also takes place in the wastewater: +-NH3 + H2O ⇌ NH4+ + OH-. Additionally, acid anions such as SO3, S2O3, HSO3, and CN are detected in the wastewater, which causes NH4+ to be converted into ammonium salts; therefore, increasing the stripping depth alone is not sufficient to remove them. Therefore, if the fixed ammonium is converted into free ammonia, it can be removed by stripping.

It exists in the form of ammonium salts such as NH4HS, (NH4)2CO3, and NH4HCO3.

Ammonium hydroxide, ammonium ion, ammonium salts

The harmful substances contained in acidic water mainly include ammonia, hydrogen sulfide, and carbon dioxide. The stripping method is primarily aimed at removing and recovering ammonia and hydrogen sulfide. The NH3-H2S-H2O ternary system is a complex system in which chemical equilibrium, ionization equilibrium, and phase equilibrium coexist. Ammonia, hydrogen sulfide, and water are all weakly volatile electrolytes; they can react with each other and ionize into ions. Ammonia and hydrogen sulfide can dissolve in water to varying degrees. • NH3 + H2O → NH4+ + OH- Hydrogen sulfide also undergoes slight ionization in water: H2S → H+ + HS-. When ammonia and hydrogen sulfide are present in water together, ammonium hydrosulfide is formed; this is a salt resulting from a weak acid and a weak base. In water, it undergoes extensive hydrolysis, thereby reforming free ammonia and hydrogen sulfide molecules, as follows: NH4+ + HS- → (NH3 + H2S) in liquid form. The free ammonia and hydrogen sulfide molecules in the liquid phase are in phase equilibrium with those in the gas phase: (NH3 + H2S) in liquid form → (NH3 + H2S) in gas form. Combining equations (3) and (4), we can write: NH4+ + HS- (i.e., NH4HS) → (NH3 + H2S) in liquid form → (NH3 + H2S) in gas form. In the gas phase: NH3 + H2S ↑↓ ; in the liquid phase: NH4+ + HS- → NH3 + H2S ↑↓ . There is a large amount of carbon dioxide in wastewater; it can also dissolve in water, but its solubility is lower than that of hydrogen sulfide. At the same temperature, its vapor pressure is higher than that of hydrogen sulfide, so its volatility is also greater than that of hydrogen sulfide. Therefore, it evaporates more easily than ammonia and hydrogen sulfide. Therefore, the presence of carbon dioxide has no effect on wastewater purification. It should be noted, however, that carbon dioxide, especially under low-temperature conditions, reacts with ammonia to form ammonium carbamate. 2NH3(g) + CO2(g) = NH2CO2NH4(s). It is an insoluble salt that can cause blockages in pipes and valves. In the single-tower side-stream process, the temperature of the stripping column sections must be maintained above 138°C; the main purpose of this is to prevent crystallizations such as ammonium carbamate and ammonium hydrosulfide from forming and causing blockages.