The "Deox" process in water purification typically refers to the removal of dissolved oxygen (DO) from water. This process is crucial in various industrial applications, such as boiler feedwater treatment, where the presence of dissolved oxygen can lead to corrosion.

Molecular Mechanisms of Dissolved Oxygen Removal

1. Chemical Deoxygenation:

   • Reducing Agents: Chemicals like sodium sulfite (Na₂SO₃), hydrazine (N₂H₄), or sulfur dioxide (SO₂) are commonly used to chemically reduce dissolved oxygen to water.
   • Reaction Example:
     • Sodium sulfite reacts with dissolved oxygen in water as follows: \(2Na2SO3+O2→2Na2SO42 \text{Na}_2\text{SO}_3 + \text{O}_2 \rightarrow 2 \text{Na}_2\text{SO}_42Na2​SO3​+O2​→2Na2​SO4​\)
     • Hydrazine reacts as: \(N2H4+O2→2H2O+N2\text{N}_2\text{H}_4 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} + \text{N}_2N2​H4​+O2​→2H2​O+N2​\)
   • These reactions effectively remove oxygen from the water, reducing the potential for corrosion in metal pipes and equipment.

2. Thermal Deoxygenation:

   • Degasification: In thermal deoxygenation, water is heated, typically in a deaerator, causing dissolved gases (including oxygen) to escape. The process is driven by Henry’s law, where the solubility of gases decreases with increasing temperature.
   • Mechanism: As water is heated, the kinetic energy of water molecules increases, leading to a reduction in gas solubility. Oxygen molecules, less soluble at higher temperatures, are released from the water and vented out.

3. Physical Deoxygenation:

   • Vacuum Deaeration: Water is exposed to a vacuum, reducing the partial pressure of oxygen and thereby encouraging its removal from the solution.
   • Membrane Deaeration: A gas-permeable membrane is used to separate oxygen from water. A sweep gas (like nitrogen) or a vacuum is applied on one side of the membrane, drawing oxygen through the membrane and out of the water.

Impact on Water Quality Parameters

1. pH:

   • Chemical Reactions: The addition of reducing agents like sodium sulfite may slightly alter the pH of the water. Sodium sulfite is slightly basic, which can increase the pH.
   • Hydrazine tends to have a negligible effect on pH, but careful control is necessary to avoid over-adding, which could impact pH and cause corrosion.
   • Deaeration: Thermal and vacuum deoxygenation typically have a minimal direct impact on pH, but the overall water chemistry changes might alter pH indirectly.

2. Conductivity:

   • Chemical Addition: The addition of chemical deoxygenation agents will increase the ionic content of the water, thereby increasing conductivity.
   • Thermal/Vacuum Deoxygenation: These methods do not introduce new ions, so they do not directly affect conductivity. However, if dissolved CO₂ is also removed (which forms carbonic acid in water), the reduction in H⁺ and HCO₃⁻ ions can decrease conductivity.

3. Mineral Content:

   • No Direct Impact: The Deox process does not directly remove or alter the mineral content of water. However, the chemical agents added can contribute to the overall ionic strength of the water, subtly changing its mineral profile.
   • Secondary Effects: Over time, preventing corrosion (by removing oxygen) can lead to a more stable mineral content as fewer metal ions are leached from pipes and equipment.

In summary, the "Deox" process primarily focuses on the removal of dissolved oxygen through chemical, thermal, or physical means. While this process is essential for preventing corrosion, it can also have secondary effects on water quality parameters such as pH, conductivity, and mineral content, depending on the method used.