Use of nitric acid for pH adjustment
Use of nitric acid for pH adjustment
(OP)
We need to use nitric acid to lower the pH water from 10-11 to about 1-3 levels. That is because its oxidizing power can break down a surfactant molecule. We are currently using HCl and I would like to ask if HNO3 is a good pH neutralizer for water treatment processes.





RE: Use of nitric acid for pH adjustment
It will depend on your downstream use of the water. For example, I used to work in a facility that could not tolerate nitrates in the process water. This could cause some funny by-product gases to be produced that had both safety and environmental concerns associated with them.
RE: Use of nitric acid for pH adjustment
RE: Use of nitric acid for pH adjustment
As Zoobie posted, nitric(HNO3) will create a nitrate pollution issue should you have to discharge the wastewater.
Nitric does not enjoy the popularity that hydrochloric or sulfuric acids do. Nitric acid is more expensive to use than either sulfuric or hydrochloric acid. As with hydrochloric acid, nitric will evolve a noxious gas that combines with water vapor already in the air (humidity) to form a very corrosive gas. The gas is very highly corrosive and will attack all metallic objects including building structures, sprinkler heads, copper wiring, stainless steel, etc. Therefore, if HNO3 is used, the area should be properly vented or else used outdoors where the gasses can easily dissipate. For these reasons, Nitric is not widely used.
HNO3 + NaHCO3 --> NaNO3 + H2O + CO2
H2SO4 + NaHCO3 --> Na2SO4 + H2O + CO2
Nitric acid, sulfuric acid and hydrochloric are all considered to be a strong acids. Sulfuric acid is more commonly used.
RE: Use of nitric acid for pH adjustment
Chlorides are usually only a problem if the local POTW recycles treated wastewater for irrigation.
Sulfuric acid is the cheapest acidifier, and local POTW's often don't mind since sulfate aids in clarifying. There is a risk of sulfate attack of concrete sewer lines, however, so effluent concentrations may be limited. Also, solids may be limited by the POTW.