Use of nitric acid for pH adjustment 2

[gall3232]

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.

 

[Zoobie]

The only answer I can offer is 'it depends'. Nitrates in drinking water can be a serious health concern. Maximum safe levels in drinking water are stated to be 10 ppm. Of course if you are producing potable water you would know this. It could also be a problem if this water eventually becomes waste water.

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.

 

[Zoobie]

An afterthought: Perhaps you can neutralize with HCl but use something like hydrogen peroxide, chlorine dioxide, or hypochlorous acid if you need some oxidizing power. If your final goal is a pH of 1-3 you may need to do this in stages for these oxidizers to work properly.

 

[bimr]

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.

 

[kenvlach]

If you are in the US, the EPA would consider you to be the generator of nitrates, which are subject to TRI reporting. Don't recall the RQ (reportable quantity), maybe 10,000 pounds/year, but this regulation caught a lot of metal finishers.

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.