What is an example of a pickling acid used in treatment processes?

In the context of wastewater treatment, pickling acids are typically used for cleaning and preparing metal surfaces by removing scale, rust, and other impurities. One of the most common pickling acids used in these processes is nitric acid. Its effectiveness lies in its ability to react with iron and various metal oxides, converting them into soluble nitrates that can easily be washed away. This makes nitric acid particularly useful in certain wastewater processes where the removal of metallic contaminants is necessary.

While sulfuric acid, phosphoric acid, and hydrochloric acid have their distinct uses in different chemical processes, they are not specifically recognized as pickling acids in the same context as nitric acid. Each of these acids serves very specific roles in treatment processes but do not focus on the surface cleaning aspect associated with pickling.