Acid tanks have hauled acid in and out of smelters and copper refineries since the early days, long before air pollution laws. The smelters around Ducktown, TN went to acid recovery in 1904, because acid was a valuable by-product of sulfide ores. And also because acid emissions made the landscape look like this:

http://en.wikipedia.org/wiki/File:Ducktown_train.jpg

Yes, that is Tennesee. Notice the freight car. The area around Wawa, Ontario looks similar, from the past roasting of iron sulfide ores.

Acids are used as the electrolyte in electrolytic copper refining, which may or may not be done at the same site as the smelter.

Peace, Rick