Fume purification systems (Goldsmith plants)

Not only does refining process leave metal residues in the water but it also leaves toxic dust and vapours (from aqua regia, a mix of nitric acid and hydrochloric acid) that must be cleaned before getting reused or released. 

Precious metal refining plants are equipped with fume purification systems that can be made of a tower or more to neutralise toxic fumes with an aqueous solution mixed with alkalis. This process requires vertical sump pumps installed inside the tank or centrifugal pumps installed outside the tower.