Question

In many industries, pickling baths are common. These are 10 cubic meter baths containing acid baths that metal components are dipped into prior to surface treatment. When the metals are dipped, some of their components are left in the acid bath and after some time he bath needs to be changed with new acid because the metals in the solution make the bath ineffective.

The old and metal contaminated acid is sent to destruction. But is it possible to remove the metals from the water and acid, to regenerate it?
Say we have a bath with 20% HNO_3 in water and lots of metals. 20% HNO_3 in water has a bp of 101°C which is slightly above water. If this was put through an evaporator, would both the HNO_3 and the H_2O evaporate and cooled down to a distillate that contains the water and acid? The metals won't evaporate of course and is left in the small amount of liquid that is left in the concentrate.
Is this possible? Also is it safe? I mean heating HNO_3 creates nitrous gases, but if they're immediately cooled down and condensed, is it a problem?

Answer 1

It is possible to regenerate nitric acid and water from a metal-contaminated pickling bath via distillation. The metals remain as a concentrate, while the nitric acid and water are recaptured. Safety measures are crucial due to the corrosive nature of nitric acid and the generation of toxic gases.

Step-by-step explanation:

Yes, it is possible to regenerate nitric acid and water solution from a pickling bath through a process known as distillation. During this process, the solution is heated to evaporate the water and the nitric acid, which can be condensed back into a liquid form, leaving the metals behind in the form of a concentrate.

However, caution must be exercised as heating nitric acid can produce toxic nitrous gases. Appropriate chemical handling systems and scrubbers must be in place to capture and neutralize these gases during the evaporation process. This ensures that the gases are not released into the atmosphere and that the operation can be conducted safely.

While the concept is theoretically sound, practical implementation requires strict adherence to safety protocols and regulations, given the corrosiveness and hazardous nature of concentrated nitric acid and the potential for the generation of harmful gases.