recover nitric acid while refining silver

I have a question about recovering nitric acid from nitrogen dioxide gas. I am trying to lower the cost of refining silver to increase my profit margin. The nitric acid is a large part of the cost of consumables.I was thinking of experimenting with making my own.

I have been looking into the process of making "poor mans nitric" by combining nitrate salt, water and hcl acid - add metallic copper to produce nitrogen dioxide gas - capture the gas and bubble it through chilled distilled water to produce dilute nitric acid.

My question is this. When I dissolve sterling in nitric acid, one of the byproducts is nitrogen dioxide gas, right? Couldn't I just process my sterling in a vacuum flask and pipe the nitrogen dioxide through distilled water in an attempt to recover as much as I can?

cadfinger said:

My question is this. When I dissolve sterling in nitric acid, one of the byproducts is nitrogen dioxide gas, right? Couldn't I just process my sterling in a vacuum flask and pipe the nitrogen dioxide through distilled water in an attempt to recover as much as I can?

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It's always a frugal choice to minimize the amount you produce and capture as much as you can. 8)

The more dilute your acid, the less is lost to NO_x, but the reaction is also slower.

The cooler the reaction, the less is lost to NO_x, but with the same speed penalty.

You can add a bit of H₂O₂, which will help minimize the loss.

Covering the beaker with a watch glass will help.

Probably the nicest solution I've seen is using a reflux condenser over the reaction vessel.

Your method is also viable.

Dave

In a sealed reactor which is vented into a scrubber filled with distilled water having a small discharge pipe so the only air passing out of the scrubber is displaced by the O₂ you are putting in to the reactor. You can dissolve silver but must provide pure O₂ to the reaction. The NO_x will react with the O₂ and collect in the scrubber as dilute nitric.

This process was developed in England in the early 20^th century to save on nitric acid while producing silver nitrate. It was called the Johnson process.

On a larger scale this is done with a stainless steel scrubber and reactor. But for smaller setups off the shelf glassware can be effective.

How much nitric are you using?
Nitric is pretty cheap.

Using concentrated sulfuric acid, or oleum, to treat the nitrates recovers almost 100% of the nitric acid used. Sulfuric acid is typically much cheaper than nitric. The fumes like 4metals said, with the Johnson. Nitric acid has become a 'controlled substance' in many parts of the world. Retarded measure, because nitrate fertilizers are available by the ton, but it is what it is.

You should be able to reclaim most of what's in the solution by distillation. You have to evaporate the solution to remove excess water. You need to add sulfuric acid to the solution. The amount depends on how much copper is in solution. As the nitric acid is driven out of solution, the copper nitrate is converted to copper sulfate and will crystallize out as the process continues or the heat is removed and the solution cools. The sulfuric acid is locked away with the copper meaning the solution can run out of sulfuric acid if you don't add enough. One of the chemist here could give you better numbers on a saturated solution.

By the way, the sulfuric acid can be reclaimed as well. There is a video from NurdRage on youtube with this process. He starts out with copper(II) chloride but the sulfuric part applies.

https://youtu.be/FjEoRidvgYE