Some Nitric Acid Questions

[FrugalRefiner]

I assume that the reason you want to reduce the copper that gets dissolved into solution is because those 6" diameter copper tubes you rotate in the solution are pricey and you don't want them to dissolve too quickly. I do not understand why you rotate the tubes, is there some sort of scraper that dislodges the cemented Silver from the rotating cylinder? I usually aerate a cylinder that copper slabs hang inside of inside the tank of liquid to be cemented to guarantee circulation and allow the aeration to dislodge the Silver.

You can see a tutorial of this technique in When In Doubt, Cement It Out. 4metals described his method, and I created a mini version. 4metals also provided a picture that's at the end of that post of his larger version.

Dave

 

[orvi]

On this scale, I would suggest (as many more experienced refiners before me) just depleting acid beforehand using more silver. As 4metals suggested, treating the solution with silver cement you already have gives you fastest reaction. If speed is not a big deal, you can just siphon the solution onto good excess of more silver feedstock and wait for it to react. It will, even at room temperature, but it would be much slower than with cement powder.

Raising pH with hydroxide is also viable technique, if you have good mechanical stirring device. Equilibration of temporary crushed hydroxides can take some time, so it need to be considered beforehand.

BTW, what is the average purity of silver cement that you are producing by copper cementation ? I am just curious, because it has a lot to do with concentration of silver nitrate and leftover acidity (at least from my observations). Through my career I produced cements ranging from 95-99.8% Ag, and there are some patterns regarding Ag concentration and free acid.

 

[jeff@performance-construc]

This so amazing so many interesting responses, suggestions and ideas I am still trying to digest everything, and we are going to test out some of these ideas and see what may work for us. To answer your question. on average we range 95-98+%. Would like to understand more about the patterns that you talked about. Depleting or consuming the acid beforehand is very interesting and makes sense. Could this be as simple as keeping the silver anode materials in the cell for extra 24 hrs. or more make difference in consuming excess nitric. Or even dropping in some solid refining bars into the solution to help consume excess acid?

 

[4metals]

Could this be as simple as keeping the silver anode materials in the cell for extra 24 hrs. or more make difference in consuming excess nitric. Or even dropping in some solid refining bars into the solution to help consume excess acid?

You mentioned speed as you need to completely treat about 25 gallons a day. In dissolving Silver to consume any excess nitric acid the 2 factors that have the greatest effect on reaction rate are temperature and surface area. Putting the waste into a tank you can easily heat may not be possible but the surface area of the Silver you add will be the greatest if you use cement Silver.