Copper contamination

[encipher]

Hi, I recently purchased '99.99%' pure silver and dissolved it in 6M nitric acid. I noticed the solution has a blue/green color, indicating copper impurity. Anyone have ideas on removal of copper contamination without losing much yeild? thanks.

[YT2095]

there are NOx gasses that when in Soln will also give this color, it may not Entitely be a copper contam.

[encipher]

Yeah, I figures it could be dissolved NOx gasses. I slow heated the solution and a lot of Nitric acid fumes came out.. for quite some time. I heated until it was just a wet slush of crystals. It was still bluish. Added water and heated again etc.. The solution is still blue, but I know that the acid isn't all gone. Any quicker way for me to get rid of the dissolved gas?

[YT2095]

I`m not 100% sure, I know Urea is used for dissolved NOx gasses though.

I can`t be certain if it works with AgNO3 soln though?

if after crystalising it`s still blue though, then it probably IS copper.

in which case you can either ignore it OR try purify it.

[John Cuthber]

Last time I was doing this I precipitated the silver with sodium acetate and washed off the copper acetate (you lose Ag this way but you can always recover it as chloride).

If you want to get the silver then you can heat the acetate carefully so it decomposes. Since the acetate is slightly soluble you should be able to convert it to Ag2O with excess NaOH, wash it then redissolve it in HNO3.

[jdurg]

Silver will always be contaminated with copper. They are in the same column in the periodic table so they have somewhat similar chemical properties too. In addition, just the tiniest portions of copper ions in solution will provide a blue color. So while the coloring may be slightly blue, that doesn't mean that it is a very high % of copper.

[woelen]

Yeah, I figures it could be dissolved NOx gasses. I slow heated the solution and a lot of Nitric acid fumes came out.. for quite some time. I heated until it was just a wet slush of crystals. It was still bluish. Added water and heated again etc.. The solution is still blue, but I know that the acid isn't all gone. Any quicker way for me to get rid of the dissolved gas?

 

If you dilute a solution with dissolved NOx gasses, then it becomes colorless at once. So, your blue color really is due to copper ions.

 

Just a check you could do: Take half a ml or so of your solution and add 5% household ammonia to this, until the liquid becomes clear again. If this liquid has a fairly strong royal blue color, then indeed you have copper in your solution.

 

If you have done this test, please do not store the liquid with ammonia. Either neutralize again with acid, or get rid of the liquid, but don't store it. Silver/ammonia complex slowly forms an explosive compound (fulminating silver).

[YT2095]

and Tetramine Copper(II) Nitrate isn`t a good thing to keep around either