Does Cementation Temperature Matter?

[ultlordx]

I've run a few batches so far using the method of cementing silver out of solution using copper. I used stranded copper speaker wire due to its high purity and high surface area. The higher surface area speeds up the process. I guess the cementing process is exothermic because I noticed that the solution heated up at least during one of the batches and maintained an elevated temperature.

I observed that when I cemented at a slower rate, the end product is much lighter in color and almost white. When i tried rushing, the solution became very warm, bubbles would even form, and the end product looks more gray. In my last batch, I added copper at an extremely fast rate, and the cemented product started turning dark gray at one point (no longer silver I would guess) and a lot of bubbles formed at the copper-solution interface. When I opened the flask, orange-brown gas (NO2 i would guess) formed. I cooled the solution down, stirred, and it became a bit lighter, but still nothing close to the first batch where I added copper slowly.

So I have three different products ranging in color from white to a light grey, but all are different shades. I would assume the color has some dependence on purity, is this true?

All in all, I am wondering if cementing at lower temperatures is beneficial in increasing silver purity? I know it slows down the process, but if pure silver is what you want, it may be worthwhile.

 

[Barren Realms 007]

Once you finish with your test take your silver and wash it in water till you don't have any color change. Then just for S#&%& and giggles wash it in some HCL and see if you get a color change, that will be the copper you have left in your silver from using very small wire to cement with that seperated. Once you have done this take your original solution and add a sheet of copper or copper tubing. Not the copper wire you used originaly and see if you cement any sliver out of your remaining solution. If you still have brown or red fumes you might have way too much nitric left in your solution. If you really feel adventurous when you cement your silver out the first time remove your copper and see if your silver settles to the bottom and see if it stays there or if it redisolves in your solution.

 

[ultlordx]

I make sure to consume all of the acid when I am originally dissolving the silver/copper alloy by running the reaction on a hot plate below the boiling point. I also make a habit of rising the cemented silver with distilled water, and allow it to dry fully before making any comparison on color. What exactly will washing with hydrochloric acid do? I have added more copper to the solution after filtering, and no more silver is produced.

Going back to the original question, does temperature matter?

 

[samuel-a]

I would assume the color has some dependence on purity, is this true?

I wouldn't hurry to make this assumption.
As different rates of deposit (cement) will produce different shades of gray even if there is no PGM's present.

The rate of deposit is determined by temp' and mainly by silver concentration.
As you probably noticed, the lower the silver concentration is, the 'uglier' the deposits are (more of gray powder then shiny white crystals at the start of the process)

At the final stages, where almost all of the silver was cemented, as Harold mentioned before, that is when PGM's tends to co-deposit with the silver to form black deposit.

I make sure to consume all of the acid when I am originally dissolving the silver/copper alloy by running the reaction on a hot plate below the boiling point.

It is also mentioned by Harold that some free nitric will actually help the cementing process and i, myself found it to be very useful.

I personally do most of cementations at room temp'