Understanding copper chloride

[Varmint]

pgms4me:

Yes, the heat absolutely drives the O2 out, that part is understood, but I had made the assumption (hate that word ), that it had also driven out the HCl which might have contributed to the gorgeous color change.

The bad part of my thinking (I assume) is the color comparison was indicating the level of acid, when it really appears to be indicating the quantity of Cl- ions bound up in the CuCl2?

I guess my expectation was the color I had was what I could expect when I reduced the H2O content and (presumably) started to get crystals of the Dihydrate also shown at the same wiki page.

So, my plans are to understand the chemistry. Yes, I tend to get hung up on stuff like this, I'm doing this to learn (no expectations of vast income from my effort) and I'm not the type to explain to someone how I got my gold button; "well, I used this compound I know nothing about to remove base metals, copper in this case, leaving the gold substantially pure enough for easy further refinement". I want to know why H2O2 or air work well, difference being you can add too much H2O2, but not air. That sort of open-ended "rule" drives me to learn "what IS too much H2O2", and If I have enough O2 concentration through air injection to cause the gorgeous color change, why is THAT not too much?

Further, if my O2 saturation wasn't too high, does that mean I can add H2O2 until I get the same color shift, or do the two differ enough in practice that the amount of H2O2 to cause the same shift is way too much and gold will go into solution?

Its all about learning and understanding. There are probably thousands of people who couldn't care less about how it works, but could be wildly successful scrapping/refining for profit. I want to be the guy that knows the actual chemistry, and again, have no dreams of being a wildly successful PM processor.

DAS

 

[butcher]

Interest and curiosity, seeking the answers to your questions, working to figure out those things you have questions about, and doing tests to see what happens, what a great way to learn this science.

Keep up the good work, keep us posted.

 

[Geo]

Oxygen does drive the reaction forward but heat will also drive the reaction as it does when using AR. Due to evaporation, you have to replace the hcl. Using air is more economical.

 

[Varmint]

OK, some more research and experimentation.

CuCl2 is an efficient catalyst for the decomposition of H2O2, releasing of course water and O2. Trouble is, the decomp is relatively speedy and complete, most of the O2 escaping at the surface to the air.

This means 2 things, H202 is an expensive and inferior method of providing oxygen to the solution, and it's impact on the dissolution of gold foils is limited to a brief timeframe.

For testing I began with (2) 50ml beakers filled to ~30ml with the same prepared CuCl2 solution described earlier. To each I added 1gr (64mg) of copper to give the solutions a load to digest.

In the first (non-peroxide) breaker I added 10ml of distilled H20 to approximate the water-only content of the 10ml of the 3% H202 I added to the second beaker.

The first beaker was aerated by means of a short section of Teflon "aquarium bubble stone" until the color seemed to stabilize at the gorgeous aquamarine-blue described earlier. since this took an hour or so, I rechecked the volume and topped off the missing 1ml or so, then returned to aeration.

In the second beaker, H202 was added in both "large" (1-2ml or so) additions as well as drop-wise to complete the 10ml addition. No stirring or agitation was used. On the large additions, portions of the column turned obviously lighter than the non-peroxide control, but soon settled to a lighter but still more Emerald color. O2 (presumed) was seen escaping the surface. By the end of the additions, aside from the localized color swings, the two solutions ended up at very nearly (extremely close) aquamarine-blue color. If I were to call one "darker", it would be the peroxide example.

It was assumed at this point the H2O2 had been fully catalytically decomposed, so the next step was to place both side by side in a water bath on the hotplate. As before, as the temperature increased, the solutions began to revert to the Emerald coloration. The intent of course was to see if any H2O2 had "survived" decomposition, in which case example 2 would return more slowly to the "base" Emerald. Instead, they changed in essential lock-step. By the time the first cavitation bubbles appeared, both were nearly the base color, a second or two of boiling of the bath water insured they were as Emerald as they were going to get.

It was then I noticed the peroxide example retained is ever-so-slight darker color. My assumption is I was either too generous in my water-content equivalent addition to example 1, or I topped off slightly too generously following the bubble up to O2 saturation.

So, my conclusion is, peroxide is a complete waste of money unless you use it solely for the short reaction time when generating your mother liquor etchant as described in the linked CuCl2 PDF above.

DAS