Chemical AP - Heating - Benefits and Limits

[ShielaMartin780]

I am running some ram fingers through my AP, but I'm hoping to speed the process up without compromising things. The biggest benefit is the reduced time, but are there any drawbacks to heating the solution throughout the process? Max limits? I've read in a couple threads that heating can increase the chance of your gold dissolving into the solution, but I think that's more of a factor of your composition than it is the heat.

The compounding factor is that I can't currently go below 135f/57c. Why you ask? Originally I was going to just use a regular hot plate with an old coffee pot, but I opened a kitchen storage door and discovered we had a plastic electric kettle that my wife hasn't used in eons. Said kettle is now part of my equipment inventory, so long as my wife doesn't find out. The lowest setting results in a ~135f temp, so I can't go lower. I'll pick up a hot plate if that temp is considered too high vs just slightly heating. Air bubbler is run constantly, with minimal H2O2 utilized, all done outdoors.

 

[Yggdrasil]

I am running some ram fingers through my AP, but I'm hoping to speed the process up without compromising things. The biggest benefit is the reduced time, but are there any drawbacks to heating the solution throughout the process? Max limits? I've read in a couple threads that heating can increase the chance of your gold dissolving into the solution, but I think that's more of a factor of your composition than it is the heat.

The compounding factor is that I can't currently go below 135f/57c. Why you ask? Originally I was going to just use a regular hot plate with an old coffee pot, but I opened a kitchen storage door and discovered we had a plastic electric kettle that my wife hasn't used in eons. Said kettle is now part of my equipment inventory, so long as my wife doesn't find out. The lowest setting results in a ~135f temp, so I can't go lower. I'll pick up a hot plate if that temp is considered too high vs just slightly heating. Air bubbler is run constantly, with minimal H2O2 utilized.

Heating will increase the speed and if heated "too much" it will also increase evaporation of both water and HCl.
The Peroxide is only used to start the AP not to run it, that's what the air bubbling is for.

 

[ShielaMartin780]

Heating will increase the speed and if heated "too much" it will also increase evaporation of both water and HCl.
The Peroxide is only used to start the AP not to run it, that's what the air bubbling is for.

Correct - I basically use a couple of capfuls of peroxide when starting a new AP batch, and it's all air after that. After that, to reactivate it for usage on another batch in the future, I just hit it with my air bubbler.

Sounds like I'm safe to heat at these temps, with potentially needing to add a bit of HCL and water at times, as needed. I'll monitor the solution level more closely and adjust as needed to keep it at the same level throughout.

 

[haveagojoe]

If the element in the kettle is exposed to acid it may corrode away. Not very safe I'd say.

Personally I don't think it's worth trying to speed up the process by heating. Copper Chloride etching is a slow process, that's just how it is. As a hobby it's vaguely similar to brewing beer- set it to run and check on it once or twice a day, and every week or so have a day where you do some work with it. Then every few weeks you get a nice reward. If you want more activity and more payoff, set more batches running concurrently to finish on different days. Although the chemistry is the most interesting part, most of the actual "doing" is in acquiring and preparing the source material.

If you must heat your solution, you don't need much extra heat to increase the reaction rate. I think in theory it should double the rate with every increment of 10 degrees, but of course there will be evaporation to take into account as well. You don't want to let it run dry. If you live in a cold place, a heat mat under the setup the raise the temperature to 20-25 degrees C might be helpful, but above that the evaporation will become a major factor, not just for loss of volume, but also the problems caused by HCl vapor, such as corrosion of nearby metal objects.

In general I think heating Copper Chloride is more trouble than it's worth. Just keep the bubbler running all the time and it will mostly look after itself. Even without the bubbler and at a low temperature it will still work if it can get air. Unless you need to sell your gold immediately, then what's the rush? You already have it in your possession.

 

[Yggdrasil]

If the element in the kettle is exposed to acid it may corrode away. Not very safe I'd say.

Personally I don't think it's worth trying to speed up the process by heating. Copper Chloride etching is a slow process, that's just how it is. As a hobby it's vaguely similar to brewing beer- set it to run and check on it once or twice a day, and every week or so have a day where you do some work with it. Then every few weeks you get a nice reward. If you want more activity and more payoff, set more batches running concurrently to finish on different days. Although the chemistry is the most interesting part, most of the actual "doing" is in acquiring and preparing the source material.

If you must heat your solution, you don't need much extra heat to increase the reaction rate. I think in theory it should double the rate with every increment of 10 degrees, but of course there will be evaporation to take into account as well. You don't want to let it run dry. If you live in a cold place, a heat mat under the setup the raise the temperature to 20-25 degrees C might be helpful, but above that the evapoation will become a major factor, not just for loss of volume, but also the problems caused by HCl vapor, such as corrosion of nearby metal objects.

In general I think heating Copper Chloride is more trouble than it's worth. Just keep the bubbler running all the time and it will mostly look after itself. Even without the bubbler and at a low temperature it will still work if it can get air. Unless you need to sell your gold immediately, then what's the rush? You already have it in your possession.

That is of course dependent on what temperatures you have.
For outdoors here at the time it is barely over freezing

 

[haveagojoe]

That is of course dependent on what temperatures you have.
For outdoors here at the time it is barely over freezing

Yeah if it's really cold it will benefit from some kind of heating. Do you use a hotplate? I've been tempted to try with one of those silicone heat mats but never got round to it, it's cheaper and easier to just wait. For a while I would use a kind of bain-marie setup with hot water from the kettle but I don't bother any more. Etching goes slower in the wintertime, but I'd rather spend my time indoors stripping scrap then anyway.

Edit- I just noticed OP is in Alberta, so yea maybe a little added warmth would be good.

 

[Shark]

A slow cooker, or crock pot, set to low works great. Being as far north as the OP is maybe a higher setting would be needed. The crock pot needs to be one of the ceramic variety with no scratches that go deeper than the glazed coating. A lid will help to keep evaporation down as well. If cracked or scratched very bad it will eventually leak. Of coarse something bigger is needed for anything bigger than slot cards, or cut off the parts that have no gold beforehand.

 

[orvi]

Heating issue tips from my DIY times:

Infrared heater - good for maintaining some reasonable temperature. Nice thing about HDPE plastic without added fillers (translucent milky -not white - canisters for example) is that it is somewhat IR transparent. That means some wavelengths of IR radiation conveniently pass through it. Reason I am speaking about this is - HDPE is very bad thermal conductor. And when you heat the outside of the canister, that is not very effective way of warming the contents. But IR radiation will to some degree heat up the insides (solution) more directly. Old IR lamps for medical purposes are great thing, if they come with parabolic mirror (or at least aluminium/stainless reflectors).

Aquarium thermostat glass stick - good for maintaining r.t. when it is cold outside (eg doing AP in the withertime). Take one with the longest glass finger possible and dip the top plastic piece in some coating at least somewhat resistant to acids. Quality paint can do for some time, then replace it. As AP isn´t that corrosive - fumes aren´t oxidizing, just acidic. Be careful and always disconnect the heater before you will approach the liquid - to be safe if some leak occured to the inside of the device.
For me, disposable, cheap, adjustable, good choice for the money and purpose.

Induction heater and graphite brick - sounds wild, work nicely. We used this approach to evaporate down liquids. Graphite nicely catch induction and doesn´t react much with AP chemistry. Also, gold isn´t dissolved in this process, so no adsorption can occur. Regular cooking induction heater unfortunately don´t radiate too far from the actual plate, so it can happen that you cannot catch the induction into the piece inside thicker wall vessel. Also, be careful about temperature on the bottom side of the block and use some thinner pieces of graphite which will conduct heat more rapidly.

 

[ShielaMartin780]

Thanks all for the answers and information. I'm using my wife's email so I find it highly dubious she won't find this..... to make a long story short, it turns out the plastic electric kettle has a base at the bottom to transfer heat - it had a thin black covering over it and I didn't even think of this at all, but do you know what is a great conductor of heat? Copper! Do you know what AP loves to eat? That's right, Copper! The black base covering was 3/4 eaten and it ripped a decent dent in the copper portion below.

Looks like I'll be getting that hot plate after all....it'll make good friends with the thrift store coffee pots.

 

[haveagojoe]

While you're at the thrift store look out for a Corningware casserole dish. We use these on the hotplate under the reaction vessel to catch potential boilovers.