HCl and Bleach, large scale refining

[DJPGold]

Hello, I’ve collected foils from 10kg of trimmed ram fingers, I recovered the foils using AP and then rinsed them all with water until the solution is clear, I then did a warm HCL wash to remove any tin etc and rinsed all of that off with water.
I began with about 400ml of distilled water in the beaker, I couldn’t pour everything off without losing lots of foils. I then added 600ml of HCL and began dissolving the gold by adding 6-9ml of bleach while stirring it and then continued stirring for a minute or two, I repeated this step every 10 minutes for about 4-5 hours, in total I added about 100ml of bleach. I then came back the next morning and there’s still a hell of a lot of foils.
I’m expecting between 30-50 grams of gold from this batch so I’m curious as to whether anyone knows the saturation level of gold in HCL and bleach.
This morning I topped it up to the current level with HCL, in case it had become too basic and added another small amount of bleach with lots of stirring.
A 2L beaker is the largest vessel I have so could I slowly evaporate the acid down to say, 500ml and then top up again with HCL and small bleach additions.
I would like to avoid pouring off this liquid and starting with a new batch of acid as I would like to keep everything in this beaker for as long as possible.
No I have not yet bothered to do a stannous test, silly me I know, but I figured since there’s been a good colour change and there seems to be much less gold sparkles that I must be dissolving gold, also some of the foils have a different colour to them now, as if they’ve been oxidised.

 

[Alondro]

I don't know the saturation, but with such a massive amount of foils, you definitely need much greater acid volume to start with.

 

[DJPGold]

I don't know the saturation, but with such a massive amount of foils, you definitely need much greater acid volume to start with.

Okay cheers mate, how would you recommend I do it? Seeing as I only have a 2L beaker my options are limited, I could either pour most of the solution off into holding containers and then start again with say 1.5L of acid, or I could pour the liquid off, remove about half the foils and then dissolve one half, and slowly add and dissolve the rest incrementally.
My glass ware collection consists of two 1L beakers, a 2L beaker, a 2L filter flask and one tall form 1L beaker

 

[olawlor]

There's a good discussion of HCl and bleach for gold dissolution in this thread:
HCL+Clorox ratio, conflicting numbers

One issue with adding a gas-generating material by pouring it on top of a beaker is the gas mostly bubbles out instead of staying in solution and reacting. I've gotten better results with hypochlorite by occasionally dispensing a few mL from a syringe down a thin tube to the bottom of the vessel. (For tubing, PTFE "bowden tube" for a 3D printer seems to survive indefinitely.)

 

[DJPGold]

There's a good discussion of HCl and bleach for gold dissolution in this thread:
HCL+Clorox ratio, conflicting numbers

One issue with adding a gas-generating material by pouring it on top of a beaker is the gas mostly bubbles out instead of staying in solution and reacting. I've gotten better results with hypochlorite by occasionally dispensing a few mL from a syringe down a thin tube to the bottom of the vessel. (For tubing, PTFE "bowden tube" for a 3D printer seems to survive indefinitely.)

Yeah I did try that as well, used a pippette to squirt the bleach lower into the solution, but for whatever reason the bleach wouldn’t stay in the pippette and I could never get a full squirt low in the liquid. And I kept sucking up the gold bearing solution

 

[Yggdrasil]

Yeah I did try that as well, used a pippette to squirt the bleach lower into the solution, but for whatever reason the bleach wouldn’t stay in the pippette and I could never get a full squirt low in the liquid. And I kept sucking up the gold bearing solution

There are a few things here.
Due to the caustic nature of bleach the acid need to be as strong as possible.
Why did you add extra water?
Bleach go bad in time and heat is not it’s friend.
There might be a date on the bottle telling when it was 5% ish.

When ever I used HCl-Cl method I used pool tablets and shaved off powder to add to my solution, works like a charm.
Regarding the pipette, exercise is good. Keep the pippete squeezed until out of solution.

Edit for spelling

 

[DJPGold]

There are a few things here.
Due to the caustic nature of bleach the acid need to be as strong as possible.
Why did you add extra water?
Bleach go bad in time and heat is not it’s friend.
There might be a date on the bottle telling when it was 5% ish.

When ever I used HCl-Cl method I used pool tablets and shaved off powder to add to my solution, works like a charm.
Regarding the pipette, exercise is good. Keep the pippete squeezed until out of solution.

Edit for spelling

The bleach is a couple years old so I’ll try some of the girlfriends secret stash if it’s not scented (I assume that matters)
I might try the pool tablet things, they don’t introduce any kind of impurities do they?

I didn’t add extra water, there was 400ml of water in there from rinses, if I tried pouring that off I would have poured off a lot of foils as well. I’ve only made additions of HCL and small amounts of bleach.
In hindsight I probably could have topped it off with acid, waited for that to settle and then pour it off until I had 400ml of HCL that I couldn’t pour off, but I wasn’t thinking about issues at that time.

 

[nickvc]

You will need to heat your solution at the end to remove any chlorine to allow precipitation so heat it now and reduce the amount of liquid in your beaker this should allow you to add more HCl plus more bleach or chlorine tablets and dissolve all your values in that beaker.

 

[DJPGold]

I checked my the bleach I was using, over a year out of date hahahah. That could explain why I’m having issues. I found some in the cupboard that’s well in date, but lemon scented. I’ll reduce the volume of my acid down to about 1.2L and take it from there

 

[DJPGold]

I put it on low heat, some slight amount of knocking but no boiling and there is steam. Looks like this has really helped the solution. During the initial dissolving the ambient temperature in the shop was about 15 degreees so the acid would’ve been similar, I thought being colder would aid the process rather than being heated

 

[Yggdrasil]

I put it on low heat, some slight amount of knocking but no boiling and there is steam. Looks like this has really helped the solution. During the initial dissolving the ambient temperature in the shop was about 15 degreees so the acid would’ve been similar, I thought being colder would aid the process rather than being heated View attachment 52703

Having it cold will keep the chlorine in solution for longer.
But when you are finished, you heat it to drive off the chlorine.

 

[DJPGold]

Having it cold will keep the chlorine in solution for longer.
But when you are finished, you heat it to drive off the chlorine.

That’s what I’ve always done. Just strange to me that I wasn’t getting anything dissolved with room temperature/cold solution after 12 or so hours, but then I heated it and 90% of the gold has dissolved. However I think a lot of it also precipitated out of solution, have you heard of this happening? Perhaps my solution is too concentrated or not acidic enough? I’ll upload a photo of the beaker in half an hour or so

 

[Yggdrasil]

That’s what I’ve always done. Just strange to me that I wasn’t getting anything dissolved with room temperature/cold solution after 12 or so hours, but then I heated it and 90% of the gold has dissolved. However I think a lot of it also precipitated out of solution, have you heard of this happening? Perhaps my solution is too concentrated or not acidic enough? I’ll upload a photo of the beaker in half an hour or so

Test the pH.
As per your description there is no way it can be too concentrated.
And the more bleach you add the higher the pH climb which is bad.
You need it to be acidic, and while being acidic is necessary, it is also one of the factors that drives off the Chlorine.
One thought struck me, there are also Peroxide based bleaches.
Which one do you have?

 

[Christian333]

I checked my the bleach I was using, over a year out of date hahahah. That could explain why I’m having issues. I found some in the cupboard that’s well in date, but lemon scented. I’ll reduce the volume of my acid down to about 1.2L and take it from there

Some bleach formulas contain sodium hydroxide/lye. Check the label and be sure the only ingredient is sodium hypochlorite.

Janie

 

[Yggdrasil]

Some bleach formulas contain sodium hydroxide/lye. Check the label and be sure the only ingredient is sodium hypochlorite.

Janie

Most if not all have their pH adjusted to a quite high level to ensure longevity of the solution. Somewhere between 11 and 13 is common.
Sodium hypochlorite will start decomposing quite fast if the temperature goes above 10 Centigrade.
It will loose 1%per year at 7 Centigrade.

 

[orvi]

Hello, I’ve collected foils from 10kg of trimmed ram fingers, I recovered the foils using AP and then rinsed them all with water until the solution is clear, I then did a warm HCL wash to remove any tin etc and rinsed all of that off with water.
I began with about 400ml of distilled water in the beaker, I couldn’t pour everything off without losing lots of foils. I then added 600ml of HCL and began dissolving the gold by adding 6-9ml of bleach while stirring it and then continued stirring for a minute or two, I repeated this step every 10 minutes for about 4-5 hours, in total I added about 100ml of bleach. I then came back the next morning and there’s still a hell of a lot of foils.
I’m expecting between 30-50 grams of gold from this batch so I’m curious as to whether anyone knows the saturation level of gold in HCL and bleach.
This morning I topped it up to the current level with HCL, in case it had become too basic and added another small amount of bleach with lots of stirring.
A 2L beaker is the largest vessel I have so could I slowly evaporate the acid down to say, 500ml and then top up again with HCL and small bleach additions.
I would like to avoid pouring off this liquid and starting with a new batch of acid as I would like to keep everything in this beaker for as long as possible.
No I have not yet bothered to do a stannous test, silly me I know, but I figured since there’s been a good colour change and there seems to be much less gold sparkles that I must be dissolving gold, also some of the foils have a different colour to them now, as if they’ve been oxidised. View attachment 52701

With these ammounts, you want to be concentrated. Saturation point of Au in chloride solutions (as AuCl4-) if very very high (hundreds of g per litre). But gold is noble metal. You need strong acid to facilitate the dissolution. Always use concentrated acid for digestion of relatively clean gold (as this). Cover the foils with undiluted HCL and then add oxidizer.
As bleach is fine to use, it comes with a cost - you need quite a bit of it, and as it was correctly pointed out, acid is not only needed to create active chlorine, but also to neutralize the base (NaOH) in it - which is present as stabilizer. Altough it isn´t a problem here, you need to bear in mind, that bleach is manufactured by electrolysis of brine without separator - so the chlorine and NaOH created mix together, producing hypochlorite. Excess NaCl from brine is ALWAYS present, as it would be wasteful for manufacturer to strip it out of the product. If you use industry-strength 10-13% hypochlorite, you need to add half or less the volume as if you use regular household 5% stuff.

If I were you, I will slowly abandon the bleach solution and use more concentrated options - such as TCCA pool chlorine, preferrably as powder. Or shock pool chlorine, which is calcium hypochlorite. And setup the chlorine generator, rather than dumping the oxidant into the beaker. Altough slightly more dangerous, if it is improperly setup, Cl2 gas is much more convenient to use, adds no dead volume to the solution, and does not spend the acid needed for digestion and precipitation of gold.

If you have access to nitric, use it (but as you use bleach, I assume you do not have nitric in hand). Alternatively, you can use nitrate (poor man´s AR) to dissolve this. You need to de-NOx the solution afterwards, but nitrate is more convenient to use compared to bleach (and also has certain composition, no unknown stabilizers, detergents etc.) and also does not add dead volume to the solution.

If you scale things up in the future (this is also kind of scaled-up refining job, as we are now handling more than ounce of gold), dead volume in solutions add considerable more time to the filtrations, heating (also account for wasted energy), manipulations and all operations in general. With raising volume of the solution in the beakers or buckets handled by hand, risk of cracking the glass because of the weight, spilling or dropping the beakers raise exponentially. And you do not want to take higher risk or spend more time doing the job unnecessarily Time is money, go as concentrated as effectively possible. Anytime. Ounce of gold can be nicely dissolved in few hundreds mL of acid. Just an advice nice haul by the way, waiting for the end result

 

[DJPGold]

With these ammounts, you want to be concentrated. Saturation point of Au in chloride solutions (as AuCl4-) if very very high (hundreds of g per litre). But gold is noble metal. You need strong acid to facilitate the dissolution. Always use concentrated acid for digestion of relatively clean gold (as this). Cover the foils with undiluted HCL and then add oxidizer.
As bleach is fine to use, it comes with a cost - you need quite a bit of it, and as it was correctly pointed out, acid is not only needed to create active chlorine, but also to neutralize the base (NaOH) in it - which is present as stabilizer. Altough it isn´t a problem here, you need to bear in mind, that bleach is manufactured by electrolysis of brine without separator - so the chlorine and NaOH created mix together, producing hypochlorite. Excess NaCl from brine is ALWAYS present, as it would be wasteful for manufacturer to strip it out of the product. If you use industry-strength 10-13% hypochlorite, you need to add half or less the volume as if you use regular household 5% stuff.

If I were you, I will slowly abandon the bleach solution and use more concentrated options - such as TCCA pool chlorine, preferrably as powder. Or shock pool chlorine, which is calcium hypochlorite. And setup the chlorine generator, rather than dumping the oxidant into the beaker. Altough slightly more dangerous, if it is improperly setup, Cl2 gas is much more convenient to use, adds no dead volume to the solution, and does not spend the acid needed for digestion and precipitation of gold.

If you have access to nitric, use it (but as you use bleach, I assume you do not have nitric in hand). Alternatively, you can use nitrate (poor man´s AR) to dissolve this. You need to de-NOx the solution afterwards, but nitrate is more convenient to use compared to bleach (and also has certain composition, no unknown stabilizers, detergents etc.) and also does not add dead volume to the solution.

If you scale things up in the future (this is also kind of scaled-up refining job, as we are now handling more than ounce of gold), dead volume in solutions add considerable more time to the filtrations, heating (also account for wasted energy), manipulations and all operations in general. With raising volume of the solution in the beakers or buckets handled by hand, risk of cracking the glass because of the weight, spilling or dropping the beakers raise exponentially. And you do not want to take higher risk or spend more time doing the job unnecessarily Time is money, go as concentrated as effectively possible. Anytime. Ounce of gold can be nicely dissolved in few hundreds mL of acid. Just an advice nice haul by the way, waiting for the end result

Cheers for that mate. I’ll upload a crappy video on YouTube of my journey hahah.
Definitely using hypochlorite form of bleach.
I can get nitric acid but would prefer to not use it if possible, being in Australia makes obtaining nitrates etc difficult.
After a good bit of heating and leaving the solution most of the foils have dissolved but it looks like it’s dropped back out. Tonight I will reduce the solution down another couple hundred mL and add some more HCL and then tiny amounts of bleach while warm to get the last bit of gold to dissolve

 

[DJPGold]

Second mornings progress

 

[orvi]

Cheers for that mate. I’ll upload a crappy video on YouTube of my journey hahah.
Definitely using hypochlorite form of bleach.
I can get nitric acid but would prefer to not use it if possible, being in Australia makes obtaining nitrates etc difficult.
After a good bit of heating and leaving the solution most of the foils have dissolved but it looks like it’s dropped back out. Tonight I will reduce the solution down another couple hundred mL and add some more HCL and then tiny amounts of bleach while warm to get the last bit of gold to dissolve

To facilitate the things up, filter undissolved foils and drop the gold from the liquid using SMB. Or you can filter the foils, dissolve them in concentrated HCL with bleach additions in covered beaker (chlorine escapes very quickly) at around 40-60°C - and then combine the two gold liquids together for one drop. Colder - reaction will be slow. Warmer - too much chlorine escapes. If possible, try to dose bleach under the level of the liquid in the beaker - it helps with adsorption into the juice, as chlorine is a gas by means of plastic tubing or pipette. Not strictly required, but helpful.

If you add anything to the existing liquid (either fresh acid or fresh bleach), resulting mix will still be way too dilute to facilitate some sane reaction rate. If you filter the remaining foils and replace the diluted acid with concentrated fresh one, reaction will be much much faster - trust me In all-right conditions, these can be dissolved in matter of minutes, despite using bleach as oxidant.

 

[Jessy_Jaymes]

New member here. First I must share that I am impressed with the supportive scientific suggestions that so many give for her question. It's great to see intelligence and tips shared in such a kind manner. I'm glad I joined. I have some questions on gold ore. It's very rich and the "dark ugly" if you will. My question is would you break it down in the same manner as DJP shared in this thread? Or could you point me in the direction of a thread that may have some process suggestions? Thank you all in advance.