Clorox Method

[Gratilla]

Rule of thumb: If hypochlorite is supplied in liquid form it is almost certainly sodium hypochlorite (NaOCl / NaClO) and if supplied as a solid (ie white powder) it is odds on calcium hypochlorite (Ca(OCl)2 / Ca(ClO)2).

There are at least three common household chemicals sold in concentrated form - hydochloric acid (HCl), sodium hydroxide (NaOH) and either of the hypochlorites; at least two of these are dangerous when mixed. Can I suggest that on this forum we try and stick primarily to chemical names and formulae (and relegate generic and trade names to suggestions for sources only).

PS If you search the container of a household product, you should be able to identify the chemical and strength of the contents in the (very) small print.

 

[Eamonn]

Here in the UK I use Tesco thick bleach (cheap) Works for me.

 

[Anonymous]

Eamonn I'm in the UK too and proper lab grade Sodium Hypochlorite is freely available and cheap

Jon

 

[Eamonn]

Thanks spaceships.
Didn't bother looking before as I've always got bleach available.
Thinking about it, the last batch of foils I dissolved,I did 100 fingers just to check my yeilds,and I did get a slight positive with stanous chloride from the clear solution after precipitation with SMB.
I'll try lab grade sodium hypochlorite and see if it makes a difference.

 

[Geo]

If you test a spent solution with stannous chloride while it still has dissolved hydrogen sulfide gas, you will get a false positive. After the gold drops, heat the solution until it steams and stir it a couple of times and turn off the heat. Allow the solution to cool and then test with stannous chloride. If you still have a color change it will be a true positive.

 

[Eamonn]

Thanks Geo. Learning all the time.

 

[VK3NHL]

We don't have Clorox brand in Australia. No one I ask has ever heard of it.

Took me about 30 seconds...
Maybe this will help
http://www.domestos.com.au/cleaning-products/new-multi-usage-bleach/

Göran

I think everyone here has Domestos. But it's not Clorox though.
Once I finally established what was meant by the product, I started using our White King. But before that, the Clorox name Googled up something like 30 different products.
Edit: Many of them would probably work too, including Domestos. But they all have different additives, and who wants to mix unknown additives with hydrochloric acid? Not me.

My point is merely that the Clorox name is not as universal as some might think. If you don't know you're meant to be looking for bleach, even "HCl/Cl" doesn't help much either. To those who understand, it's plain, but from the outside it's another language.

BUNNING'S SELL SOD. HYPOCHLORITE in 5 Litre drums find it in the the pool chems section.
It is a stronger solution that the Generic brands of household bleach..
Regards
Tony.

 

[Geo]

I'm not sure that this is a case for "more is better". Standard 5%-8% sodium hypochlorite and HCl can cause enough chlorine gas to be evolved that it can suffocate someone with no problem. There comes a time when less is actually more. The trick is not to evolve more gas more than just keeping what is evolved in solution for a longer period of time. Very small, steady evolution of gas is much better than a sudden burst of gasses that just cause a big cloud of poison gas.

 

[lanfear]

And the acid gets neutralized by the alkaline hypoclorite and stops doing it's job. You want to be able to control the ph with small additions.

Jon

 

[Anonymous]

And the acid gets neutralized by the alkaline hypoclorite and stops doing it's job. You want to be able to control the ph with small additions.

Jon

Huh what?

 

[g_axelsson]

Bleach is alkaline to keep the sodium hypochlorite stable. In acidic environment it breaks down into chlorine and sodium salt.
I don't feel the amount of lye in the bleach to be so much that you need to take it into account. According to wikipedia it is about 0.01-0.05% sodium hydroxide in ordinary household bleach.

Ref:
http://en.wikipedia.org/wiki/Sodium_hypochlorite
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=37&t=8931

I have never needed to add extra HCl when dissolving gold because the pH of the solution became too high.

Göran

 

[Gratilla]

Bleach is alkaline to keep the sodium hypochlorite stable. In acidic environment it breaks down into chlorine and sodium salt.

Hypochlorite chemistry is like the layers of an onion.

1) First, it's necessary to appreciate that hypochlorites exist as dominant species at different pHs. Looking at the graph below it's obvious that these species exist individually over certain pH ranges - Cl2 below pH 1, HOCl between pH 4-5 and OCL- above pH 10. Also, the species exist in equilibrium pairs over the other pH ranges. Why this is important will become obvious shortly.

2) All three species are oxidising agents (HOCL strongest, Cl2 next, OCl- weakest) and all three have redox potentials above that necessary to dissolve gold. However, redox potentials generally decrease as chemical reactions progress. So in the real world with real mixed ores, the redox potential will generally fall below that for dissolving gold and any gold already in solution will plate out.

3) The hypochlorites are amphoteric, that is they act as BOTH acids and bases. This becomes clear when we dissolve in water.

NaOCl + H2O -> HOCl + NaOH
Ca(OCl)2 + 2H2O -> 2HOCl + Ca(OH)2

This is moot with sodium hypochlorite which is generally sold already in solution. With calcium hypochlorite is dissolved, calcium hydroxide is produced and a large amount of acid is necessary to neutralize this if you want to work in the low pH range. Alternatively, the hydroxide (not very soluble) can be filtered out.

4) Then there are the hypobromites.

 

[g_axelsson]

Okay, it was more complicated than I expected... I feel like a newbie now. :mrgreen:

I'm not surprised and never doubted that controlling the pH when leaching gold from ore would be critical. But how important is it when dissolving solid gold from electronic scrap recovery? I'm pretty sure that 99% of the members here is dealing with electronics and not ore.

I've always covered the gold with HCl, added a dab of bleach and in a minute or two, if there are any more gold left, added a dab more. Worked for me, but then I've never used it on more than a few grams at a time, often as a second dissolving when the initial drop created very dirty gold.

Göran

 

[Grelko]

I've always covered the gold with HCl, added a dab of bleach and in a minute or two, if there are any more gold left, added a dab more. Worked for me, but then I've never used it on more than a few grams at a time, often as a second dissolving when the initial drop created very dirty gold.

Göran

Do you happen to know the ratio of HCL/CL needed to dissolve gold foils and/or powder? I'm trying to generate the least amount of fumes and waste product. "Approximate values are fine, gram, dwt etc." I couldn't find the calculations on here.

The foils or powder will be as clean as I can get them with a couple hot HCL and water rinses because, I know this could make a big difference depending on how dirty the batch is or, the amount you are dissolving.

Edit - Sorry for asking questions in this section, I felt that it would add to the tutorial if someone knew the ratios. Please move it to the other section if needed.

 

[g_axelsson]

Sorry, always done it by watching the reaction and adding more if needed. If you add all bleach in one go most will go up as gas and not contribute to the reaction. There could also be big variations of the concentration of the bleach. It is also depending on temperature.

So a fixed ratio is hard to give even if you would make a theoretical calculation.

Göran

 

[Grelko]

It's no problem, I'll just barely cover the foils/powder with HCL, then add Cl to it with a dropper, lets say a couple cc's at a time then wait a couple minutes between until it's all dissolved. It'll be my first time using HCL/CL so, I've been reading all I can about this step.

It's just going to be a small batch for a gold standard to check if my stannous solution is going to work properly. "acquaintance test"

 

[Pantherlikher]

Interesting and thought provoking...

I wash allot of gold trim on glassware as it's all free except chemicals..and time.
I use a tupper ware plastic container and put in enough HCL so it covers the edge where the gold is and then slowly pour some bleach/Sodium Chloride in and it bubbles violently and quickly stops.
I then place glass, plates on edge and roll the plate so it contacts all of the gold. I find I can do this for about a half hour. Adding a little more "bleach" when the reaction slows, gold trim doesn't completely come off right away.
Time is what I use to gauge the solution. After about a half hour, the PH must get high enough to all but stop dissolving so I add a small amount more of HCL and move the solution into the "dirty gold" container where it sits and dissolves all the gold it will until I have another batch ready. "dirty gold" container currently has solids from my waste stream from last time processing. Fingers, pins in waste with other plated crap put in to eat base material. Surprised me how much material was in the first waste acid container. I filter this solution then and test and so far it's been positive every time which is great.

The problem I see with this is it must be the high PH that keeps the chlorine in solution as it takes several days for anything to drop. I use extra amounts, based on my reading here, of SMB added in little amounts days apart. Last batch run I added 1 "pill" sized amount. I get it here from a wine making store and it's in little pill sized pieces. I need to weigh and start logging things...my bad there...
Anywho... I add 1 crushed up pill and stir and get the slight smell of it working so let it sit for a day, nothing on the bottom and still tests positive so in goes another crushed pill and let sit for about a week. Last big batch of glass I did, several hundred pieces, I kept adding solution to my dropping container so didn't expect anything until it filled 3/4 full. About 5 pills later and 2 weeks go by and now there's a nice layer of mud at the bottom and a negative test. This gets separated. Solution poured off into bigger settling tank until full. Mud into washing glass. After washing and had enough, I dissolved again and dropped and now looks nice after first round of washing. Going to wash some more to be sure and then give melting a go...soon.
After about a week or more, I pour off the "waste" solution from the settling glass into my first crock pot with plated crap and find some mud at the bottom of that glass which goes into the "dirty glass" for dissolving.

Sounds like allot when I go back and read it... again...
From my work in progress experience with washing dishes of gold trim, this seems to flow right along but takes allot of time as you can imagine, washing dishes for gold... My first JOB was washing but not for gold...

The "bleach" is cheap but the HCL is questionable here. Except I was able to trade pool filters and pumps for 4 gallons of "PH Down"...AKA HCL. I look at my cost and time and then remember watching "Alaskan Gold ", the TV show and I'm guessing I'm doing about as good as they are so... Just not much to show for that effort yet... I do have to finish that to make room in my shed so I can get to processing electronics that are now piling up...everywhere I can hid it.

Sorry to dump this in this thread but it's in line with what's being talked about.
PH seems to make a difference in how "Chlorox", "Bleach", "Sodium Chloride" can dissolve gold, and keep it in solution...

B.S.

 

[Grelko]

Pantherlikher,

Did you add some water to your solution to dilute it a little before adding SMB, it should help your gold drop a bit faster. (I read that some people add water to SMB and some don't so, I'm not sure if this is entirely accurate.)

You could always test the solution with litmus paper and see what PH is when the gold starts to drop. "If anyone has this information, please share it."

Heating the solution will help drive out excess chlorine, which should drop the gold faster.

Some of these responses are from other posts I've read, so hopefully I'm not accidently spreading mis-information.

The "bleach" is cheap but the HCL is questionable here.
B.S.

Edit - Check Walmart, Lowes, Home Depot etc, HCL is usually outside with the gardening supplies/plants in 1 gallon containers "Muriatic acid". They run approximately $6 each, or $11 for a box of 2 gallons. They might keep it near the paint department or swimming pool supplies also.

 

[Pantherlikher]

Yes Grelko, I add rinse water to the solution before SMB while it sits on the sand covered heater.
Forgot to add the heating step... I filter solution and rinse water and then in to sit on the heater for an hour or more. Then test and add SMB while still warm.

HCL is easy to get but is $6-7/ gal... This brings cost up to where it's questionable for washing the little bit from each plate, cup, and Christmas ornament. There's so little each piece that the process stops before the solution if full so there's allot of solution for so little gold.
I'm into my 3rd gal. and I might have 2-3 grams cleaned and ready for me to blow it away on my first melt. Hope not but..

B.S.

 

[Geo]

The solution isn't really needed to dissolve the gold. The chlorine gas will dissolve the gold without the need for the gold to be submerged in solution. Use a 4 or 6 inch piece of schedule 40 PVC pipe about three foot long. Fit the pipe with a cap on one end and a threaded clean-out on the other end. Break the material up in pieces to fill the pipe. Add 200ml's HCL. Add 50ml's house hold bleach and screw in the plug. The pipe and fittings are rated for 480 psi. It will pressurize the tube. Shake the tube up and down, back and forth a few times and leave it closed for a few hours safely away from people and pets in a secure area with the screw cap up. After a few hours time, slowly and safely unscrew the cap (always wear eye protection and other PPE's) and let the pressure off the tube. For a few cents and a little time more, add a PVC ball valve in the cap to let off the pressure. Gently rinse the material with a spray bottle of water until all the material is rinsed. The gold should be gone from the material and in solution.