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Geo

Geo

Well-known member
Joined
Mar 1, 2011
Messages
7,069
Location
Decatur,Ala.
I have decided that i will try to do a sodium thiosulfate leach on gold and precipitate the gold with copperas or a very fine steel wool. First, i am planning to make my own thiosulfate leach by adding sulfur to a boiling solution of NaOh. After carefully filtering the hot solution, crystals of sodium thiosulfate will drop from solution upon cooling. A good non-magnetic stainless steel pot should work for this. For a ratio of 6 parts NaOh and 4 parts sulfur, the formula is pretty simple. I can source the sulfur and NaOh locally as Dudadiesel has actually moved closer to my house. For about $40, I can buy enough of both chemicals to make about 10 pounds of crystals. When the weather breaks and i can work outside, i have bought a small sample of both chemicals (4 OZ sulfur USP and 16 OZ of NaOh) and with these using 6 to 4, i should make around 8 OZ of crystals. Using distilled water to make the leach, i will saturate the solution with as much gold as it will hold. By precipitating the gold and melting, it will give me a ball park estimate of what I can expect from my own chemistry. I will record everything and quite possibly make videos of as much of it as i can. If this works as well as i hope, i will try the leach on incinerated chips next to see how it will work on bonding wires. Processing chips this way is what led me to try this. Pulling the gold from the ash without pulling out the other metals first would be great.

This may be old stuff to some people here but its brand new to me. Any thoughts would be helpful.
 
I wondered about the way you would make your thiosulfate. Thiosulfate is produced by the reaction of sulfite ion (hot solution) with elemental sulfur, by incomplete oxidation of sulfides (pyrite oxidation) or by partial reduction of sulfate. In my opinion sulfur will disproportionate in hot NaOH to sulfide & sulfite. Of course in sulfidic solution it will form polysifides and in a solution containing sulfite it will become thiosulfate.

Perhaps the separation will be difficult or the purity bad. Have you already tried your route?
 
Hi Geo!
This is cool! I'm curious to see how it works. Hearing that chemistry sure brings back memories. When I was like eleven years old, I was reacting NaOH with sulpher and it would make what they called sodium polysulphite. I'd then add ethylene dichloride and like magic it would drop a ball of white rubber. I would warn you! It was the stinkiest stuff you could ever imagine. I poured the remaining liquod down the basement floor drain and it took years for the nausiating oder to leave .
artart47
 
You will first need to neutralize the NaOH with SO2, then you have Na2SO3, which then can be boiled with sulfur to form Na2S2O3 ... if wikipedia is right.
 
from wiki:

Industrial production and laboratory synthesis

On an industrial scale, sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture.[2]
In the laboratory, this salt can be prepared by heating an aqueous solution of sodium sulfite with sulfur or by boiling aqueous sodium hydroxide and sulfur according with the following equation:[3]
6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O
Upon cooling sodium thiosulfate crystallizes out of solution.
 
If Na2S is just a little bit like K2S, maybe you will not love it. It generates H2S with moisture, at least when it is solid. Though in solution it reacts slowly with H2O and O2 to thiosulfate. Might work well. Hard to say which one of the two is the nicest process. To me it seems both of them are harder to do than to read.
 
im thinking that the Na2S, being more soluble than the thiosulfate, will stay in solution. since i will only use enough water to dissolve the NaOh, the excess H2O produced in the reaction will lock up the Na2S.

really, the only way to find out if it will work is to try it and find out. i was hoping to hear from someone that has actually tried it. i can totally understand if its being kept as a secret but sooner or later, someone like me will figure out how to make it work.

the secret is not that sodium thiosulfate will leach gold more than it is with how to recover the gold from the solution without contaminating it with massive amounts of sulfur. electrolysis is one method for removing the gold and being able to re-use the solution. im not as interested in re-using the solution as i am about the concept of reclaiming visible gold (or unseen gold) from Escrap. im not expecting to start a revolution in the hobbyist refining niche as much as i am furthering my self education.
 
Platdigger said:
40 dollars seems a bit much for 10 pounds.
I paid around 1.50 per pound or less for sodium thio in a 50 or 55 pound bag.
Click to expand...

thats just a rough estimate. i cant find a good source nearby.
 
so figure 3 on page 9 shows the reaction times at different temperatures. that is some useful information to have.

thank you Deano, very much. :)
 
Hoi,

I have browsed my documents and I found a review paper about that process. Enjoy the reading 8)
 

Attachments

  • Thiosulfate leaching of Au - A review.pdf
    2.6 MB · Views: 232
Quite amazing those leaching methods, I enjoy this thread!

Something I never understood is, under what conditions are they the preferred methods? Maybe, when the gold content of the source is low like in ores and you have to use a lot of liquid? How is cementation prevented? Is it like in a filter, when you "wash" by pouring fresh water on the top?
 
Both methods have their advantages and disadvantages. Both dissolve gold faster than cyanide, have a better efficiency in the leaching rate, can better handle difficult ores and low concentrations (where cyanide might have some troubles), selectivity is higher and be more energy efficient (especially thiourea since it is better at low temperatures than at higher ones).

BUT the main problem is, and this is also the reason why it is not really used in the industry, is that the chemical consumption is higher than in the cyanide process, which leads to higher costs and so on.

Another difficult is the recovery of the gold from the solution. This processes still need some R&D to be really interesting for the industry.

And yes you are right, this methodes are really interesting!
 
What I gather from studying these alternative leaches used to try and replace cyanide, is they were not widely used in the industry, I see a lot of papers or study on them, but not a whole lot of use, they also seem to be leaches that are very hard to keep the leaching process working properly, with sodium thiosulfate and gold keeping the pH, concentration, ammonium complex and copper catalyst, oxidizer, and everything in the proper proportions seem to be a very difficult task, there are a few members here that have used, or tried to use the process, and from what I can gather they had a very difficult time keeping the leach within the working limits.

Cyanide although slower seemed to work extremely well, I still do not see where these other leaches have been able to replace cyanide.

sodium thiosulfate I feel would make a better leach for silver ore that has been converted to silver chloride after a chloridized roasting process, here it seems to have worked well, but for leaching gold ore the process seems be just riddled with difficulty...

I agree with Loito, I find them interesting, but I do not see where they have been proven the best alternative to leaching gold from ore over the proven cyanide process, and with the difficulty in keeping the leach in the parameters where it works to leach the gold, just a problem not easy to deal with.
 
Thank you Loito, that is a very nice document and i will read it fully. Reading through some of the pertinent information, some things jump out at me. This document was written on leaching ore and not necessarily for Escrap. The problems that might arise from leaching from a source material already high in sulfates (ores), may not be an issue since i will be using things like bare pins and fingers and (hopefully) incinerated chips. Instead of maintaining a PH of 10 to 10.5, i am planning on keeping the solution as basic as possible to reduce the attack of base metals. Actually bringing the PH down to 10 will let me be able to cement the gold out of solution using steel wool and since ferrous sulfate is acidic already, should precipitate the gold directly. Of course this will render the solution unusable for further leaching. I may try adding a little copper oxide as an experiment to gain more speed if necessarily, but the videos ive seen of the reaction, it happens fairly quickly.

To tell the truth, cyanide scares the hell out of me and sodium thiosulfate is non-toxic. For me, its either this or sticking with the older tried and true methods of AP and AR.
 
Geo

Mr Maxwell House had his silver and Gold baby of 0.2grams.I went back and electrocuted him again and now I'm waiting for his stomach to settle out again.I'm hoping to get a better weight from this next baby!LOL It works.Good luck on your end!



modtheworld44
 
@ Loito: Thanks for this very interesting, well founded review, which confirms a few practical experiencies I gathered in leaching and recovering gold and silver with/from cyanide-solutions and with the silver-thiosulfate-system ("green" and "black" photographic films).

@ Geo: I have no doubt that you will reach your goal, to produce your own sodium thiosulfate, and that it will work in the dissolution of gold. However, recovering the gold from thiosulfate-leach in an economically feasible way, is a different matter. There is only scarce experience, and according to the reviews authors, a lot of research-work will still be needed, surmounting our capabilities as hobby-refiners.
 
On this process I would like to mention two major drawbacks(in the hobby department):

1) monitoring the PH(time consuming,giving the fact that the process is a long.
2) cost of (let's say fuel) to keep the solution warm (between 40-60 C)

P.S: In the papers I do not see the involvement of Sn....this can cause some consumption of reagent(thiosulphate).
 

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