Chemical Glycine method

[Samir Das Gupta]

All gold plated components arent the same. Many gold plated components are often blended with cobalt or nickel which makes dissolution/ recovery longer/ more expensive/ less efficient. Also, plated gold tends to be harder to dissolve than ore gold. The typical alkaline: amino acid: oxidant formula that works on ore may not work as well on e waste. Lots of experimenting required to perfect it and even then it requires to be tweaked constantly.

When excess amino/ glycine is required then its feasible only when the manufacturing system incorporates the re-use of the excess amino acid otherwise the cost can be greater than the recovered gold.

Has anyone worked on electrolysis/ electrowinning dissolved gold glycinate instead of carbon leaching? Sounds like a cleaner process.

 

[Yggdrasil]

All gold plated components arent the same. Many gold plated components are often blended with cobalt or nickel which makes dissolution/ recovery longer/ more expensive/ less efficient. Also, plated gold tends to be harder to dissolve than ore gold. The typical alkaline: amino acid: oxidant formula that works on ore may not work as well on e waste. Lots of experimenting required to perfect it and even then it requires to be tweaked constantly.

When excess amino/ glycine is required then its feasible only when the manufacturing system incorporates the re-use of the excess amino acid otherwise the cost can be greater than the recovered gold.

Has anyone worked on electrolysis/ electrowinning dissolved gold glycinate instead of carbon leaching? Sounds like a cleaner process.

Welcome to us.

 

[4metals]

Has anyone worked on electrolysis/ electrowinning dissolved gold glycinate instead of carbon leaching? Sounds like a cleaner process.

@anachronism has used a system involving 2 peristaltic pumps pumping the solution through a carbon based cathode fabric to recover metals. If he see's this he can offer his opinion relevant to this process.

 

[MareNextDoor]

All gold plated components arent the same. Many gold plated components are often blended with cobalt or nickel which makes dissolution/ recovery longer/ more expensive/ less efficient. Also, plated gold tends to be harder to dissolve than ore gold. The typical alkaline: amino acid: oxidant formula that works on ore may not work as well on e waste. Lots of experimenting required to perfect it and even then it requires to be tweaked constantly.

When excess amino/ glycine is required then its feasible only when the manufacturing system incorporates the re-use of the excess amino acid otherwise the cost can be greater than the recovered gold.

Has anyone worked on electrolysis/ electrowinning dissolved gold glycinate instead of carbon leaching? Sounds like a cleaner process.

The electronegativity of gold is higher than that of the oxidation of glycine at the electrode. This is the problem I ran into trying to electrowin the copper out of solution. The oxidation of glycine is favored even more than the evolution of oxygen gas at the anode. Therefore as far as I was able to find via research and experimentation, the lowest voltage to run any electrowinning cell involving glycine is going to degrade the glycine rendering it non-reusable. I was able to electrowin the copper out of the solution, but the solution was completely unable to leach any more metals afterwards.

 

[Samir Das Gupta]

Sam,, I am currently building a leach tank(4000 Ltr) , heated and insulated for au reduction in Glycine. it would be interesting to share notes on ur failures,,, success's in your trial. Btw ,, we dont have a Cu problem, will be using Hydrogen peroxide for di-oxy,, CuSO4 ( 4 nMol) 1 Mol Glycine. running thru a carbon collumn . cheers

I don't mean to pry into your working formula but if I may add to this discussion; I find 1M Glycine solution very excessive. That's 240 kg of Glycine in 3200 litre if you maintain a S/L ratio of 0.2. A really good stretch of ore after beneficiation yields around 0.001-0.002% gold. Given a solid content of 800 kg in 3200 litres leach solution (0.2 S/L ratio), the Au recovery is at best 8-16 grams. At 240 kg Glycine for 8-16 grams of Au, it is anything but feasible (given its current prices) unless you have a process to recover and reuse the excess glycine continuously by only adding additional glycine to make up for the consumed glycine or if you are leaching from carefully segregated e-waste i.e. higher yield/ kg.

Glycine does not leach the gold. It is the alkaline/ oxidant combination that leaches the gold from the ore/ e-waste at which point glycine acts as a chelating agent (an agent that bonds to metal ions being liberated into the leach solution) and not as a lixiviant (an agent that dissolves metal ions in a leach solution). So while the lixiviant combination may require greater quantities for leaching, the chelating agent (often the expensive one) may not necessarily need to be in high quantities. That being said many lixiviants also consume glycine in a leach solution hence contributing to the additional consumption of glycine so that needs to also be factored in.

Also, has anyone tried electrowinning gold from the leach solution? I find this may be a cleaner and faster process to achieve a higher purity. This method also has an energy generation angle where hydrogen peroxide and ammonia are used in the leach solution. There will be evolution of Hydrogen gas at the cathode which can be collected and utilised as an energy source which may, to some extent, contribute to the energy requirement. If this theory holds true then its possible that the extraction process may contribute to a degree of clean energy independence. Don't know much about the electrowinning process. Just a theoretical assumption.

 

[Samir Das Gupta]

That is quite promising.
I like the way Amino acids dissolve copper at room temperature, but need to be heated to 40-50 degrees to dissolve gold. Very handy! me like things you can target accurately.

Read more at: http://phys.org/news/2014-10-amino-acids-key-gold-leaching.html#jCp

"You have other amino acids which are even more selective and more powerful dissolvers of gold compared to glycine, but they are much more expensive, much more exotic," he also says.

Even better if it saves time it is worth the extra cost.an interesting line of research.

Try adding an oxidant to the glycine alkaline solution (KMNo4 or H2O2). Keep it agitated and aerated. You may not require heating.

 

[Samir Das Gupta]

The electronegativity of gold is higher than that of the oxidation of glycine at the electrode. This is the problem I ran into trying to electrowin the copper out of solution. The oxidation of glycine is favored even more than the evolution of oxygen gas at the anode. Therefore as far as I was able to find via research and experimentation, the lowest voltage to run any electrowinning cell involving glycine is going to degrade the glycine rendering it non-reusable. I was able to electrowin the copper out of the solution, but the solution was completely unable to leach any more metals afterwards.

So would it make sense to reduce the glycine content (from a feasibility perspective) while increasing the oxidant and maybe the pH? Also, how feasible is it to put in a sytem that utilises the hydrogen collected at the cathode to power the agitator and electrowinning process?

 

[Samir Das Gupta]

Welcome to us.

Thank you

 

[Samir Das Gupta]

@anachronism has used a system involving 2 peristaltic pumps pumping the solution through a carbon based cathode fabric to recover metals. If he see's this he can offer his opinion relevant to this process.

Very interesting. Thank you.

 

[MareNextDoor]

So would it make sense to reduce the glycine content (from a feasibility perspective) while increasing the oxidant and maybe the pH? Also, how feasible is it to put in a sytem that utilises the hydrogen collected at the cathode to power the agitator and electrowinning process?

No. The literature on this is quite clear that a decrease in glycine concentration leads to a decrease in gold entering solution. The best possible gold extraction I have seen achieved in any paper under optimal controlled conditions is 0.5mg/L of solution. From what I remember reading, pH above 11-12 makes no difference in gold recovery. I believe there is no hydrogen generated at the cathode during the electrowinning process (I have only tried electrowinning copper as 0.5mg/L of gold is not worth my time with the glycine process) as you are not splitting water into H2 and O2, the electrons to reduce the metals back to deposite come from the destruction of the glycine module itself.

If you are speaking to lower glycine concentration = lower cost = more feasible, this consideration is moot considering electrowinning destroys the glycine.

EDIT - Here's some literature if you have any questions about the specifics, or the effects of changing variables:
Paper showing propensity for destruction of glycine in electrolytic cells:
Electrochemical oxidation of glycine by doped nickel hydroxide modified electrode
Paper discussing optimal solutions for the leaching of gold:
Leaching and recovery of gold from ore in cyanide-free glycine media