a new plan

[bmgold2]

By the way. I finally started my expermiments on a thiourea leach. The leaching looked very promising. Tomorrow my steel cathodes will arrive and I try the electrowinning tests. I will start e new threat for that in a few days with some pictures.

Please do. A few/several years back, I bought Charles Butler's book on Nitrate Leaching and he uses thiourea and also plain urea for his nitrate leaching. I've never done many tests with it though. I know the thiourea is a carcinogen. The directions I have used very weak solutions of it though. I'd have to check but I'm thinking it was like 0.1 percent. He also used zinc powder to recover the gold. I have never been able to find out if the leaching solutions can be tested with stannous chloride. It always seemed like a lot of work to do the 5 or 10 minute quickie leaches and then have to do the torch assay to see if you had ANY gold in the solution.

 

[goldsilverpro]

Thank you solar_plasma, this is not going to be like mixing a cake recipe. :shock: It's like learning a new language for me as i have no chemistry background. I will eventually have enough numbers to formulate a recipe type process for the chemistry challenged. There are some things I am working out. Like sodium thiosulfate is 148.21 g/mol. and water is 18.015 g/mol. At a 0.2 m solution, how many grams of sodium thiosulfate pentahydrate would i need for 20 liters of solution.

Anhydrous sodium thiosulfate, Na2S2O3, is 158.13g/M. Sodium thiosulfate pentahydrate, Na2S2O3.5H2O, is 248.21g/M. Therefore, the pentahydrate is only 158.13/248.21 = .637, or 63.7% sodium thiosulfate..

0.2M of 248.21g/M is 248.21 x .2 = 49.6 g/liter. 20 liters would require 49.6 x 20 = 992g of the pentahydrate.

 

[FrugalRefiner]

Sorry Geo. I didn't check the molecular weights you provided for the thiosulfate and water molecular weights, so I'm afraid I led you astray in my calculation.

I'm going to edit my original post in this thread.

Dave

 

[Geo]

Thanks Goldsilverpro. We finally warmed up and thawed out. Now i can get back to experimenting. 8)

 

[Hoad413]

How much urea is needed to dilute nitrice acid?

Say I have 30ml of nitric acid in my ar along with 120ml of hydrocloric acid

How much urea would be needed to dilute the nitric acid to a ph 1.0?

How do I go about doing this proses do I just use urea on it's own or do I also need to add water?
Thank you

 

[butcher]

Urea will not dilute nitric acid, water can be used to dilute nitric acid.
urea will not destroy nitric acid if mixed with nitric acid it can make a dangerous substance of urea nitrate, a small amount of urea will destroy NOx gases in nitric acid.

In my opinion you should not use urea to remove nitric acid from an aqua regia solution, it will not destroy free nitric acid, although it can destroy decomposed nitric acid in solution (if you did not do what most new people do and use too much nitric acid), urea will just add more contamination, and can possibly cause a dangerous solution either in the recovery process or even in the waste treatment process, it will also cause problems if you have platinum group metals involved where the urea can decompose to ammonium compounds...


My suggestion is forget about using urea or studying how much you need, instead learn to refine where you do not need urea.

Use only the bare minimum amount of nitric acid needed, so that at the end of the process you have no free nitric acid to get rid of.

Use the evaporation method taught by C.M.Hoke.

Use gold to remove free nitric from the solution (Harold's gold button trick).

Use sulfamic acid to remove free nitric acid.

Learn to recover and refine gold, study Hokes book and the forum...

 

[Geo]

No worries Dave, it was my fault. You were still closer than me. :lol: Please feel free to offer any help that you can, and I will try to check my numbers before i post them.

 

[solar_plasma]

After reading "THIOSULFATE LEACHING OF GOLD--A REVIEW" several times I believe I am starting to understand ammonical thiosulfate copper system:

a) Leaching gold and silver will work best around Eh 0,3eV and pH 9,5. Depending on the setting, the range can be more or (mostly) less wide.

b) The pH is modified by NH₄OH.

c) The Eh is determinated by the concentrations of all electrolytes dissolved.


Can anyone tell, if this is correct so far?

 

[Loito]

(a) Yes, most leaches carried out at near pH 9-10 to allow free ammonia to be present to complex copper (II) and reduce the interference of some foreign cations such as iron or manganese.

(b) Yes

(c) I am not sure what you exactly mean. For effective gold dissolution an oxidation potential between 150-250mV vs SHE is required (depending upon pH). At higher potentials there is significant oxidation of thiosulfate to tetrathionate. But Gold thiosulfate is reduced at -0.15V vs SCE and is independent of pH for values above 4.

 

[solar_plasma]

(a) Yes, most leaches carried out at near pH 9-10 to allow free ammonia to be present to complex copper (II) and reduce the interference of some foreign cations such as iron or manganese.

(b) Yes

(c) I am not sure what you exactly mean. For effective gold dissolution an oxidation potential between 150-250mV vs SHE is required (depending upon pH). At higher potentials there is significant oxidation of thiosulfate to tetrathionate. But Gold thiosulfate is reduced at -0.15V vs SCE and is independent of pH for values above 4.

oooops ...I meant 0,3V ...don't know how I came to write eV... *shaking head*

Thank you, then I got the most basical basics!

 

[a_bab]

Question for those who made the thio leach: does it stink like ammonia?

I'm afraid it does since there is some free ammonia and it is supposedly used at 40-50 degrees C (ammonia leaves the solutions quite fast in these conditions).

 

[butcher]

The ammonia (besides being basic pH ) is to form a copper amine complex which acts as a catalyst for the reaction.
Cu (2+) + 4NH3 --> Cu(NH3)4

Oxidation of gold by the cupric amine.
Au + Cu(NH3)4 + 5 S2O3 --> Au(S2O3)2 + Cu(S2O3)2 + 4NH3
(here most of the ammonia is still in solution)

Oxidation of cuprous thiosulfate back to cupric amine.

Cu(S2O3)3 + 4NH3 +1/4 O2 + 1/2 H2O --> Cu(NH3)4 + 3S2O2 + OH-

Gold forming thiosulfate complex.
Au + 2 S2O3 + 1/4 O2 + H2O --> Au(S2O3)2 + OH-

Copper and ammonia acts as the catalyst.

Loss of the thiosulfate from formation of polythiontes, oxidation from cupric amine oxidizing thiosulfates is a problem...

2Cu(NH3)4 + 8S2O3 --> 2Cu(S2O3)3 + S2O6 + 8NH3
(Here is where you may smell ammonia released).
Also problems of Oxidative degeneration of thiosulfates by oxygen to polythionates S2O6, S6O6...
Which rob solution of thiosulfate.

Other oxidations involved
Tetrathionate formation.
S2O3 + 1/2 O2 + H2O --> S4O6 + 2OH-
Tri-Thionate formation.
3 S4O6 +5/2 O2 + H2O --> 4S2O3 + 4H+

Sulfite formation.
S2O3 + 2 O2 + H2O --> 2SO4 + O2 + 2 H+

Ammonium back to ammonia.
NH4 + OH- --> NH3 (aq) + H2O --> NH3(g) + H2O
Here you may smell the ammonia fumes.

Also notice hydroxides and acids forming in the solution make keeping pH in range to keep the leach working properly becomes a challenge.

 

[Geo]

Im glad sometimes that it's hard for me to follow chemical equations. If i weren't so ignorant, I may never try to do things for myself. :lol: So when i ran concentrated O2 through the solution all night, i was just wasting the thiosulfate solution. This process is one that needs close inspection and regular PH testing. Will this meter hold up to the basic solution to use for this? http://www.ebay.com/itm/Digital-PH-Meter-Tester-Pocket-Aquarium-Pool-Water-Wine-Urine-LCD-Pen-Monitor-/310807986488?pt=US_Garden_Tools&hash=item485d998138

 

[niteliteone]

Geo,
I have a Ph meter just like that one.
They are great for hydroponics, but Not for the strong acids we use.
They will work a time or two, if you don't wait a week between tests.
Mine failed during the second test.

 

[Geo]

Geo,
I have a Ph meter just like that one.
They are great for hydroponics, but Not for the strong acids we use.
They will work a time or two, if you don't wait a week between tests.
Mine failed during the second test.

I'm so silly, I almost posted one of those "here's your sign" things. :lol: There should be no acids involved in testing this solution. Your main worry would be whether the tester can hold up to the BASIC solution. Strong bases can be just as hard on some metals as acids so this is my question, will this tester work on a basic solution?

 

[butcher]

I have one of these from Hanna HI 198129, I have had it several years and still have not had a problem with it.

http://www.hannainst.com/usa/prods2.cfm?id=030&ProdCode=HI%2098129

 

[Loito]

The ammonia (besides being basic pH ) is to form a copper amine complex which acts as a catalyst for the reaction.
Cu (2+) + 4NH3 --> Cu(NH3)4

Oxidation of gold by the cupric amine.
Au + Cu(NH3)4 + 5 S2O3 --> Au(S2O3)2 + Cu(S2O3)3 + 4NH3
(here most of the ammonia is still in solution)

...

Ammonium back to ammonia.
NH4 + OH- --> NH3 (aq) + H2O --> NH3(g) + H2O
Here you may smell the ammonia fumes.

I have corrected some mistakes in your equations.

Au + Cu(NH3)₄²⁺ + 5 S₂O₃^2- --> Au(S₂O₃)₂^3- + Cu(S₂O₃)₃^5-+ 4 NH₃
(here most of the ammonia is still in solution)

Oxidation of cuprous thiosulfate back to cupric amine.
2 Cu(S₂O₃)₃ + 8 NH₃ +1/2 O₂ + H₂O --> 2 Cu(NH₃)₄ + 6 S₂O₃^2- + 2 OH^-

4 Au + 8 S203^2- + O₂ + 2 H₂0 <--> 4[Au(S₂O₃)₂]^3- + 4 OH^-

Tetrathionate formation.
2 S₂O₃^2- + 1/2 O₂ + H₂O --> S₄O₆^2- + 4OH-

Tri-Thionate formation.
(3 S4O6 +5/2 O2 + H2O --> 4S2O3 + 4H+) I have no idea where you got this equation, but the sulfur-degrading works diffrent from tatra to tri and thio.

Sulfite formation.
S₂O₃^2- + O₂ + 2 H₂O --> 2 SO₄^2- + 4 H⁺

Ammonium back to ammonia.
NH4⁺ + OH^- --> NH₃ (aq) + H₂O --> NH₃(g) + H₂O

 

[niteliteone]

Geo,
I have a Ph meter just like that one.
They are great for hydroponics, but Not for the strong acids we use.
They will work a time or two, if you don't wait a week between tests.
Mine failed during the second test.

I'm so silly, I almost posted one of those "here's your sign" things. :lol: There should be no acids involved in testing this solution. Your main worry would be whether the tester can hold up to the BASIC solution. Strong bases can be just as hard on some metals as acids so this is my question, will this tester work on a basic solution?

I think it would have been fitting :lol:
It completely slipped my mind (what little is left) of what process was being used here.

 

[nh6886]

Geo,

First I wanted to say thanks to you and all those who have contributed, and those pins look fantastic, congratulations!
I wanted to mention that I get most of my silver from used ammonium thiosulfate (fix) after 30,000 square inches of industrial radiography film has been processed in it. I recover the silver by using Manuel's Sodium Sulfide method which drops the the silver as Ag2S and leaves the "fix" ready to do more work. I have not reused it to process film but it works great to strip the silver from green film (unexposed) without removing the gelatin. Which for me means No sodium hydroxide, no oxalic acid, and no incineration is needed when I recover the silver.
I have completely saturated this solution to the point where it appeared not pick up anymore silver and it was stable for a couple of days until I dropped with Sodium Sulfide. I hope that's stable is the right word but in any case it didn't drop any visible silver from the solution. I have reused some of this solution five times so far with no visible or performance change.
I don't know if this helps but I thought I would share what I've experienced incase it does.
I can post a PDF of the Fix MSDS (there is a part A &B) from AGFA if you think it's of value.

All the Best,
John

 

[Geo]

John, any information would be useful, if not to me personally, then maybe the next person trying this.