I have been trying to find out more about this thiosulfate leach, have not found very much useful information on it yet.
but it seems the ammonia and copper can act as a catalyst in the reaction, in correct proportions will form some type of copper amine catalyst Cu(NH3)3, (helping to promote the chemical reaction of the leach but not being chemically part of it).
Problem if too much copper it will spoil the leach, as copper will also form a complex with thiosulfate, Cu(S2O3)3. Too much added copper tends to precipitate as cupric sulfide.
Too much or lack of ammonia in solution is important to leach, as the copper forms Cu(NH3)3 with copper.
Cupric Ion is what acts as oxidizer in leach.
With the oxygen (bubbled air) is what regenerates the(cupric) Cu 2+ ion, and when doing this leaves S2O3 thiosulfate to complex with gold.
Oxidative degradation of thiosulfate to polythionates and sulfates is accelerated markedly in the presence of excess copper ions and/or ammonia. The oxidative degradation reactions are slowed considerably at elevated oxygen partial pressure in the absence or near-absence of copper and ammonia.
If copper or ammonia in solution is not in proper proportions it seems the chemistry may not work well at leaching gold.
(and I assume may just carry base metals like iron in solution my guess here)
Too much copper seems to also lead to Oxidative degradation of thiosulfate to polythionates and sulfates is accelerated markedly in the presence of excess copper ions and/or ammonia in leach, too little ammonia will not form copper catalyst needed,
(which I believe would not form insoluble iron hydroxides, and this may just leave iron in solution)
Lead oxide will also form a complex PbO(S2O3)2 no mention of conditions needed,
Minerals of gold like chalcopyrite , and pyrite can be leached, from what I understand is chalcopyrite will break down easily in this leach.
but the pyrite crystals do not release the contained gold and seem to only soften,these hard pyrite crystals do not decompose much in thiosulfate leach, thus preventing leach from getting gold from them, although the free gold will leach easily (if conditions are maintained favorable condition in this leach.
(which seems to me would be like trying to juggle a basket full of rotten tomatoes while standing on your head)
the pyrite may hold considerable portion of gold locked up in its crystal bond,besides free gold this cold be a major portion of your gold in these pyrite bonds, and should be DECOMPOSED (broken down before leaching) to me this means to roast ore PRETREATMENT and break sulfide pyrite bond with gold.
if ammonia and copper is maintained in proper proportions : copper ions are a key factor to this leach along with ammonia, too much or too little of either and leach will not work properly,
Copper will be in solution as a copper amine (unless too much copper or not enough ammonia) too much copper, or too little ammonia copper sulfide forms,
Ammonia is important to keep leach balanced (copper in solution)
Ammonia is also very important to Iron (a major portion of most ore)
As the ammonia changes iron to Fe(NH3)3
Then Fe(NH3)3 + OH- --> Fe(OH)3
Fe(OH)3 is what that the (red powder in photo) looks like to me iron hydroxide.
(I believe but cannot find anything to prove this yet:
That if leach was not run properly Iron would NOT precipitate iron as Iron hydroxide, and would possibly be in solution (pH improper or too much ammonia in solution or possible lack of ammonia,) , (copper may be replaced by iron in solution if lack of ammonia), this is a guess here on my part).
During leaching ferric oxide, Iron hydroxide and elemental sulfur will be in solids and copper in solution acting as oxidizer (oxygen rejuvenating the cupric Ion) and gold will be left with the thiosulfate IF this leach is working and IF all conditions are maintained in solution, (< 9 pH, and temperature also seem to be factors).
Gold with free thiosulfate:
4Au + 8S2O3 --> 4Au(S2O3)2
This seems to me would be a very difficult leach to maintain in proper working order.
And my study of this so far reaffirms my belief the red powder in picture is iron, with possibly some gold (or your gold may have never been leached out) (but I have been wrong many times before).
Testing on what you have should be done to determine what happened and what is where.
Do tests for iron and gold.
without testing all of us just shooting in the dark trying to guess what is going on.
when some simple tests will tell you for sure.
Now you had another solution you mentioned leaching gold plated copper pins, and stated you also had a red (or orange I cannot remember )colored powder you thought was copper. I really was not concerned with this powder or solution, but only if you dissolved the copper and then reduced it back to metal would it give a red-brown color, otherwise I would expect Green, blue or white copper powders.
I would not use thiosulfate leach for gold plated copper pins, if you do not see why re-read the above statements.
(If leaching gold with this thiosulfate leach, and maintaining leach in favorable conditions was like trying to juggle a basket full of rotten tomatoes while standing on your head, then trying to leaching gold from copper metal pins may just upset your balance and you can make something similar to Cambells toe mater soup).
This seems that it would be a fast and effective leach but almost impossible to get it, and keep it working properly, without closely monitoring pH, ammonia, cupric ions. Copper sulfide, sulfur, and iron hydroxide, or at least monitor some of these in solution to be able to keep conditions working in this leach.
some of you Guy's are saying this is an acid leach? (I keep reading it is maintained less than pH 9), (pH 7 is neutral), (above pH 7 is caustic or alkaline), (and some have been talking alkaline), the leach works with ammonia in solution (an alkaline solution), (granted < pH 9 could be acidic if it was way below pH 9,(actually below pH7), but then you could not keep the ammonia or the amines in solution) so one of us has this wrong.
what is it alkaline or acid? (looks alkaline to me), (but then again I have no expierience useing this leaching process).
my two red cents
but it seems the ammonia and copper can act as a catalyst in the reaction, in correct proportions will form some type of copper amine catalyst Cu(NH3)3, (helping to promote the chemical reaction of the leach but not being chemically part of it).
Problem if too much copper it will spoil the leach, as copper will also form a complex with thiosulfate, Cu(S2O3)3. Too much added copper tends to precipitate as cupric sulfide.
Too much or lack of ammonia in solution is important to leach, as the copper forms Cu(NH3)3 with copper.
Cupric Ion is what acts as oxidizer in leach.
With the oxygen (bubbled air) is what regenerates the(cupric) Cu 2+ ion, and when doing this leaves S2O3 thiosulfate to complex with gold.
Oxidative degradation of thiosulfate to polythionates and sulfates is accelerated markedly in the presence of excess copper ions and/or ammonia. The oxidative degradation reactions are slowed considerably at elevated oxygen partial pressure in the absence or near-absence of copper and ammonia.
If copper or ammonia in solution is not in proper proportions it seems the chemistry may not work well at leaching gold.
(and I assume may just carry base metals like iron in solution my guess here)
Too much copper seems to also lead to Oxidative degradation of thiosulfate to polythionates and sulfates is accelerated markedly in the presence of excess copper ions and/or ammonia in leach, too little ammonia will not form copper catalyst needed,
(which I believe would not form insoluble iron hydroxides, and this may just leave iron in solution)
Lead oxide will also form a complex PbO(S2O3)2 no mention of conditions needed,
Minerals of gold like chalcopyrite , and pyrite can be leached, from what I understand is chalcopyrite will break down easily in this leach.
but the pyrite crystals do not release the contained gold and seem to only soften,these hard pyrite crystals do not decompose much in thiosulfate leach, thus preventing leach from getting gold from them, although the free gold will leach easily (if conditions are maintained favorable condition in this leach.
(which seems to me would be like trying to juggle a basket full of rotten tomatoes while standing on your head)
the pyrite may hold considerable portion of gold locked up in its crystal bond,besides free gold this cold be a major portion of your gold in these pyrite bonds, and should be DECOMPOSED (broken down before leaching) to me this means to roast ore PRETREATMENT and break sulfide pyrite bond with gold.
if ammonia and copper is maintained in proper proportions : copper ions are a key factor to this leach along with ammonia, too much or too little of either and leach will not work properly,
Copper will be in solution as a copper amine (unless too much copper or not enough ammonia) too much copper, or too little ammonia copper sulfide forms,
Ammonia is important to keep leach balanced (copper in solution)
Ammonia is also very important to Iron (a major portion of most ore)
As the ammonia changes iron to Fe(NH3)3
Then Fe(NH3)3 + OH- --> Fe(OH)3
Fe(OH)3 is what that the (red powder in photo) looks like to me iron hydroxide.
(I believe but cannot find anything to prove this yet:
That if leach was not run properly Iron would NOT precipitate iron as Iron hydroxide, and would possibly be in solution (pH improper or too much ammonia in solution or possible lack of ammonia,) , (copper may be replaced by iron in solution if lack of ammonia), this is a guess here on my part).
During leaching ferric oxide, Iron hydroxide and elemental sulfur will be in solids and copper in solution acting as oxidizer (oxygen rejuvenating the cupric Ion) and gold will be left with the thiosulfate IF this leach is working and IF all conditions are maintained in solution, (< 9 pH, and temperature also seem to be factors).
Gold with free thiosulfate:
4Au + 8S2O3 --> 4Au(S2O3)2
This seems to me would be a very difficult leach to maintain in proper working order.
And my study of this so far reaffirms my belief the red powder in picture is iron, with possibly some gold (or your gold may have never been leached out) (but I have been wrong many times before).
Testing on what you have should be done to determine what happened and what is where.
Do tests for iron and gold.
without testing all of us just shooting in the dark trying to guess what is going on.
when some simple tests will tell you for sure.
Now you had another solution you mentioned leaching gold plated copper pins, and stated you also had a red (or orange I cannot remember )colored powder you thought was copper. I really was not concerned with this powder or solution, but only if you dissolved the copper and then reduced it back to metal would it give a red-brown color, otherwise I would expect Green, blue or white copper powders.
I would not use thiosulfate leach for gold plated copper pins, if you do not see why re-read the above statements.
(If leaching gold with this thiosulfate leach, and maintaining leach in favorable conditions was like trying to juggle a basket full of rotten tomatoes while standing on your head, then trying to leaching gold from copper metal pins may just upset your balance and you can make something similar to Cambells toe mater soup).
This seems that it would be a fast and effective leach but almost impossible to get it, and keep it working properly, without closely monitoring pH, ammonia, cupric ions. Copper sulfide, sulfur, and iron hydroxide, or at least monitor some of these in solution to be able to keep conditions working in this leach.
some of you Guy's are saying this is an acid leach? (I keep reading it is maintained less than pH 9), (pH 7 is neutral), (above pH 7 is caustic or alkaline), (and some have been talking alkaline), the leach works with ammonia in solution (an alkaline solution), (granted < pH 9 could be acidic if it was way below pH 9,(actually below pH7), but then you could not keep the ammonia or the amines in solution) so one of us has this wrong.
what is it alkaline or acid? (looks alkaline to me), (but then again I have no expierience useing this leaching process).
my two red cents
Dr. Poe
