Palladium precipitation with ascorbic acid - preferable conditions ?

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orvi

Well-known member
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Joined
Apr 13, 2021
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Hi
as I am currently in the state of exploring new possibilities to refine various feeds, I started to think about implementation of ascorbic acid to my general refining procedures - as it is somewhat different reducing agent than metals/SO2 or formic acid.
I have some experience with ascorbic acid Pd precipitations from nitrate solutions, but this was in my beginnings, and I didn´t measured things like pH or ammounts precisely... So not much meaningful memories :)

From what I read in various articles issuing ascorbic acid reduction, there is written that Pd will drop even from acidic solutions, like 0,5M HNO3 (one article about nuclear waste treatment). Does this stand, or it is just another BS "wow" article ?

My intention will also be to apply it to the chloride media palladium feeds. But there I found not too much info regarding any favourable conditions, pH control or anything in general. From my theoretical sight/background, coordination of Pd into tetrachloro complex anion will result in lowering it´s oxidation potential - thus making it harder to reduce.

Why I want to explore more routes:
Many times, I work with awfully contamined feeds containing up to 10 elements inside. pH adjustment is very difficult, since a lot of various compounds drastically lower the solubility and they precipitate as various hydroxides, or even compounds upon slight pH rise, and are very difficult to filter/retain values in the filter cake viciously.
So classic formate reduction is great pain to do, as you need to firstly adjust pH to say 2, then filter that formed goo (which took ages), then add formic, adjust pH second time... And pray no more junk will come out :D
On the other side, I want to slowly minimize DMG use - as I know there are better practices, tho beating the selectivity and simplicity of DMG would be very hard.
I also considered something like formaldehyde, as it has very low molar weight and it is also fairly strong reducing agent. But also, not much information regarding formaldehyde as reducer also. Cheap tho :)

Ascorbic acid is attractive possibility - even knowing the fact that it will drag copper (Cu2O/Cu) to the precipitate (this is still possible to wash out with ammonia/peroxide). Unlike hydrazine, non-toxic, easily accessible, OTC...
So I want to firstly ask here, if anyone done palladium with ascorbic acid and is willing to share his experiences on some specifications about conditions, pH management, temperature of the drop - maybe favourable conditions how to not reduce copper to metal, but only Cu2O etc... I searched the forum before and only found some hints.

Thanks for the responses
orvi
 
orvi said:
Hi
as I am currently in the state of exploring new possibilities to refine various feeds, I started to think about implementation of ascorbic acid to my general refining procedures - as it is somewhat different reducing agent than metals/SO2 or formic acid.
I have some experience with ascorbic acid Pd precipitations from nitrate solutions, but this was in my beginnings, and I didn´t measured things like pH or ammounts precisely... So not much meaningful memories :)

From what I read in various articles issuing ascorbic acid reduction, there is written that Pd will drop even from acidic solutions, like 0,5M HNO3 (one article about nuclear waste treatment). Does this stand, or it is just another BS "wow" article ?

My intention will also be to apply it to the chloride media palladium feeds. But there I found not too much info regarding any favourable conditions, pH control or anything in general. From my theoretical sight/background, coordination of Pd into tetrachloro complex anion will result in lowering it´s oxidation potential - thus making it harder to reduce.

Why I want to explore more routes:
Many times, I work with awfully contamined feeds containing up to 10 elements inside. pH adjustment is very difficult, since a lot of various compounds drastically lower the solubility and they precipitate as various hydroxides, or even compounds upon slight pH rise, and are very difficult to filter/retain values in the filter cake viciously.
So classic formate reduction is great pain to do, as you need to firstly adjust pH to say 2, then filter that formed goo (which took ages), then add formic, adjust pH second time... And pray no more junk will come out :D
On the other side, I want to slowly minimize DMG use - as I know there are better practices, tho beating the selectivity and simplicity of DMG would be very hard.
I also considered something like formaldehyde, as it has very low molar weight and it is also fairly strong reducing agent. But also, not much information regarding formaldehyde as reducer also. Cheap tho :)

Ascorbic acid is attractive possibility - even knowing the fact that it will drag copper (Cu2O/Cu) to the precipitate (this is still possible to wash out with ammonia/peroxide). Unlike hydrazine, non-toxic, easily accessible, OTC...
So I want to firstly ask here, if anyone done palladium with ascorbic acid and is willing to share his experiences on some specifications about conditions, pH management, temperature of the drop - maybe favourable conditions how to not reduce copper to metal, but only Cu2O etc... I searched the forum before and only found some hints.

Thanks for the responses
orvi
Click to expand...
If you google nano palladium and ascorbic you may find articles dealing with the subject. My experience, not about nano, is that only partial precipitation occurs
 
I know ascorbic will co precipitate Pd from gold solutions if present but not sure if it will precipitate Pd completely , if you only have Pd values in the solution why not cement with copper.
 
nickvc said:
I know ascorbic will co precipitate Pd from gold solutions if present but not sure if it will precipitate Pd completely , if you only have Pd values in the solution why not cement with copper.
Click to expand...
I had small batch of AgPd20 alloy, so I dissolved around 5g of it in nitric, eliminate silver by silver chloride, collected Pd mother liquor+HCL washes and proceeded with ascorbic acid treatment.

From my observation, in highly acidic pH (around zero and less), nothing happens whatsoever. But slight pH raise to pH around 1-2 resulted in rapid precipitation and formation of very fine suspension of Pd particles. Solution was still quite hot from NaOH neutralization of free acid (solid NaOH was added till first precipitate of Pd hydroxide appeared, then it was cleared by addition of small ammount of HCL) tho.

Upon stirring, precipitate nicely clump together (it took around 10-15 minutes), and is easily decantable.

So, overall, from chloride media, it appears only advantage over formate would be the speed of reduction - dramatic reduction of reaction time. Disadvantage would be copper co-precipitation.

Nevertheless, few of my procedures of Pd feeds refining result in relatively pure palladium solution in the end, so this reduction technique could be cleverly implemented to cut down the procedure time. Considering that ascorbic could be purchased below 8 euros/kg here... Nice to know :)
 
eaglekeeper said:
Did you get a complete reduction... was there any Pd that stayed behind in solution.
Click to expand...
No Pd colouration, stannous negative. Maybe some tidbits were in solution, but I didn´t have prepared DMG testing solution in hand to see.

But confidently saying 95+% was out. In the future run, I will add DMG after Pd cement collection - to see how it was done. There was 1,25g of Pd in ca 300-400 mL. Resulting solution was clear and colourless. With imagination on maybe slighetest yellowish tinge. Assuming this was discolouration from ascorbic residues.
 
Awesome.. thanks

What was your source of ascorbic acid.... Just a standard powder off Amazon. I might give that a go the next time I do a catalytic converter instead cementing with zinc.

Maybe that would be cheaper than buying pure zinc, plus a little less metal in waste solutions to deal with.
 
orvi said:
Hi
as I am currently in the state of exploring new possibilities to refine various feeds, I started to think about implementation of ascorbic acid to my general refining procedures - as it is somewhat different reducing agent than metals/SO2 or formic acid.
I have some experience with ascorbic acid Pd precipitations from nitrate solutions, but this was in my beginnings, and I didn´t measured things like pH or ammounts precisely... So not much meaningful memories :)

From what I read in various articles issuing ascorbic acid reduction, there is written that Pd will drop even from acidic solutions, like 0,5M HNO3 (one article about nuclear waste treatment). Does this stand, or it is just another BS "wow" article ?

My intention will also be to apply it to the chloride media palladium feeds. But there I found not too much info regarding any favourable conditions, pH control or anything in general. From my theoretical sight/background, coordination of Pd into tetrachloro complex anion will result in lowering it´s oxidation potential - thus making it harder to reduce.

Why I want to explore more routes:
Many times, I work with awfully contamined feeds containing up to 10 elements inside. pH adjustment is very difficult, since a lot of various compounds drastically lower the solubility and they precipitate as various hydroxides, or even compounds upon slight pH rise, and are very difficult to filter/retain values in the filter cake viciously.
So classic formate reduction is great pain to do, as you need to firstly adjust pH to say 2, then filter that formed goo (which took ages), then add formic, adjust pH second time... And pray no more junk will come out :D
On the other side, I want to slowly minimize DMG use - as I know there are better practices, tho beating the selectivity and simplicity of DMG would be very hard.
I also considered something like formaldehyde, as it has very low molar weight and it is also fairly strong reducing agent. But also, not much information regarding formaldehyde as reducer also. Cheap tho :)

Ascorbic acid is attractive possibility - even knowing the fact that it will drag copper (Cu2O/Cu) to the precipitate (this is still possible to wash out with ammonia/peroxide). Unlike hydrazine, non-toxic, easily accessible, OTC...
So I want to firstly ask here, if anyone done palladium with ascorbic acid and is willing to share his experiences on some specifications about conditions, pH management, temperature of the drop - maybe favourable conditions how to not reduce copper to metal, but only Cu2O etc... I searched the forum before and only found some hints.

Thanks for the responses
orvi
Click to expand...
 
orvi said:
Hi
as I am currently in the state of exploring new possibilities to refine various feeds, I started to think about implementation of ascorbic acid to my general refining procedures - as it is somewhat different reducing agent than metals/SO2 or formic acid.
I have some experience with ascorbic acid Pd precipitations from nitrate solutions, but this was in my beginnings, and I didn´t measured things like pH or ammounts precisely... So not much meaningful memories :)

From what I read in various articles issuing ascorbic acid reduction, there is written that Pd will drop even from acidic solutions, like 0,5M HNO3 (one article about nuclear waste treatment). Does this stand, or it is just another BS "wow" article ?

My intention will also be to apply it to the chloride media palladium feeds. But there I found not too much info regarding any favourable conditions, pH control or anything in general. From my theoretical sight/background, coordination of Pd into tetrachloro complex anion will result in lowering it´s oxidation potential - thus making it harder to reduce.

Why I want to explore more routes:
Many times, I work with awfully contamined feeds containing up to 10 elements inside. pH adjustment is very difficult, since a lot of various compounds drastically lower the solubility and they precipitate as various hydroxides, or even compounds upon slight pH rise, and are very difficult to filter/retain values in the filter cake viciously.
So classic formate reduction is great pain to do, as you need to firstly adjust pH to say 2, then filter that formed goo (which took ages), then add formic, adjust pH second time... And pray no more junk will come out :D
On the other side, I want to slowly minimize DMG use - as I know there are better practices, tho beating the selectivity and simplicity of DMG would be very hard.
I also considered something like formaldehyde, as it has very low molar weight and it is also fairly strong reducing agent. But also, not much information regarding formaldehyde as reducer also. Cheap tho :)

Ascorbic acid is attractive possibility - even knowing the fact that it will drag copper (Cu2O/Cu) to the precipitate (this is still possible to wash out with ammonia/peroxide). Unlike hydrazine, non-toxic, easily accessible, OTC...
So I want to firstly ask here, if anyone done palladium with ascorbic acid and is willing to share his experiences on some specifications about conditions, pH management, temperature of the drop - maybe favourable conditions how to not reduce copper to metal, but only Cu2O etc... I searched the forum before and only found some hints.

Thanks for the responses
orvi
Click to expand...
How to pronounce pd with ascorbic acid from ar and nitric acid? I tried but it didn't work.
 
ólom said:
Sorry! How can palladium be precipitated with ascorbic acid? I tried but it didn't work.
Click to expand...
You can do this, but you will need to adjust the pH. Ascorbic for Pd does not work in very acidic conditions. If you have de-noxed AR solution, pH of 1,5 is relatively OK for drop (with heating). Without de-noxing, you will need to go much higher with pH, and it will cause other metals to also reduce, like copper, bismuth etc.

Ascorbic is not the best for selective drop of Pd, however it does great job if you need to just convert Pd liquid to the metal - it does not add any metal ions, it just reduce the palladium. It can be done in matter of minutes. With formate reduction it can take hours of boiling.
 
orvi said:
You can do this, but you will need to adjust the pH. Ascorbic for Pd does not work in very acidic conditions. If you have de-noxed AR solution, pH of 1,5 is relatively OK for drop (with heating). Without de-noxing, you will need to go much higher with pH, and it will cause other metals to also reduce, like copper, bismuth etc.

Ascorbic is not the best for selective drop of Pd, however it does great job if you need to just convert Pd liquid to the metal - it does not add any metal ions, it just reduce the palladium. It can be done in matter of minutes. With formate reduction it can take hours of boiling.
Click to expand...
Nice to hear, can you elaborate a bit?
It seem like a good tool for the tool box😊
 

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