CP, TC Chemicals

[overdriv]

HI again. Here is the question. I have tried the technique of precipitating the gold with oxcalic acid. I am not sure, so please correct me if I am wrong but the procedure asks for CP oxcalic acid. I just bought TC oxcalic acid which it says on the bag is 32%.

Question 1
If a refining recipe calls for CP acid and I have TC what should I do?

Question 2
Do I have to use 3 times the amount of oxcalic acid because CP Oxcalic acid is 90% pure?????

I have been messing around with the stuff for a day now. I keep adding more oxcalic and the gold does not drop... So being the angry newbie that I am........ I threw a whole bunch of the $^*^&(()( stuff in to the AR with out even diluting it... lol That was when I saw the familiar brown fumes (yahoo), which told me I had not even added enough oxcalic acid to kill the nitric acid. Then I just boiled the &^R$^*((( out of the stuff and started to see some gold precipitate. I came back home to watch the World Series.

I am going back to the office and check on it tonight. I will post later.


Coool. I went to the office for the last 3 hours and this is what happened.

When I got there the liquid had cooled down and was a light yellow. There were lots of white crystals from the excess oxcalic acid that I put in. But (yahoo) there was a nice pile of brown stuff at the bottom. So, heated the whole thing up and tested the solution with staneous (sp) solution. UGH. There was still gold in solution. I added at least 1/3 more water a pinch of ammonia and boiled about an hour more. The solution went from a light yellow to a golden color and tested clean for gold in solution...
I will check it in the morning.

 

[Harold_V]

"A pinch of ammonia"?
Be very careful about adding ammonia to solutions of gold and silver. You may be inviting an explosion.

Harold

 

[Lou]

You need to remove all nitrogen oxides present in your solution before using oxalic acid. Also, remember that most oxalic acid is the dihydrate, so account for the extra two moles of water in your calculations as appropriate. Also, your solution must be quite hot (near boiling) for it to work effectively.


Lou

 

[overdriv]

Be very careful about adding ammonia to solutions of gold and silver. You may be inviting an explosion.

Harold

That is what Hoke suggests so I did so. I it seemed to work without the ammonia but I was not sure so I added it. Thank you for your warning. I will do more research on this and find out if others use the ammonia as well.

I hope others appreciate your wisdom.


Nick

 

[overdriv]

You need to remove all nitrogen oxides present in your solution before using oxalic acid. Lou

That is done by boiling the liquid or not adding too much nitric acid to begin with. Right?

I used Harold's method, which I found superior, by adding the nitric acid last and looking for the NO2 to stop. Adding the button and weighing before and after.

But I must have left some in the solution because I did get some brown fumes.


I will melt down today.

Also, remember that most oxalic acid is the dihydrate, so account for the extra two moles of water in your calculations as appropriate. Also, your solution must be quite hot (near boiling) for it to work effectively.
Lou

Lou, Here is where I admit my ignorance. What is a mole? My cats caught a few of them in the garden this summer.. Ugly looking things. LOL

The supplier I talked to this morning says he sold me CP, but I think I saw 32% on the bag.. The bag I bought from him was a 50Lb bag and I put it in a huge black plastic bag that I could close so that the air and moisture could not get to the oxcalic acid. It is dark where I store the chemicals so I will have to go in with a flashlight and look at it this morning to verify.

You are right in that it was in powder/crystalized form. So does that mean I have to use three times as much when the recipe calls for 1 liquid oz of oxcalic acid, I will need three oz of dry oxcalic acid and (x) number of (little) moles of water. (How much water can those little buggers hold.)

Hey Lou.

I tried to Thank you for all of your input and help. I do not think my PM got through to you. I sent pics too.

 

[butcher]

Mole's not the ones eating up your garden are very useful in figuring out how much you need or how much you have. they come from molecular weight.
spending some time learning about these moles is very helpful when working with chemicals or equation's.
http://www.google.com/#sclient=psy&hl=en&site=&source=hp&q=calculating+molarity+of+a+solution&aq=1&aqi=g10&aql=&oq=calculating+molarity&gs_rfai=ChSFN3_TQTK_0AYa8igOw_MzqAwAAAKoEBU_Q33oA&fp=8e8f35a77978fbf6

 

[Harold_V]

I used Harold's method, which I found superior, by adding the nitric acid last and looking for the NO2 to stop. Adding the button and weighing before and after.

But I must have left some in the solution because I did get some brown fumes.

When you use this method, it requires that you have an excess of HCl, so any nitric that remains will consume some of the added gold. Considering excess HCl does no harm, it was my practice to add a few ounces to a large volume. For a small lot, an ounce is likely to be sufficient. Add some and allow the evaporation to take place, keeping watch on the added gold button. It will be obvious if it is being dissolved, or not (bubbles emanate from the surface). When bubbling stops, add a small amount of HCl once again. If there is no further bubbling, nitric has likely been consumed.

Do all of this heated, otherwise the reaction will be so slow that you may not detect the true status of the lot.

When making AR, I always recommend a ratio of 4:1. Again, an excess of HCl isn't troublesome, unlike an excess of nitric.

Harold

 

[Lou]

A little free nitric acid won't hurt, especially if you've followed Harold's sage advice about adding only as much nitric as possible. I usually add about 75% of what I think I'll need aqua-regia wise, then add an excess of HCl and add nitric in small 100 mL additions (for a large lot) until cessation of fumes. I dissolve gold while the solution is hot, about 80C, then cool it before diluting and filtering to remove any AgCl.


If the "recipe" (I hate that term :/) calls for an ounce of liquid oxalic acid, I suggest getting a new cookbook!

I gutted these from wikipedia:

Molecular formula C2H2O4
Molar mass 90.03 g mol−1 (this is for anhydrous, for the dihydrate, add 36.5 g*mol-1 to get 126.53 g/mol)
Appearance white crystals
Density 1.90 g/cm³ (anhydrous)
1.653 g/cm³ (dihydrate)
Melting point 101-102°C (dihydrate)
Solubility in water
9.5 g/100 mL (15 °C)
14.3 g /100 mL (25 °C?)
120 g/100 mL (100 °C)

You almost certainly have the dihydrate, as anhydrous stuff is very rarely used (has to be dried with CCl4 otherwise it sublimates). Oxalic works over a pH range, going as low as 1.5 if the anion in solution be mostly sulfate.

Anyway, use from 1.1-2.6 X times the molar quantity of gold in solution. A ratio of 1.5-1.8 seems best for higher purity, anymore and side reaction reduction is possible.

This is an easy way to think! Take however many grams of fine gold you are expecting and divide it by its molar atomic weight, 196.97 g/mol, this will give you moles of gold you're expecting. Take that number and multiply it by 1.5 and that's how many moles of oxalic acid dihydrate you'll need. To get grams, simply multiply moles by grams/mole and voila! that's how much oxalic you need.

So, hypothetically let's presume you're expecting 500 g of fine gold.

That is 500 g/196.97 g*mol-1 =2.54 mol of Au. We need 2.54 mol Au * 1.5 molar excess of oxalic acid dihydrate = 3.81 moles of oxalic acid, which is 3.81 * 126.53 g/mol =482 g required to quantitatively reduce it. So weight wise, you can see they're about 1:0.96 (that is for every 10 g Au you want 9.6 g of you oxalic acid dihydrate).

That reduction should take no longer than 3 h, and quicker if you add in ammonia and start from pH of ~2.

Done right, oxalic acid will give 4N+ gold first drop. See my post on ultra high purity gold at the top of the techniques section.

Harold, keep ammonia from gold and silver solutions only if the pH is above neutral; the unstable nitrides only form at higher pH values.

Lou

 

[overdriv]

Thank you Lou. I have read this several times now and am getting the gist of it and will try it out tomorrow.

Nick

 

[Harold_V]

Harold, keep ammonia from gold and silver solutions only if the pH is above neutral; the unstable nitrides only form at higher pH values.

Lou

Thanks, Lou. That is information I didn't have at my disposal. Now to file it mentally for future reference!

Harold

 

[butcher]

Many members are new and may not even know what PH means, some do not do their homework and barely understand processes they try, (they seem to get too exited to get valuable metals) some just read enough to get themselves into trouble, they may not know a low PH means an acid, and high PH is caustic or basic, or have an understanding of the risks involved with these metals,

It is a good idea to keep ”ammonia” (ammonium hydroxide) out of most any recipe.
(Only using “ammonia” solutions after understanding the chemistry involved, and following really good “cookbook” written by a knowledgeable source). (I have seen some very dangerous things written on the web by half-informed people).

Ammonium hydroxide solutions and metals can form shock or temperature sensitive compounds, which can explode when, dried; they should be acidified for safety if you do use them.

Hopefully someone who is better at explaining these concerns can help our new members understand these dangers.

 

[Oz]

Butcher, You have said all that I wanted to. I have seen several threads recently that talk about ammonium or ammonia that gave me the willies. I held my tongue watching what followed.

I am between a rock and a hard place in saying what should be shared/advised as I have learned great things when experienced members share openly. Yet at the same time I fear the new person on here that is fearless in experimentation. I also have a certain aversion to things that go boom (especially unexpectedly), from personal experience.

Sad as it is, we must post things from the viewpoint that someone asking a question could be a kid or an adult with no clue.

I do think the OP is trying to be careful, please do not misunderstand my commentary.

 

[HAuCl4]

Hoke advises 1:1 weight of oxalic to expected fine gold. Lou kindly showed the exact calc to be around that.
Then Hoke advises to prepare ammonium oxalate in slightly acidic solution, before mixing in with the gold chloride.

Beating a dead horse to death again: READ HOKE!!.

I believe excess ammonia into gold chloride gives a precipitate that is explosive, even when wet!.

Some people can make explosives faster than cook cakes... With almost the same ingredients!. Be careful what you make unadvertently!

Edit to add: Buying and using ammonium oxalate directly (and re-crystalizing it) instead of acid is an option too for UHP gold enthusiasts.

 

[slouma37]

Hi all,
I'm righting here about the use of ammonia, is it dangerous ? or safe ?
Well, for me the answer is evident, because when we added BDG to our gold solution (even with the presence of Nitric), we just picked up the HAuCl4 from our A.R diluted 3 times, then we washed our DBG 3 times with HCl (1/20) , so where are the nitric anions ? ...They stayed in the A.R diluted and ripped out from its gold-chlorides by the DBG.

I hope this is logic and will work safe ...

Regards

 

[butcher]

slouma37, Hello, I am not sure I can help here, that is a process I have never tried, how long have you been refining? Some types of chemicals can precipitate gold with nitric in solution, and I know very little about BDG, but it could be one of them( I have only read about it and can not recall details), from memory I think it is an organic like carbon, and gold may be able to complex with it (?like a binder?) leaving nitric in solution. or ???

some members have used it and understand it, ( I do not), they can help with this question.

Using any combinations of chemicals can be very dangerous if you are not sure what your mixing or how they will react, even then sometimes they may not react as the scientist expects them to, ammonia and metals can be dangerous as we discussed in the posts above this one, be very careful with its use, if you are not sure do not have ammonia in your lab.

there are only a few places most of us on the forum would suggest someone use it, and then in controlled ways, with steps to make the solution you made safe before drying.
and we will usually tell you to use an acid wash to make them safe.
but you must understand a process and not just try things blindly (which could blind you)
the primers in guns can be made from these ammonium salts, but some can be so reactive that a just drying or a feather touching them would set them off violently, so study, know how these chemical reactions work before you do them, understand the safety precautions to take.

I hope you get what I am trying to say. It seems we may speak differing languages, just be careful.

 

[Geo]

Ive been concentrating the metals from my gold precipitation. sometimes it test yellow and others its very orange. Ive been cementing with copper and making filter cakes of the solids. should i use ammonium hydroxide to dissolve the PD first and filter or should i dissolve in hot AR first to precipitate PT and filter. i havent really gotten to the point of actually trying this process but a point in the right direction will get me started.

 

[freechemist]

As a first thing to say: Please don't post abbreviations like "BDG" and others. Instead post full names and/or designations, so that we, the readers, understand what you exactly mean, and that you really understand, what you are dealing with - and we, for an answer, probably should be dealing with, too.
As far, as I can understand "BDG" stands for "butyl-diglyme" (also an abbreviation or a short name), an organic solvent, which often is used to extract gold from acid solutions selectively, leaving base metals and other precious metals (if present) back in the aqueous layer. The organic "butyl-diglyme"-layer, contains the gold, dissolved as an ion-pair, formally resulting from the reaction of H2O (water) with HAuCl4 (tetrachloro-auric acid):
HAuCl4 + H2O => [H3O(+)][AuCl4(-)].
This organic layer can be washed with diluted hydrochloric acid, to remove remnants of base metals and other precious metals.
Reaction of gold, dissolved in hydrochloric acid (or aqua regia), with aqueous ammonia, leads to explosive compounds, so called fulminating gold. This reaction does not involve nitric acid. It occurs the same with gold solutions obtained by dissolution of gold in hydrochloric acid by oxidation with different oxidants, e.g. chlorine or sodium chlorate.

freechemist