How to recover the solved gold in the AR completely

[majidmadadi]

hi everybody. It is my first question since i gathered the forum. i read several things about gold refining including Hoke's the great. i also did several tests including PCB scraps and karat gold up to 2 kilograms. about PCB scraps there is no question. but when i am working with karat gold i never can recover the gold completely. by my last test of 20.13 gr of 750 karat gold i did the followings:
1. solving the gold in the aqua regia solution for 3 hours with continuous agitation and staying over night
2. filtering the solution and removing silver chloride and other residues
3. adding saturated NaOH solution to the aqua regia with continuous agitation until the pH of about 3
4. add 20 gr of SMB to the resulted solution with continuous agitation and staying for about 2 hours more
5. removing the gold powder and rinsing with water several times and drying
6. rinsing and investigating the silver chloride for unsolved gold
7. treat the silver chloride with NaOH solution and zinc powder
8. melting both gold (which was 14.96 gr) and silver (which was 2.01 gr) powder
9. sending to analysis and assaying
the result was: for gold sample: 999
for silver sample: Ag 976
Pd 14
Au 5
other 5
as i expected the the resulting gold must be 15.097 or so much near to it. but as the result shows here there is about 0.13 gr of loss and in bigger cases it can bring about difficulties. i hope somebody could help me about the subject. stannous chloride test shows no remaining gold in the solution and i promise that all the aforementioned items did in clear, clean, complete and without wastes manner.

 

[butcher]

Ma jid Mad Dady , I cant even figure yer name, since this is your first post I would like to welcome you to the forum, I'm not sure I am able to help you here or not? but if I were you I would go back and read through Hoke again, it will be like a movie you will see the things you missed the first time, some of your discription of the way you process is a little strange to me, you seem to have taken step's I would not, and missed steps I would have included, also I would start studying Harold's posts on the forum you will learn a world of information from them, after some study things will get much simpler and clearer Heck Harold can teach a monkey to refine gold to High purity and even recover small traces the Monkey left behind.

again welcome

 

[nickvc]

The answer to your problem may be in the material you started with,if the material was below assay or had dirt or stones in it thats your answer,try melting and assaying your starting material then refining the bar and see if you are losing gold.The advice to follow Harold V is sound he is certainly a master of his art.

 

[Irons]

Don't rely on the Karat mark on the jewelry, much of it will be less than what is marked. Based on your recovery and the fact that the test for gold was negative, I would guess that you recovered all the Gold that was actually there.

 

[goldsilverpro]

majidmadadi,

Aren't you basing everything on the assumption that the gold is exactly 18K to start with? How do you know that to be true? If I follow you correctly, based on your yield, I calculate the gold to have been 17.83K. That to me, seems very possible. I can't ever remember seeing gold overkarated and rarely have seen gold perfectly karated. It's almost always at least a little underkarated.

i promise that all the aforementioned items did in clear, clean, complete and without wastes manner.

I find that impossible to believe. When processing such a small amount of gold, you can easily have significant traces scattered here and there - filters, crucible, dissolving effervescence, etc. Assuming the gold was exactly 18K plumb to start with, this is where all the losses are, no matter how perfectly you think you avoided any wastes. In my experience, it is impossible to 100% avoid small losses. 0.13 grams is a very small amount. When you run larger amounts, the percent of loss should be less. Actually, most of these so-called losses can be recovered eventually.

From the numbers you gave, I think you did an excellent job.

 

[Irons]

majidmadadi,

What was the porosity of the filter paper you used, and how long did you allow the precipitated Gold to settle before you filtered it?

 

[majidmadadi]

Ma jid Mad Dady , I cant even figure yer name, since this is your first post I would like to welcome you to the forum, I'm not sure I am able to help you here or not?again welcome

My name is just Majid, my family is Madadi. So is it help?
Thank you for your kindness.

The answer to your problem may be in the material you started with,if the material was below assay or had dirt or stones in it thats your answer,try melting and assaying your starting material then refining the bar and see if you are losing gold.The advice to follow Harold V is sound he is certainly a master of his art.

My starting materials was some pieces of jewelry making scraps which I picked them up one by one and checked them so I was sure about its quality.

Don't rely on the Karat mark on the jewelry, much of it will be less than what is marked. Based on your recovery and the fact that the test for gold was negative, I would guess that you recovered all the Gold that was actually there.

Aren't you basing everything on the assumption that the gold is exactly 18K to start with? How do you know that to be true? If I follow you correctly, based on your yield, I calculate the gold to have been 17.83...

I agree with you. But the scraps I used were from a jewelry workshop of one of my friends and he always uses 995 bars and reduces them to 750. Other than that by accepting your theory we must consider the amount of loss. By the current situation it must be 743 or less and it seems impossible. I could accept this if it was one, two or three less than 750.
I did the job in a balloon of 5 liters capacity. So there is no possibility for effervescency. I used only two filters one for silver chloride and one for gold. I fired the gold filter with the powder. And about the crucible as I checked I found a very tiny piece of gold trapped in the glass phase, but it is much less than my loss.

What was the porosity of the filter paper you used, and how long did you allow the precipitated Gold to settle before you filtered it?

And about the filter you asked, unfortunately there is no information on the filter paper box. But once I tested with slurry of clay and water and only clear water was passed. As you know the clay particles can be at the scale of down to 1 micron. As I mentioned (4) I stayed two hours for complete settling of gold powder.

and last
It was not my first job. Before my last test I did with much greater amounts. But by this last experience and evidences from previous ones it seems that I can only drag out only about 990 out 1000 part of gold. Here there are some assumptions:
1. I did something wrong all the time.
2. A small part of gold is in the scale of nanometers; hence they cannot be seen or be filtered by convenient methods.
3. Stannous chloride cannot tell everything and so is not much useful.

 

[Irons]

Majid,

This may be a clue:

http://tinyurl.com/yhvfl2m

 

[qst42know]

Were there any solder joints in the jewelery scraps?

Any brazing done must be done with a lower karat alloy to avoid melting the original piece. If any of the filings were included they are often created while cleaning up solder joints.

Did you save your waste solutions in a stock pot? Gold particles too small to be caught in your filter will settle out over time to be collected later.

 

[goldsilverpro]

Majid,

It doesn't just disappear. It must be there somewhere, assuming it was there to start with. About my only advice is to go over everything again, evaluate your process, and just keep looking. It has to either be in your process or in the assumed 18K stuff you're starting with. You're a bright guy and you seem to know what you're doing. I have no doubt you'll figure it out. On a highly detailed problem of this sort, it's hard to help much when you're there and I'm here. I would suggest that you assay the material you're starting with. It might also be interesting to take some very pure gold through your complete refining process - maybe re-refine some of the 999 gold that you've produced and had assayed. If you get closer to 100% recovery from this, I would think the main problem would be in the 18K alloy.

When your friend makes up this 18K alloy, I assume he's considering the 1/2% difference in the 995 gold and pure gold. If he isn't, about 60% of your loss could be explained by this.

 

[butcher]

3. Stannous chloride cannot tell everything and so is not much useful.

Majid Madadi, sorry I was joking about the name, I assumed it was a made up stage name, as that is what most people do, few people use their real name as you and I do, please accept my appology.

stannous chloride is a very good indicator, and can detect very small amounts of gold in a solution.

this kind of sounds like an expieriment, and if you start the expieriment with unknown values, the results would usually come out suspect. I like GSP suggestion of re-doing the process with a known amount of gold like a mapleleaf, also I seen no mention of inquarting, using nitric to eliminate the base metals, and the sodium hydroxide step instead of evaporation, after aqua regia, is another part I do not do, and question,( I just learned a different way) it would be interesting if you took a sample and split it in two, ran one with your process and another using Harold's method comparing the results.
kind of like an assay they may do several samples and compare,