Opinions on pitfalls before attempting unorthodox procedure:

[HAuCl4]

Hello all. Very nice forum, lots of knowledge, and pictures, and procedures. A gem.

I would like to get feedback from members here on the possible pitfalls of this plan, and/or how to make it work better, improvements, etc.

The goal is to reach 9999+ fineness in gold material that contains silver, copper, and other base metals, but no platinum group. I wish to achieve 9999 without dissolving the gold into solution, i.e. The metal is to stay in metallic form all the way from the beginning to the end.

Call this stupid, or a search for the truth, or an experiment, or exercise, or whatever. Let's see if it can be done.

The procedure (in summary) I intend to use is (please feel free to criticize, suggest, etc.):

1-Inquartation with lead. Fusion of the gold, and lead added to the melt.
2-Melt dropped in water to make shot/leady flakes.
3-Digestion in boiling dilute nitric acid, several times, till absolutely no reaction occurs in fresh acid.
4-Thorough wash with distilled water till no acid remains in gold powder left.
5-Boiling in HCL.
6-Repeat step 4.
7-Wash in concentraded sodium hidroxide (to remove any remaining silver compounds).
8-Repeat step 4.
9-Dry gold powder, wrap in 10 times its weight of lead foil and place on large magnesite or bone ash cupel.
10-Cupel at about 950 °C till all lead is absorbed or volatilized as litharge.
11-Raise the temperature till the metal in the cupel melts again, and carefully add sprinkles of sodium or potassium nitrate mixed with borax. Could do this in a fresh cupel/dish?.
12-Let button cool, and then test for fineness.

Would the button left even approach 9999 ?.

Thanks in advance for all opinions.

 

[machiavelli976]

"inquartation with lead"! where to find very pure lead? my best result , inquarting with 90% electrolytic copper ,10 % carat gold wasn't above 99.5 % after all kind of washing and acid leaching. got round shiny buttons without any flux but i know there still was some contaminant in every button. 999.9 maybe using a electrolytic cell.

 

[machiavelli976]

another thing. to reach the highest purity gold must pass thru a solution atom after atom, not crystal after crystal like in inquartation does.

 

[HAuCl4]

I'm not so certain mach. During a fire assay, a similar process is used, and the gold never goes into solution (except into the lead), and always remains as metal. What gold remains is better than 9999 unless some mistakes are made in the assay. If there is a lot of silver in the lead, that could bring an issue. Point taken.

This is why I want to get to the bottom of this.

 

[goldenchild]

I think no matter how many times you repeat step 4 there will always be contaminants. Even the tinyest grains of gold can be encasing inferior metals. You are also re-introducing lead into the mix when the gold is at a fairly high purity in the process. That makes no sense to me.

I now think to myself this, before I try cockamamie(not saying this is)experiments. If it was an easier and more efficient way to do it, someone probably would have already done it already.

I say just try it with a small amount of gold and let us know what you get. The worst that can happen is it doesnt work and you have to refine it the old fashioned way

 

[Palladium]

Miller process will give you about the best your going to get without wet refining.

 

[goldsilverpro]

During a fire assay, a similar process is used, and the gold never goes into solution (except into the lead), and always remains as metal. What gold remains is better than 9999 unless some mistakes are made in the assay

I don't think you can make this assumption. According to Bugbee, when using proper procedures, about .05% silver is retained in the gold after parting. Therefore, the gold purity would be 99.95%, at best. Even worse, Shepard and Dietrich give a figure of .1% silver retained in the gold, which would give a gold purity of 99.90%, although their statement is vague and I may be misinterpreting it.

I don't understand the logic of using lead for inquartation. I would that the that lead would be more difficult to part than silver. You would have to use very weak nitric, say 1:7, nitric:H2O to have any chance of removing the lead. Lead nitrate is not very soluble in strong nitric and will form crystals, which block the dissolving.

Concerning the cupellation portion of your scheme, Bugbee gives figures, from various researchers, of lead and other metals being retained in the gold assay beads. One found that from .30 to .37% lead is retained in the gold bead. Another found .45% total impurities. And it seems that the larger beads retained more than the smaller ones. Also consider that, if metallic silver is retained in the gold during parting, you won't be able to remove it by oxidation after cupellation.

I could probably think of other problems but, in general, I personally don't think you have any possible chance of your scheme producing 9999 gold.

 

[HAuCl4]

Thanks guys for all comments. I think I had several wrong beliefs about assays. I thought that the beads were finer than they actually are it seems. What is the current standard way to measure fineness and where can the equipment be purchased/leased?

 

[goldsilverpro]

When you get up into the 9995, or better, range, I would think the most reliable way is to first have all the impurities analyzed. The percentages of all the impurities are then totaled and and this figure is subtracted from 100% to get the purity, in percent, of the gold. I believe that ICP is used for this.

BTW, I really don't know the exact accuracy of the fire assay, as it is dependent on many variables. One source that seems reliable says it is accurate to .02%, using best techniques.

 

[goldsilverpro]

Several years ago, an Italian company made closed-circuit gold refining equipment, called Aure8, based on inquartation and the subsequent dissolving of the copper or silver in nitric. They claimed that, by using several fresh batches (3) of of progressively stronger nitric, a gold purity of 9999 could eventually be reached, thus avoiding the aqua regia step. The success of this seems dubious, since it seems the equipment is no longer being made. About the only thing left on the internet concerning this is this study of the process.

http://www.ganoksin.com/borisat/nenam/wgc-refining.htm

Although not perfect, I made a Word doc of the article

 

[HAuCl4]

Thanks GSP. It seems that to actually properly test this, I'd need an ICP assay machine. It seems rather expensive.

 

[Harold_V]

This is why I want to get to the bottom of this.

Then lose the idea of processing with lead. It is very damaging to the quality of gold, and has a considerable affinity for same.

If you'd like to process without dissolving, I encourage you to explore the Miller chlorine process, or zonal refining. Likely both are beyond your ability, however.

Harold

 

[HAuCl4]

This is why I want to get to the bottom of this.

Then lose the idea of processing with lead. It is very damaging to the quality of gold, and has a considerable affinity for same.

If you'd like to process without dissolving, I encourage you to explore the Miller chlorine process, or zonal refining. Likely both are beyond your ability, however.

Harold

Cheers Harold. Found very little on the zone refining method (link below). Looks interesting.
http://www.tutorvista.com/content/chemistry/chemistry-iii/metals/metals-refining.php
http://www.tutorvista.com/content/chemistry/chemistry-ii/metals/metal-refining-methods.php

Do you have any, more detailed info regarding zone refining?.

It may be beyond my ability now, but I can learn or try at least.

 

[goldsilverpro]

HAuCl4,

No offense, but I'm having trouble understanding your motive in all of this. Is this just a mental exercise or are you really looking for a way to process gold? You seem to have some knowledge of fire assaying and basic refining. Is this derived from only book learning or is it from actual experience? If the former, I would suggest you get some hands-on experience, using the traditional methods, under your belt before trying to re-invent the wheel.

The Miller chlorine method is not really a refining method, since it only raises the the gold to about 99% pure. It is used to prepare gold for the Wohlwill cell, which is a refining method and can produce 9999 gold. Both are expensive to set up and are generally only viable for large volume.

I have only read about zone refining and have never seen it done. I know it's quite expensive to set up. In very simple terms, the impurities in a bar are pushed to one end by melting only a small zone of the bar and moving this melted zone from one end of the bar to the other. The zone moves very slowly and it can literally take days to do one bar. Therefore, only a section of the bar is pure and, I think, the greater the amount of impurities, the smaller this pure section is (actually, I think the purity is graduated throughout the length of the bar). The zone refining can be repeated. I don't think this would be applicable for something with a lot of impurities, such as karat gold. As I understand it, its main purpose is to further purify already quite pure materials. For example, I seem to remember reading of 12 nines silicon being produced by this method. To get this, they probably start with at least 4 nines material.

 

[HAuCl4]

I have hands on experience GSP.

I just want to know, for certain, if very pure gold can be produced without passing the metal thru a solution.

Call it a mental exercise or whatever. Search for knowledge?.

 

[Harold_V]

Do you have any, more detailed info regarding zone refining?.

Sorry, I do not. GSP's comments in that regard are pretty much on target for that which I would have said. I have heard of it, but did no exploration. In all the years I refined, I simple double refined my material, and was more than satisfied with the quality. So much so that the small Wohwill cell I built was never put in service.

It may be beyond my ability now, but I can learn or try at least.

I hope my comment wasn't taken as a personal affront. I don't mean to judge you as a person---but the fact that the equipment that would be required in order to accomplish the task is generally well beyond that which a person can afford, especially if they are nothing more than a hobbyist. The zonal process would ultimately be best performed with an induction heater. It might even perform faster than GSP proposed, a great deal depending on the wattage of the furnace and the coil design----but induction furnaces of any consequence are expensive and require considerable power---often three phase. I offer you as an example, the one I own. It is a 50 kw motor generator type (old technology), built by Ajax Magnethermic. It requires 240 volt 400 amp three phase service. At full load, it requires nearly 200 amps to operate, plus you must be able to start the motor/generator, which is a 75 horse motor. Were it not for the soft start capability, 400 amps would not be adequate.

Sorry I'm not more help.

Harold

 

[HAuCl4]

Thanks Harold. I had never heard about zone refining. It seems fascinating, but as you said, very involved with expensive equipment,etc.

I watched a Miller chlorination setup years ago. It's much simpler than people think, but it is for lots of 100 oz min.(my guess). And no matter what they tried, they said they could never get above 997-998 in fineness. They were processing up to 500 oz in a few hours.

 

[Barren Realms 007]

Do you have any, more detailed info regarding zone refining?.

Sorry, I do not. GSP's comments in that regard are pretty much on target for that which I would have said. I have heard of it, but did no exploration. In all the years I refined, I simple double refined my material, and was more than satisfied with the quality. So much so that the small Wohwill cell I built was never put in service.

It may be beyond my ability now, but I can learn or try at least.

I hope my comment wasn't taken as a personal affront. I don't mean to judge you as a person---but the fact that the equipment that would be required in order to accomplish the task is generally well beyond that which a person can afford, especially if they are nothing more than a hobbyist. The zonal process would ultimately be best performed with an induction heater. It might even perform faster than GSP proposed, a great deal depending on the wattage of the furnace and the coil design----but induction furnaces of any consequence are expensive and require considerable power---often three phase. I offer you as an example, the one I own. It is a 50 kw motor generator type (old technology), built by Ajax Magnethermic. It requires 240 volt 400 amp three phase service. At full load, it requires nearly 200 amps to operate, plus you must be able to start the motor/generator, which is a 75 horse motor. Were it not for the soft start capability, 400 amps would not be adequate.

Sorry I'm not more help.

Harold

That thing sounds like a monster Harold. That is a heck of a load.

 

[Harold_V]

Thanks Harold. I had never heard about zone refining. It seems fascinating, but as you said, very involved with expensive equipment,etc.

I watched a Miller chlorination setup years ago. It's much simpler than people think, but it is for lots of 100 oz min.(my guess). And no matter what they tried, they said they could never get above 997-998 in fineness. They were processing up to 500 oz in a few hours.

That's pretty much my understanding as well. Speed is its one outstanding feature. I included it only because you had asked about bringing metal fine without dissolution.

I got so comfortable with the AR process that I thought nothing of dissolving 75 ounces per session, which was my normal procedure.

Harold

 

[Harold_V]

That thing sounds like a monster Harold. That is a heck of a load.

Heh! The load is large, no doubt, but so is the power supply. The motor/generator is a single unit, hung vertically. The entire power supply unit weighs 3 tons.

Harold