third time help

[arthur kierski]

i have gold powder mixed with iron and do almost every action to eliminate this iron and when i finish the action(hcl,h2so4,hcl+h2o2,incineration ,etc) ,the magnet indicates iron----it is the third time that i ask for help,but the problem repeats itself and no way to find a solution---please help

 

[Smitty]

If it's in powder form, it should be easy enough to treat with nitric under some heat to remove the iron or nickel, then ar it after a clean wash and the usual precipitate. That's sorta a rough description assuming you already know the refining process.

 

[Smitty]

Can you supply some pictures?

 

[Harold_V]

I agree---a picture may be very helpful in understanding how the iron is mixed with the gold. If it is alloyed, all the washing with acids you can do won't make a difference. The entire lot would have to be dissolved, then selectively precipitated. If the iron is mixed amongst fine particles of gold, like sand and sugar mixed together, it's entirely possible that it would me eliminated by a wash. That apparently is not the case.

Understanding the nature of the material would go a long ways towards suggesting a solution.

Harold

 

[arthur kierski]

i receive large quantities of custom jewellery with plating problems---they are usually made of brass with gold plating and over the gold, rhodium plating----usually 1kilo of this materials yealds 4grams of gold and 0,7grams of rhodium---- i use ar to dissolve the material---the gold goes to solution and the rh stays us fine brilliant speckels----i filtrate the rhodium and to the ar solution i add iron powder to precipitate the copper+gold---- i kill the excess iron with h2so4---then to the copper +gold i add hno3 which dissolves the copper and i am left with gold(sometimes with iron(which is the reason for the help request---------i use this process because i have dificulty in dropping gold with smb--- i use 4liters of ar(cold) per kilo and as i do 5kilos of material per day ,it is 20liters of ar------note:when i obtain 20gram of gold from 5kilos i then incinerate the material and try to remove impurities with hcl and then to the powder left i use ar and precipitate the gold with smb--- the gold obtained which i sell is 98,5%------the rhodium i make plating solutions that i sell to the people who sent me the jewellery with the plating problems for 50% of the normal price------hno3 is very expensive here --if not i would use hno3 to dissolve the material and would not have all these problems.question:could i use nano3 to dissolve the material?or have to make poormans Ar?

 

[Smitty]

What concentration of HNO3 are you using by the way. I use 70 percent clean room grade Nitric and never have problems dissolving iron and copper from any materials in powder form. Instead of using Iron to precipitate the gold, maybe you can try precipitate using sulfur dioxide to decrease the amount of base metals being dragged down. I have never used Sulfur Dioxide to precipitate before , but I'm pretty sure Harold did mention it was his choice of use.


Good Luck

 

[Harold_V]

I have never used Sulfur Dioxide to precipitate before , but I'm pretty sure Harold did mention it was his choice of use.

When you precipitate with SMB, you precipitate with SO2. The differnce is I used it from a bottle instead of creating it from SMB.

Key to his success lies in NOT using iron to precipitate. That's not a good idea, not at all.

What would work, and very well, is to use ONLY the amount of acid necessary to dissolve everything, so evaporation wasn't a requirement. The rhodium would be in flake form, as it is now, and would be recovered via filtration. Assuming all of the material has been dissolved (one of the hazards of dissolving everything with AR, which I speak against regularly), the gold would be in solution, not removed with the rhodium. If that were the case, it could then be recovered by precipitation with ferrous sulfate, or SMB, with success. The problem appears to me to be the use of iron because too much nitric remains, preventing precipitation. Frankly, the process being used is terrible, and I'd recommend it not be used.

To be perfectly clear on this matter----Arthur would be far better served, if he must dissolve with AR, to precipitate the gold by the addition of a little copper (a flat piece that can be retrieved easily, not by adding wire). The gold would be cemented by the copper, leaving behind the solution of base metals. That way none of the copper would be precipitated, avoiding not only iron that is not easily eliminated, but the copper as well.

Under no circumstance, unless I was recovering material for future refining (think stock pot), would I use iron to recover gold when it is mixed with a large amount of copper in solution. It's like taking two steps forward, and one step backwards. It works, but it's a lot of unnecessary work when there are other ways to avoid most of the problems, with the added benefit of much cleaner gold as an end product.

Harold

 

[arthur kierski]

thanks Harold and Smitty,i know by experience that Harold is absolutelly right and i do this because of (force majeur) the hno3 price here---as i told you ,if i had nitric at a reasonable price,i would use it and no more problems--- i have a similar problem to recover silver(50grams per kilo) from silver plated wires used in plating custom jewllery--------Smitty,do you use 70%hno3 without dilution with water?if so ,perhaps i will eliminate the iron---i use 50% hno3(70%) and 50%water--thanks again
Arthur

 

[Smitty]

I also use 50% hno3(70%) and 50%water, usually twice with a hot water wash in between each treatment. The second treatment usually comes out clear. It is also done under a heat source. Then I start my refining after I feel that it is clean enough. Typical composition of the powder I have consist of gold, copper and nickel mainly from the stripping cell.

 

[arthur kierski]

thanks Smitty,i will try today

 

[Oz]

The few times I have had a base metal mix including iron in significant amounts with gold I have had difficulty with SMB as well. It was under these conditions that I tried ferrous sulfate and did not care for it, however it as well may have underperformed due to the mix of base metals.

I have found that cementing on copper was the best route as Harold suggests. It cemented the majority of values in a day but the remaining values were slow to come down. I did not use heat to speed this as I did not wish to consume more copper than needed. I found that decanting after 24hrs recovered the majority, but leaving copper in the remaining solution for a week was very worthwhile for additional recovery.

This is probably not what you wished to hear. I have found solutions containing significant iron to be the most problematic to precipitate. I certainly would not wish to use a powdered iron instead of bars or plate with the risk of having it in solution as finely divided elemental iron with my cemented values.

 

[Harold_V]

but the remaining values were slow to come down.

Speed is a function of the available surface area. If using copper is an ongoing process, simply add more copper. The volume you use has no relationship with the amount that will be consumed----that's a function of the amount of free acid, or the volume of gold in solution. In theory, if you have little free acid present, you will consume only that which is required to provide the electron that causes the gold to go from a liquid to a solid.

Harold