Has anyone ever tried an HNO3 electrolytic cell?
- Thread starter GTmurph
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Very interesting, GT. I hadn't seen this one before. It's basically a method for separating the karat gold layer from the substrate of gold-filled materials. It uses a 304 or 316 SS cathode and a very weak nitric/distilled water solution. The gold filled material is the anode. The karat gold layer is undermined and flakes off. Supposedly, the copper base isn't appreciably attacked and what copper does dissolve deposits on the cathode. Also works on nickel and other base metals. Might work well on stainless watch bands. Might work on gold plated materials.GTmurph said:
Were it me, for the cathode/container, I would first try using a stainless Bain Marie pot from a restaurant supply. They come in all sizes, from 1.25 quarts to about 3 gallons. I recently bought 4 of the smallest ones, for about $3 each, at a local restaurant supply for making steamed Boston brown bread. They were non-magnetic, which is what you want. Here's what they look like.
http://www.foodservicewarehouse.com/kitchen/bain-marie-inserts/c4877.aspx
Or, just use a beaker with a stainless sheet as a cathode. It would probably work better with 2 cathodes, one on each side of the anode.
In the patent, here are the wide range of parameters given.
Nitric acid - .02% to 2%, by weight, in distilled water
Temp - 120F to 200F
Anode current density - .05 to 10 amps/square foot
Voltage - .5 to 25V
Electrode spacing - at least 2"
These were narrowed somewhat in the patent, for more idealized conditions.
Nitric acid - .02% to 1%, by weight, in distilled water. With 70% nitric, that's about .2 to 10ml/liter. I would probably start with 3-5ml/l
Temp - 180-196F
Anode current density - It doesn't say but I would first try 5 amps per square foot - that's 0.035A/sq.in.
Voltage - 5 to 20V
Time - he says it only takes 5 to 25 minutes
Stirrer - He also mentioned the possibility of using a stirrer. Most of this type stuff works better if stirred.
Who knows? It might just work. Certainly worth a try. Sure would save a lot of nitric. If anyone tries it, keep us posted.
I might note that the patent has a method of collecting the gold that falls off. This probably isn't necessary unless it causes shorting between the electrodes. I would keep it simple at first.
Evidently, the use of low nitric and distilled water limits the amount of copper, etc. that can dissolve.
Geo
Well-known member
i just read the entire patent and it is very interesting. if i can follow it then it must be pretty simple. im wondering if the cathode can be a stainless steel container like the sulfuric cell? that would make it easy to to keep warm because you can use direct heat. at only 2% nitric by weight, i feel almost any small centrifugal pump (like a fountain pump) may work.most use stainless steel and plastic.with the solution being pumped in on one side, the solution with gold flakes will go over the other side through a filter into a catch basin containing the pump.an aquarium filtering setup would work for this nicely. heck, an aquarium may work for the whole setup. a small two gallon fish tank and use an aquarium heater to keep the solution warm.
im beginning to wander, sorry.
im beginning to wander, sorry.
I read through the patent as well. Very interesting. It mentions a couple of times that the 2% is the upper limit for the nitric and that the preferred concentration is actually 0.03% to 0.06%. I'm not sure that's concentrated enought to even yellow the skin. :shock:
Certainly sounds safer than the sulfuric cell.
I can't wait to hear someone try this! Especially if it can work on gold filled.
Dave
Great first post GTmurph!
Certainly sounds safer than the sulfuric cell.
I can't wait to hear someone try this! Especially if it can work on gold filled.
Dave
Great first post GTmurph!
You're right. It says, preferably, between .02-1%, but MOST preferably, between .03-.06%, and ideally .05% - that's only .5ml (about 8 -12 drops)/liter. Most straight glass eyedroppers from the drug store will dispense about 23-25 drops per ml. You can determine the drops/ml from any eyedropper by counting the number of drops of water it takes to weigh 5 grams and divide by 5 or, weigh 2 grams and divide by 2, although that's not as accurate.FrugalRefiner said:
patnor1011
Well-known member
This looks very interesting.
Thanks for the replies.
I tried this in a small scale test and it didn't work as well as I had hoped but it didn't fail completely either. I went with the 0.05% nitric solution @ 85C in a 1-L beaker with a stir bar. Cathode was a small piece of 316 stainless. I ran the cell at 20 V which gave me a current of ~1 Amp and a current density of ~16 A/sqft for 20 minutes. In the end maybe 1/10th of the gold was removed from the substrate.
I think the main reason that it didn't work completely was because of the lack of circulation of the HNO3 solution. In all likelyhood I saturated the solution with base metal ions long before the 20 minutes were up. There was definitely a color change in the HNO3 solution indicative of the dissolution of base metal. I think I will try again with a much larger volume of HNO3 to see if that helps. If it does work then I can work towards a way of pumping in fresh HNO3 solution and filtering that flakes as described in the patent.
Sorry I'm being so vauge. This is a side project at my job and I'm not at liberty to discuss the details of the material(s) that I'm attempting to recover from. A can say this however, the main reason I want this to work is that it will completely eliminate the need to process the gold once collected since it would be collected in a four nines pure form. I have had success in recovering this gold using a sulfuric cell, well minus the melting part as I'm still waiting on some supplies to come in. I'm hoping this HNO3 cell will be a safer method that eliminates the processing (wash, dissolve, precipitate, wash, dissolve, precipitate) that goes with the black gunk collected in the sulfuric cell.
I'd also like to thank everyone who contributes to this forum. It has been very helpful in providing ideas and information for me in this project.
I tried this in a small scale test and it didn't work as well as I had hoped but it didn't fail completely either. I went with the 0.05% nitric solution @ 85C in a 1-L beaker with a stir bar. Cathode was a small piece of 316 stainless. I ran the cell at 20 V which gave me a current of ~1 Amp and a current density of ~16 A/sqft for 20 minutes. In the end maybe 1/10th of the gold was removed from the substrate.
I think the main reason that it didn't work completely was because of the lack of circulation of the HNO3 solution. In all likelyhood I saturated the solution with base metal ions long before the 20 minutes were up. There was definitely a color change in the HNO3 solution indicative of the dissolution of base metal. I think I will try again with a much larger volume of HNO3 to see if that helps. If it does work then I can work towards a way of pumping in fresh HNO3 solution and filtering that flakes as described in the patent.
Sorry I'm being so vauge. This is a side project at my job and I'm not at liberty to discuss the details of the material(s) that I'm attempting to recover from. A can say this however, the main reason I want this to work is that it will completely eliminate the need to process the gold once collected since it would be collected in a four nines pure form. I have had success in recovering this gold using a sulfuric cell, well minus the melting part as I'm still waiting on some supplies to come in. I'm hoping this HNO3 cell will be a safer method that eliminates the processing (wash, dissolve, precipitate, wash, dissolve, precipitate) that goes with the black gunk collected in the sulfuric cell.
I'd also like to thank everyone who contributes to this forum. It has been very helpful in providing ideas and information for me in this project.
Geo
Well-known member
if i read the patent correctly, its not the nitric acid that removes the gold but rather copper nitrate. i may be wrong but from what i got out of it the color change is to be expected.
GT, what was the anode? Plated? Gold-filled? Copper? What?
modtheworld44
Well-known member
Geo said:
Geo
If your right and it is the copper nitrate thats doing the stripping,couldn't you use the left over copper nitrate from a cementing silver project as the electrolyte instead. Kind of away to reuse some waste material for good use.Just a thought but might could work.
modtheworld44
@Geo: I don't think so because the author mentions various base metal substrates where no copper nitrate would be present. From my understanding the nitric is dissolving the base metal beneath the gold which thereby delaminates it.
@GSP: A sheet of nickel plated on one side. I'm sorry I can't really say anymore.
@GSP: A sheet of nickel plated on one side. I'm sorry I can't really say anymore.
etack
Well-known member
GTmurph said:
This should give you a green solution. as Nickel dissolved in nitric is green. your not dissolving that much so it should be light.
GTmurph said:
This just seems like an ion exchange to me. as when the X metal substrate is dissolved in the nitric it is then plated back out on the cathode as X metal. Nitric is used cause it wont exchange gold ions.
Will have to try it.
Eric
