Acid Peroxide on Teflon Fiberglass

[FrugalEE]

I'm new to the forum and this is my first refining project. The material I have to process is primarily 12 X 17 inch teflon fiberglass .0062 in. thick. It has etched runs (some .023 In. wide and some .050 In. wide plus some 3/8 In. pads) covering about 10% of the board on both sides. It was manufactured back in about 1982 and I have good reason to think that the applicable specifications are 1/2 ounce copper (.0007 In.) plated with nickel at .000100 In. minimim with gold on top of .000050 In. minimum. I have painstakingly measured the area and calculated the amount of gold (assuming 50 microns) and it comes out at .76 grams per board and that definitely looks worthwhile to me.

In searching the forum I have not found any other reference to recovering gold from teflon fiberglass PWD. Last night I started an AP process about 9 PM in a new white dishpan with a third of a board using Steve's recommended 2 parts HCL to 1 part peroxide. It is going to be very slow, but thats OK, especially if I get most of my gold in the form of foils. We are now over 12 hours into the process and most of the runs are off, but we're still working on some 3/8 In. diameter pads and the solution is still not very green. The foils seem to be black on the bottom when they first come off, but seem to get better with time. Is that the nickel?

Steve's AP videos were great for teaching me techniques, but there are some very significant differences with what I have to work with:
1. I have very little copper mass compared to his 600 grams of card edges
2. My Cu is .0007 thick and his was probably .0014 In.
3. G10 board is much more of a sponge than teflon board so etchant can more easily get to the Cu.
4. Teflon is hard to wet
5. Teflon sheets are going to stick together much worse than fingers and I have to process sheets much like developing a photo print - one at a tiime. I don't have plastic tongs yet so I'm poking and scraping the runs with a plastic rod.
6. My material has been in a PVC bag since 1982 & part of time in a hot garden shed. It probably has a film on it similar to windshield fog in new car.
7. Temperature: I believe Steve got a pretty good reaction that fed on itself and heated up his solution. Also he is in a much warmer climate. I as processing at about 70 degrees.
8. I don't have any solder or solder mast to deal with only clean unused PWB.

Interventions: I added a few drops of Kodak Photoflo to reduce surface tension. It foamed a bit and I think it helped. I also used a tiny patch of bare Cu PWB to check etch power a couple of times. My next piece I plan to clean first with Pro windshield spray that I got with a new windshield.

Questions: Because of the slowness I'm concerned that a shelf life sort of thing will cause peroxide to die before it has a chance to create the CuCL2 etchant. Is that likely? I believe Steve was adding peroxide refreshers primarily because he used it up etching Cu.

Should I raise the temp? My inclination is to do this by putting etchant dishpan in a larger pan with hot water.

My immediate objective is sort of an assay ie to process enough so that my $12 HF digital scale will confirm the gold content. I may send off the rest for processing.

Suggestions please and thanks for all the great info on this site. I've been burning up my eyeballs trying to soak it all in.

FrugalEE

 

[gold4mike]

If you have some foils floating free you have begun to dissolve copper. As many people have stated on the forum "Patience is a virtue", especially when working with A/P. As more copper gets into solution the reaction will start to work a bit faster. I have never seen it generate any noticeable increase in temperature. 70 degrees should be fine, but if you want to add heat, don't overdo it.

I have used the same gallon or so of A/P for about 15 pounds of edge fingers and it continues to work very well. I have added to the solution when I rinse my foils by dumping my rinse acid or rinse water through the filter right into my A/P bucket. The additions allow for more dissolution and I already have the dissolution power built up from much copper in solution. It's now probably closer to two gallons in volume so I store some of the extra in another bucket, ready to start over when my main bucket finally gets saturated with copper.

As for additions of H2O2 - I use an air bubbler like you would use in a fish aquarium and haven't had to add any H2O2 since my original mixture was created. I don't have to worry about putting any gold into solution and having it drop as fine powder that might go through my filter.

If your pieces are large you might benefit from cutting them into smaller pieces so you can fit more in your container. The extra access on the edge of the cut might help the solution get at the copper a bit quicker.

It sounds like you're on the right track, just don't try to rush it. The longer it takes the more value your gold button will probably have!

 

[FrugalEE]

Mike,

Thanks for quick reply. What I started with was only a third of a board as my dish pan was too small otherwise. I added another piece and was surprised to find that sheets sticking together wasn't the problem I expected. Maybe chopping into small pieces would be a good idea and deliberately cutting acrosss the max number of runs. I wonder if this material in a completely stripped form would be useful to anyone.

I bought a bubbler yesterday, but haven't used it yet as the solution is still pretty light. Perhaps I should have jump started the solution by adding pure Cu before adding my gold plated boards which obviously have the Cu pretty well covered. My concern was the peroxide would die before enough Cu got attacked. A second board I put in 90 minutes ago still is holding tight to it's runs. This board holds runs far better than G10. I tried hair drier and knife to get a run sample and didn't have much luck. Torching teflon doesn't sound like a good idea as I've heard it puts out a very poisonus gas at high temperature. I'm willing to let the process take days especially if it avoids putting Au into solution and lets me judge Au content by foil weight.

When you terminate the batch are your foils shiny gold on both sides? Mine look black. I also get black on the board after part of the little round pad has come off. I suspect that is some kind of carbon used to get conductivity to electro deposit the copper.

FrugalEE

 

[gold4mike]

The black is probably a little bit of gold that dissolved initially and cemented back out as copper started going in. That's part of the reason I keep using the same A/P over and over again. Eventually I'll run my spent liquid through a much tighter filter to try to catch all that I can. Since another fresh batch of fingers is going in the bucket anyway, I filter through one coffee filter for speed and if a few foils run over the edge I'll catch them next batch. I just finished a run of 2 pounds of fingers, every other day, until I hit 10 pounds. I got a 21.5 gram button already, have two beakers still settling the last bit of powder, and have the original fingers to sort through and reprocess those that still have some gold stuck to them. I had a three day weekend and was determined to melt my first button.

I'll be interested to see what you get from your material. From your description it is something I have not yet seen.

You are correct about the Teflon and toxicity. I used to haul piping to a place in TN from the Dupont plant in Washington, WV. When a process would screw up the material would stop moving and solidify in the piping. They would disassemble it, load it on my truck, and I would take it to TN to have it burnt out of the piping. This was (I was told) the only place in the Eastern half of the US that had the permits to burn this material out. It was a 12 hour burnout, then a cool down, load my truck and off I would go back to WV.

There is currently a big to-do about C-8 from their manufacturing process getting into the drinking water of several surrounding communities.

I wouldn't recommend trying to burn it at home!

Good luck and keep us posted on your progress.

 

[goldsilverpro]

How many sheets of this material do you have? It there are many sheets, I would try to find a way around doing only one sheet at a time.

Sheets of x-ray film also stick together when wet and this greatly slows the stripping solution from getting in between the sheets. Some people first run the sheets through a paper shredder. This distorts the shredded pieces of film and totally prevents the pieces from mating together and sticking. The only problem is that this great distortion produces a product of low bulk density - maybe 1/5 of that of the same film cut into small flat pieces.

Were it me, I would try one sheet (or, 1/4 of a sheet) of your material in a paper shredder and see what happens. It's very thin and should shred easily. I would first get the shredder immaculately clean in case some of the gold/copper flakes off - or buy a new shredder. Also, I would think that this would expose more copper and make the acid work faster.

After the copper is gone and the material is rinsed, the gold could easily be leached from the teflon with AR or HCl/bleach.

Just an idea, but I think it's worth a shot

Chris

 

[FrugalEE]

Mike,
Thanks again for some more good ideas and I'm impressed with how much you have run through that solution. You haven't said if you bubble while etching or just after a batch. I've been running my small fish air pump since about noon and I'm sure it helps agitate the mix. Some of the runs I just brushed off from boards I added about noon today have a silver color (nickel?) underneath. My first board put in over 24 hours ago still has not etched off all of the 3/8 inch pads.

Interesting story on your tie with teflon.

Chris,
Shreading sounds like a pretty good idea. Thanks! I don't have one, but this batch is certainly big enough to justify buying one. I have about 100 of the 12 X 17 boards and about 25 boards 12 X 12.

From what I've read this sounds like a job for your cement mixer cyanide process.

FrugalEE

 

[Oz]

I have not seen Teflon boards let alone boards without masking, where did these come from?

Since you do not have a lot of this material (as to # of boards) I would run them in dilute nitric. Get a plastic dishpan #2 plastic (high density polyethylene) and stack the boards on top of each other with glass or stainless steel pieces between them to keep a gap. This is not cost effective for most boards but if your gold content math is correct it makes sense in this case.

If you do not have access to nitric I would run a sample for you free of charge to determine the gold content for you, mainly because I am curious to see a Teflon board.

 

[goldsilverpro]

Chris,
Shreading sounds like a pretty good idea. Thanks! I don't have one, but this batch is certainly big enough to justify buying one. I have about 100 of the 12 X 17 boards and about 25 boards 12 X 12.

From what I've read this sounds like a job for your cement mixer cyanide process.

FrugalEE

In this case, due mainly to the configuration of the material, I don't think that the cement mixer cyanide process (using NaCN and H2O2) would be the way to go. This system relies on 2 things - that a nickel barrier exists between the gold and copper and that the stripping be done very quickly (maybe, within 1 to 4 minutes. If it is not done quickly, the nickel will slowly degrade in the cyanide or it will abrade by the tumbling action. Once any nickel is gone and copper is exposed, the gold that is dissolved will tend to immerse (cement) back onto the copper. Another problem with long cycle times is that the H2O2 destroys the cyanide quickly. If you tried to run multiple sheets in the tumbler, they would stick together and this would increase the time considerably. If you shredded the material, this would expose copper and would create big problems.

If I were to use cyanide (which I probably wouldn't), I would use m-NBSS (ludigol) as an oxidant, rather than H2O2. It's a little slower, but it doesn't destroy the cyanide as badly, if at all. I would put it in a tank or bucket and heat it to about 120F. However, unless you made a plastic rack (or, something) to keep the sheets separate, you would have to run the sheets one at a time.

I'm still thinking about what is the best way to process this material. I wrote you up a long procedure for shredding and then using nitric but then I saw potential problems and deleted it. The problem was that the gold foils would be trapped in a very large volume of shredded teflon. This would take a lot of acid (AR or HCl/Bleach) to dissolve the gold or it would take a lot of batches.

Two possible reasons you are having trouble dissolving the copper are that (1) There is a film of something on top of the gold or (2) The gold is non-porous and the acid can't penetrate through it to get after the copper. If (1) is the answer, you'll have to clean it off somehow. I noticed that you've already thought of this but you'll have to careful with what you use. Some windshield wiper fluids contain silicone and that would not be good. If (2) is the problem, it will take forever in the HCl/H2O2. I lean towards (2) but I could be wrong.

This may be heresy, but I'm wondering if dissolving all the metals, Cu, Ni, and Au, in HCl/bleach (or, AR) might be the best way to go. This would solve (2) above, if that is the only problem. Also, it would make it a one-step deal. This could be done by shredding or leaving the sheets whole (or cutting them into smaller pieces). If shredded, it could be placed in a bucket with holes in it and this would be placed in a larger bucket containing the solution and the inner bucket could be bobbed up and down occasionally. If sheets are run, you'll need to figure out some way to run multiple sheets by keeping them separated - Oz had an idea about how to do this. The clean teflon doesn't wet and could then be simply rinsed of solution and it would be out of the picture. According to your data, there is a total of about 8 oz of Cu and 1.2 oz of Au on the sheets - not a terrible ratio. The gold precipitated would probably not be clean but it would be simple to re-refine it. You'll probably need to evaporate the solution down (say, to 1 gallon) to make the precipitation more efficient. Or, maybe you could add a little nitric and then cement out the gold on copper buss bar.

Please note that these are just ideas. I'm here and the material is there. If I had a lab (which I don't) and started experimenting with this (in very small amounts), I might find problems, change my mind, and go in a totally different direction.

 

[dtectr]

do you have any of this laying around?

check out the CuCl pdf from Lazersteve's profile page. Since this is basically hwat you're doing by copper etching,
adding Copper Oxides can speed saturation of your solution, i believe.

but i could be wrong.

 

[FrugalEE]

Three good replies. Thanks guys!

Oz,

This is RF circuitry and the boards I am working with are the conducting part of a stripline sandwich. 30 mil teflon fiberglass panels are laminated to either side and then metal plates containing the connectors on one side and held together with bolts or rivets complete the assembly. There was no soldering involved in the assemblies I worked with and mechanical connections were used. The boards I have were rejects that never got sandwiched. If you find working assemblies in the field you are going to have to use something like a 400 degree oven and a pair of pliers to rip apart the sandwich. Most RF microwave circuitry now is done with microstrip where there is only one ground plane and the circuitry is readily accessible.

I have a small quantitiy of dilute and very pure nitric, but I should be able to buy nitric locally. I'm going to have to do the math on this and study it more, but it seems like a pretty good idea. I presume it would attack the gold less than A/P and might also have advantages in recovering the Cu and Ni. I'm a bit surprised you mentioned using stainless spacers. I doubt all types of stainless would be suitable and there is so much plastic available I would probably stick with that, but I believe I read somewhere on this forum that nylon is susceptible to some acids.

GSP,
There is probably no way this teflon material is going to tumble without trapping some pieces requiring some human intervention and I see how that rules out your tumbling cyanide process. As I see it the quantities here are too small to think about a slow cyanide process as the usage of acids to etch all of the metals involved are not that high.

dtectr,
Yah, I got some oxidized copper. I've treated copper almost like gold for most of my life. I'll study the CuCL2 etch process some more.

My etch bath has some runs coming off that are several inches long. I expect to terminate this batch sometime this week end and cut out any areas that still show metal and put them in another batch.

I'll see if I can do some pictures. I'm quite familiar with editing & sizing photos, but I've never posted one.

FrugalEE

 

[FrugalEE]

GSP,
I went back to reread everything before going to a study phase and I found a lot more great material in your post that I either overlooked or you somehow added at a later date. I have little experience using forums. I finally printed out all this thread so I can refer while writing.

I'll comment a bit:

Windshield spray: I avoid silicon as I know it messes up finishing. I failed to read the label before using, but in this case I appeared to luck out as there is no mention of silicon. The spray is from Safelite Auto Glass and contains in descending order: Water, Butoxyethanol, Ethyl alchohol, Methanol, n-Butane, and Propane. I couldn't see that it did anything. I said the boards were is PVC bags, but I expect it's polyethylene.

The process seems to be working better now that it's aged a bit and I'm using a bubbler. The first board, which is approaching 48 hours now, is almost bare even at the 3/8 In. round pad. The second board I put in has some strange blackish deposits that won't etch off, but the pieces put in afterward seem to be running better. I'm getting more foils now that are gold shiney on both sides. If I were to start this over I would get my bath working better with some oxidized copper before putting any of my teflon boards into it and I would use the bubbler from day one and maybe no H2O2 at all. If I have a good settup and can process at least 6 boards at a time it's acceptible to me to have it take 2 days per batch if I can process something like 5 boards at a time with only occassional tending.

I've been pulling off some spoonfuls of runs and putting them in a separate dish with some of the A/P. That makes it easier to evaluate the boards I'm still trying to finish up.

I think the thicknesses are: 50 microns of gold over 100 of Nickel over 700 of copper. The copper should be pretty close, the others are minimum. The worst case ratios should be 14:1 copper/gold or 16:1 base/gold. You somehow got 8:1. Are you basing that on average thickness in use in early 80's? By the way I used your eraser test and dozens of strokes didn't seem to phase it. From what I remember of reading the spec the gold has to be 98% pure or something like that. I'm wondering what the impurities might be?

It's probably not economical, but I would like to have a pile of nickel and a pile of copper, at least in powder form out of this at the end and no significant hazardous waste. Which process A/P, dilute HNO3, or A/R is easier to remove base metals from?

My only previous experience with HNO3 was back as a freshman in college where we dissolved a dime to measure the silver content. That tells you I'm over 65.

I really appreciate your time.

FrugalEE

 

[Oz]

I personally would use nitric on these boards as if your yield estimates are correct it becomes cost effective. The nitric will not affect the gold and will digest the other metals you have. Any solution containing hydrochloric can put gold into solution.

As to my stainless comment...
I have 300 series stainless that has been in nitric for over a year with no problem. There are stainless alloys that you may have troubles with but I have never had a problem if I use food grade stainless. I actually use glass rod as spacers for this type of material, but it is not worth buying just for 1 use. Most craft stores would have glass buttons or such in a convenient shape for a couple of dollars. They would also likely have stainless tweezers or forceps that are nice for playing in nitric with.

 

[goldsilverpro]

I think the thicknesses are: 50 microns of gold over 100 of Nickel over 700 of copper. The copper should be pretty close, the others are minimum. The worst case ratios should be 14:1 copper/gold or 16:1 base/gold. You somehow got 8:1.

You're talking thickness and I'm talking weight. Gold is about twice as dense as copper. If you want me to go through the math, I will.

 

[FrugalEE]

Chris,

You are right and I realized it a couple of hours later. I hoped to correct my error before you posted. I've been working through some math & studying chemistry while baby sitting grandkids. My ratios are on volume, but mass is what is important and the mass ratio of Cu to AU is about 6.5 to 1. It could be even lower if Gold exceed the 50 micron minimum by very much. Gold being so dense really helps things.

I did some further calculations on amount of Nitric needed. Your rule of a "liter of 50/50 Nitric and water will dissolve 120 grams of Cu" says that about 4 liters of solution or something like half a gallon of concentrated HNO3 would be enough to do 100 of my boards. The question is whether nitric will penetrate the gold layer on my boards and speed up the process any better than A/P method. Oz states it will at least be more selective in that it won't attack the gold. The cost of chemicals doesn't seem to be much of a factor, it's more the labor and minimizing the mess. I'll run some tests on a small scale with HNO3. I have about a liter of 2%. I could concentrate that some or try as is.



OZ, Approximately what strength HNO3 do you recommend? I would like to send you some kind of sample of my board for you to experiment on, but I don't know how to get a private communication going. I'll try to figure out the forum proceedure for doing that tomorrow.

I have nice stainless tongs left from photo work years ago. I"m not puttin them in A/P, but you've given me reason to believe they would be OK in HNO3.

FrugalEE

 

[Harold_V]

I have nice stainless tongs left from photo work years ago. I"m not puttin them in A/P, but you've given me reason to believe they would be OK in HNO3.

FrugalEE

Should you make an inquiry for a large volume of nitric, you'll come to understand it is packaged in stainless. 300 series stainless, as Oz has explained, does not react with nitric, and is the metal of choice for such use. I have an 8 gallon container (military surplus) that is likely nearly as old as I am, and has contained nitric acid for the past 25 years it has been in my possession. I kept a small amount of nitric when I sold my refining business, knowing it would be useful for passivation of stainless (I am a retired machinist/toolmaker).

Harold

 

[Oz]

2% nitric is very weak but given time it would still do the job. I would add heat to help but I really have no idea as to how long that would take as I have never worked with it that dilute. At 2% and high purity I would guess it is intended for photography and it would be expensive to waste it on these boards.

I use 70% ACS grade nitric and have never found the need to add more than an equal volume to water. I would do my best to estimate the nitric needed to digest the base metals then start with a container (that you can place your boards in) that has an equivalent quantity of distilled water as the nitric you expect to consume. Put some of your boards in the water and measure your nitric into a seperate container. Start by adding small amounts of nitric giving it 15-30 minutes between additions until you reach an acceptable dissolution rate. Adding too much nitric at once causes you to waste it as a fast reaction will cause much of it to gas off as red NOX fumes. To economize on fluid volumes I would run multiple batches of boards in the same solution adding nitric as it is needed.

I doubt you will want more than a 25% by volume of 70% nitric at any given time replacing it only as it is consumed. Be patient in adding nitric as the reaction to copper is exothermic and as it heats up the reaction rate speeds up and you can find yourself with a runaway reaction foaming acid and gold foils out of your container.

I have replied to your PM.

 

[goldsilverpro]

Sorry, but it seems my math was terrible in my previous posts. I went by your figure of .76 g of gold per board and that isn't right. There are 12 x 17 x 0.1 = 20.4 sq.in. of plated area per board. At gold .00005" thick, the total gold per board would be .00005 x 16.38 x 19.3 x 20.4 = .322 g. You have an equivalent of 117, 12x17 boards. Therefore, the total gold would be .322 x 117 = 37.7 g, or 1.21 tr.oz.

For the total copper, it would be .0007 x 16.38 x 8.9 x 20.4 x 117 = 243.6 g. The Cu/Au ratio is 243.6/37.7 = 6.46/1

Don't forget the nickel. The nickel is .0001 x 16.38 x 8.9 x 20.4 x 117 = 34.8 g.

The total Cu + Ni = 243.6 + 34.8 = 278.4 g.

A gallon of 70% nitric will dissolve about 2# of Cu + Ni, or 908 g. To dissolve 278.4 grams, it would take about (278.4/908) x 3.785 = 1.16 liters or 2.32 liters of 50/50 nitric.

To explain the math. In the 1st paragraph, one sq.in. of .00005" thick gold has a volume of .00005" x 1" x 1" = .00005 cu.in. The 16.38 figure converts this to cu.cm. (cc). The 19.3 figure is the density of gold in g/cc. The same logic was followed in calculating the Ni and Cu. Ni and Cu both have a density of 8.9 g/cc and it takes about the same amount of nitric to dissolve either Ni or Cu.

In case you wanted to dissolve everything (Au, Cu, Ni = 316.1 g) in AR, the calculations are about the same as nitric. It would take about 1.32 liter of 4:1 aqua regia. The AR could be diluted somewhat to increase the volume but, the more it is diluted, the slower it will be. It would probably work faster if the dilution were made with extra HCl, rather than with water.

I think all the math is right this time but, if anyone spots a flaw, please let me know.

Experiment! Experiment!

 

[Oz]

Great post showing the math behind calculating these things when plating thicknesses are known. I have not checked all the math as I have not finished my first cup of coffee yet, but I think you may have missed the boards had traces on both sides equaling 10% of the surface area.

 

[FrugalEE]

Oz, Thanks for the general proceedure on HNO3. When you first mentioned dilute HNO3 I thought you might have meant a much weaker solution. I found my HNO3 stock and it is only about 35 ml of 2% so I"m going to have to use that very carefully in my one and only test tube to try and gauge speed of response to samples of my PWB.

Harold, Nice to have you join us. That fact about stainless containing concentrated nitric for years is one of those mind warping things. Some day I'm going to have to find out how that works. I could use a hint on figuring out if a stainless implement is OK or not. My photo tongs I bought back in the 60's are marked CESCO and are non-magnetic. I suppose one could test with a drop of acid and look for reaction, but I wouldn't chance use in anything where purity or accuracy was critical. Can one easily determine if something unmarked is 300 series?

GSP, I calculated much like you, but there are pretty similar runs on BOTH sides of the PWB. (That's to provide controlled coupling to form quadrature hybrids.) Also 10% was an approximation and I actually got 24 sq.In. on the side I evaluated. While digesting your math I realized my first post is in error on the size. The large board is actually 12 X 21 inches instead of 12 X 17. Sorry about that.

I can use your acid estimates just by doubling to cover both sides. I see an interesting dilemma in using A/R in that to run multiple boards convienently you need a lot of solution that isn't going to be used up. If we have to go that way I hope that the time per board is at least fairly short. I expect it will be, but have no experience at all. It appears to me that short of keeping temp down there is no way to slow down the fuming like there is in the proceedure using only Nitric that Oz wrote.

FrugalEE

 

[Oz]

I see an interesting dilemma in using A/R in that to run multiple boards convienently you need a lot of solution that isn't going to be used up. If we have to go that way I hope that the time per board is at least fairly short. I expect it will be, but have no experience at all. It appears to me that short of keeping temp down there is no way to slow down the fuming like there is in the proceedure using only Nitric that Oz wrote

When using AR you can start with concentrated HCl and only add your nitric incrementally as needed. It is actually the preferred way to use it as any excess nitric will need to be removed before precipitating your gold.