# Remove Hvy Gold Pltng from Aluminum Hexagonal Laser Mirrors



## Xsfacade (Sep 7, 2013)

I need help trying to figure out the best way to recycle the gold from these mirrors. I have a total area of 376 square inches on seven octohedral mirrors. I am guessing electroplating since the ends have some gold but not a lot of course. I don't want to use anything to caustic if possible but most of all I need it to be something i can do in an apartment or if outside it cannot take more then a day. I would love to use something that would eat the aluminum if possible since it would leave the eight slabs of gold from each mirror. They are around 5" tall x 3.5" thick with a stainless steel rod through the center that supports two bearings and a magnet. They came from the Accu Sort DM-3000. I have searched everywhere for info on these since they are worth more then the gold no matter how much I obtain. I know the original machine price included $1000.00 due to the single mirror in each machine back in 1996.
Thanks for any help.


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## Geo (Sep 7, 2013)

ideally, a stripping cell is the best choice. hcl will will digest the aluminum as well as NaOH (lye,caustic soda). if i had to pick between the two, i would use NaOH. if you are not familiar with sodium hydroxide and its properties, you should study on it before you try to use it. it is dangerous to work with if you dont know how to handle it. wear rubber gloves and eye protection. wash any spills or splatters as soon as possible. you can use vinegar to neutralize the caustic soda if it gets on your skin. you can use it safely in the kitchen sink but keep it off counter tops and away from aluminum pots and pans.


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## chlaurite (Sep 7, 2013)

If you haven't already, you may want to try a drop of acid/chlorox as a test patch on one of the mirrors. I've seen similar mirrors to those, from lotto-ticket scanners, and they didn't really have a thick gold plating - They had a silver (or maybe even just aluminum, I hadn't gotten into recovery/refining yet back then) plating with a literally transparent gold electroplate to chemically protect the surface from oxidizing. Looked shiny and yellow, but the whole thing had less gold than your average CPU pin.


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## goldsilverpro (Sep 7, 2013)

What is your definition of Heavy Gold Plating and why do you believe the plating is heavy? Can you provide a technical reason why the plating on this would be thicker than normal?

I have never seen gold plated directly on aluminum. Directly sputtered or evaporated, but not plated. Most likely, there will be a layer of nickel between the Al and the Au. I would guess the gold thickness would be no greater than 30 microinches. This is about $.42/square inch or $22/unit. It could very well be *much* thinner than that. In most cases, gold plating baths do not "build" brightness. The final reflectivity is mainly dependent on the brightness of the metal underneath the gold and not the gold itself. As the thickness of the gold plating increases, it tends to dull. For this reason, gold plating on a mirror would probably be thinner rather than thicker.

You can't estimate plating thickness simply by looking at it. My guess is that, if you dissolve the substrate, the gold will break up into small pieces. In general, it has to be about 100 micro" or more to stay in one or several large pieces. Hot NaOH or HCl would dissolve the Al but there would probably still be a layer of nickel on the back of the gold. If the gold is thin, hot nitric might dissolve the nickel. In all cases, I wouldn't even consider doing this in an apartment.

For several reasons, you would be much better off selling these than refining them.

If I were to try and recover the gold, I would probably use the electrolytic sulfuric stripper, but certainly not in an apartment.


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## Xsfacade (Sep 8, 2013)

You have given me a lot to work with. As for the thickness I did a check on the end of one and it is more then the industry standard of 25 microns used today. I did learn they were made at a time when more metals were used because the process was not as efficient. The other issue is the aluminum which I am guessing since the weight seems fairly less then what other metals might weigh. They still weigh around 3 pounds each so I imagine an alloyed aluminum of some sort. Can't I buy a gold testing kit locally so I know the exact ratio? I thought I saw something about it in another posting on here? Thanks for all the advice.


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## g_axelsson (Sep 8, 2013)

If the gold is plated onto another metal, silver or nickle then a drop of nitric should attack the intermediate layer and leave the gold and aluminum unaffected.
If the gold layer is thin it would attack the metal below through the gold, if it is thicker then a few scratches is needed to let the acid penetrate the gold.

If you select to try this route, read up on dangers with nitric acid first and start with a single drop.

I got two IR-reflectors with gold on aluminum that I have planned to do something about for a while now. Haven't tested it myself yet.

Göran


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## goldsilverpro (Sep 8, 2013)

Xsfacade said:


> You have given me a lot to work with. As for the thickness I did a check on the end of one and it is more then the industry standard of 25 microns used today. I did learn they were made at a time when more metals were used because the process was not as efficient. The other issue is the aluminum which I am guessing since the weight seems fairly less then what other metals might weigh. They still weigh around 3 pounds each so I imagine an alloyed aluminum of some sort. Can't I buy a gold testing kit locally so I know the exact ratio? I thought I saw something about it in another posting on here? Thanks for all the advice.


In other words, you have no idea what you are talking about. You have talked yourself into believing that you have a little gold mine there, where none really exists. There is no industry thickness standard and if there were one, it surely wouldn't be 25 microns. I've been in this business for 47 years and have only seen gold plated that thick a few times. And, the process was just as efficient 47 years ago as it is today and they would not have plated any thicker than was technically necessary - I doubt if those mirrors are that old anyway. Looking at the end will provide absolutely zero information as to the gold thickness, even to an expert. A 3# chunk of aluminum is pretty large - an example would be about 2" x 3" x 5", if my math is right. 

If one of those units contains more than $20 worth of gold, I'll eat my hat.


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## etack (Sep 8, 2013)

I had some gold plated Al that were in rings. There were two type I got. The foil came off in sheets that looked like the thickness of Mylar. It was thick enough that I had two of each of rings gave 7.21g of gold. It was real simple to do score and soak in nitric. This was for 10#s of Al.




Eric


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## g_axelsson (Sep 9, 2013)

g_axelsson said:


> I got two IR-reflectors with gold on aluminum that I have planned to do something about for a while now. Haven't tested it myself yet.


Quoting my self, how lame isn't that! :lol: 

Now I have tested, one of the reflectors were plated and nitric attacked the nickle plating and the gold floated away. A few drops of nitric was all it took.

The other reflector apparently had gold directly on aluminum as the nitric didn't do anything here. I tried to scratch the surface and the gold plating broke off in small flakes. Prolonged soak in diluted NaOH only loosened the thinnest gold at the edge of the reflector, the thicker gold in the center just got more shiny. Same result with HCl, it goes on the deep without creeping under the gold. This seems to be gold evaporated or sputtered onto the aluminum bar.

Plated gold with a drop of nitric acid.



Stripped of gold, only unaffected aluminum.



The resulting gold and dissolved metal.



Sputtered gold after a while in lye.



Göran


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## etack (Sep 9, 2013)

g_axelsson said:


> I tried to scratch the surface and the gold plating broke off in small flakes.



The large rings this happened with.(look on the right side of the right ring by the green paint mark on the table.) It looked like it was plated on chrome it would chip off if you hit it with a hammer. I had to score them and let them soaked in nitric for some time. It did get under the plating with time. Moore scoring the faster it would work I presume.

Eric


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## g_axelsson (Sep 9, 2013)

etack said:


> g_axelsson said:
> 
> 
> > I tried to scratch the surface and the gold plating broke off in small flakes.
> ...


Too bad there is no chrome under my gold... where the gold was thin I could attack it with lye and it left no chrome in the beaker, only thin gold. In the last picture you can see the piece I'm talking about, the end of the aluminum profile has been soaking for an hour and the white area is where the gold has fallen off. The reflector only looks cleaner.

I have an idea that I have to test when I get back home after work. Aluminum is passivated by the nitric as it is formed an oxide layer (actually sapphire). If I use a strong nitric acid mixed with just a few drops of hydrochloric acid maybe I can dissolve the gold without dissolving the aluminum.

Well, if I don't find any other way I think I can get it with reverse plating.

Göran


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## etack (Sep 9, 2013)

g_axelsson said:


> Well, if I don't find any other way I think I can get it with reverse plating.



Sulfuric is not a fan of Al. This is how some rudimentary bottle B-ombs are made.

youtube it lots of dumb morons showing you what happens like this one. give him a thumbs down for moronity. 

http://www.youtube.com/watch?v=X07V0iDaHS4

Eric


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## goldsilverpro (Sep 9, 2013)

I have stripped gold from aluminum using the sulfuric stripper several times with great success. Keep the sulfuric strong and don't use too much current to allow the solution get too hot. 

As a service for a large electronic company in the Silicon Valley, I once stripped very heavy gold plating from several very expensive machined aluminum boxes that were about 3" x 3" x 3". They wanted to re-plate them and they could tolerate no attack on the aluminum. The deal was that I got the gold and returned the pristine clean boxes. This was very successful and generated more business for me. It took 20-30 minutes to strip due to the very thick gold. Using about 1/2 gallon of solution, I probably didn't exceed 2 amps.

Those acid bombs utilize weaker sulfuric and confine the H2 generated. HCl would do the same thing, probably faster.


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## Xsfacade (Sep 9, 2013)

First let me say I do not mean to upset anyone by quoting info I researched online. I am not a pro and do not know how to do this or I would be telling others instead of asking for help so please keep that in mind. No disrespect is meant. I like to say that if it were not for ignorance I would have nothing to look forward to, hehehe. As for expectations I truly have none. I paid $5 for each from a salvage yard and actually wrote it off since they are actually very unique plus I just enjoy them as one might a piece of crystal. I have since decided to see about getting my hands dirty by recycling the gold so as to learn and maybe do it on the side with other items since I have an unlimited supply of computer parts including cpus, ram, and other items plated in gold. I designed the website for the salvage dealer and he gets computer parts but really doesn't want to deal with them since China has blocked shipments to his wholesaler. As for the mirrors they are not mylar so I am on to the nitric acid. I am a certified lab tech used to handling the really fun stuff like hydrofluoric acid but I cannot do this in a lab since it is personal. I also have no experience with gold other then schooling very long ago. The lab I worked in the longest dealt with petroleum samples for the EPA. I cannot thank everyone enough for all the advice. This board is a true cornucopia of information. I am in the midst of reading Hoke's book but since it was published so long ago I thought it prudent to ask about theses mirrors since lasers were only science fiction in his time :lol:


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## Harold_V (Sep 9, 2013)

While I have no experience in recovering gold from aluminum, one thing I know is that aluminum does not dissolve in nitric, but it will most likely cause the gold to release if you allow the mirrors to soak for a period of time. In my opinion, it would be worth the attempt, as you need nothing more than a 300 series stainless vessel (or a glass vessel) and time. If you're not in a hurry, I fully expect you can recover the gold without issue. You would then have the base aluminum, which can be sold as scrap. I make mention of a stainless vessel in lieu of a glass vessel in the name of safety. Do not use plastic---not for nitric. 

This is not to discourage a sulfuric stripping cell, assuming you'd have future need. If not, the nitric process would be my first choice. 

Harold


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## pattt (Sep 10, 2013)

Hi xsfacade, welcome to the forum,

just as info:



Xsfacade said:


> I am in the midst of reading Hoke's book but since it was published so long ago I thought it prudent to ask about theses mirrors since lasers were only science fiction in his time :lol:



Hoke is a she 

Pat


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## Harold_V (Sep 10, 2013)

pattt said:


> Hi xsfacade, welcome to the forum,
> 
> just as info:
> 
> ...


Indeed, and she was likely far better informed on the subject than most people of today, save for those who have an extensive education in the field. 

Don't be concerned about the time frame within which the book was published. The information contained within is still very valid, keeping in mind safety was no consideration. As far as the refining techniques are concerned, if a reader understands what she teaches, said reader can be successful in refining. What she taught was the basics of refining, which one must know and understand in order to progress. 

Harold


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## Xsfacade (Sep 10, 2013)

Hoke is a "she". Wow! I thought women were treated poorly back then so I never noticed anything other then the initials and last name. Shame on me for that faux pas. Another lesson learned in one short thread.


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## Harold_V (Sep 10, 2013)

Xsfacade said:


> Hoke is a "she". Wow! I thought women were treated poorly back then so I never noticed anything other then the initials and last name. Shame on me for that faux pas. Another lesson learned in one short thread.


Why do you suppose she used only her initials? :lol: 

For the record, her name was Calm Morrison Hoke. 

Harold


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## FrugalRefiner (Sep 10, 2013)

Xsfacade said:


> Hoke is a "she". Wow! I thought women were treated poorly back then


Has something changed? I think they're still treated poorly.

Dave


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## g_axelsson (Sep 13, 2013)

g_axelsson said:


> I have an idea that I have to test when I get back home after work. Aluminum is passivated by the nitric as it is formed an oxide layer (actually sapphire). If I use a strong nitric acid mixed with just a few drops of hydrochloric acid maybe I can dissolve the gold without dissolving the aluminum.


That worked better than I hoped for!

First I added a few drops of nitric and a drop of hydrochloric acid, in approximately 10:1 proportions. The gold disappeared fast and I got a few drops of yellow liquid. No trace of any damage to the aluminum.
I actually left the AR and gold chloride mixture on the aluminum for over an hour and it still didn't cement back.

First trial, a few drops of nitric with little HCl, a few minutes after adding it.



Stannous test of the wash water from above. The result is in the beaker to the right.



The next day a new test, a few ml of HNO3 and a couple of drops of HCl, this time I used a dropper to the gold covered aluminum bar and let the acid drop back into the beaker. It took longer time as the gold were covered by only a thin film, but eventually the gold were gone and only aluminum left.

Third trial, mixed a new batch of a few ml HNO3 and a bit more HCl. Approximately in 5:1 proportions. Now the acid attacked the aluminum a bit but it dissolved the gold faster. Only on sharp edges are there any gold left, it was hard to get the acid to stay long enough to dissolve the gold.

I saw no cementing of gold in any of the tests. There could have been some at the end. I had a black spot that didn't disappeared until suddenly when it went all yellow and then it dissolved and left clean aluminum. It appears that the nitric acid passivated the surface so no cementing could happen.

Almost done, only a bit left. Dropper and gold chloride in the background.



For once, a plan worked perfectly! 8) 

Göran


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