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Replenishing HCL + H2O2 PCB etchant?

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Steve Ward

Sat Jul 28 2007, 12:03AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Im certainly not a chemistry guy (i mean, i passed chem 1 just fine, but didnt learn a whole lot) so excuse some of my ignorance here. I will get straight to the point... has anyone toyed with replenishing the common PCB etchant : 1 part 28% conc. HCL with 2 part 3% H2O2? I read something about bubbling air through it to as an oxidizer rather than adding more H2O2. Im wondering if its really that simple to make this stuff active again. I found that i could etch much more copper with a freshly mixed solution, when compared with stuff that was already used (but reheated in hot water bath). I find it hard to believe that so much solution would get used up by so little copper... so there must be a way to extend its lifetime.

All help is appreciated.

Steve

Hazmatt_(The Underdog)

Sat Jul 28 2007, 12:53AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I don't bother with the 3% peroxide because the 3% is active, the rest just adds to the problem of disposal. I get the 30% peroxide from the salon supply and the 34% HCl from the hardware store as usual. That way you don't have a lot of volume to store prior to disposal. CuCl2 is toxic so you can't just dump it down the drain, unlike what Radio Shack suggests on its Ferric Chloride product.

Once H2O2 decomposes, that's pretty much it. The only way you're going to get peroxide in that solution is to dump in a solid peroxide salt (NaO2) that would react with the excess HCL. So once its spent (Reduced) that's pretty much it.

The spent solution does work marginally as a deoxidizer for dirty boards, but that's mostly due to the fact that the HCL reacts with the Copper oxides.

I think you'd be better off making a fresh batch every time or have a Ferric Chloride etch tank. I have the etch tank (5 gal poly bucket) and it solved my waste problems (no more dumping).

Chris

Sat Jul 28 2007, 02:44AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

You can regenerate the HCl by adding concentrated H2SO4 to the CuCl2 which can be derived by drying or boiling away the solution. You probably want to use the dihydrate of cupric chloride which is left by heating the salt not past 100Â°C, since this is an aqueous reaction and does not work too well with perfectly anhydrous reagents. CuCl2 + H2SO4 --> 2HCl + CuSO4. The solution must be so concentrated that HCl bubbles out as a gas, and by bubbling that into water you get your hydrochloric acid.

By heating the copper sulfate you now have to over 650C it will decompose to copper oxide and SO3. CuSO4 --> CuO + SO3. SO3 is the anhydride of sulfuric acid, but you probably won't want to try just adding it to water to regenerate your H2SO4. The reaction is too exothermic and will just make acid steam and mist. Instead, SO3 is added to already concentrated H2SO4 to form oleum (any complex of SO3 and H2SO4, including pyrosulfuric acid, H2S2O7 , which is a solid). This substance (oleum in general, not neccessarily pyrosulfuric acid itself) is then added slowly to an amount of water until any concentration up to 100% of H2SO4 is yielded.

The copper oxide left from the prior decomposition can be smelted with carbon at something like 1200Â°C to yield copper metal again, if you are that worried about it.

Impractical? Possibly, though each of these reactions by themselves have been historically important ways of producing these pure acids and metals. Also, you asked for it, and they are fun and interesting.

This will get you everything you started with back except the H2O2, which, as others have mentioned, is gone. You can try to synthesize and distill that too if you want but I will say right now the explosive dangers are great and it's probably not worth it. HCl and SO3 gases are nasty enough...

Eric

Sat Jul 28 2007, 03:31AM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
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Steve, this looks very simple. It doesn't use any peroxide, just the CuCl2 + HCl to etch. It could be slow but you can regenerate just using air.

sparky

Sat Jul 28 2007, 04:45AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I would NOT be adding H2O2 to Muriatic Acid... thats HCl in 28% solution + .... this forms a very reactive mixture that will decompose violently. You've been warned!! Try this with Muratic acid and 35% strength H202 --- watch out!! It may take a few minutes but it will heat up - steam and release its contents violently - sometimes explosively!

Swany

Sat Jul 28 2007, 07:10AM

Registered Member #261 Joined: Mon Feb 27 2006, 12:34AM
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Small amounts of certian acids make H2O2 more stable; but chloride ions (perhaps halide in general) catalyze H2O2 decomposition. I heard a story of a person who had some NaCl and conc. H2O2 in solution for something or another, in a bottle. Stepped into sunlight and it warmed, then erupted. Delayed, as sparky described.

However, in the forming of organic peroxides (do not attempt, please, the danger cannot be overstated), HCl is used as as the acid along with an appropriate ketone and relatively concentrated H2O2. I've notice bubbling when the HCl is added to concentrated solutions, but chances are the activated complex reacts with the ketone before it decomposes to oxygen and water... that would be my guess anyhow. I will have to look at the reaction mechanism. In lit. conc. H2SO4 is used as the acid catalyst, yeilds are also higher.

EDIT: I know nothing about circuit board etching, but I have gathered it is FeCl3 solution that oxidises the copper and is reduced to Fe+2. To regenerate that, simply adding H2O2(decomposes due to the chloride ions in solution; green turns to rust colour with bubbling), bubbling air through, adding an oxidiser, etc. The Cu+ in solution should be oxidised as well. Like said, I dont know about etching, but the resulting solution should oxidise copper. I think.

Steve Ward

Sat Jul 28 2007, 07:49AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Hey Eric, I ran across that page when i was doing my initial research. He says he generates the Cupric Chloride by initially mixing HCl and H2O2 with some chunks of copper in it (at least that is what i got out of it, maybe im missing something). Im tempted to just take my collected "waste" etchant and try bubbling it for a few days to see if it clears up and allows more etching. That site does make more sense to me now that i read it a second time, though. Unfortunately he doesnt have a detailed "how-to" on using the H2O2 to start the reaction off.

I think you'd be better off making a fresh batch every time or have a Ferric Chloride etch tank. I have the etch tank (5 gal poly bucket) and it solved my waste problems (no more dumping).

The main reason im looking into this is to reduce my waste (chemicals are cheap enough, but i don't want to be harming the environment). I may in fact just switch to ferric chloride if i can find a reasonable source for it. Id rather not have a 5 gallon bucket of it around, though. How much PCB have you etched with that amount of FeCl3? I plan on doing quite a few boards (maybe averaging 1 per week in the long run) and in the past i havent had too much longevity with the FeCl3 i had.

Also, what is the proper way of disposing of my left-overs? I know it has CuCl2 in it now... so dousing it with NaOH to neutralize the acid probably isnt gonna cut it. I did try this with some of my waste and it consumed an enormous amount of powder before i just gave up :(.

Marko

Sat Jul 28 2007, 10:58AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Also, what is the proper way of disposing of my left-overs? I know it has CuCl2 in it now... so dousing it with NaOH to neutralize the acid probably isnt gonna cut it. I did try this with some of my waste and it consumed an enormous amount of powder before i just gave up :(.

Yes. Flush it into drain like nothing happened.
I use 19% muriatic acid together with 12% H2O2 hair-bleaching 'cream' in a small amount, 20-30% is usually enough.

What do you think, that there are some special safety procedures? (Here, at least?) The hair cream and cleaning acid will anyway go to sewerage no matter of use. CuCl2 will dilute up very quickly.

Both ingredients are so cheap that I never bothered about recycling. Any other chemical or effort is practically not worth the price.

...

Sat Jul 28 2007, 04:09PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The correct way to get rid of it is to take it down to your local Household Hazardous Waste Roundup, which are required by law 2x a year in the US, and I would assume that there are similar programs in other countries. Just drive whatever you have down to the location, and some guy will unload it from your car and life is good.

In any case, it is true that the few grams of CuClx won't really hurt the environment, but the treatment plant can't take out heavy metals, so you are essentially dumping it strait into the local groundwater.

Personally I prefer the ammonium persulfate etchant, it comes as a powder that you add to hot water, dump in the board, let it soak for like an hour (it is really slow when it isn't being heated), and you are left with CuSO4 (pretty harmless).

Hazmatt_(The Underdog)

Sat Jul 28 2007, 07:09PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I just wanted to remind you that HCl without the H2O2 isn't going to do much to the Copper. HCl cannot dissolve Cu on its own, you learn that from chemistry and the redox series, so it needs a strong oxidizer like H2O2 to start the oxidation of Cu to Cu2+.

You can get H2O2 as 30% in a liquid in a white bottle from the salon supply. I don't use the gel stuff. The label has some kind of '30' on it and you should be able to open the cap and take a look inside. It should be a clear liquid not a white paste. You could even shake the bottle to make sure its a liquid in there and not a paste. Unfortunately I forgot the brand name.

The reason for the 5 gal bucket: Almost any board will fit in it.
I have etch trays too and sometimes I have a hard time getting a 12" long board to fit in there, so I put it in the bucket diagonally.
Ferric Chloride or Ammonium Persulphate, or whatever you like would be great in a bucket because you can leave a fish tank heater in there, it contains your waste effluent, is reasonably portable, and if you have to you can seal the lid.
There are also 3 gal poly buckets available too, so if you need a smaller etch tank you can get one and use a small fish tank heater too.
Other then that you can go to your local plastics dealer and have a poly pro tank welded in any size you like, its just not as spillproof as a bucket.

I have etched lots and lots of boards in my tank, maybe a hundred by now. Every once-in-a-while the tank effectivity gets low due to sludge ferrous hydroxide in the bottom. But this is easy to deal with. I pour the contents into one of my jugs and remove the hydroxide for drying, then pour the etchant back in the tank. I can buy FeCl3 as powder and add that to the tank without increasing the volume of the tank, this I like. That way I can 'rejuvinate' my tank anytime I wish without increasing volume. The concentrate comes in a baggie from DATAK, as well as the liquid concentrate.

Once the Ferrous Hydroxide dries out and looses its water it becomes an iron oxide with some latent copper chloride. I have played with this in reactions a bit and its not really a desirable oxide to play with because its fairly low quality, but if you really want to you can use it for other things, I probably don't need to mention what I've used it for.

Anyhow, the bucket specified is used because boards will fit and waste is not an issue, just rinse the board off sparingly back into the tank. The tank will sludge up on the bottom after a lot of copper has been etched away, but you can either 'treat the tank' or ignore it and add powder, its your option.

I forgot to mention, I've had no problem with concentrated HCl and H2O2. It will begin to decompose rapidly and make a 'volcano' sort of mess, so just cut the concentrate down with water. I work with a lot of chemicals and usually have no problems with concentrates, so long as you mix them sparingly. Once you get to a constantly boiling mixture definately stop, there is no need to add anything more to that, and it should be diluted by half at least before adding any metal to it.

Matt

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