Disposal of Hydochloric Acid and Hydrogen Peroxide etchant - Page 1
Forum section: electronics / beginners

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 09:08:09 am
content: Hi All,I am moving house next week and the time has come to dispose of a small stock pile of Hydochloric Acid and Hydrogen Peroxide etchant. I have about 2 litres of the used etchant in plastic bottles. I live in South Africa and unfortunately our local rubbish disposal does not handle chemicals so I would have to take it to a private waste disposal company for a large fee.I can't seem to find any information on the internet about disposal of this etchant. Any ideas on how I can safely dispose of this stuff?

author: Ian.M
author_rank: Super Contributor
timestamp: March 24, 2016, 09:24:00 am
content: That's difficult on such a short timescale. Yes you can neutralise it and precipitate out the copper as oxide or carbonate, but then you need to let it settle and separate the copper containing sludge for safe disposal, after mixing it with cement or similar to make it solid and reasonably inert. I don't think its realistic to expect to get that done while in the last stages of packing for a move. If you really cant take it with you to process when you have the time and equipment available to do it safely (either for disposal or to regenerate as acid cupric chloride etchant), you'll have to bite the bullet and pay for disposal.

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 09:28:41 am
content: Damn, I just got a quote to dispose of the stuff privately and the lowest estimate was $750 US since it needs to a lab for testing first. Would there be any danger in just letting the stuff evaporate in the sun?

author: Ian.M
author_rank: Super Contributor
timestamp: March 24, 2016, 09:41:29 am
content: If you can keep pets, kids and livestock away, the only risk is from the acid fumes. The dry residue of copper chloride can be used to make PCB etchant in the future.As you are on a tight schedule, maybe boiling it down to a concentrate or even to dryness outside in a glass or ceramic pan, would be more practical, then take the residue with you either for future use or safe disposal.

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 10:11:54 am
content: That sounds more reasonable than keeping the liquids. What would a safe distance be to keep humans and pets away from the fumes?

author: amyk
author_rank: Super Contributor
timestamp: March 24, 2016, 10:47:14 am
content: You can neutralise the acid with a base first, which will just leave water containing chloride and ions of whatever base you used, plus the copper.

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 10:50:03 am
content: So I could add some baking soda and then leave the solution to bake in the sun? This would leave me with a solid brick?

author: ElektroQuark
author_rank: Unknown
timestamp: March 24, 2016, 11:06:00 am
content: Use CaO or CaCO3 to neutralize.

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 11:08:12 am
content: Quote from: EdoNork on March 24, 2016, 11:06:00 amThank you. Unfortunately I'm as far from a chemist as one could be, why would calcium carbonate be better than sodium bicarbonate?

author: mij59
author_rank: Frequent Contributor
timestamp: March 24, 2016, 11:18:09 am
content: The reaction of sodium bicarbonate and HCL gives NACL2 ( kitchen salt ) , CO2 and water.The end product of the etching should be CuCL2, which is also a salt ( mineral).

author: bitshift
author_rank: Regular Contributor
timestamp: March 24, 2016, 11:50:35 am
content: Awesome, so if I slowly add sodium bicarbonate and leave to bake in the sun, I will be left with some kitchen salt and CuCl2. Any hydrogen peroxide left in the solution, I'm assuming will boil off in the sun? These solids would still then need proper disposal because of the CuCl2? It would just be easier to handle since it will be in a solid form?

author: mij59
author_rank: Frequent Contributor
timestamp: March 24, 2016, 12:15:37 pm
content: Maybe it's safe to flush it down the drain after neutralising .

author: mmagin
author_rank: Frequent Contributor
timestamp: March 24, 2016, 02:26:41 pm
content: In the past when I did Ferric Chloride etching, I precipitated out the copper using 'washing soda', Na2CO3 to make an insoluble copper carbonate. It was pretty easy to pour off the liquid (after giving it a bit to react and settle out). This left essentially copper-free liquid to pour down the drain. The copper carbonate (and excess sodium carbonate) precipitate I just tossed in the trash at the time. Modern landfills in the US tend to be lined and I'm sure there are plenty of worse things. Keeping copper ions out of the sewer (where they may eventually end up in streams/rivers/bays/etc.) is a bigger priority IMHO, since a lot of aquatic life has a much harder time with copper toxicity.I'm not enough of a chemist to know if sodium bicarbonate can be substituted for sodium carbonate.

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2016, 02:48:08 pm
content: Copper sulphate has been used in drains to kill invasive roots and has been sprayed on plants as a fungicide. So small amounts of copper in the environment are not some kind of ecological disaster.You have two litres of a solution containing a small amount of dissolved copper. If you were to flush it down the drain one cup per day with lots of water it would be so dilute by the time it mixes with thousands of gallons of other waste water that it would never be noticed. This is not a suitable method for regular disposal, but as a one time thing it's going to be pretty harmless.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 24, 2016, 02:58:38 pm
content: After first agreeing with Ian, I will point out that if your concern about toxicity in the environment is higher than this you should never have started down the path of making boards in the first place. The lowest impact on the environment would have been to start a hobby weaving place mats from invasive weeds in your neighborhood. After carefully destroying their seed pods.

author: ElektroQuark
author_rank: Unknown
timestamp: March 24, 2016, 07:48:01 pm
content: CaCl2 is highly soluble, so you will end with a sort of fluid, that will be easily disposable.

author: TheAmmoniacal
author_rank: Unknown
timestamp: March 24, 2016, 08:01:29 pm
content: Evaporate the stuff down to a solid, throw that in your regular garbage bin (i assume they just burn it, reducing it to the metal).If you neutralize with excess baking soda, making insoluble copper carbonate, that's safe to throw away outside in the rocks.

author: KL27x
author_rank: Super Contributor
timestamp: March 25, 2016, 12:06:04 am
content: QuoteIME, definitely do NOT neutralize it to precipitate out the solids. Some of the solids precipitate out, but what's left is a royal mess.And I would certainly not mix it with cement. You will be left with copper salts and copper is worth money. And it is not some crazy poison. It is soluble in acidic water, in which form it is toxic to ocean invertebrates in high enough concentration, is all. What you got there isn't going to be a pimple on a pimple on the ass of a gnat.I would definitely just let it evaporate in the sun. If you have a place where you can put it that is protected from rain, it won't take long.I use a different etchant (cupric chloride), but I just leave my tank outdoors. If I don't use it for awhile, it dries up into dry green solid/crytals in very short order during the summer. What's left in 2L of used peroxide/HCl probably won't be all that much solid, I imagine.Don't even throw it away. Keep it. When you have enough you can make a liter of cupric chloride by adding HCl and water to it.In small amounts of it, we call this stuff hazardous waste. If you have enough of it, it's a refined chemical. It took work/heat to create this stuff, and returning it to the environment and letting entropy take its course is just simply wasteful.

author: Lee Leduc
author_rank: Regular Contributor
timestamp: March 25, 2016, 12:40:35 am
content: Adafruit has a paper detailing etchant disposal. Here's the link.https://blog.adafruit.com/2009/01/25/the-chemistry-of-home-etched-pcbs/