I am a beginner with PCBs and wanted to start making some. But before I did, I wanted to make sure I was completely prepared. I just wanted to make sure that the information I have is correct and had another question. How do you dispose of Ferric Chloride? While researching, I found out that the most popular way is using washing soda to neutralize it and then pour it down the drain after it is completely neutralized (measured with pH paper). Is this correct? Also, I read that using this method leads to a copper "sludge" being left behind. How do I then dispose of this "sludge"? Finally, how much can I reuse the ferric chloride? I just want to know how to dispose of this with keeping the environment in mind.
Asked
Active
Viewed 1,515 times
6
-
This will almost certainly vary with local regulations. – JYelton Oct 01 '20 at 20:14
-
2If you are going to attempt it, be careful, the reaction is exothermic and if you apply too much too fast you can end up with the mixture getting exceedingly hot and release a cloud of Chlorine gas. – Tom Carpenter Oct 01 '20 at 20:54
-
How many boards are you going to make? I did a few dozen before I decided to let the professionals do it (dead cheap nowadays) and the amount of waste was I think less than a few hundred grams of sludge and two or three litres of solution on top. It's still in its canister. Some day I will bring it to a waste disposal facility. – Janka Oct 01 '20 at 21:30
-
1@Janka While professionals are dead cheap, they still require you to wait 3 to 4 weeks to receive your boards, so etching will stay a common practice because it elimlinates that enormous wait time. – Elcan Oct 02 '20 at 06:47
-
When you etch with ferrous chloride as a hobbyist, you can easily see the result is not worth any single minute of your time. 30 years ago this was different. Plus, you have to drill all the stupid holes yourself and you can't have proper vias with hobbyist means. It's okay to try it, but you certainly won't get to an amount of waste that gives you a headache. – Janka Oct 02 '20 at 11:58
2 Answers
5
Both Sodium Hydroxide and Sodium Carbonate (washing soda) can be used to neutralise Ferric Chloride. Once the pH has risen above 7 the etchant is neutralised. If you are going to attempt it, be careful, the reaction is exothermic and if you apply too much too fast you can end up with the mixture getting exceedingly hot and release a cloud of Chlorine gas. The sludge left at the end will be primarily Iron Oxides (rust) and Copper Hydroxides, which are not particularly harmful.
However, my advice would be to check local regulations, and see if there are any waste disposal sites around which can deal with the waste properly.
When using Ferric Chloride as an etchant, you can end up with large amounts of wastage because the Copper Chloride that is left behind ends up weakening the reaction, until you end up with a mixture that is incapable of performing its job, even though there is still large amounts of FCl3 left.
If you want to minimise the amount of wasted etchant, the best technique I've found is to use a wiped sponge approach to etching rather than a submersion approach.
Typically people dunk their boards in the etchant and leave it a while, perhaps with some agitation. This means that your etchant solution become full of the Copper Chloride remnants.
Instead, a better approach is to, wearing rubber gloves, dip a small sponge (e.g. old washing up sponge) into the etchant solution, and then wipe that sponge gently across the surface of the copper. The combined agitation and strong etchant will rapidly etch the board. Once it stops etching, drain the excess fluid from the sponge (CuCl) into a container, and then repeat the process. The end result is you end up with a container of etchant with little copper contaminant, and a container of mostly copper chloride. This way your echant lasts much longer and there is less wastage.
Tom Carpenter
- 63,168
- 3
- 139
- 196
0
- Contact your local hazardous waste disposal company
- The solution must not be put down the drain because of residual copper ions left in it. To make it safe for disposal, you can add sodium carbonate (washing soda) or sodium hydroxide to neutralize it, until the pH value goes up to between 7.0 and 8.0, testing it with indicator paper. Copper will be deposited as a sludge. Allow the sludge to settle, pour off the liquid, further dilute it with water and pour it down the drain. Collect the sludge in plastic bags and dispose of it as required by your local waste authority.
Frankly, I don't think the ferric-chloride is such a environmental threat. That small amount of copper won't do nothing if you drain it.
Marko Buršič
- 23,562
- 2
- 20
- 33