Ferric chloride questions

[Geoff Keyes]

My current mix is pretty tired.  I want to replace it. 

 

What is the best way to dispose of the old tub?  There is no copper in it, I only use it to etch ferrous metals

 

Has anyone ever used the powdered, mix your own material?  What I'm looking at says mix 4-1, is that good for steel, or should I mix it differently?

 

Thanks

 

Geoff

[Jaron Martindale]

I use the powder (reminds me, I need to order another bottle...) and I use the ratio of 4ounces of powder to 1 gallon of water as recommended in this thread, It seems to work well enough

[J_Martin]

There are several videos on Utube on how to make your own. It looks pretty simple.

[Alan Longmire]

16 hours ago, Geoff Keyes said:

What is the best way to dispose of the old tub?

 

I did a quick check to see if adding sodium carbonate (washing soda) would detox it, and looks like it can.  The reaction should produce iron hydroxide (goethite), salt water, and CO2 gas.  I neutralize in sodium carbonate after etching wrought in ferric, since the porosity of wrought usually results in delayed rust from trapped FCL the Windex can't reach.

 

 

[Alan Longmire]

Carrying this to its logical conclusion, if you add sodium carbonate until it stops fizzing and let the tank settle, you'll have a tub of slightly salty water that should be safe to pour into a septic system plus a lot of nasty-looking iron sludge that can be dried and left in a pile somewhere.

 

I'm going to need to do this soon, one of my old tanks is also exhausted and my current method of disposal (giving it a dirty look and thinking about it from time to time) has not produced results in the year I've been doing it...

[Brian Dougherty]

37 minutes ago, Alan Longmire said:

my current method of disposal (giving it a dirty look and thinking about it from time to time) has not produced results in the year I've been doing it...

 

I think there are a number of people in my life using that same strategy on me 

[Jerrod Miller]

6 hours ago, Alan Longmire said:

a lot of nasty-looking iron sludge that can be dried and left in a pile somewhere

You mean form into a puck that will be used for a future smelting project, right?

[Alan Longmire]

1 hour ago, Jerrod Miller said:

You mean form into a puck that will be used for a future smelting project, right?

 

I wasn't gonna say it, but yeah.  Mine has some copper as well from dipping hawk heads with sterling silver inlays, but not enough to bother. I hope...

[Bob Bryenton]

I make my own mix: 

 

[Brian Dougherty]

11 hours ago, Jerrod Miller said:

You mean form into a puck that will be used for a future smelting project, right?

Wait, that's a thing?

[Alan Longmire]

1 hour ago, Brian Dougherty said:

Wait, that's a thing?

 

It can be!  The precipitate from the reaction is just FeO(OH), aka bog ore.  There won't be much from a two-gallon tank, but it can go with the mounds of grinder swarf out back that have been slowly returning to oxide form over the years.  All smelting is is taking iron oxide and converting it to iron via reduction, the actual source of the oxide isn't really important.  Grinder swarf, bandsaw swarf, forge scale, precipitated iron hydroxide, it's all potentially smeltable.  If you do with with unoxidized iron in a shaft furnace it's called grappage, if you do it in a short shaft hearth it's hearth steel.  If you do direct reduction in a crucible with added carbon and carbide-formers, it's crucible steel.  All sorts of ways to go down that rabbit hole.

 

Is it worth it? Nope, not financially!  That's why Jeff Pringle lights his wootz furnaces with $20 bills.  For the cool factor?  Yes, if that's your thing.

[John Page]

On 5/11/2026 at 7:04 AM, Alan Longmire said:

 

 I neutralize in sodium carbonate after etching wrought in ferric, since the porosity of wrought usually results in delayed rust from trapped FCL the Windex can't reach.

 

 

 

This is a great tip, thanks! I always run into that issue, looks like I have to find some and make up a neutralizing tank 

[Alan Longmire]

49 minutes ago, John Page said:

 

This is a great tip, thanks! I always run into that issue, looks like I have to find some and make up a neutralizing tank 

 

Any grocery store ought to have it.

 

 

Just use a plastic bucket or pipe and make a warm saturated solution in water.  Basically keep adding until it won't dissolve any more.  It'll last a long time in use and will neutralize most etching solutions and browning/blueing salts as well.  Wear rubber gloves, it's highly alkaline and very slippery.  Costs about $5 for a box that size.

[Brian Dougherty]

I love this:

 

Improves Liquid Detergent Performance by 15% *

 

*- For Mustard and Blood Stains

 

You have to have your priorities right in this world.

[John Page]

Pretty slick! To neutralize the bluing too is great!

[Francis Gastellu]

The other option is to use electrolysis (with an inert anode, say using graphite) to remove some of the iron from the solution, then adding a bit of hydrogen peroxide. That will refresh the ferric chloride. Unfortunately 1) it's hard to tell how much iron you really need to remove or hydrogen peroxide to add, and 2) that will generate chlorine so that should be done outside with a nice breeze.

 

It's certainly a bit more involved than just replacing a batch but it's also less wasteful.

 

The other advantage is that if the ferric chloride contains copper, the electrolysis will preferentially take out the copper, so that's a way to clean a dirty solution too (stop when the cathode starts plating iron instead of copper and skip the hydrogen peroxide step).

 

edit: it occurs to me that a lot of the hobby grade graphite is low density with a binder, and that will quickly fail in the solution and erode the anode. You'd want electrode grade or EDM graphite, or a piece of SiC crucible (though I'm not sure about the conductivity), or carbon rods from old zinc-carbon batteries. Or you could switch to platinum or titanium, but that's a bit beyond hobby budget

Edited May 14 by Francis Gastellu
caveat

[Alan Longmire]

I like it!  Is the cathode just mild steel?  Not too keen on the chlorine part, though.  

[Francis Gastellu]

1 hour ago, Alan Longmire said:

I like it!  Is the cathode just mild steel?  Not too keen on the chlorine part, though.  

 

Stainless makes it easier to take out the plating since it won't bind but unless you want to harvest it, mild works just fine. And yes, chlorine isn't great... that's why I use ferrous sulfate in that other thread since that gives out hydrogen instead, but here you don't have a choice.