How I chemically remove scale from steel ...the clean way recycling chemicals
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- Опубликовано: 23 апр 2021
- Many videos show how to remove mill scale by pickling metal, but few to none show how to deal with the spent chemicals. In this video I address this problem and show the procedure I used to chemically remove the mill scale from steel generating little waste and with some ideas on how to recycle the acidic liquor or to make it safe and easily disposable.
When the mill scale is consistent and the steel is meant to stay indoor, the removal of the scale can be safely disregarded. This was the case when I made the frame of my hydraulic press that you can see here: • Hydraulic Press (brake... . But in other cases it is really necessary to remove it.
The mill scale is a mix of various iron oxides that adhere to the surface of the metal forming a tough layer. Mechanical methods or heating can be used to remove the scale, but they may sport some undesirable drawbacks. No method is perfect but pickling is quite effective particularly on smaller parts and where no deformation and thermal stress is required.
So this video focuses on simple chemistry, applied to process mild steel in metalworking.
I just followed a class in chemistry, but I'm not a chemist therefore, even though I felt the need to explain the reactions showing the related formulas, I hope no major errors slipped in the show.
CAUTION-DISCLAIMER
This video is not meant to be a tutorial, it just shows my experience and experiments.
Working with chemicals requires precautions: always wear safety goggles, gloves and wear proper clothing to protect yourself. Wear closed shoes. Remove rings and jewels. DO NOT eat or drink while working with chemicals. Keep children and animals out from the area. Some chemicals may generate very harmful fumes so good ventilation is of paramount importance, and sometimes still not enough requiring a specially designed fume hood.
Also some chemicals may unexpectedly react with the materials the furnitures are made.
Credits for photos of oxides:
By en.wikipedia.org/w/index.php?t... - en.wikipedia.org/wiki/Image:Ir..., Public Domain, commons.wikimedia.org/w/index...
By Benjah-bmm27 - Own work, Public Domain, commons.wikimedia.org/w/index...
By Leiem - Own work, CC BY-SA 4.0, commons.wikimedia.org/w/index...
Other images shown in the video, when not proprietary, come from public domain. 
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Thank u a million. Forged a piece and didn't want to scratch it. Very thorough tutorial.
@accidental science. I want to etch some Damascus I made but cannot get ferric chloride at a reasonable price. In this video you did produce some ferric chloride and I would like to know if you can do a short video explaining the safest way to make ferric chloride.
Very nice video. I like the idea of using the remaining for PCB etching.
Excellent! Trying this on forge scale. Much appreciated Sir.
Good idea.
Forge scale is essentially the same as mill scale (surface oxidation at high temps.) So should work.
Like to know the results 🙂
I never liked chemistry in school. But I have to admit, this was interesting.
Thank you!
Great video
Thanks
Good tutorial and the best is the disposal part. I think the iron oxide can also be used as polishing powder.
Great point!
I use white vinegar. Use a plastic tote dump in vinegar submerse metal leave for about three days comes out beautiful.
I just use regular distilled white vinegar and submerge the part in it for 24 hrs. Does a really good job and less hazardous. Takes longer but I don't have any waste to deal with.
Well that is the thing I tested first, using aceitc acid at 10% concentration, with no significative results. I also read various sources to understand better the possible reaction and it seems only concentrated aceitc acid is able to react with iron(III) oxide, and at quite high temperature. Not sure here though. So I don't know how vinegar, which should be acetic acid at 5...6% concentration, could work. Please, may you provide more information? What kind of oxides the metal had? Was it rust (reddish) or actual mill scale (gray tough coat)?
@@AccidentalScience I use distilled white vinegar, I submerge the hot rolled steel part in it for 24 hours. It takes the mill scale off. Not much to the process, I use a kiddie pool if it is a large piece. Once it has been in the vinegar for 24 hours or so, I can scrub the mill scale off with a wire hand brush. Comes off with little effort.
Cool
Really interesting. Now if there was a similarly easy way to deal with used pcb etch. I hear the copper is the problem which shouldn't be put down the drain.
Yes, you are right. Copper chloride can even corrode your pipes. But it should be possible to neutralize the liquor with a similar method even though the salt should be recovered in that case being still toxic.
What is the mixture ratio in volume that you used for the hydrogen peroxide? I'm using muriatic acid at a 3:1 by volume in a 550 gallon tank. 300 gallons of water, 100 gallons of muriatic acid, how much peroxide would I need using a 3% H2O2?
550 gallon tank? Are you gonna remove scale to an air carrier? My experiment was just for small scale, not at industrial scale to remove scale (ouch, the pun :) ). I don't really know what happens at that volume. For small scale, say no more than a quarter of a gallon, the stoichiometric ratio would be (in weight) 5 parts of H2O2 at 3% and one of HCl (aqueous solution at 33%). Though, since the quantity of magnetite that would be converted into ferrous oxide (if my guess is correct) is not known but it should be relatively small, making a non-stoichiometric mixture of 2 by 1 would be enough. However, again, my experiment was meant for small scale, not for that large quantities. Even when neutralized that amount of liquor could not be disposed down to the drain or dispersed on the ground and must be treated properly. I am not titled to direct you how to deal with such a large amount, sorry. In chemistry I am just a hobbyist.
Thanks, yes it was very interesting. A question please, could I substitute sulfuric acid for the hydrochloric acid as I have a 20 litre drum of sulfuric acid. Thanks Stuart 🇦🇺
I have no experience with H2SO4 and you can deem ma as a hobby chemist, but as far as I understand it should work, first through a redox reaction with magnetite (mostly the composition of the scale) and then from ferrous to ferric sulfate. However sulfuric acid should react very well even with the underlying iron (in the steel). Also the neutralization should work but I haven't checked it out yet and I am not sure of the result. BTW I would have traded your sulfuric acid with HCl if you were not from the other side of the planet 😃. Cheers. Claudio.
P.s. iron sulfates are useful compounds, you can make merdents and inks out of them, among other things.
@@AccidentalScience Thanks Claudio, I appreciate the answer as I am hopeless at chemistry. I will give it a try and see how it goes.
Cheers Stuart 🇦🇺
@@scroungasworkshop4663 be careful with sulfuric acid, also look at the concentration: I wouldn't play with it at concentrations higher than 37%. Never give an acid water to drink: dilute acid into water and no the other way around. Use small quantities and outdoor. Remember you are the sole responsible of your actions.
Sorry for this disclaimer but I don't want to take any liability.
@@AccidentalScience Thanks for the warning. I am one of those people that takes responsibility for my own actions and I’m familiar with acid so sleep well my friend. Cheers Stuart 🇦🇺
I use HCL a lot when removing mill scale. Adding hydrogen peroxide is new to me. So if you would please give me some insight. Can I mix the two is a pump up sprayer? Or do they need to be applied separately? How much hydrogen peroxide to a litter of HCL? Thank you.
I think hydro peroxide helps to remove the passivated upper layer. In my experiment I've seen that a little amount of about 10% at 3% of concentration is enough. *This is experimental* though so in the case you'd like to try you'll do it *at your own risk only!* You must know what you're doing, the video and this comment are not a tutorial but merely a showcase of my experience.
Spraying acid is dangerous, adding hydrogen peroxide would make it even more dangerous. I'd avoid it altogether.
Great video thanks
Would Hydrogen peroxide make using white vinegar more effective.
Many thanks
No.
i dip my metal in HCL and some water. pull out after 30mints and wash with water with lots of dish washing liquid. the soap make a chemical reaction then dry with a rag, it turns gray and wont rust if you keep inside out of the weather . if you wash with water and bicarbonate it will rust in 40 mints
Interesting. What kind of soap? What's the reaction?
I see you mixed the bicarb directly into the HCl and mixed with a brush. What effect does adding extra water have to the neutralising process? I'd prefer to use a less concentrated liquid I can swirl in a bottle (less labour).
Many thanks.
Adding water simply dilute the liquor and you need the same amount of bicarb. to neutralize it.
@@AccidentalScience I'm not a chemist so I just wanted to check that an excess of water wouldn't stall it or something. :) Thanks for the video!
@@200milesaway6 Don't worry, I'm not a chemist too, I just took a three semester course in chemistry. I'm experienced in electronics.