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sodium bisulphate as a pickle for copper?

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fizzy25/01/2018 20:19:44
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In recent times conc Sulphuric acid has become near impossible to buy in low volume and at a reasonable price. Picking five or more boilers a week has taken its toll on my pickle tank solution and it needs renewing, so has anyone experience of using Sodium bisulphate - its cheap and easy to obtain?

vintagengineer25/01/2018 21:23:13
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Oneshot drain cleaner is 90% pure sulphuric acid and you can buy this from most from plumbers supplier.

roy entwistle25/01/2018 21:39:59
1172 forum posts

Brick cleaner I believe is also good

I've never actually tried it though

Roy

DMB25/01/2018 22:56:07
999 forum posts

Roy,

I think brick or patio cleaner could be hydrochloric acid, not sulphuric.

I have used hydrochloric to remove mill scale from hot rolled mild steel but the container appeared to smoke with the nasty fumes. I did it out doors of course. Wouldn' store either indoors as even in tightly sealed container, hydrochloric seems to rust nearby steel items so no longer store in workshop.

John

John Olsen26/01/2018 00:27:28
1034 forum posts
86 photos
1 articles

Citric acid works fine and you can buy it at the supermarket in powder form. I haven't done anything quite as big as a loco boiler yet but have done lots of smaller jobs.

John

Wout Moerman26/01/2018 07:32:50
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To answer the original question. I can't imagine that sodium bisulfate will work for pickling. It is a salt and not an acid.

JasonB26/01/2018 07:47:01
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I do all my pickling with Brick cleaner now, shifts Tenacity 5 as well as the above mentioned mill scale..

I find it far quicker than citric acid and as Fizzy is doing a lot of boilers can't see him wanting to wait several hours for the copper to clean up in citric.

Brass and Bronze fabrication before and after a 20min pickle, flux was HT5

Russell Eberhardt26/01/2018 08:09:30
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2577 forum posts
85 photos

Most brick cleaners are hydrochloric acid. Hydrochloric acid will not react with copper but it will disolve with tin so could affect the bronze bushes on your boiler. It might be worth doing some tests on your bronze before using it on your boilers to see how quick the reaction is.

Russell

fizzy26/01/2018 08:36:02
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The reason it works for pickling is : NaCl + H2SO4 → NaHSO4 + HCl

jaCK Hobson26/01/2018 08:45:29
170 forum posts
28 photos

I think sodium bisulphate is the main thing in many safety pickles. Safety pickle works so I'd expect soduim bisulphate to.

https://www.ganoksin.com/article/pickling-notes/

Martin Kyte26/01/2018 08:47:33
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1839 forum posts
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Seems to be the pickle of choice for jewelry makers.

NaHSO4 disaasociates in water to give the ions Na(+), H(+) and SO4 (2-) so acts like dilute sulphuric acid.

regards Martin

Muzzer26/01/2018 18:22:42
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Yes, with a pH of 1, you wouldn't want to rub it in your cuts and bruises.

It's sometimes mixed with salt solution to carry out a more aggressive salt spray test. It makes the test a lot more unpleasant, even for what you might consider to be "stainless" steel like 316.

Murray

Samsaranda26/01/2018 19:37:54
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927 forum posts
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Citric Acid may be more gentle in its action but this is an advantage as nowhere near as aggressive as other acids so much safer to use, it takes longer but are we all in such a rush that we can’t spare the odd hour or two. Citric Acid readily available in any quantity that you want on EBay and Amazon.

Dave W

Norman Billingham28/01/2018 09:30:39
34 forum posts

Sodium bisulfate is the material you get by taking sulfuric acid and adding enough base (e.g. sodium hydroxide) to get half-way to neutrality. I used it as a pickle for gilding metal in a silversmithing shop when doing a course. I don't know what concentration it was but the pickle bath was maintained at 50C electrically. Copper alloy black from annealing was gleaming clean in a few seconds and the stuff seemed to have no problem in removing borax flux, so I'd say very good indeed - but we used long tongs and I wouldn't have wanted to get it on my skin. For general amateur use I'd say citric acid is a much safer choice as long as you are not in a hurry.

SillyOldDuffer28/01/2018 12:14:27
5753 forum posts
1217 photos

For what it's worth, my take:

Sulphuric Acid:

  • For: Cheap, fast, clean, compact in concentrated form. Washing afterwards easy.
  • Against: May be hard to source, special care in storage and use - hazardous in concentrated form and when being diluted. Don't splash dilute acid about. Not recommended if you don't understand the rules.

Brick Cleaner (Strong rather than concentrated Hydrochloric Acid.)

  • For: Cheap, fast, clean, easily obtained, less risky than concentrated Sulphuric Acid.
  • Against: moderately hazardous in storage and use: read the label. Don't splash it about. Salts produced during pickling may be less soluble so more care needed cleaning the metal after pickling. The chief objection to using Hydrochloric Acid as a pickle is the acid's tendency to leave rust promoting chlorides trapped in the pores of the metal. These are hard to remove and may cause trouble years later.

Sodium Hydrogen Sulphate (aka Sodium Bisulphate)

  • For: Cheap, moderately fast, easily obtained, Washing afterwards easy. Safer to handle than Sulphuric Acid.
  • Against: Extra care in cleaning after pickling. In addition to the salts produced by pickling, Sodium Hydrogen Sulphate is itself a salt. Rinse thoroughly - you don't want to leave any behind when the water evaporates.

Organic Acids (Citric Acid, Formic Acid, Acetic Acid, Vinegar etc.)

  • For: easily obtained and safe to handle.
  • Against: expensive and dead slow. Rinse well. Perhaps 24 hours to do a job Sulphuric Acid would do in 5 minutes.

One Shot Drain Cleaner is mostly concentrated Sulphuric Acid. It's not pure; presumably there's something else in it to help unblock drains or discourage misuse. I've no idea what the additives are or if they're detrimental to pickling. Has anyone tried it?

Harpic Toilet cleaner in powder form used to be Sodium Hydrogen Sulphate. No longer true though the stronger commercial versions may still be. Supermarket Harpic is mostly dilute Hydrochloric Acid.

Material Safety Data Sheets are available for all these chemicals on the web. Stick to Citric Acid if understanding MSDS isn't your thing.

Dave

PS I know it's spelt Sulfuric. Forgive me - I'm a retired Englishman and set in my ways.

Richard S228/01/2018 13:27:22
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Posted by SillyOldDuffer on 28/01/2018 12:14:27:

PS I know it's spelt Sulfuric. Forgive me - I'm a retired Englishman and set in my ways.

You've made all that clear enough for me !.

I'm same as you and also have no 'F- in Sulphuric !!!. smiley

not done it yet28/01/2018 14:19:04
4630 forum posts
16 photos

I don’t see a problem in procuring sulphuric acid if you are a legitimate user. Tighter precautions (due to abuse by the dregs of society) should not prevent the proper and legitimate use of chemicals such as this.

Thirty years ago I used concentrated acids (mainly nitric and hydrochloric), concentrated caustic soda and several other potentially offensive chemicals by the 50l carboy or 50kg bag. Never ever considered abusing those chemicals, but there are those that will do so. A bit like the demise of ammonium nitrate as fertiliser....

Requesting a suitable dilution, rather than just ordering concentrated acid, may be a better way to realise an order without the initial point blank refusal. Discussing your needs with the company, beforehand, is also far better than trying to change their attitude later. Using bisulphite may be a cheaper process, even if slightly slower.

Expect some checks on your disposal methods, these days, mind!

As an aside, salts can range from strongly acidic to strongly basic, with all values between. Bisulphite - acidic, sodium chloride - neutral, washing soda - basic. The pH of an aqueous solution depends on the radicles in solution and their concentration. Simple basic chemistry.

Samsaranda28/01/2018 19:03:10
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927 forum posts
5 photos

For those who choose to use them, sulphuric and hydrochloric acids are readily available by mail order from both EBay and Amazon, in whatever quantities you choose, me I will be sticking with Citric Acid, don’t want to temp fate, have enough personal injuries from screwdrivers and Stanley knives.

Dave W

fizzy28/01/2018 20:12:26
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1710 forum posts
115 photos

Hi Dave. I only see battery acid on the sites nowadays which with a requirement of at least 5 gallons works out a tad expensive. Twelve months ago you could buy conc acid mail order (albeit from spain) but not now. I can easy enough get what I need commercially but not in low volumes. Ive bought 5kg of NaHSO4 and will give it a try. I just need to find an active volcano to pour the old stock into......

Trevor Drabble28/01/2018 23:52:08
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Fizzy , A bit off the wall , but would either a local chemical plating shop (as in say chromium plating ) or furniture/door stripping shop have any suitable chemicals available , and if so , could you "piggy back" with their orders to their suppliers ? Trevor.

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