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Anonymous Poster #1

Byproduct When Citric Acid and Iron Oxide Combine

01/12/2019 5:49 PM

Hi folks.

i am using citric acid to dissolve rust which works well enough , what I need to know is how to dispose of it ethically so I need to know what happens in that chemical reaction.

can any chemistry experts advise what is produced when the process is completed ?

does the rust remain as iron oxide or is it converted into something else ?

are any other byproducts created in that solution ?

i use around 4 - 8 % anhydrous citric acid mixed with water when I put the rusted parts in it , after treating lots of rusted parts the solution becomes dark brown and ceases working so I have to mix a fresh batch every few months.

the quantity is 150 litres each time.

i understand that treating it with bicarbonate soda would neutralise the acidity.

some people tell me just pour it down the drain , I think that sucks.

if I knew it was harmless in the garden for example I could dispose of it there.

If the only solution is to pay a chemical waste processing company then I will do that.

thankyou.

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#1

Re: What is the byproduct when citric acid and iron oxide combine

01/12/2019 6:20 PM

Iron citrate and water when completed.

Fe2O3 + C6H8O7 = Fe2C6H2O7 + 3H2O

https://www.quora.com/Does-red-iron-oxide-react-with-citric-acid-If-yes-what-is-formed-in-the-process

Iron Citrate properties:

https://en.wikipedia.org/wiki/Iron(III)_citrate

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#2

Re: What is the byproduct when citric acid and iron oxide combine

01/12/2019 6:35 PM

If the goobermint weren't closed, you might get an answer from the EPA. Whether it does so or not, helping with questions like this is what it should be doing.

Your approach to this is highly commendable.

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#27
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Re: What is the byproduct when citric acid and iron oxide combine

01/14/2019 9:40 AM

EPA is partially shutdown. The pollution inspectors aren't on the job but some elements still are, so a call won't hurt to find out. There's a chance someone is there to answer questions.

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#3

Re: What is the byproduct when citric acid and iron oxide combine

01/12/2019 7:35 PM

I don't think there is anything toxic or hazardous about this solution....I do the same thing with white vinegar....After use I let the solution settle, pour the top down the drain, and the sediment in the garbage...With stronger acidic solutions I keep baking soda on hand for neutralization and just hose it off....

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#4

Re: What is the byproduct when citric acid and iron oxide combine

01/12/2019 9:27 PM

Thanks people.

i will spray a little bit on the lawn and a shrub and see how they respond to it.

i have googled up iron citrate as per Rixter , it might work as a fertiliser in small concentrations but not sure yet on response if I spray it liberally on the lawn to get rid of it.

pouring things down the drain just doesn’t fit with my philosophies in life though if I can avoid it.

hmm , could be a whole new topic “ethics , effects and alternatives to the many products we dump in the ocean via stormwater drains”

think soaps , industrial hand cleaners including those with micro poly beads , shampoo , dishwashing detergents , a million builders who wash their paintbrushes into stormwater.....

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#7
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Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 2:10 AM

It works to green up the lawns and shrubbery as a soil supplement in proper doses...

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Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 2:35 AM
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#5

Re: What is the byproduct when citric acid and iron oxide combine

01/12/2019 9:49 PM

I never thought of rust as dangerous in any way, but a few years ago I heard of cases of textile artists being poisoned through occupational contact - specifically by repeated skin contact, using rust dissolved in a weak acid as a mordant and/or pigment.

Reading several MSDS for ferric citrate and ferric ammonium citrate, the risk of acute or chronic iron poisoning by ingestion is known, the end result is damage to liver or pancreas. Systemic effects can occur by absorption through open cuts or abraded skin, according to the third one below, which explains what happened to those artists who were using it without protecting their hands.

https://hazard.com/msds/mf/baker/baker/files/f0930.htm

https://www.silverprint.co.uk/wp-content/uploads/2015/07/Ferric-Ammonium-Citrate-MSDS.pdf

http://datasheets.scbt.com/sc-286019.pdf

So I think in the amount you are talking about, pouring it into the garden would likely create a hazard for children or pets - just besides the damage to plants, which do require iron as animals do, but are subject to toxicity when it is in excess, as well.

Ferric citrate is also used as a medication - for some reason "Accidental overdose of iron containing products is a leading cause of fatal poisoning in children under 6 years of age"

https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/205874s000lbl.pdf

So a backyard rust pit is not a place you want your children or pets to play.

Some toxicity to aquatic organisms is reported, and most MSDS specify not to pour dissolved ferric citrate down the drain. Requirements of course vary... In Illinois, it is listed as safe to dispose by drain (after neutralizing pH to 6-10) with copious water 10-20 X volume for amounts less than 5 gallons.

https://www.drs.illinois.edu/Waste/DisposalofLiquidNonHazardousChemicals

Some jurisdictions may have a chemical recycling program where the large quantity in your case, can safely be disposed. That would certainly be better than a DIY, so check with your local authorities.

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#6
In reply to #5

Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 1:01 AM

Superb GA Artsmith thankyou.

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#9
In reply to #5

Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 7:17 AM

The last link you provide states that both citric acid and ferric citrate can be poured down the drain if less than 5 gallons , or if greater than 5 Gal then seek advise on disposal through a specialist waste disposal company.

I have requested advice from two waste management companies and will post updates if it fine tunes our understandings any further.

And my garden will need a week or two to respond to its clandestine dosing with 300 ml of ferric citrate .

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#10
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Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 7:59 AM

Sounds like a 'medicinal' amount to me.

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#11
In reply to #9

Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 9:18 AM

How often are you allowed to dump 5 gallons at a time? Without know that it's meaningless, but the link doesn't say.

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#16
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Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 11:45 PM

Some people would cheat and do as you suggested , dumping 5 Gallons per day but that stuff will impact the rivers / oceans eventually.

my grandkids might like to swim at a beach one day without their DNA becoming mutated.

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#17
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Re: What is the byproduct when citric acid and iron oxide combine

01/14/2019 5:02 AM

I didn't suggest anything. All I said was if the rules don't say how often you may dump the 5 gallons it could be anything. And it won't necessarily build up somewhere, that depends on the nature of the effluent and the receiving body of water. A small input of eg oil might be tolerable, as it could be broken down biochemically.

BYW I applaud your concern for the environment.

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#18
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Re: What is the byproduct when citric acid and iron oxide combine

01/14/2019 6:59 AM

Yes the wording they used was a bit open ended , btw I wasn’t suggesting you were advocating dumping .

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#12

Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 9:39 AM

<...just pour it down the drain...>

"The solution to pollution is dilution" - Anonymous Poster #0

<...If the only solution is to pay a chemical waste processing company...>

Any guesses as to what that organisation will do with it after taking cash to go with it?

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#13
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Re: What is the byproduct when citric acid and iron oxide combine

01/13/2019 10:33 PM

“ Any guesses what a waste management company will do with it “

the exact thoughts crossed my mind too , there will be some who would take your money then dump it down a drain, in fact some years ago a major waste company here was recorded on video doing exactly that and were justifiably smashed in the environmental courts.

so far one waste company has asked for a sample of the solution for lab analysis so hopefully their intentions are honest.

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#14

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/13/2019 11:04 PM

Find someone that has a factory contaminated with 1,1,1 Trichloroethane. It works quite well as an electron donor and source for combined biotic/ abiotic breakdown of chlorinated alkanes and alkenes.

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#15
In reply to #14

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/13/2019 11:36 PM

I am giving GA on that .

rather than pay to have it disposed of safely , why not pay a little or pay nothing so it can be used to eliminate another problem.

kill two birds with one chemical waste...ooops that sounded wrong.

:)

dunno who marked your post off topic but they need to recalibrate their finger ..

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#21
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 7:50 AM

I might have made it sound a bit facetious- the emoticon probably didn't help!- but it is quite true. Thanks for the comment (I'm not worried about the o/t or GA's).

Our company does environmental remediation, and we use citric acid combined with iron salts to catalyze oxidation of petrol hydrocarbon and chlorinated solvent contamination. Some iron compounds (such as ferrous gluconate) are also used to reduce chlorinated compounds instead of oxidizing them; ferric citrate should have a very similar effect. The iron reacts with sulphides in groundwater and precipitates to form iron sulphide compounds that can reduce chlorinated solvents on contact, and the citric acid provides an electron donor (essentially fermenting) that acts as an energy source for anaerobic bacteria that can use the chlorinated compound in lieu of oxygen. Along the lines of sulfate reducing and methanogenic bacteria.

As for your comment about chemical wastes- that is so true! Very often they are just compounds that someone no longer has a use for, which magically turns them into some monster to be feared. Sometimes this is true but very often it's way overblown. The concern with ferric citrate is likely due to the fact it is not just a salt (ionically bound) but that the citrate ion also very effectively chelates ferric iron and can carry it through membrane barriers in solution that would normally block excessive transfer of ionic compounds. I do VERY firmly support anyone who is looking to handle things like this in a responsible manner.

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#19

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 7:11 AM

In our metal cleaning process, we use sulfuric acid at 5%. When the solution iron content gets to a predetermined point, we reduce with sodium hydroxide to neutralize (6.5 < pH <7.5) and dispose in a local land fill under supervision with testing. It is about 1/5 the cost of outside contractors doing the same thing. Contact your local or state DEQ...I'd bet they have a liaison officer who works with industry and others.

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#20
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 7:25 AM

Thanks for sharing.

Do you know what the percentage of iron content is where the sulphuric stops working ?

Are you doing galvanising or chrome plating ?

i have used both 16 % phosphoric and 30 - 50 % hydrochloric for rust removal before and while they work perfectly well their environmental implications are unattractive , both from the fumes they produce and for difficulties with disposal.

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#22
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 8:05 AM

We dump and reduce the solution when dissolved iron is 5%...I imagine our Chem Lab goes by weight. Our 5% sulfuric is also heated to 185 F. This makes it easier to work with and less risky, but we do have to 'scrub' the fumes well.

This is all part of a preservation (clean and prime) process for steel and pipe components that are not suitable for mechanical (wheel or air-blast) cleaning.

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#23
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 8:08 AM

From a worker standpoint your citric acid solution is much safer than the sulphuric acid solution- and also for the effect on surrounding equipment. In fact it is probably one of the most benign options you could use for this. I'd far rather be around the fumes from this than sulphuric acid!

If you are happy with the way it works I'd suggest you look into neutralizing it when finished with it using lime. Do NOT use caustic potash or soda, as these form very soluble salts that still chelate the iron, and also note that ammonia actually increases the effectiveness of citric acid at chelating iron. You need to use calcium.

Doing this should precipitate a mixture of calcium citrate (which has low solubility) and iron. The remaining solution could then be decanted off of the solids and reused with more citric acid several times if it's not to loaded up with other contaminants. This way you're only disposing of a small amount of solids most of the time, similar to doing the same with sulphuric acid. Note also that the same thing could be done with sulphuric acid (to form calcium sulphate instead of soluble sodium sulphate).

I assume that you are probably using a warm and fairly saturated solution of citric acid for this?

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#24
In reply to #23

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 8:35 AM

Thankyou.

i like your idea of precipitating out the solids with lime because ;

it reduces the volume of waste product to be disposed of.

I will get more accurate statistics on how much iron oxide is being removed and carried in solution.

and I get to use the liquid citric solution again by dosing it up a little bit .

I didn’t yet google up what calcium citrate might be useful for but will later.

btw my citric solution is 4 - 8% by volume , I didn’t make a heater in the system so currently use it at ambient ~ 30 Celsius.

awesome thankyou.

by the way , do you know what can be used to inhibit rust from forming after it has been stripped ? There are products available such as holdtite or holdblast but they are $250 per 20 litres , typically used to prevent rust for 3 - 4 days after abrasive blast or Wetblast processes.

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#25
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 9:02 AM

We use a 2% phosphoric acid solution, also heated to 185 F, and are allowed 48 hours to coat or re-clean...we call it RDP...rust displacing preservative.

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#26
In reply to #24

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/14/2019 9:12 AM

Right now here in Canada ambient is NOT 30 C.... (I've been in Sydney at Christmas time and WOW that's something else).

Not having the solution heated should make it easier to precipitate. Afraid I don't really know much about the rust inhibition, but DO know that for afterwards the order of preference is probably phosphoric > citric >> sulphuric >>>>>>> muriatic! Maybe a phosphoric acid dip after, or ascorbic acid ( vitamin C)?? Citric acid is pretty good for this in my experience, but then again I've used a mixture of citric or sulphuric acid and ammonium biflouride for this....

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#29
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/15/2019 10:24 AM

Agricultural lime is stipulated in one of the msds for this purpose.

The calcium citrate byproduct is not toxic or hazardous (with the usual caveat for plant or human consumption that too much of anything is a problem). Depending on the ratio of iron in the mix, it could even form the basis for a useful plant supplement - ie where soil conditions are acidic or low in calcium and iron. (peaty and other soilless potting/container mix comes to mind).

Sludge - a mixture with some water content - is also the safest form to handle or dispose insofar as you avoid all the airborne particulate hazards which are general to powdered substances. The volume that needs to be contained is much reduced, and if there isn't some application to recycle/re-use, the small amount might be acceptable to dispose with ordinary solid waste if there is no use for it. Even if it is still disposed or recycled by a professional outfit, the handling cost will be much reduced.

Also, reusing the aqueous part by adding citric acid to it for the same purpose is a huge saving on water, compared to the 'dilution of pollution' approach (50 to 100 gallons of water per 5 gallons of waste is pretty gross and would add up quickly).

GA for this suggestion!

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#30
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Re: Byproduct When Citric Acid and Iron Oxide Combine

01/15/2019 4:55 PM

Electrocoagulation is a process for precipitating metals from solution. It would be fairly easy to try on a small sample. You could put some in a glass jar with a pair of electrodes and a battery charger. If it does precipitate the iron you would reduce the amount of Haz-Mat to deal with.

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#28

Re: Byproduct When Citric Acid and Iron Oxide Combine

01/15/2019 4:58 AM

I suggest that you contact your local sewer treatment facility (municipal council) as they usually directly accept "liquid trade waste".

Some use ferric chloride dosing and such and their process is designed to create a concentrated sludge that they deal with. Your volumes become inconsequential relative to the millions of gallons they handle each day. Thus the presence of iron will not be alarming to them and pH correction is simple.

As far as ambient temps, we maxed at 42.6C today, forecast to be 45+ tomorrow and Thursday. Overnights are getting down to 32C. (This par obviously OT)

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