Potassium Ferricyanide Regeneration

Hello,

Does anyone know if there are any machines that can automatically regenerate spent potassium ferrocyanide back to potassium ferricyanide? I'm ideally looking for an electrolysis setup of some kind

Welcome to Photrio!

I imagine this is possible - in any case, according to Wikipedia, ferrocyanide can be oxidized into ferricyanide. Furthermore, this paper gives some more details: https://www.nature.com/articles/s41598-021-02355-3

However, given the low cost of ferricyanide and the small amounts generally needed in a small-scale / home darkroom, I really wonder why you'd want to pursue this route? What kind of application are you working on, and what kind of volumes are we talking about? Surely, we must be talking about volumes involving kilos (or more) of ferro/icyanide for this to be a sensible enterprise.

Hi Koraks,

Thank you for the quick reply!

You are correct, this is for a large scale application for a process called photochemical milling. We go through around 1.5 tons of potassium ferricyanide a month and currently have no regeneration process in place. Disposal alone is £5k/week!

I have done some research on the topic and found that electrolytic, ozonation and potassium persulfate are all viable options, which I am currently running experiments on. I just wanted to double check though if there are any already commercially available solutions for ferricyanide regeneration in the photoprocessing market that I might have missed out.

Ah yes, I understand; then it makes perfect sense. Interesting application BTW! Never looked into it deeply, but I'm aware of its existence. Very fascinating; it's kind of like etching on steroids, isn't it?

I'm afraid I don't know of any products in the photochemical realm that would suit your needs. An obvious reason is that the large-scale use of ferricyanide in the photo industry was abandoned many decades ago with the advent of other (EDTA, PDTA etc.) bleaches. I guess that the last labs that would have done something along these lines probably migrated away from it in the 1980s. And I doubt if they really regenerated anything back then...

Perhaps @Mr Bill or @Kino can comment; they have experience with large lab operations and/or the cine industry and might be able to comment.

Another obvious route would be to contact Eastman Kodak and see if you can reach someone of the older staff who could give some hints. There must still be some chemical engineers running around who worked on this kind of stuff and they might give some general directions.

Otherwise, you'd have to face the challenge of custom-made equipment in collaboration with a suitable manufacturer with some basic R&D capability, but this gets very expensive very quickly, as you undoubtedly know.

Yes, photochemical milling really makes a massive difference on etch rates when compared to etching in solution, although it can be quite a temperamental process to deal with

I noticed that ferricyanide had a lot of used in the past, but guess it makes sense they moved to EDTA and other bleaches. Ferri is tricky on large scales and mixing with strong acids is lethal. We're stuck with it unfortunately for our process though.

I have tried contacting Kodak in the past, but with not too much success. I will try again though. I wish there was a way for me to access the Eastman Kodak Publications, as there are a lot of papers from them that I wish to read, such as "Kodak Photosensitive Kesists for Industry, (Eastman Kodak, Co.. Rochester, llew York, Publication P-7, Revised First Edition. October 1964) p. 13.".

We have a machining shop here, so building some of the kit shouldn't be too tricky, but I'm definitely no electrical engineer so that part will be challenging. As to the R&D, I have tried electrolysis before, but I didn't have the right membrane so it didn't really do anything. The cation exchange membranes I'd need are typically expensive and I might need to make a custom setup for trials, so none of this stuff is cheap but it currently costs us around £300k a year with no regeneration, so getting the capital isn't that difficult as long as it's in small bits at a time.

patrickktr said:

Kodak Photosensitive Kesists for Industry

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Well, you can buy that on ebay

patrickktr said:

Hi Koraks,

Thank you for the quick reply!

You are correct, this is for a large scale application for a process called photochemical milling. We go through around 1.5 tons of potassium ferricyanide a month and currently have no regeneration process in place. Disposal alone is £5k/week!

I have done some research on the topic and found that electrolytic, ozonation and potassium persulfate are all viable options, which I am currently running experiments on. I just wanted to double check though if there are any already commercially available solutions for ferricyanide regeneration in the photoprocessing market that I might have missed out.

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Patrickktr,

Sounds like an interesting problem!

I would suggest you check with the good people of Photomec; luckily for you, they are at Kings Lane, Oxfordshire.


They are truly one of the last, great photo chemical equipment manufacturers in the World, they have highly skilled and knowledgeable engineers and their products are superb.

While they deal in motion picture photo chemical processors, a problem such as yours might tweak their interest.

I toured their facility in 2000 when I took the restoration of "All Quiet on the Western Front" (1930) to the BFI for it's European premier.

Tried desperately hard to purchase their machinery for our laboratory after the visit, but political interference in the form of "Buy USA" legislation forced us to purchase machines from a company that sold us old stock and then went out of business. That still bothers me to this day...

Beyond that, I could only suggest Houston/Fearless in the USA, but they have ensconced themselves so deep in the Military/Industrial Complex of the US that it's hard to even get them to respond, let alone be affordable.

Good luck with your search!

patrickktr said:

You are correct, this is for a large scale application for a process called photochemical milling. We go through around 1.5 tons of potassium ferricyanide a month and currently have no regeneration process in place. Disposal alone is £5k/week!

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This may be a completely naive statement on my part but if the cost of disposal is 5K per week in your case then unless your volume of usage of ferricyanide and thus the disposal cost is unique then I am surprised why there are not others who are doing this who would be prepared to share their knowledge

Even if the saving is only a percentage of 5K per week then you'd think that it would be worthwhile to "commission" research

pentaxuser

(Thanks for the referral koraks)

Hi, I don't have any directly useful information. I spent a lot of years in photofinishing, but the only standard process that used ferricyanide bleach was Kodak C-22 (color neg) which was replaced by the current C-41 process in roughly the late 1970s (I think). I was actually working as a fresh QC tech in a large lab at the time, and was involved in machine conversions, but the chemical mixing and regeneration was done in a different area. (Plus I would have barely understood what was going on.) I think that likely we were using persulfate to help regenerate it.

In more modern times I believe motion picture processing did continue to use ferricyanide bleaching as an option. Information on this can be found in Kodak's H-24 motion picture processing manual. I presume it is still available online? See specifically module 5, section 5-11 "Bleach Recovery." Page 5-16 has more detail on the "electrolytic method," where the "membrane" is referred to as "Celgard 2500 microporous polypropylene film" or "Dynel." Page 5-17 lists two "current vendors" (circa 2004, it appears) for so-called Nash Cells.

A couple of notes to clarify what may seem unintelligible regarding the photo systems: in continuous photo processing there is a so-called working tank solution that is directly used in processing film. This tank solution is gradually "exhausted" by being 1) gradually diluted as wet film from the previous tank comes in and 2) whatever chemical reactions normally take place. In order to keep the working tank in a stable condition a so-called "replenisher" is used, being added in some proportion to the film being processed. The replenisher is essentially over-concentrated with respect to the deficiencies in the working tank.

Because this replenishment adds volume to the working tank there is an excess (so-called overflow from the tank) that can be collected. In larger labs this overflow might typically be "regenerated," meaning that it would be chemically converted to replenisher specs, whereby it can be used as replenisher. Ultimately there are unwanted byproducts that eventually build up; these are kept within limits by keeping some moderate amount of dilution in the regeneration process.

One other note: the photo process typically contains some bromide ion for part of a necessary reaction with film. (In case you were wondering what is the deal with bromide.)

Another potential source of info is "Handbook of Industrial and Hazardous Waste Treatment" (2nd edition, 2004). It has a section on photographic wastes, authors including a couple of (I presume former) Kodak employees. (These would likely be the people you'd wanna start with if you'd been able to tap into Kodak expertise in the past.)

Page 309 starts a discussion on ferricyanide bleach.

Perhaps more important is the list of near 150 references. (This also includes the Kleppe and Nash paper per the H-24 manual.)

FWIW there have historically been two key industry-related associations publishing research. They are IS&T (Society for Imaging Science and Technology), formerly SPSE, Society of Photographic Scientists and Engineers, and SMPTE (Motion Picture and Television Engineers).

Things such as the Journal of Applied Photographic Engineering, Journal of Imaging Technology, etc., and a handful of others were published by IS&T/SPSE.

Regarding equipment availability Kino has run in a different circle than I, and has different sources. In my experience, in the US, in the general photofinishing (etc.) industry, the common routine is that film/paper manufacturers (Kodak, Fuji, Konica, etc., would publish research and then various companies would manufacture equipment based on said research. One of the really big names in effluent control was CPAC (originally Computerized Pollution Abatement Corp, based in New York state). I don't know if they're still around, but possibly some of the former employees do consulting work (?) and might be found on LinkedIn?

Best of luck with your project.

patrickktr said:

I wish there was a way for me to access the Eastman Kodak Publications, as there are a lot of papers from them that I wish to read, such as "Kodak Photosensitive Kesists for Industry, (Eastman Kodak, Co.. Rochester, llew York, Publication P-7, Revised First Edition. October 1964) p. 13.".

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I would consider reaching out to the George Eastman museum.

@fgorga might be able to help

Mr Bill said:

Another potential source of info is "Handbook of Industrial and Hazardous Waste Treatment" (2nd edition, 2004). It has a section on photographic wastes, authors including a couple of (I presume former) Kodak employees. (These would likely be the people you'd wanna start with if you'd been able to tap into Kodak expertise in the past.)

Page 309 starts a discussion on ferricyanide bleach.

Perhaps more important is the list of near 150 references. (This also includes the Kleppe and Nash paper per the H-24 manual.)

FWIW there have historically been two key industry-related associations publishing research. They are IS&T (Society for Imaging Science and Technology), formerly SPSE, Society of Photographic Scientists and Engineers, and SMPTE (Motion Picture and Television Engineers).

Things such as the Journal of Applied Photographic Engineering, Journal of Imaging Technology, etc., and a handful of others were published by IS&T/SPSE.

Regarding equipment availability Kino has run in a different circle than I, and has different sources. In my experience, in the US, in the general photofinishing (etc.) industry, the common routine is that film/paper manufacturers (Kodak, Fuji, Konica, etc., would publish research and then various companies would manufacture equipment based on said research. One of the really big names in effluent control was CPAC (originally Computerized Pollution Abatement Corp, based in New York state). I don't know if they're still around, but possibly some of the former employees do consulting work (?) and might be found on LinkedIn?

Best of luck with your project.

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Hi Mr Bill,

Thank you for your detailed feedback and references! I will read through them as I can, although quite a few I have already read (Kodak modules 3, 4, 5 and 6), most important of all the Nash Cell paper. I found that the Nash Cell is sold by Kobelcell Inc. and The Allen Products Company, however I was unsuccessful when I last tried to find and contact these companies. I have looked into Celgard 2500 already but wasn't able to get a small sample for an initial R&D trial, so I have bought some Dynel which is commercially available and much cheaper, all I need now is the time to design and make a simple electrolytic cell with the Dynel fabric seperating the two cells. I tried doing an experiment previously with a porous clay cup, but it didn't seem to work too well and the cathode chamber went all blue for some reason.

"Handbook of Industrial and Hazardous Waste Treatment" is a very good source I have previously looked at, but haven't thought of contacting the authors, I will give this a go. As to the 150 references, these all look very good, however I have a lot of difficulty finding these references online. I imagine they're in some library somewhere in the world, but not sure where to start looking or if it's even worth the effort.

I have also tried ozonation in the past with a cheap commercial ozone generator, however I didn't have the best setup at the time and it took a long time for the ferrocyanide to oxidize to ferricyanide. If I had a better setup and an oxygen fed ozone generator, I think I would get much better results, however the electrolytic method seems for feasible long-term, as then I don't need to worry about controlling the toxic ozone gas.

Lastly, I will look into CPAC and see if I can find one of their original employees who dealt with this kind of stuff. Our company are looking at expanding this section of the business and our H&S and maintenance staff want to buy an expensive fume scrubber (£100k or so) for the potassium ferricyanide fumes, which I think is silly considering all the research indicating there is no toxicity to the fumes from ferricyanide. Maybe getting some consultancy from people who have dealt with ferricyanide in the past will help them change their mind.

patrickktr said:

I tried doing an experiment previously with a porous clay cup, but it didn't seem to work too well and the cathode chamber went all blue for some reason.

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Sounds like you made some Prussian blue. It's what us photographers use ferricyanide for!
E.g. this publication explores the electrolytic formation of Prussian blue from ferrocyanide; I guess you stumbled upon this mechanism experimentally: https://www.sciencedirect.com/science/article/abs/pii/S0022072805003529

pentaxuser said:

This may be a completely naive statement on my part

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Not really; I agree with you that the cost savings alone, combined with the fact that other enterprises are probably employing similar technologies, should make for a feasible R&D effort for an interested equipment supplier. The main trick is to find the right one.

koraks said:

Sounds like you made some Prussian blue. It's what us photographers use ferricyanide for!
E.g. this publication explores the electrolytic formation of Prussian blue from ferrocyanide; I guess you stumbled upon this mechanism experimentally: https://www.sciencedirect.com/science/article/abs/pii/S0022072805003529

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I think it was either Prussian Blue or Prussic Acid (hopefully the former). Our ferri etch solution contains KOH which keeps the pH at around 12, however I noticed that the blue solution that formed was slightly acidic (pH 2-4), which worried me a bit for H&S concerns, as we always try our best to keep ferricyanide solutions alkaline to avoid HCN evolution.

koraks said:

Not really; I agree with you that the cost savings alone, combined with the fact that other enterprises are probably employing similar technologies, should make for a feasible R&D effort for an interested equipment supplier. The main trick is to find the right one.

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As to the feasability, this project is definitely worth pursuing, even if it is expensive. We spend £300k/year including everything (chemical purchase, disposal, etc.). I would like to see even if we could get a UK government grant to work on this R&D project and maybe a patent and paper done for the final device, but this all remains to be seen

patrickktr said:

As to the 150 references, these all look very good, however I have a lot of difficulty finding these references online. I imagine they're in some library somewhere in the world, but not sure where to start looking or if it's even worth the effort.

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Hi, a good place to start is probably through the IS&T. Through my former employer I was a 30-some years off-and-on member (we always kept someone in the department as a member in order to get hard copy of the main photofinishing journals) and read probably better than half of those references. Unfortunately none of those were the ferri-related papers as we never had to deal with it.

Unfortunately the pertinent SPSE (later IS&T) papers are old enough that they may have not been digitized, and so not available. If you contact IS&T you might ask if their publication "Selected Readings in Photoprocessing and the Environment" (1995, Austin Cooley editor) is still available. It MIGHT include some ferri-related papers.

Regarding CPAC it looks to me like the former incarnation is essentially gone. If you try looking for possible contacts on LinkedIn try also Trebla chemical; they once were part of the operation, and Trebla reps dealt with CPAC equipment in labs.

I suspect you are gonna be on your own, at least with respect to the (former) photofinishing industry.

Ps, I sent you a personal message with a specific name; look for your "inbox" near top of the screen.

patrickktr said:

As to the feasability, this project is definitely worth pursuing

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Yes, the case you're putting up for it is very convincing. I don't know the UK landscape, but for innovation projects like these, there are generally facilitating entities that are worthwhile to get in touch with. These tend to be highly specific to the industrial and regulatory context so I don't know how it's set up in the UK (and specifically your location within the UK!) It might also be useful to get in touch with a university in your region; they are generally quite interested in helping out in instances like these - even though they can often be a tad slow compared to the usual pace of things in industry.

Mr Bill said:

Ps, I sent you a personal message with a specific name; look for your "inbox" near top of the screen.

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Ah, great; to facilitate further attempts I've enabled the possibility for @patrickktr to initiate private conversations as well.

CPAC was the manufacturer of the Silver Recovery Systems still in use at my former employer.

From what I understand, our installation was the last one before they closed and there is no technical support whatsoever available now. The machines are in dreadful condition and failing constantly; only a matter of time before they die completely.

I will try to contact a former colleague to see if he has any additional information on anyone connected with CPAC.

Meanwhile, Rotex of Springfield, Ohio MIGHT still be in business;


As I understand it, they were successfully contacted when a search was undertaken to replace the failing CPAC machines, but they were uninterested in collaborating as the volume of production at our workplace was not sufficient for them to travel from Ohio to Virginia to service the machines (at least that is what I was told).

Hi everyone,

Thank you so much for your feedback and comments! I have briefly tried to find the companies CPAC and Trebla chemical, but without success. I will try again later this week and see potentially if I can find any old contacts on linkedin.

In the meantime, I have contacted our local univeristy and will see if we can apply for a government grant together for this project. I think that the electrochemistry shouldn't be too complicated as long as we are able to seperate the two half cells, but it will be quite a large project to develop a full industrial system from scratch. Maybe once it's finished we could advertise to sell the final unit? As it seems that no one else sells this. Maybe there's no market for this kind of device anymore.