Questions about chemistry and responsible disposal for B&W reversal processing

[AnalogueWendy]

My first three attempts at B&W reversal processing.
5x7" on Kentmere VC.
I'd got it sorted by number 3 (it's a bit brighter in real life)

This process is likely to be useful for me because I have been making studio portraits using Harman Direct Positive paper. DPP is unavailable again right now and it is really picky, expensive stuff when I can get it.

I began with the Ilford article https://www.ilfordphoto.com/reversal-processing/
Then this work by Dave Walker suggested substituting readily available Sodium Bisulphate for Sulphuric acid https://substack.com/home/post/p-172490949

This means my 'bleach' step is Potassium Permanganate in an acid solution which is, presumably, oxidising and dissolving the developed silver halides from the paper.
Whether I use KMnO4 or 'safer' Hydrogen Peroxide, my used solution must contain dissolved silver salts, in the same way as used fixer. I have not yet found a good explanation of the chemistry involved so I don't know what form these salts are likely to be.

There is also a hypo clear bath after the bleach. I'm using Sodium Sulphite. Perhaps some of the silver ends up here too?

The 'bleach' step is one-shot in all the formulations I have seen, so I'm likely to generate a fair bit of this needing safe disposal. (I neutralised by first batch with the sodium carbonate I had on hand). I don't want to do anything that could release silver into the environment. I manage used fixer safely and now I'm looking for a way to use this reversal process for studio work, without adding to the pollution I generate.

An explanation of the chemistry of the 'bleach' would be useful, please? And then perhaps someone can also suggest a safe, effective way to precipitate the silver out of the solution? Maybe there another way to remove or bind the silver leaving a solution that can be disposed of responsibly in municipal waste water?

Thank you so all the knowledgeable people here who patiently help with my questions. I'm looking forward to using this process for bigger prints soon - just need to have the disposal question properly in hand.

 

[Ian Grant]

The first development converts the exposed Silver Halides into metallic Silver, leaving the unexposed Halides.

The bleach typically Dichromate or Permanganate oxidise the metallic Silver into a soluble salt that diffuses into the solution, they can dissolve the Silver halides.. The Sulphite removes the staining of the gelatin by the bleach.

In terms of Silver content in the Sulphite it's a low level, similar to the first wash water after fixing, it will be below the permitted levels once diluted.

The Bleach can be treated like fixer for Silver recovery, cheapest way to precipitate the Silver is iron wool, most efficient is electrolysis.

Silver recovery was part of my job at one time, I helped large labs get discharge permissions from their water boards. I had meetings with the chief chemist of Thames Water, he said in general they assumed most amateurs were discharging untreated, as the degree of dilution was so massive by the time anything reached the treatment plants.

Ian

 

[AnalogueWendy]

Thanks Ian.
Should I neutralise the acid and permanganate solution before adding the iron wool? ie Bring it back to Ph 7ish with sodium Carbonate?

 

[Ian Grant]

Doesn't need to be pH 7 just lowered to about pH 5 or 6. I'm thinking about simple electrolysis, it's much cleaner.

Ian

 

[Nas]

Nice results, Wendy. Thanks for sharing. I would like to learn this process from you. I dispose of my film fixer at Redbridge recycling centre. There's a chemical cabinet there where you can leave your plastic containers.