Potassium Dichromate - Disposal (UK)

[Mac064]

Hi all,

Being new to APUG, I have a basic question. I am interested in pursuing the oilprint process. It requires the application of and washing out of potassium dichromate. Before I start attempting this, what is the best/safest way of disposing of potassium dichromate solution (at most 5%)?

Welcome any thoughts.

 

[Mike Wilde]

keep using it

Reuse it until the orange colour turns green - then it has been oxidized to a less toxic form. Combining it with a sulfite clearing bath when doing traditional bleach and redevelop processes will speed this along.

Allowing it to dehydrate to a slurry will minimize the amount of hazardous waste you turn in. Mist wet any areas that have dreid entirely before you scrape/spatula the sludge into a small bottle - label it and turn it in to a HHW depot.

 

[Mac064]

Mike,

Great advice and thanks for the quick response. What should I do with the wash baths (when I have to wash/clear the matrix once exposed to UV)? I guess the % level is small but should I just tip water into container and dispose at depot also?

 

[Mike Wilde]

2 bath?

a quick way to get 90% of it is to do a quick dunk in 1 tray that you keep using until you virtually can't see the paper for the dichromate. Keep it, and HHW recylce it (dehyate works, as does re-using spare 2l soda bottles, appropriately labeled.) The second etc baths should be so dilute in dichromate, just put it down the drain.

The advise might vary a bit if you are on septic; you may need to look at a polymer resin filter. I have one for silver that is commecially made; I'm not sure if there is one for dichromates.

Another idea is to dump the wash water effluent though an iron wool packed cylinder. It should turn the iron bits from ferric to ferrous, and in turn go from dichromate to bichromate, a less toxic form. I am winging it from memory here at work; all my references are at home. Others are more than welcome to chime in an say if this idea is full of holes.

 

[Mike Wilde]

research bromoil?

I presume that the dichromate is being used to tan the gelatin - that sounds like a bromoil process to me. Perhaps title your query as bromoil waste and see if it gets more hits.

 

[Alan Davenport]

Here in the states, the best way to dispose of Dichromate is to treat it with Potassium or Sodium Bisulfite or Metabisulfite. This will reduce the Hexavalent chrome to Trivalent chrome. The conversion is completed when the solution turns a brilliant emerald green.

If you are not allowed to flush this treated solution down the drain, you may neutralize it with a mild caustic solution which will cause the chrome to precipitate as chromium hydroxide. Chromium hydroxide is a common green pigment. Filter the green precipitate and throw it in the garbage.

Alan

 

[Ole]

If you want to reduce the hexavalent chromium to trivalent and at at the same time get it out of solution as chromium(III)hydroxide, mixing it in spent developer should do the trick.

 

[Mac064]

Thanks everyone for taking the time to respond. We have a pretty good HHW policy in our area (they collect anything from the doorstep once a month). I will probably do a Mike sugests and simply put it all in plastic milk/drinks bottles label it up and send it on it's way.

Mike - I will be attempting to do oil/Rawlins oil work. It is similar to Bromoil (but preceeded it). In Rawlins oil work you coat gelatin sized paper (usual suspects watercolour paper) with 3% dichromate solution and contact print it with a negative, dry, re-soak and do the inking like Bromoil. As I am aware, Bromoil uses a gelatin-bromide photographic print rather than a negative. The processes are pretty close but I think that's the difference.

Anyway thanks for all the help it is appreciated.

Ewan

 

[Gene_Laughter]

The bromoil bleach/tan formula that I use calls for 30 mls of a 1% solution of pot. dichchromate (along with 70 mls of a 10% soluton of copper sulphate and 70 mls of a 10% solution of pot. bromide) that is further diluted with 1000 mls of distilled water for a working solution. I discussed the disposal of this bleach with the proper folks in my county. I was told that the dichromate is so dilute and is in such small quantities, to put it down the drain and not to be concerned. That's what I do.

Cheers.

Gene