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  1. #21

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    I am aware the discussion is about KSCN used in photography. However I noticed that some of the posters are quite knowledgeable chemists that may be able to help with a roadblock in the chemical process that I am a part of that uses Ammonium thiocyanate. We have a solution at the end of the process containing about 3g/L of Rhenium as perrhenate in an ammonium thiocyanate solution. I have found a method that can reduce the Rhenium content to approx. .1g/L, but in order to proceed I need to acidify the solution to below a pH of 2. I have been told by some of my my co-workers that the addition of acid will result in the release of HCN. I understand thier logic but don't fully agree, thats why I wanted to pose this question to this thread to get some outside opinions of the situation.

  2. #22
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    I don't think that there is too much of a problem with acidic Thiocyanates. Just make sure that you don't allow them to become very hot. By hot I mean hot enough to pyrolize it. It is known that you can heat thiocyanates to drive off water, so that should be safe as long as you stay rather cool.

    Even so, there is not too much danger of forming cyanide. In fact there are no special precautions listed in any of my texts nor in the Merck index.

    PE

  3. #23

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    Thanks PE

    For the method I've been looking at the temperature range is 60-85C at pH of 1-3 so it should be good to go then.
    The other part of the method involves sulfidizing the solution with a common sulfide(we would likely use NaHS as it is already on site for our scrubber system) and cementation on a metal powder liek iron or nickel or zinc, nickel being our most likely choice as we already have a method in place to remove it as Ni(OH)2. Essentially the plan is to reduce the soluble +7 rhenium to its lower insoluble states then put it back into the main process. Are there any risks that might be forseeable under these conditions, i've tried to do as much research on my own but I want to make sure I have as many angles covered as I can before I present it to my boss before I can start doing small scale test runs.

    Mac

  4. #24
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    Mac;

    You have two bigger problems!

    Rhenium and H2S.

    Have fun.

    PE

  5. #25

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    The rhenium shouldn't be too much of a problem considering we are a rhenium recycling facility. But I do here you about the H2S being a problem. We have a brand new 4 stage nox scrubber system to replace our current 3 stage one. I'm sure we could modify it in such a way to reduce H2S emmisions.

    Thanks for your advice and hopefully I can figure this one out because we have 35000L+ of this stuff at 3g/L that has already been written off as waste. I've calculated it out to be >$600K worth of product.

    Mac

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    Well, the toxicity of Rhenium is considered to be an unknown, but low. The value, Priceless! Geez, that stuff is valuable. Don't throw it away!

    PE

  7. #27

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    Thats exactly why I'm trying to get it out...I've only been working here for 2 months. Wouldn't the higher ups be impressed if the new kid can make them $500k pure profit minus reagent costs.

  8. #28
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    OTOH, if it were done easily, maybe they would already be dong it!

    PE

  9. #29
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    OP: Thiocyanate is a result from cyanide and thiosulphate used as a antidote for cyanide poisoning, so I definately wouldn't be worrying about that.

  10. #30

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    Quote Originally Posted by Macchemist View Post
    Thanks PE

    For the method I've been looking at the temperature range is 60-85C at pH of 1-3 so it should be good to go then.
    The other part of the method involves sulfidizing the solution with a common sulfide(we would likely use NaHS as it is already on site for our scrubber system) and cementation on a metal powder liek iron or nickel or zinc, nickel being our most likely choice as we already have a method in place to remove it as Ni(OH)2. Essentially the plan is to reduce the soluble +7 rhenium to its lower insoluble states then put it back into the main process. Are there any risks that might be forseeable under these conditions, i've tried to do as much research on my own but I want to make sure I have as many angles covered as I can before I present it to my boss before I can start doing small scale test runs.

    Mac
    Since the perrhenate ion is stable over a wide pH range is there a particular reason to keep the solution in the pH range 1 to 3?

    Perrhenate can be preciitated with the use of various organic cations. In addition, the perrhenate ion can be oxidized to rhenium tetroxide through the use of iodate ion. The rhenium tetroxide can be extracted since it is volatile with steam.

    The chemistries of rhenium and osmium have many similarities. For extraction methods you might also look under osmium.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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