Potassium Thiocyanate

Discussion in 'B&W: Film, Paper, Chemistry' started by Alessandro Serrao, Aug 6, 2010.

  1. Alessandro Serrao

    Alessandro Serrao Member

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    How much is potassium thiocyanate toxic?
    I know it must not come in contact with strong acids, but what about strong alkalis?
    As far as I know it could potentially be life-threatening (-CN fumes)...
     
  2. Photo Engineer

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    It is virtually harmless in acid or alkali. It does not release cyanide fumes at all.

    You would have to boil it with acid or alkali to cause it to decompose.

    PE
     
  3. georgegrosu

    georgegrosu Member

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  4. Photo Engineer

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    Thiocyanate is not related to Cyanide in any direct way chemically! SCN is not CN! The latter is a very violent poison, but the former is used in many harmless OTC photo chemicals and in some toothpastes. SCN is not a "complex combination" of cyanide, rather it is a separate chemical compound that is stable and rather harmless unless mistreated.

    This argument played out over several months on Photo Net about 5 years ago and I am rather tired of the repetitive nature of this question coming up over and over by non-chemists. Please look at Kodak's C-41 RA Fixer MSDS. It contains SCN salts and is rather harmless. http://www.kodak.com/eknec/documents/08/0900688a80296008/PF790AENG.pdf or: http://www.3eonline.com/ImageServer/NewPdf/10234bf82b034eb394c1e62a296bca45.pdf

    In fact, the MSDS of SCN containing fixers lists the Sulfite as being of greater concern than the SCN!

    Remember, KCN is not KSCN. Nor are the two directly related. They are only very indirectly related.

    PE
     
  5. Ian Grant

    Ian Grant Subscriber

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    Will still probably kill you if you mix Thiocyanates with conc Sulphuric Acid especially if it's absorbed moisture, it'll boil isntantly, so basic safety is an issue. Storing Acids and Alkali's safely (and separately) away from dry or pre mixed chemicals.

    A lack of very basic Chemical safety missing in this post, Allessandro realises the potential issues.

    Ian
     
  6. Photo Engineer

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    Ian;

    I always advise safety, and you are quite aware of that fact.

    I just am unhappy at the regular confusion between Thiocyanate and Cyanide and am answering that point.

    Also, boiling in acid is very unlikely to produce cyanide according to my sources. The reverse reaction is more likely, that is, cyanide can form thiocyanate in the presence of sulfur. I have no references that suggest that the reverse takes place under normal conditions up to 100 C either in water or alone.

    In summary: since pyrolysis (heating melted thiocyante salts at about 500C) can produce cyanide, it is best to avoid dropping any on a hotplate. Adding thiocyanates to strong acid is also not advised, but it does not form HCN. Heating Thiocyanates to their melting point does not produce any harmful effects but if they are heated to 500C they decompose.

    PE
     
  7. Alessandro Serrao

    Alessandro Serrao Member

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    PE: I'm perfectly aware of the differences between -CN and -SCN groups.
    The point imho is another: reading properly a MSDS sheet requires some lab practices if one has to understand fully and correctly what's written in them.

    "Thiocyanate is produced by the reaction of elemental sulfur or thiosulfate with cyanide:

    8 CN− + S8 → 8 SCN−
    CN− + S2O32− → SCN− + SO32− "

    So it's chemically related to cyanide.

    I was asking only if under common photographic chemistry handling the use of thiocyanates poses particular problems.
    For example, some paper developer (Tetena Eukobrom I'm currently using) contains NaOH.
    Can I safely use thiocyanates with that developer?
     
  8. Photo Engineer

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    You can safely use Thiocyanate containing photographic processing solutions if you use the same precautions you use for handling and storage of any other processing solution.

    It is not worse than anything else in the lab, and does not approach Cyanide in any way for toxicity.

    And, as an analogy for you, you can easily produce Sulfiric acid from Sulfur Dioxide, but this does not mean that you can easily produce Sulfur Dioxide from Sulfuric acid. That is the sense in which I was referring to your above equations.

    PE
     
  9. georgegrosu

    georgegrosu Member

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    PE, you are right. KSCN is not a complex combination.
    PE, I put here KCN, KSCN and K3 [Fe (CN) 6] for the following reason:
    KCN is highly toxic (referance) and not used in photographic chemistry.
    KSCN and K3 [Fe (CN) 6] are substances which are used in photographic chemistry.
    I hope that you can compare the lethal doses of different chemical and toxicological evaluation can be made.
    From what I understand from KSCN (Merck) LD50 lethal dose is 854 mg / kg.
    This value is about 40 times higher than the lethal dose for KCN (not used in photo).
    About 40 years ago a colleague wanted to kill. What do you think he chose from the lab?
    K3 [Fe (CN) 6]. Not dead. At low concentrations is a diuretic. She done wash gastric.
    I saw that at low concentrations is used to clarification of Wine!
    George
     
  10. Photo Engineer

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    George;

    Thanks. I have the LD50 values here in my own Merck Index, thanks. That is part of my reference material.

    I can name many benign substances in the lab that can be very toxic in acid or base.

    Na2SO2 solution with acid generates a poison gas below about pH 4.5.
    Na2S solution generates a poison gas in acid solution below about pH 6.
    NH4OH solution generates a poison gas if NaOH is added.
    Sodium Hypochlorite solution and any Amine solution such as Ammonia generates a poison gas.

    I don't expect anyone to test this and I mention it for you all to avoid these mixtures in the interest of safety. Also, the above are generalizations. For example, Na2S continually exudes a minor amount of the poison gas H2S even in alkaline solution.

    PE
     
  11. georgegrosu

    georgegrosu Member

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    PE
    .
    I do not know how I could make that mistake.
    By definition, complex combination consists of: ion complex and outer sphere.
    Complex ion is plotted by square brackets. So, complex combination is recognizable by a square brackets.
    I wrote the potassium thiocyanate chemical formula and not have any square brackets. How I pulled myself that KSCN is a complex combination???
    In other news, KSCN has kept a hygroscopic tendency, to draw water.
    While becoming a soup with some crystals. I want to say that this is after decades of storage. Same thing happened to me with sodium sulphide - that smell is.
    George
     
  12. Photo Engineer

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    George;

    And a hydrate such as forms with many salts is written with a dot, not brackets.

    So, Na2CO3 is the anhydrous (water free) salt and Na2CO3.H2O is the monohydrate. A number designates the amount of water taken up and so we have Na2S2O3.5H2O or Sodium Hypo (Thiosulfate) pentahydrate.

    For those interested. :wink:

    PE
     
  13. srs5694

    srs5694 Member

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    Please don't be unhappy about it. Most people are not chemists, and have only vague memories that cyanide is a very dangerous poison, so they're uncertain, confused, or cautious about anything with a name that resembles "cyanide" (not being chemists, they aren't very comfortable with chemical formulas and think about these substances in terms of English (or other natural language) names). Naturally, the same questions and misconceptions will come up repeatedly because they're coming up from different people. That's the nature of how information is relayed: Those who possess it pass it on to those who don't, and given how much knowledge our species has accumulated, it's inevitable that, for most pieces of information, those who don't possess it will vastly outnumber those who do. Thus you as an expert may be asked the same basic question again and again and again. Try to be happy about it: You're helping more people understand this one thing.

    Now, if the same person kept asking this question, you might suggest a neurological workup, but that's another matter.... :wink:
     
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  15. Gerald C Koch

    Gerald C Koch Member

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    Sodium thiosulfate is used as an antidote for possible cyanide poisoning because it converts the cyamide to thiocyanate. One has to be quick though.
     
  16. sonal123

    sonal123 Member

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    if potassium thiosufate swallowed can cause death?

    if potassium thiosufate swallowed can cause death? if not how can we make potassium thiocynate toxic to health?
     
  17. Pat Erson

    Pat Erson Member

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    "For those interested"

    Thank you!
     
  18. Gerald C Koch

    Gerald C Koch Member

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    Exposure to hydrogen sulfide for more than 30 minutes at concentrations of greater than 600 ppm have been fatal. Continuous inhalation of low concentrations may cause olfactory fatigue, so that the odor is no longer an effective warning of the presence of hydrogen sulfide. This toxicity is approimately 1/3 to 1/2 that of hydrogen cyanide. Therefore sulfur toners such as sodium polysulfide should only be used in a well ventilated room.
     
  19. Gerald C Koch

    Gerald C Koch Member

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    I don't understand your comment as we are talking about potassium thiocyanate not thiosulfate.

    However, ingestion of large amounts of potassium salts can cause poisoning, the condition is called hyperkalemia. The potassium ions can cause an irregular heart beat and can case death. People with reduced kidney function are of particular risk and they are warned not to use salt substitutes. Potassium chloride is the third component used in execution by lethal injection. Certain medications such as some used to treat high blood pressure can cause the potassium level in the blood to reach a toxic level. As Pasteur pointed out is not the poison but the dosage that is important.
     
    Last edited by a moderator: Mar 29, 2012
  20. Kirk Keyes

    Kirk Keyes Member

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    Sodium chloride (NaCl) is "chemically related", as you say, to chlorine gas (Cl2). In fact, sodium chloride can be made directly by reacting metallic sodium with chlorine. But I'm sure you know there is a huge difference in the toxicity of the chorine in those two very different, but chemically related, compounds.
     
  21. Kirk Keyes

    Kirk Keyes Member

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    Remember, Google is your friend.
     
  22. Macchemist

    Macchemist Member

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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.
     
  23. Photo Engineer

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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
     
  24. Macchemist

    Macchemist Member

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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
     
  25. Photo Engineer

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    Mac;

    You have two bigger problems! :D

    Rhenium and H2S.

    Have fun.

    PE
     
  26. Macchemist

    Macchemist Member

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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