To the original question as stated: If thiocyanate, NCS(-), reacts with 2.4N acid at all, it will not be cyanide. Acid hydrolysis may liberate hydrogen sulfide though, so watch out for that. When finished with this solution, add to it sodium hydroxide solution in a high concentration. 250ml of 5N NaOH will keep the resultant salt solution volume compact enough and the heat rise (about 25degC) will be noticeable but still safe enough.
PS. I despise the burocracy rules that distracts us from clear chemical thinking in dealing with these situations. It should be chemical knowledge first and rules second.
BTW: I'm not with UW safety any longer, I'm retired but still interested..
Before you do anything, check with your EHS staff to determine if that is permissible under your state's EPA or the Fed rules for the purposes of determining if that is "treatment". Federal EPA only allows neutralization for the purpose of pH adjustment ONLY and anything else would be considered a hazardous waste treatment process and may subject your university to be classified as becoming a "Treatment, Storage and Disposal Facility". Start by checking with your campus professional EHS Staff and have them determine/clarify your state/federal limitations to see if this is even possible, or if you could be moving your university into a higher standard of regulated activity - which they may or may not be prepared for. I think you're asking the wrong group. If you encounter any roadblocks or incomplete answers, immediately push this up the chain and request in-house Counsel provide an interpretation and begin with: are these the right questions to ask? What may I be subjecting my university to from a regulatory standpoint? And could I be held accountable for the regulatory actions of treating hazardous waste without a permit?
If I had to dispose of that, I would reduce the complication by neutralization. If you're concerned about the violence of the reaction, use a dilute solution of sodium hydroxide or use magnesium sulfate or something less reactive. Contact your hazardous waste people to see what the price is for disposal of the resulting quantity of sodium thiocyanate/calcium thiocyanate and weigh that price against the disposal of the non-neutralized solution.
They may not be able to take the non-neutralized solution in the same load with the rest of your hazardous waste. Let the price be your guide but always inform your waste handlers of the containers' contents.
On Mar 8, 2016, at 3:09 PM, Bell,Martin <mwb32**At_Symbol_Here**DREXEL.EDU> wrote:
We received a request from a Materials Engineering student for assistance on the proper handling of an electrolyte that contains sulfuric acid and potassium thiocyanate. This particular reaction will evolve hydrogen cyanid gas. The student plans to make 500 ml of the electrolyte. The student plans to use 66.6 ml of H2SO4 and 4.9 g of KSCN. The balance of the solution will be water.
The current plan is to scrub the hydrogen cyanid gas that is generated during the reaction by bubbling it through NaOH. This practice was determine from wet scrubbing literature.
The problem we are trying to solve concerns the handling of waste. I am concerned about the generation of HCN in the waste collection vessel which will pressurize the container. We obviously don't want to use a vented cap. We are kicking around the idea of adding more sulfuric acid to the reaction vessel to force the reaction to completion by using up all the CN- ions. I don't want to add NaOH to the reaction vessel because the reaction with Sulfuric acid is extremely violent.
Is this approach reasonable?
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