From: JOHN L STRAUGHN <john.straughn**At_Symbol_Here**WISC.EDU>
Subject: Re: [DCHAS-L] Sulfuric Acid and Potassium Thiocyanate Electrolyte
Date: Thu, 10 Mar 2016 19:18:33 +0000
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: CO2PR06MB585B73B823B17D2C0653C7F83B40**At_Symbol_Here**
In-Reply-To <99080534A99D89479A51A4EB6489672E05FF429E**At_Symbol_Here**>

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..

From: DCHAS-L Discussion List <dchas-l**At_Symbol_Here**> on behalf of Michael D Ahler <mahler**At_Symbol_Here**HANCOCKCOLLEGE.EDU>
Sent: Wednesday, March 9, 2016 1:26 PM
Subject: Re: [DCHAS-L] Sulfuric Acid and Potassium Thiocyanate Electrolyte

I believe the the Federal hazardous waste rules (and most states) allow for chemical treatment in a specific case if it is done to alleviate an impending or ongoing release or leak or to prevent a violent reaction.   In that case you are not treating as a disposal strategy, but treating to prevent an uncontrolled release of HCN gas.   I assume that Cornell is already an LQG, so the size of this Extremely hazardous waste won't be an issue.    Treating this electrolyte will unavoidably make the mass/volume of the waste larger.     I can't tell from the original wording, but I suspect someone is expecting to add this "treated" waste to a larger existing waste "collection vessel".    I strenuously encourage you to NOT DO THIS. Even well managed waste programs will see the occasional fugitive incompatible material get into the wrong container (personal experience).  You don't want this vessel to start venting HCN unexpectedly.   If this electrolyte is off-gassing HCN, I think you should take steps to stop the off-gassing.  I recommend neutralization in this case.  

       Adding aliquots of the acid electrolyte to 2.5 Liter of 1 M NaOH over time should be sufficient.   Best would be to do this in two smaller batches and surround the receiving NaOH solution containers with an ice bath.    Overkill?  maybe.   The solution will warm up as the acid is added and warm up further because of the neutralization reaction. This sulfuric acid is about 2.4 M and contains (when it was first mixed) about 1.2 moles of H2SO4.   2.5 Liters of 1M NaOH should cover it.   Check pH at the end.    Keep this treated cyanide waste in a separate bottle without combining it with anything else.   Your waste hauler or EHS folks know how to make a Lab Pack for transport.

Best of Luck.

Mike Ahler

Michael Ahler
Part-Time Faculty Member
LPS (Chemistry)
and formerly CHO, Cal Poly San Luis Obispo

From: DCHAS-L Discussion List [dchas-l**At_Symbol_Here**] on behalf of Bruce Van Scoy [bvanscoy**At_Symbol_Here**TWC.COM]
Sent: Tuesday, March 08, 2016 3:38 PM
Subject: Re: [DCHAS-L] Sulfuric Acid and Potassium Thiocyanate Electrolyte


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? 

Just asking,



From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**] On Behalf Of Steve's RR
Sent: Tuesday, March 8, 2016 3:24 PM
Subject: Re: [DCHAS-L] Sulfuric Acid and Potassium Thiocyanate Electrolyte


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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