Aqua Regia Disposal...

shott at stanford.edu shott at stanford.edu
Mon Oct 29 16:38:16 PDT 2007


Kevin:

Thanks for raising this issue and checking before handling this stuff.  
  A quick Google search seems to indicate that explosions of aqua  
regia in closed waste containers is a common .... and serious ....  
problem.

For example, I've a attached short PDF document describing accidents  
related to both aqua regia and pirahna from the University of  
Manitoba.  It seems to me that we need to come up with a better  
solution than a closed waste container.

Let me ask a couple of questions:

1. Are there other etchants that might be used?

2. How many grams of etched gold and/or platinum do you expect to have  
in the waste material?

In particular, I'm wondering why we can't rely on the acid waste  
neutralization system to handle this.  Certainly if it were "only"  
aqua regia, the AWN system could handle it as long as we took  
appropriate precations at the pouring/diluting stage at the wet bench  
(that is, we don't want a reaction with water to spatter this stuff on  
you or anyone else).  Depending on the weight of gold and/or platinum  
in the solution may cause us a problem with the concentration of  
metallic material that we are allowed to introduce into the waste  
stream.  However, if we don't have a metal concentration problem, I  
think that cooling the aqua regia and then carefully disposing of it  
in the "normal" acid drains may be a safer option.

Comments or additional information from anyone else on this list?

Thanks,

John


Quoting Kevin Crabb <kcrabb at stanford.edu>:

> Hello SNF Safety Folks,
>
> I am hoping to use aqua regia (mixture of 3:1 concentrated hydrochloric acid
> to concentrated nitric acid) to remove platinum and gold grid structures
> from my wafer.  I was told it is okay to do this at the wetbench general, as
> long as I collect my waste separately.
>
> However, after doing more research, it has come to my attention that aqua
> regia will fume (it produces chlorine gas) for hours/days (depending on the
> temperature, volume), and I was wondering how best to deal with this.  Would
> it be possible to leave the waste container open in the fume hood until it
> finishes fuming?  If not, is there a vented bottle cap that could be used?
> Any information/suggestions on how to handle this situation would be greatly
> appreciated.  Thanks,
>
> Kevin
>
> kcrabb at stanford.edu
>
> PS-If it matters, I expect to only need ~200mL of the aqua regia mixture.
>
>


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