Aqua Regia Disposal...

Mary Tang mtang at
Tue Oct 30 06:28:40 PDT 2007

Hi John --

Thanks -- yes I spoke with Kevin brought up exactly those concerns (if 
only ALL labmembers were so conscientious!)  He's etching a few 
nanometers of gold and Pt on a single wafer and using only a couple 
humdred ml.  This seems well within the acceptable dilution capacity of 
our system -- and these metals are not toxic.  So we agreed that 
aspirating this should be OK, in this case.


shott at wrote:

> 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>:
>> 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
>> PS-If it matters, I expect to only need ~200mL of the aqua regia 
>> mixture.

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