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6Re: Disposal guidance: heavy metals

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  • Dave Waddell
    Feb 22, 2006
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      Thanks Rosemary. I always enjoy our conversations and always learn
      something new.

      I like the treatment methods you've described. One challenge we and
      California face is our state toxicity criteria includes acute toxicity
      measured in oral-rat LD50, inhalation-rat LC50, Dermal rabbit LD50 and
      aquatic tox to salmonids (usually rainbow trout) as a TLM-96. Copper
      sulfate designates as a Washington State-only dangerous waste at
      concentrations over 1% in compounds or solutions due to oral toxicity
      of 300 mg/kg. So we always have to be careful about assuming non-RCRA
      substances aren't hazardous.

      Since the copper (II) sulfide resulting from precipitation of the
      Benedict's is completely insoluble, toxicity won't be an issue. Can I
      assume it won't generate hydrogen sulfide gas when exposed to pH
      conditions between 2 and 12.5 so it doesn't designate as reactive?

      Dave W.

      -- In labcleanout@yahoogroups.com, "rosemary bottcher" <rbottcher@...>
      Hi, Dave. First, I'd suggest that hazardous and non-hazardous wastes
      not be mixed, for obvious reasons. Benedict's solution is not a RCRA
      waste and isn't particularly worrisome. I wouldn't recommend puting a
      lot of it down the drain, however, because the copper ion can make the
      POTW's precious bugs sick. Evaporation of solutions will certainly
      reduce the volume of waste to be disposed of, but it can take a looong
      time. I prefer to speed things up by adding Na2S to precipitate the
      sulfides of "heavy" metals. I put that in quotes because can anyone
      out there tell me exactly what is the definition of "heavy metal?"
      Folks call arsenic a "heavy metal" and it's not even a metal!) I also
      use Na2S to detect the presence of "heavy metals" in unknowns. As for
      the Benedict's solution, how about this: add an excess of reducing
      sugar, cook it and throw the mess away? Rosemary

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