DETERMINATION OF ACUTE HG EMISSIONS FROM SOLIDIFIED STABILIZED CEMENTWASTE FORMS/

The chemical form of mercury in wastes to be solidified/stabilized may lead to volatile losses from the finished solidified/stabilized monol ith. Elemental mercury vapor (Hg vapor) was detected in the headspace of batch reactors that contained solidified/stabilized ordinary Portla nd cement doped with mercuric oxide (HgO) or liquid elemental mercury [Hg degrees(l)]. Vapor concentrations increased as a function of time and temperature; the headspace over the HgO samples was saturated in a bout one hour, while the samples containing Hg degrees(l) reached appr ox. 20% of saturation in about two hours. Increased temperatures due t o cement hydrolysis lead to increased Hg vapor evolution. Mercury soli dified/stabilized as mercuric sulfide (HgS, black) emitted no Hg vapor . Data for the HgO and Hg degrees(l) experiments was fit to a reversib le first-order rate expression. Samples containing HgO displayed the g reatest volatility as a result of the rapid dissolution of HgO and the subsequent formation of a strong driving force across the air-water i nterface. The evolution of Hg vapor from samples solidified/stabilized as Hg degrees(l) is limited by mass transfer resistances that kinetic ally limit the dissolution of Hg degrees(l) into the aqueous phase. Th e inert character of HgS (extremely low solubility and resistance to o xidative dissolution) prevents the evolution of detectable Hg in waste s solidified/stabilized as HgS. The findings of these studies may be i mportant when considering treatment and disposal scenarios for Hg-cont aining wastes. (C) 1997 Elsevier Science Ltd.