Kinetic study on elemental mercury release from fly ashes and hydrated fly ash cement pastes.

The kinetics of elemental mercury (Hg) release from fly ashes and hydrated fly ash cement pastes was investigated using a homemade Hg measurement system. Three types of fly ash (FA) and ordinary Portland cement (OPC) were used to prepare cement pastes. After standard curing for 28 days, the hydrated cement paste (HCP) was ground into a fine powder for Hg emission measurements. Detectable Hg was found released from both fly ashes and hydrated fly ash cement pastes. The results show that elevated temperatures and evaporation of the capillary pore water in wet HCP samples accelerate Hg release. Both desorption of Hg from the particle surface of HCP powder and migration of Hg from the inner pores contribute to Hg release. The kinetic calculation indicates that the hydration products of hydrated fly ash cement have little immobilization effect on Hg, which is mainly physically encapsulated in the HCP particles by hydration products.