Mercury Interaction with Langøya gypsum sludge : Bonding to solid particles, stability and potential evaporation

Abstract

Abstract

Stabilizing mercury is still a major challenge throughout the world and no consensus has been reached on the safe disposal of mercy until now. Several methods have been suggested on how to stabilize mercury waste but their big scale applicability is still under research especially with high Hg content wastes. Langøya Island has been used to store mercury containing wastes in a gypsum sludge landfill. The stability of Hg waste under this environment and its potential to stabilize mercury containing wastes has been studied.

This paper describes the potential of the gypsum sludge (GS) to stabilize mercury containing wastes through laboratory experiments. A series of tests were carried out to investigate the adsorption of mercury to GS and its stability under different environmental conditions. Adsorption isotherm experiment was carried out by using GS with different concentration of HgCl2 solution. The results showed a close-to -linear adsorption isotherm with coefficient of distribution (Kd) value of 2035 kg/l. Leaching test undergone to the gypsum-mercury mixture (GS-Hg) showed that there is little leaching of mercury with the excess pore water suggesting that the adsorbed mercury is stable under storage environment. However leaching test undergone on GS-Hg with sea water showed higher leaching of Hg from the mixture suggesting that any seepage from the sea to the land fill will mobilize the Hg bound to the GS.

1-D diffusion tests were also carried out to examine potential evaporation of Hg from GS-Hg and evaluate the potential of GS to trap diffusing Hg by providing GS cover with varying thickness (0-15cm) over the GS-Hg mixture. The experimental set up has been run for three weeks till the compilation of this report and the results so far found showed that GS has a potential to retard up-diffusing Hg, if not completely block. Setups with thicker GS cover (8-15cm), has little or no Hg diffusion while there has been significant diffusion from thinner GS cover setups (0-5cm). Over the three weeks, Hg was able to diffuse around 8cm into the GS cover and the results correspond well with the results found from computer simulation by PHREEQC.

Keywords: GS; GS-Hg; Hg; adsorption; leaching; diffusion