Final Report Summary - HG-197 MEHG ASSESS (Evaluation of Methyl-mercury production and decomposition by using Hg-197 radiotracer produced out of mercury enriched in Hg-196 isotope)
The project started with preliminary experiments in the flue gases pilot plant at Institute Jozef Stefan, using the radiotracer 197Hg. The pilot plant at the Reaktor Centre, Institute Joef Stefan, is an experimental array simulating chemical processes of the flue gasses purification systems, particularly Hg retention, consisting, basically, of a glass tube containing water with air bubbling. The air supply system includes an Hg0 (vapour) source, by heating liquid Hg0. The water circulates forced by a pump through a chemical cell, that allow pH control, addition of the reduction agent SO2 and other chemicals, and measurement of water temperature and REDOX potential. After bubbling, the air flows out of the system through a plastic tube that allows different measurement on the out coming gasses that gives information about the chemical processes within the bubbling column. The experiments tested the potential of the 197Hg radiotracer produced at the TRIGA Mark II research reactor to assess the Hg2+ reduction capacity of the system by adding 197Hg2+ in the chemical cell and evaluating the tracer activity in the outgoing air flow and in the bubbling water, in time trend sequences.
A second stage of the project consisted in the evaluation of the Hg2+ retention capacity of gypsum (calcium sulphate dihydrate; CaSO4*2H2O) small size particles in aqueous suspension by using the 197Hg radiotracer, testing the retention dependence with the suspension pH. The gypsum is a solid material used in the FGD systems which retains Hg together with the desulphurisation process.
The experimental series on Hg retention in FGD systems were completed by testing the Hg2+ behaviour in an aqueous solution under different conditions in a chemical reactor providing gas bubbling in the solution, pH and REDOX control, and Hg0 collection in a KMnO4 trap. The Hg2+ traced with 197Hg is spiked in the solution, measuring the activity in the water solution, both in total and filtered by 0.45 µm pore size to evaluate 197Hg association to any precipitate formed during the experiment, and in the KMnO4 solution along the time evolution of the chemical system. The composition of the solution, the gas bubbling in the solution, pH and REDOX were changed in different experimental runs to study the behaviour of the Hg in this system under different conditions.
A complementary study testing the preservation of Hg in natural waters was the last experimental run performed. The experiments consisted in the evaluation of different conditions for the preservation of water samples to analyse Hg contents in natural levels. Water samples from different sources (lake, river, marine, coastal lagoon, and rain water) were spiked with Hg2+ traced with 197Hg and stored in different conditions, determining the time trend of the 197Hg specific activity in order to evaluate Hg2+ losses from the water solution. The traced Hg2+ spiked was determined in order to obtain similar concentrations to those expected for the analysis of natural water, ranging in 10 ng L-1.
Study on validation of a methodology for mercury methylation in marine waters was implemented due to an emergent need to understand the relative contribution of mehg produced in water column as opposed to sediment compartment. Improved methodology using a 197-Hg radiotracer is a valuable tool in future Hg research in the coastal environment and lakes.
A second stage of the project consisted in the evaluation of the Hg2+ retention capacity of gypsum (calcium sulphate dihydrate; CaSO4*2H2O) small size particles in aqueous suspension by using the 197Hg radiotracer, testing the retention dependence with the suspension pH. The gypsum is a solid material used in the FGD systems which retains Hg together with the desulphurisation process.
The experimental series on Hg retention in FGD systems were completed by testing the Hg2+ behaviour in an aqueous solution under different conditions in a chemical reactor providing gas bubbling in the solution, pH and REDOX control, and Hg0 collection in a KMnO4 trap. The Hg2+ traced with 197Hg is spiked in the solution, measuring the activity in the water solution, both in total and filtered by 0.45 µm pore size to evaluate 197Hg association to any precipitate formed during the experiment, and in the KMnO4 solution along the time evolution of the chemical system. The composition of the solution, the gas bubbling in the solution, pH and REDOX were changed in different experimental runs to study the behaviour of the Hg in this system under different conditions.
A complementary study testing the preservation of Hg in natural waters was the last experimental run performed. The experiments consisted in the evaluation of different conditions for the preservation of water samples to analyse Hg contents in natural levels. Water samples from different sources (lake, river, marine, coastal lagoon, and rain water) were spiked with Hg2+ traced with 197Hg and stored in different conditions, determining the time trend of the 197Hg specific activity in order to evaluate Hg2+ losses from the water solution. The traced Hg2+ spiked was determined in order to obtain similar concentrations to those expected for the analysis of natural water, ranging in 10 ng L-1.
Study on validation of a methodology for mercury methylation in marine waters was implemented due to an emergent need to understand the relative contribution of mehg produced in water column as opposed to sediment compartment. Improved methodology using a 197-Hg radiotracer is a valuable tool in future Hg research in the coastal environment and lakes.