Reactive mercury flux measurements using cation exchange membranes

Abstract. A method was developed to measure gaseous oxidized mercury (GOM) air-surface exchange using 2 replicated dynamic flux chambers (DFCs) in conjunction with cation exchange membrane (CEM) filters. The experimental design and method was developed and tested in a laboratory setting, using materials collected from industrial scale open pit gold mines in central Nevada, USA. Materials used included waste rock, heap leach ore, and tailings, with substrate concentrations ranging from 0.1 to 40 μg g⁻¹ total mercury (THg). CEM filters were used to capture GOM from the DFC sample lines while a Tekran^® 2537A analyzer measured GEM concurrently. Previous and ongoing work demonstrated that CEM do not collect GEM and efficiently collects multiple compounds of GOM. Positive GOM emission rates up to 4000 pg m⁻²h⁻¹ were measured from tailings materials with high Hg substrate concentrations, and this has significant implication with respect to air-Hg surface exchange. GOM flux was variable for lower Hg concentration substrates, with both emission and deposition observed, and this was affected by ambient air GOM concentrations. For substrates that experienced GOM deposition, deposition velocities were in the range 0.01–0.07 cm s⁻¹.