Mercury (II) reduction and co-precipitation of metallic mercury on hydrous ferric oxide in contaminated groundwater.
Mercury (Hg) speciation and sorption analyses in contaminated aquifers are useful for understanding transformation, retention, and mobility of Hg in groundwater. In most aquifers hydrous ferric oxides (HFOs) are among the most important sorbents for trace metals; however, their role in sorption or mobilization of Hg in aquifers has been rarely analyzed. In this study, we investigated Hg chemistry and Hg sorption to HFO under changing redox conditions in a highly HgCl2-contaminated aquifer (up to 870μgL(-1) Hg). Results from aqueous and solid phase Hg measurements were compared to modeled (PHREEQC) data. Speciation analyses of dissolved mercury indicated that Hg(II) forms were reduced to Hg(0) under anoxic conditions, and adsorbed to or co-precipitated with HFO. Solid phase Hg thermo-desorption measurements revealed that between 55 and 93% of Hg bound to HFO was elemental Hg (Hg(0)). Hg concentrations in precipitates reached more than 4 weight %, up to 7000 times higher than predicted by geochemical models that do not consider unspecific sorption to and co-precipitation of elemental Hg with HFO. The observed process of Hg(II) reduction and Hg(0) formation, and its retention and co-precipitation by HFO is thought to be crucial in HgCl2-contaminated aquifers with variable redox-conditions regarding the related decrease in Hg solubility (factor of ~10(6)), and retention of Hg in the aquifer.
Institut für Geoökologie, Abt. Umweltgeochemie, Technische Universität Braunschweig, Germany. Electronic address: j-h.richard@tu-bs.de.
Jan-Helge
JH
Richard
Institut für Geoökologie, Abt. Umweltgeochemie, Technische Universität Braunschweig, Germany.
Cornelia
C
Bischoff
Institut für Geoökologie, Abt. Umweltgeochemie, Technische Universität Braunschweig, Germany.
Christian G M
CGM
Ahrens
Institut für Geoökologie, Abt. Umweltgeochemie, Technische Universität Braunschweig, Germany.
Harald
H
Biester
D011232:Chemical Precipitation; D004784:Environmental Monitoring; D005290:Ferric Compounds / Q000737:chemistry*; D019015:Geologic Sediments; D060587:Groundwater / Q000737:chemistry*; D008628:Mercury / Q000032:analysis* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
D005290:Ferric Compounds; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D008628:Mercury
DOM bound mercury; Dissolved gaseous mercury; Elemental mercury; Geochemical modeling; Hg thermo-desorption; HgCl2