Oxidation of cinnabar by iron(III) in acid mine waters

Abstract

Fe(III) concentrations occurring in acid mine drainage water oxidized cinnabar (HgS), the most common natural mercury mineral. With Clpresent at environmental levels, significant mercury was released to solution. The rate of oxidation of cinnabar was much higher than the rate of mercury release to solution. Most of the mercury was bound to the remaining cinnabar by an unknown mechanism. An isotopic dilution technique was used to calculate the total mercury, both in solution and bound to the remaining cinnabar, released by oxidation.

Evaluating the role of re-adsorption of dissolved Hg2+ during cinnabar dissolution using isotope tracer technique

“…Experimental results have provided both direct and indirect evidences for the occurrence of Hg re-adsorption on cinnabar surface [7,10,13,15,24]. For instance, the amount of Hg released was found to be much lower than that of S (normally represented by SO 4 2− ), in strong disagreement with the stoichiometric estimation, indicating the adsorption of released Hg back on cinnabar particles [7,10,13,15]. Hg 2+ added into cinnabar suspension was observed to decrease quickly, further proving the occurrence of this process [10].…”

“…However, previous studies showed that dissolution of mercury sulfide (e.g., cinnabar) can also serve as a continuous source of inorganic Hg in natural environment due to the fact that a variety of environmental factors can facilitate its dissolution. These factors include the presence of iron(III) in acidic water [4], sulfide in water [5], and dissolved organic matter (DOM) [6][7][8]. The enhanced dissolution of cinnabar could be an important process controlling Hg cycling in aquatic environments as this process would make the originally stable Hg more reactive and bioavailable, increasing the possibility of Hg transport, methylation and bioaccumulation, posing a great risk to humans and wildlife.…”

“…A variety of environmental factors are expected to enhance or inhibit cinnabar dissolution via affecting the fate of cinnabar dissolution products. These factors include pH, redox potential (Eh), and Hg binding ligands [4,7,12,13]. Sulfide (S 2− ), one of the cinnabar dissolution products, could be eliminated from the system via oxidation to SO 4 2− at pH 5-8 under aerobic condition [4,10,12,14,15] or conversion to HS − and H 2 S under anaerobic condition [2].…”

“…These factors include pH, redox potential (Eh), and Hg binding ligands [4,7,12,13]. Sulfide (S 2− ), one of the cinnabar dissolution products, could be eliminated from the system via oxidation to SO 4 2− at pH 5-8 under aerobic condition [4,10,12,14,15] or conversion to HS − and H 2 S under anaerobic condition [2]. The former pathway may play a more important role as quicker dissolution of cinnabar was observed in the presence of O 2 [4,10,13].…”

“…Sulfide (S 2− ), one of the cinnabar dissolution products, could be eliminated from the system via oxidation to SO 4 2− at pH 5-8 under aerobic condition [4,10,12,14,15] or conversion to HS − and H 2 S under anaerobic condition [2]. The former pathway may play a more important role as quicker dissolution of cinnabar was observed in the presence of O 2 [4,10,13]. Hg 2+ , the other product, could bind with organic ligands, in particular thiol-containing moieties in dissolved organic matter (DOM) [7,11,16].…”