Abstract
Cinnabar (alpha -HgS) and metacinnabar (beta -HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO (sub 4) (super 2-) production, cinnabar dissolution rates were 2.64 to 6.16 mu mol (SO (sub 4) (super 2-) ) m (super -2) day (super -1) , and metacinnabar dissolution rates were 1.20 to 1.90 mu mol (SO (sub 4) (super 2-) ) m (super -2) day (super -1) . Monodentate-bound thiosulfate (S (sub 2) O (sub 3) (super 2-) ) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140-1145 cm (super -1) and 1006-1014 cm (super -1) regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO (sub 4) (super 2-) concentration underestimates alpha -HgS and beta -HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO (sub 4) (super 2-) production, but were significant: 0.47 mg (Hg) m (super -2) y (super -1) from cinnabar [6.45 nmol (Hg) m (super -2) day (super -1) ], and 0.17 mg (Hg) m (super -2) y (super -1) from metacinnabar [2.29 nmol (Hg) m (super -2) day (super -1) ]. The Hg mobilized during alpha -HgS and alpha -HgS dissolution is sufficient to form natural Au-Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during alpha -HgS and beta -HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg (super 2+) to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg (super 2+) on the electrode at open circuit potential. Abstract Copyright (2007) Elsevier, B.V.