Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.v31b..01s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #V31B-01
Physics
6235 Mercury
Scientific paper
The release of mercury from mine waste tailings at historic mining sites in the California coastal ranges is a significant pollution threat to local water sources and fish populations. The transport of mercury associated with nanometer-scale (¯50-400 nm) colloidal particles is one of the major pathways for mercury release from these mine sites. This study has used laboratory column ex-periments to generate colloids from calcines and unprocessed waste rock from the New Idria (NI) and Sulphur Bank (SB) mines. Colloid generation was initiated by flowing two solutions of vary-ing ionic strength through the columns in the presence of malonic acid. The colloidal material generated was characterized by ATEM, Extend X-ray absorption fine structure (EXAFS) analysis, and chemical sequential extraction techniques. ATEM analysis indicates that the colloids generated from the NI calcines consist of crystalline alunite-jarosite and hematite, a poorly ordered Si-Al gel and HgS. This mixture is very similar to that present in the bulk calcine material and suggests that these colloids are formed by detach-ment/breakup of the bulk material. Hg-LIII-EXAFS and sequential extractions indicate that 90% of the mercury present in these colloids is in the HgS form. The column experiments on the SB calcines produced only a small amount of colloidal material when the first few pore volumes of solution were flowed through. These consist of quartz, poorly ordered Si-Al-Fe gel and HgS. Hg-LIII-EXAFS spectra confirms that HgS is the dominant mercury species in these colloids. Raising the pH of the colloid-free column effluent from the SB calcines experiment results in the precipita-tion of a poorly ordered Si-Al-Fe rich gel, which is similar to that observed at the waste pile/lake interface next to the SB mine (Clear lake, CA). EXAFS and ATEM results indicate that mercury can be associated with this precipitated colloidal material. Colloids generated using unprocessed waste rock from the SB mine site consist of Cr-oxide, hematite, mackinawite (FeS0.9), and HgS formed via the detachment/breakup mechanism. As for the two previous systems Hg-EXAFS re-sults indicates that HgS is the dominant mercury-bearing phase in these colloids. This study shows that the colloidal transport of mercury from these particular mine sites occurs predominantly as HgS and not as Hg sorbed to minerals phase as previously thought. Also the mechanisms of colloid generation (i.e. detachment/breakup or dissolution/reprecipitation) varies according to the composition of the starting material.
Brown Gerald E.
Kim Chaehyun
Lowery G. V.
Rytuba James
Shaw Sam
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