engleski

The effects of acid volatile sulfides on the use of hydrochloric acid for determining solid-phase associations of mercury in sediments

The use of dilute HCl for the selective extraction of mercury from suboxic and anoxic sediments has been evaluated. The effect of acid concentration (1-6 M HCl) on the extraction of Hg and on the recovery of aqueous Hg preextraction spikes from sediments containing various amounts of AVS has been studied. The results obtained by using 1 M HCl as extractant (~90 % of added Hg was recovered in the solid phase after extraction) indicated that acid-soluble Hg may react with H2S released from AVS phases (e.g. FeS, MnS) and precipitate in the form of HgS. The modeling of Hg speciation in HCl solutions in the presence of sulfide predicted the HgS(s) precipitation in 1 M HCl, observed experimentally. The precipitation of HgS(s) was found to be considerably lower when greater (2-6 M) HCl concentrations were used for Hg extraction. The modeling calculations confirmed that the extent of HgS(s) formation in the solution was controlled by the applied HCl concentration. The difference between HCl-soluble Hg fraction in an estuarine sediment core extracted by 1 M (1-5 % of Hgtot) and 6 M (50-60 % of Hgtot) HCl was consistent with the model experiments. These results suggest that the use of 1 M HCl extraction procedures must be questioned for methodological artifacts and that 6 M HCl could advantageously replace 1 M HCl for extracting Hg in the presence of AVS.

sediments; mercury; hydrochloric acid; extraction; sulfides; phase studies

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