Reduction of silver solubility by humic acid and thiol ligands during acanthite (beta-Ag2S) dissolution.
Precipitation of highly insoluble metal sulfide minerals like acanthite (beta-Ag2S) or red cinnabar (HgS) is in principle an effective means to reduce metal availability and toxicity in contaminated soils. Unfortunately, experiments have shown that red cinnabar may be solubilized in the presence of dissolved organic matter or thiol ligands. To determine whether the same applies to acanthite, a laboratory synthesized beta-Ag2S mineral was incubated for up to 3 weeks in the presence of KNO3, dissolved humic acids, cysteine, methionine and thiosulfate. XPS analysis identified Ag2O (52%), Ag2SO4 (8%) and Ag2S (40%) on the particle surfaces. Ag was released into solution in the presence of KNO3 and methionine, presumably from mixed-oxidation surface layers. Contrary to earlier results with cinnabar, however, humic acids reduced Ag concentrations in solution by about 75%, and cysteine and thiosulfate, each containing a free -SH functional group, almost completely suppressed Ag release into solution.
Jacobson
Astrid R
AR
Department of Crop and Soil Science, Cornell University, 1002 Bradfield Hall, Ithaca, NY 14853, USA. arj5@cornell.edu
Martínez
Carmen E
CE
Spagnuolo
Matteo
M
McBride
Murray B
MB
Baveye
Philippe
P
D006801:Humans; D006812:Humic Substances; D008628:Mercury / Q000737:chemistry; D017669:Mercury Compounds / Q000737:chemistry; D008670:Metals / Q000737:chemistry* / Q000633:toxicity; D008906:Mining; D010084:Oxidation-Reduction; D012834:Silver / Q000737:chemistry; D012989:Soil Pollutants / Q000633:toxicity; D012995:Solubility; D013438:Sulfhydryl Compounds / Q000737:chemistry; D018505:Waste Management
D006812:Humic Substances; D017669:Mercury Compounds; D008670:Metals; D012989:Soil Pollutants; D013438:Sulfhydryl Compounds; D012834:Silver; D008628:Mercury; C034211:cinnabar