In sediment porewaters, metal sulfides play an important role in the removal of many metals; however, understanding of the influence of environmental factors on multiple metal sulfide species released into aquatic waters is still needed. This study evaluates the competitive precipitation of metal sulfides as they are affected by organic ligands (cysteine, gallic acid, and Pahokee Peat humic acid), inorganics ligands (Cl- and Ca2+), and oxidants. Centrifugation and ultrafiltration, coupled with inductively coupled plasma mass spectrometry, was employed to characterize ZnS, PbS, CdS, and CuS particle size distributions (PSDs; i.e. 30, 60, and 100 nm) and differentiate between nanoparticle (NP) and dissolved concentrations (a component not typically examined when using TEM and light scattering techniques). The presence of the organic ligand cysteine slows particle growth rates and limits bulk precipitation. Additionally, the presence of cysteine in 10-fold excess of initial metal/sulfide concentrations resulted in narrower PSDs (~ 3nm to 30 nm) for metals considered. However, for three-hour time scales, Pb and Zn sulfide particles demonstrate mixed trends with initial precipitation followed by subsequent dissolution even in the presence of excess organic ligands, which could be contributed to ligand promoted dissolution and/or chemical oxidation. This study illustrates that for multiple metal sulfide species in more complex aqueous matrices, several processes, including precipitation, dissolution, and chemical oxidation, can remain significant mechanisms in the lifetime of certain NPs even in the presence of excess capping agents.

Influence of organic ligands and environmental factors on metal sulfide nanoparticle precipitation

2019 Spring National Meeting

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