Role of Organic Acids in Promoting Colloidal Transport of Mercury from Mine Tailings

Slowey, Aaron J.; Johnson, Stephen B.; Rytuba, James J.; Brown, Gordon E.

doi:10.1021/es0504643

Cited by 47 publications

(33 citation statements)

References 36 publications

(54 reference statements)

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“…In the pH range from 1.4 to 6.0, the lower pH, the higher is the loss risk of WDC. Furthermore, with the decreasing pH, total (<1 μm) and colloidal amounts of Al, Fe, Si, and Mn increased, which often acted as the cementitious phase coating or encasing the fines as well as the main composition element of WDCs (Ryan and Gschwend 1994;Swartz and Gschwend 1998;Slowey et al 2005). This suggested that the dissolution of inorganic cement made up by these minerals released some colloidal species, and then portions of Al, Fe, Si, and Mn were transformed from the colloidal species to the dissolved species as well.…”

Section: Inorganic Cement Dissolution At Low Phmentioning

confidence: 99%

“…Soil pH change could significantly influence contaminant transport (Moreira et al 2008), and also the colloid-facilitated P mobility by destroying the inorganic and organic cement of potentially mobilized matrix fines, or cause stronger repulsion by the negatively charged soil matrix and decrease of inter-particle attraction (Klitzke et al 2008). Laboratory experiments have demonstrated that low pH mobilized colloids by inducing the dissolution of inorganic cementing phases, mainly Al and Fe oxides, and clay content (Ryan and Gschwend 1994;Swartz and Gschwend 1998;Slowey et al 2005). In addition, pH is also an important factor affecting the sorption of organic matter on soil and sediment components (Guan et al 2006), which might act as coating around inorganic colloids and hence affect the behavior of colloids.…”

Section: Introductionmentioning

confidence: 99%

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Effect of pH on the release of soil colloidal phosphorus

Liang¹,

Liu

Chen³

et al. 2010

J Soils Sediments

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Purpose Colloid-facilitated phosphorus (P) has been proved as a significant contributor to eutrophication. Release of colloidal phosphorus (P coll ) depends on the released soil colloids and their P adsorption abilities, both of which are greatly affected by pH. The aim of the study was to assess the effect of pH in a wide range on P coll loss of the top silt loamy soil rich in organic matter and P for the successful description and prediction of P transport. Materials and methods In batch experiment, soil samples were shaken with deionized water in a wide range of pH from 1.4 to 9.9 for 24 h. Then water-dispersible colloids (WDCs) were extracted by pre-centrifugation, microfiltration, and ultracentrifugation processes orderly and determined gravimetrically. The P coll values at each pH were calculated as the difference between the concentration of total P in nonultracentrifuged and ultracentrifuged samples. The same method was applied for the released colloidal mineral elements (Al, Fe, Ca, Si, Mg, Mn). Colloid morphology and P distribution on colloid surface were directly illustrated by transmission electron microscope (TEM) and scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDS) mapping scanning analyses. Results and discussion Over pH 4.6-6.0, the released P coll was below 5.5 mgkg -1 soil, while up to 66.8 mgkg -1 soil and 28.5 mgkg -1 soil at pH 1.4 and 9.9, respectively, indicating that both high and low pH values enhanced the mobilization of P coll . At the low pH, the potential loss of P coll mainly resulted from the dissolution of inorganic encasing cement such as Al oxides and clay mineral. However, besides electrostatic repulsion, dissolution of organic coating at high pH enhanced the P coll release as revealed by the SEM-EDS results. The P was heterogeneously distributed on the WDCs and might be associated with soil organic matter, Al oxides, Fe oxides (oxyhydroxide), and clay mineral at the low pH, while mainly with Fe oxides and less clay mineral at the high pH. Conclusions Both high and low pH enhanced colloid and P coll releases. This study first visually revealed that the dissolution of organic cement at high pH enhanced the release of WDCs and their facilitated P coll release. The exceptional loss risk of P coll may be caused by soil acidification due to the dissolution of inorganic cements, especially in Al-rich soils, and by the enhanced high soil pH due to the dissolution of organic coating in the organic matter-rich soils.

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Section: Inorganic Cement Dissolution At Low Phmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of pH on the release of soil colloidal phosphorus

Liang¹,

Liu

Chen³

et al. 2010

J Soils Sediments

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“…In nearly all Hg-contaminated natural systems, strong particle association has been identified as the primary mode of transport to aquatic environments, whether from mercury mines (Whyte and Kirchner, 2000;Conaway et al, 2003;Lowry et al, 2004;Kim et al, 2004c;Slowey et al, 2005a), alluvial gold mine tailings (Slowey et al, 2005b), or industry (Gagnon et al, 1997;Rolfhus et al, 2003;Bloom et al, 2004). Although particles account for a minor fraction of Hg deposited from the atmosphere to aquatic settings (Ryaboshapko et al, 2002;Poissant et al, 2004;Sakata and Marumoto, 2005), Hg sorption onto particles enhances downward transport to methylating zones in the water column or sediments (Lamborg et al, 2002).…”

Section: Mercury Speciation and Transportmentioning

confidence: 99%

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Slowey

Brown

2007

Geochimica et Cosmochimica Acta

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Methylmercury can accumulate in fish to concentrations unhealthy for humans and other predatory mammals. Most sources of mercury (Hg) emit inorganic species to the environment. Therefore, ecological harm occurs when inorganic Hg is converted to methylmercury. Sulfate-and iron-reducing bacteria (SRB and FeRB) methylate Hg, but the effects of processes involving oxidized and reduced forms of sulfur and iron on the reactivity of Hg, including the propensity of inorganic Hg to be methylated, are poorly understood. Under abiotic conditions, using a laboratory flow reactor, bisulfide (HS À ) was added at 40 to 250 lM h À1 to 5 g L À1 goethite (a-FeOOH) suspensions to which Hg(II) was adsorbed (30-100 nmol m À2 ) at pH 7.5. Dissolved Hg initially decreased from 10 3 or 10 4 nM (depending on initial conditions) to 10 À1 nM, during which the concentration of Hg(II) adsorbed to goethite decreased by 80% and metacinnabar (bHgS (s) ) formed, based on identification using Hg L III -edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The apparent coordination of oxygens surrounding Hg(II), measured with EXAFS spectroscopy, increased during one flow experiment, suggesting desorption of monodentate-bound Hg(II) while bidentate-bound Hg(II) persisted on the goethite surface. Further sulfidation increased dissolved Hg concentrations by one to two orders of magnitude (0.5 to 10 nM or 30 nM), suggesting that byproducts of bisulfide oxidation and Fe(III) reduction, primarily polysulfide and potentially Fe(II), enhanced the dissolution of b-HgS (s) and/or desorption of Hg(II). Rapid accumulation of Fe(II) in the solid phase (up to 40 lmol g À1 ) coincided with faster elevation of dissolved Hg concentrations. Fe(II) served as a proxy for elemental sulfur [S(0)], as S(0) was the dominant bisulfide oxidation product coupled to Fe(III) reduction, based on sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In one experiment, dissolved Hg concentrations tracked those of all sulfide species [S(-II)]. These results suggest that S(-II) reacted with S(0) to form polysulfide, which then caused the dissolution of b-HgS (s) . A secondary Fe-bearing phase resembling poorly formed green rust was observed in sulfidized solids with scanning electron microscopy, although there was no clear evidence that either surface-bound or mineralized Fe(II) strongly affected Hg speciation. Examination of interrelated processes involving S(-II) and Fe(III) revealed new modes of Hg solubilization previously not considered in Hg reactivity models.

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“…The minerals cinnabar and metacinnabar, native (or elemental) mercury (Hg), calomel (Hg 2 Cl 2 ), and mercury oxychlorides Hg 2 ClO and Hg 4 Cl 2 O have been identified at mercury ore deposits. Mercury sulfide particles are thought to play an important role in the colloid transport of mercury from mercury mine tailings (Lowry et al 2004, Slowey et al 2005. review the absorption behavior of mercury.…”

Section: A145 Mercurymentioning

confidence: 99%

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

Cantrell¹,

Zachara²,

Dresel³

et al. 2007

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Companion reports that review other subject matter areas relevant to contaminant transport within the vadose zone beneath the SST WMAs, the IDF, and groundwater have been recently published. The specific subject areas include the geology of the SST WMAs iv contaminants released to the vadose zone exhibit a wide range of mobility behaviors. Many tank waste contaminants have been strongly retarded by adsorption and precipitation reactions (e.g., cesium, plutonium, americium, and europium), while others have remained mobile (e.g., technetium, nitrate, and selenium). Still others show variable, waste-specific behaviors (e.g., cesium [where sodium concentrations are very high], strontium, chromium, and uranium) that are closely tied to evolving composition of pore water in the sediments, and for chromium, a change in oxidation state. The temperature of in-ground tank waste has moderated by heat exchange with the subsurface sediment, and high concentrations of base (OH -) have been neutralized through reactions with sediment minerals and secondary mineral precipitation. Major geochemical features that may potentially affect the mobility of key contaminants of interest in the vadose zone include oxidation state, aqueous speciation, solubility, and adsorption reactions.Processes suspected of facilitating the far-field migration of immobile radionuclides, such as formation of stable aqueous complex formation and mobile colloids, were found to be potentially operative, but unlikely to occur in the field. An exception is the enhanced migration of cobalt-60 facilitated by the formation of highly stable aqueous-cyanide complexes. Certain fission-product oxyanions (e. • Adsorption is suppressed by large concentrations of tank waste anions (e.g., NO 3 -, OH -, and CO 3 2-)• Surface charge of clay-size minerals is negative and will therefore tend to repel anions• Unlike chromium, their less-soluble, less-mobile reduced forms are unstable in oxidizing environments.Laboratory studies conducted through PNNL's Vadose Zone Characterization Project and basic-science geochemical studies are expected to continue in partnership to provide information to further refine the conceptual model used for risk assessment modeling. Results of these studies can be used to help ascertain uncertainties associated with the refinement of the conceptual models for contaminant migration in the vadose zone beneath the single-shell tanks. Results can also provide improved parameterization, such as distribution coefficients (K d ), and mathematical constructs used by modelers to predict contaminant mobility under these conditions, and to decrease the degree of conservatism incorporated in these models.For various reasons, risk assessment models typically use various approximations to represent the conceptual model developed for the site. Adsorption is frequently approximated using empirical distribution coefficients (K d s). Although the use of empirical distribution coefficients can potentially lead to erroneous results under certain conditions where the...

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Role of Organic Acids in Promoting Colloidal Transport of Mercury from Mine Tailings

Cited by 47 publications

References 36 publications

Effect of pH on the release of soil colloidal phosphorus

Effect of pH on the release of soil colloidal phosphorus

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

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