Progress 10/01/97 to 09/30/04
Outputs
Over the period this project was conducted a number of studies were carried out on the rates and mechanisms of metal and oxyanion sorption/desorption on soil components and soils. In many cases, these studies were complimented with molecular scale in-situ x-ray absorption fine structure (XAFS) and attentuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic studies. Sorption was characterized by a rapid followed by a slow process. The rapid process was usually completed in several hours and often comprised the bulk of the total sorption; this was especially the case for oxyanions such as selenate, selenite, arsenate, and arsenite. In the case of metals, sorption was somewhat slower, particularly with metals such as lead. The slow reactions were attributed to sites of varying reactivity, diffusion, and in the case of metals such as Ni and Zn, particularly at pHs above 6.5 and higher metal loadings, the formation of three dimensional (mixed) metal
hydroxide precipitates. However, on model systems such as kaolinite, surface precipitation occurred within 15 minutes. With most metals and oxyanions, XAFS and ATR-FTIR spectroscopy revealed the presence of predominantly inner-sphere surface complexes that were either monodentate or bidentate. However, the average local chemical environment on soil surfaces is very dependent on environmental factors such as ionic strength and pH. The metal surface precipitate phases were of the layered double hydroxide form. The formation of the latter greatly enhanced the sequestration of the metal, reducing its bioavailability. Residence time effects were seen with certain metals and desorption hysteresis was noted, particularly with metals such as Pb. This can often be ascribed to tight binding on humic substances. In other cases, the hysteresis was related to the formation of metal surface precipitates. One of the major conclusions of the studies is that when modeling sorption behavior on soil
surfaces, environmental factors and time must be taken into account.
Impacts
The results of this investigation have provided useful and predictive information on the fate, transport, retention, and bioavailability of important nutrients, metals and oxyanions in soils. This information should help in improving environmental quality, provide more cost effective approaches for remediating contaminated soils, and enhance human health.
Publications
- Arai, Y., and D.L. Sparks. 2002. Soil Sci. 167:303-314.
- Roberts, D.R., R.G. Ford. 2003. Environ. Sci. Technol. 37:908-914.
- Nachtegaal, M., M.A. Marcus, J.E. Sonke, J. Vagronsveld, K.J.T. Livi, D. van der Lelie, and D.L. Sparks. 2005. Geochim. Cosmochim Acta 69:4649-4664.
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Progress 01/01/02 to 12/31/02
Outputs
Bioavailability, fate, and transport of contaminants can be affected by contact time (residence time) in soils and sediments. There is little information on the long-term effects of metal/metalloid partitioning reactions in soils and soil components. There are great concerns about arsenic contamination of soil and water and its impact on animal and human health. In this study, residence time effects (3 days-1 year) on arsenate [As(V)] adsorption/desorption reactions and on arsenate speciation at the aluminum-oxide-water interface were investigated using batch experiments coupled with time-resolved in-situ extended x-ray absorption fine structure (EXAFS) spectroscopy investigations. Biphasic arsenate adsorption kinetics were observed at pH 4.5 and 7.8, and whereas the the reaction at pH 4.5 was nearly completed after 3 days, slow adsorption continued at pH 7.8 after one year. The longer the residence time, the greater the decrease in arsentate desorption at both pHs.
EXAFS analyses showed that arsentate was bound to the soil mineral surface as a bidentate binuclear complex, confirming the strong binding of arsenate.
Impacts
To address concerns about arsenic in drinking water, it is imperative that we understand the mechanisms and rates of arsenic reactions with soils. In this study, it is shown that if arsenic has been in the soil environment for long periods of time it is more stable and may be less bioavailable.
Publications
- Arai, Y., and Sparks, D.L. 2002. Residence time effects on arsentate surface speciation at the aluminum oxide-water interface. Soil Sci. 167:303-314.
- Elzinga, E.J., and Sparks, D.L. 2002. X-ray absorption spectroscopy study of the effects of pH and ionic strength on Pb(II) soption to amorphous silica. Environ. Sci. Technol. 36:4352-4357.
- Peak, D., Sims, J.T., and Sparks, D.L. 2002. Solid-state speciation of natural and alum-amended poultry litter using XANES spectroscopy. Environ. Sci. Technol. 36:4253-4261.
- Peak, D., and Sparks, D.L. 2002. Mechanisms of selenate adsorption on iron oxides and hydroxides. Environ. Sci. Technol. 36:1460-1466.
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Progress 01/01/01 to 12/31/01
Outputs
Formation of surface-induced metal hydroxide precipitates appear to play an important role in the sequestration of metals such as Co, Ni, and Zn in soil environments. To investigate the influence of commonly present organic ligands on precipitate formation, we investigated the sorption of Ni by gibbsite and pyrophyllite in the presence of citrate and salicylate for 4 weeks and identified the Ni hydroxide precipitates with diffuse reflectance spectroscopy (DRS). In the absence of organic ligands, Ni uptake proceeded by formation of Ni-Al layered double hydroxide (LDH) precipitates. Citrate and salicylate decreased both the Ni removal from solution and precipitate formation. The suppression by citrate was more pronounced than that by salicylate due to the stronger complexation of Ni by citrate. In the presence of citrate and salicylate, the precipitate phase was Ni-Al LDH on pyrophyllite, but predominately a-Ni hydroxide on gibbsite. This difference can be explained by
the differing Al solubilities of the two minerals. Only after a longer period of 30 days and at a low citrate concentration did enough Al become available to transform a-Ni hydroxide into the thermodynamically more stable Ni-Al LDH.
Impacts
A better understanding of how competitive sorbents and sorbates in soils affect metal immobilization could significantly impact soil and environmental quality.
Publications
- Yamaguchi, N. U., A. C. Scheinost, and D. L. Sparks. 2001. Surface-induced nickel hydroxide precipitation in the presence of citrate and salicylate. Soil Sci. Soc. Am. J. 65:729-736.
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Progress 01/01/00 to 12/31/00
Outputs
During this period, we studied the kinetics and mechanisms of metal (nickel, zinc) and metalloid (arsenate and sulfate) sorption/desorption on soil minerals and soils and conducted speciation studies on zinc in contaminated soils. For this report, the focus will be on the arsenate results. Arsenate sorption on goethite, an important metal oxide in soils, was studied over a range of residence times (time of contact between the mineral and the arsenate) and at two pH levels (4 and 6) found in soils. The rate of arsenate sorption was rapid, with over 93% of the aresenate sorbed in a 24 hour period at both pHs. X-ray absorption fine structure (XAFS) spectroscopic studies revealed that a bidentate binuclear surface complex formed and there was no change in the complex as residence time increased. Residence time also did not affect the degree of arsenate release when phosphate was the desorbing oxyanion. Initially, arsenate desorption was rapid, with >35% of the total
arsenate desorbed within 24 hours. However, further desorption was slight even after 5 months of desorption.
Impacts
Toxic metals and metalloids are of great concern in terms of soil and water quality. Arsenic is of increasing importance as the critical level in water has recently been lowered. Our data show that arsenate is strongly held on soil minerals, and competition from other oxyanions commonly found in soils, such as phosphate, have little effect on arsenate release. This has important implications with respect to the mobility and bioavailability of arsenate in soils.
Publications
- O'Reilly, S.E., Strawn, D.G., and Sparks, D.L. 2001. Residence time effects on arsenate adsorption/desorption mechanisms on goethite. Soil Sci. Soc. Am. J. 65:67-77.
- Arai, Y., Elzinga, E.J., and Sparks, D.L. 2001. X-ray absorption spectroscopic investigation of arsenite and arsenate adsorption at the aluminum oxide-water interface. J. Colloid Interf. Sci. 235:80-88.
- Matocha, C.J., Sparks, D.L., Amonette, J.E., and Kukkadapu, R.K. 2001. Kinetics and mechanism of birnessite reduction by catechol. Soil Sci. Soc. Am. J. 65:58-66.
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Progress 01/01/99 to 12/31/99
Outputs
The kinetics and mechanisms of plant nutrients (ammonium-nitrogen, phosphorus), metals (nickel, lead, zinc) and metalloids (arsenate, sulfate, borate, selenate, and selenite) were investigated on an array of soil minerals ( clay minerals, metal oxides), soil clays, and soils using a number of in-situ spectroscopic (x-ray absorption, diffuse reflectance, and attentuated total reflectance Fourier transform infrared) and microscopic (scanning force, scanning electron) techniques. Time scales of minutes to years were investigated. Surface complexes (ranging from outer-sphere to surface precipitate phases) were identified depending on environmental (pH, ionic strength, time, surface loading) effects. Particularly noteworthy was the identification of metal hydroxide phases forming on field soils and in soils contaminated with metals such as zinc for long time periods. The precipitate phases were very stable which indicates that the formation of surface precipitates could be
an important way to sequester metals in the environment such that they are less mobile. Metalloid retention was characterized by a range of outer-sphere and inner-sphere surface complexes, depending on ionic strength and pH. Residence time had a significant effect on the "fixation" and release of nonexchangeable ammonium in illite and vermiculite. The kinetics of its release appeared to be diffusion-controlled.
Impacts
The use of cutting-edge analytical techniques that enable one to better simulate the soil environment, i.e., in-situ techniques where studies can be done with moist suspensions, have resulted in significant findings about the mobility and speciation of plant nutrients and toxic metals and metalloids. Such information could prove invaluable in the areas of soil remediation and nutrient managment, and in making sound predictions about bioavailability and transport of nutrients and contaminants in soil and water environments. This would greatly benefit agriculture and industry.
Publications
- Steffens, D., Sparks, D.L. 1999. J. Plant Nutr. Soil Sci. 162:599-605.
- Scheinost, A.C., Ford, R.G., and Sparks, D.L. 1999. Geochim. Cosmochim. Acta 63:3193-3203.
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Progress 01/01/98 to 12/31/98
Outputs
During this reporting period, metal (nickel and lead) and metalloid (sulfate) sorption kinetics and mechanisms were studied via macroscopic and molecular scale (x-ray absorption fine structure [XAFS], diffuse reflectance [DRS] and attentuated total reflectance Fourier transform infrared [ATR-FTIR] spectroscopies) approaches. Nickel sorption, on an array of mineral surfaces, including soils, resulted in the formation of metal hydroxide precipitates on time scales of minutes to hours. These precipitates became very stable with time resulting in little nickel release. Lead sorption on montmorillonite resulted in weaker surface complexes (outer-sphere) at low ionic strengths and stronger surface complexes (inner-sphere) at high ionic strengths. Sulfate forms both outer-sphere and inner-sphere complexes on goethite at pH less than 6. At pH greater than 6, sulfate forms only an outer-sphere complex.
Impacts
By using advanced analytical techniques, one can definitively determine how metals and metalloids are retained in soils. This information is critical for developing economically and environmentally sound recommendations related to agricultural productivity, soil and water quality, and soil remediation.
Publications
- Peak, D., Ford, R.G., and Sparks, D.L. 1999. J. Colloid Interf. Sci. 218:289-299.
- Elzinga, E.J., and Sparks, D.L. 1999. J. Colloid Interf. Sci. 213:506-512.
- Strawn, D.G., and Sparks, D.L. 1999. J. Colloid Interf. Sci. 216:257-269.
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