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DIVISION S-2—SOIL CHEMISTRY

Desorption Kinetics of Cadmium²⁺ and Lead²⁺ from Goethite

Influence of Time and Organic Acids

^a Dep. Crop and Soil Environmental Sciences, 236 Smyth Hall, Virginia Polytech. Inst. & State Univ., Blacksburg, VA 24061
^b Sandia National Laboratories, Albuquerque, NM 87185

* Corresponding author (eick{at}vt.edu)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
It is generally accepted that trace metal concentrations in soil solution are primarily controlled by sorption and desorption reactions at the particle-water interface. While numerous studies have been conducted to understand adsorption of these metals to soil minerals, less is known about long-term adsorption-desorption processes. The objective of this study was to examine the influence of residence time and organic acids on the desorption of Pb²⁺and Cd²⁺ from goethite. Adsorption experiments were conducted at pH 6.0 for 1 wk (short-term) and 20 wk (long-term). Lead adsorption was nearly complete after 4 h, with very little additional sorption occurring during a 20-wk period. In contrast, Cd showed a continuous slight increase in the remaining adsorption. Desorption experiments were conducted at pH 4.5 and desorption kinetics for Pb²⁺and Cd²⁺ were slow compared with the sorption reaction. Trace metal removal from the goethite surface was not completely reversible during an 8-h desorption period for all of the experiments, except for short-term Cd²⁺ in the presence of salicylate. For all experiments except long-term Pb²⁺ desorption, the quantity of metal desorbed from goethite followed the order salicylate > NaNO₃ > oxalate. It is postulated that the greater effectiveness of salicylate compared with oxalate was related to the ability of oxalate to form bridging or ternary complexes between the metal and the goethite surface. For all experiments except Pb²⁺ sorption in the presence of oxalate a greater quantity of metal was desorbed for the short-term compared with the long-term experiment. However, these results were only statistically significant for Pb²⁺ in the presence of salicylate. These results suggest that residence time effects observed by many researchers are much less prevalent at low pH values, and hence natural or anthropogenic reduction in soil pH may reduce the ability of the soil to naturally sequester trace metal cations over time.

Abbreviations: AA, atomic absorption • Fe_o, oxalate extractable Fe • Fe_t, total Fe • ICP-AES, inductively coupled plasma atomic emission spectrometer • TEM, transmission electron microscopy • TGA, thermogravimetric analysis • XRD, x-ray diffraction

	INTRODUCTION

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IN NATURAL SYSTEMS, the bioavailabilty of trace metals is primarily controlled by adsorption-desorption reactions at the particle-solution interface (Backes et al., 1995). Although a great amount of research has been conducted examining these reactions, the accurate prediction of trace metal potential bioavailability in natural systems has remained elusive. Natural systems are composed of a heterogeneous mixture of mineral and organic solid phases as well as a myriad of organic and inorganic solutes that compete with trace metals for adsorption sites on solids. This inherent heterogeniety makes modeling the potential bioavailability of trace metals problematic. Moreover, recent evidence has suggested that trace metal potential bioavailability decreases with increased residence time (McLaren et al., 1986; Ainsworth et al., 1994; Backes et al., 1995; McLaren et al., 1998; Eick et al., 1999; Ford et al., 1999). Many explanations have been proposed for these observed residence time effects, including solid-state diffusion within oxide particles (Bruemmer et al. 1988), diffusion into micropores and intraparticle spaces (Backes et al., 1995), change in the type of surface complex (McBride, 1994), incorporation into the mineral structure via recrystallization (Ainsworth et al., 1994), surface catalyzed oxidation and incorporation into the crystal matrix (McKenzie, 1970; Backes et al., 1995), surface catalyzed hydrolysis and precipitation (Backes et al., 1995), and phase transformation of surface precipitates (Ford et al., 1999).

Most trace metal-impacted environments have existed for several years to decades. Understanding the influence of residence time on trace metal desorption is critical to accurately predict the potential bioavailability of trace metals in natural systems, thus allowing regulators to determine sites where corrective measures are required. However, there is limited research on residence time effects and most studies examining the influence of residence time on the desorption of trace-metal cations from mineral surfaces have done so at near neutral pH values and in the presence of inorganic cations (i.e., Na⁺ or Ca²⁺). Recent evidence has suggested that naturally occurring low molecular weight organic acids may play an important role in the fate of trace-metal cations (Naidu and Harter, 1998; Benyahya and Garnier, 1999). Low molecular weight organic acids such as oxalic, citric, formic, and lactic acid have been identified in soil environments at varying concentrations depending on the type of soil environment and time of year (Stevenson, 1994).

Accordingly, we have investigated the short- and long-term adsorption kinetics of Cd²⁺ and Pb²⁺ on goethite at pH 6 and the influence of residence time and organic acids (salicylate and oxalate) on their desorption kinetics at pH 4.5. A pH of 4.5 was chosen to examine how changes in pH affect natural attenuation processes. Lead and Cd²⁺ were chosen as trace-metal cations because they are highly toxic common soil contaminants and have markedly different hydrolysis constants. Oxalate and salicylate were chosen as the low molecular organic acids because they have been identified in soil environments and they contain the more common organic matter functional groups (carboxylic and phenolic). Finally goethite is a common soil Fe oxide that may act as a sink for trace-metal adsorption.

	MATERIALS AND METHODS

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Oxide Preparation and Characterization
Goethite was synthesized by slowly titrating 0.20 M reagent-grade Fe(NO₃)₃ with 4 M NaOH. The suspension was aged at pH 12 at room temperature (298 ± 3 K) for 14 d followed by 24 h at 313 ± 1 K. Excess salts were removed by electrodialysis until the conductivity of the wash solution was equal to that of double-deionized water (2 wk). All solutions were prepared with double-deionized water and contact with glassware was avoided. The clean goethite precipitate was subsequently washed for 1 h with 0.40 M HNO₃ to remove any remaining amorphous phases, redialyzed, and freeze-dried. The goethite was characterized using x-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and ratio of oxalate extractable Fe (Fe_o) to total Fe (Fe_t). X-ray diffraction analysis, TGA, and TEM micrographs were diagnostic for goethite and consistent with those presented in Schwertmann and Cornell (1991). The Fe_o/Fe_t was <1%, indicating the absence of significant amorphous phases. The specific surface area and microporosity were determined using N adsorption with a Micromeritics 2010 surface area analyzer (Micromeritics, Norcross, GA). Results indicated nonporous goethite particles with a Brunauer, Emmet, and Teller (BET) surface area of 70 m² g^-1.

Adsorption Edges
Adsorption edges were obtained to examine the influence of pH on trace metal and organic acid adsorption on goethite. The four adsorption edges were obtained using a batch technique with 5 g L^-1 suspensions of goethite, a background electrolyte solution of 0.01 M NaNO₃, and 1 x 10^-4 M Pb⁺², 1 x 10^-4 M Cd⁺², 2 x 10^-3 M oxalate, and 2 x 10^-3 M salicylate. Samples of goethite were weighed into a 500-mL teflon lined flat-bottomed, water-jacketed reaction vessel covered with a removable glass lid containing entry ports for a mechanical stirrer, pH electrode, N₂ gas, burette tip, and pipette. Goethite was placed in 350 ml of 0.01 M NaNO₃, sonicated using a Fisher Scientific 550 Sonic Dismembrator (Fisher Scientific, Atlanta, GA), and hydrated for 24 h. Each trace metal and organic acid was dispensed in stepwise quantities from a stock solution to minimize local supersaturation of the suspension. Stock solutions were made from analytical grade reagents using distilled double-deionized water. The pH of trace-metal adsorption edges was increased from pH 3 to 8 with 0.10 M NaOH dispensed by an automatic titrator (Brinkman, Metrohm 718 Stat Titrino, Brinkman Instruments, Westbury, NY) at 2-h intervals. Organic acid adsorption edges were decreased from pH 9 to 3 with 0.10 M HNO₃ dispensed by an automatic titrator at 2-h intervals. Each adsorption edge was kept well stirred with the aid of a mechanical stirrer (Caframo RZR-2000, Caframo LTD, ON, Canada). All experiments were conducted at 298 K ± 0.1 K and 0.101 MPa (1 atm) pressure under a N₂ environment to eliminate CO₂ influences. Lead and Cd were analyzed using either inductively coupled plasma atomic emission spectrometer (ICP-AES) or atomic absorption (AA) with graphite furnace and the organic acids were analyzed using a Dohrmann 180 (Dohrmann, Santa Clara, CA) organic C analyzer.

Short- and Long-Term Adsorption Experiments
Adsorption experiments were conducted using a batch technique with 5 g L^-1 suspensions of goethite, 1 x 10^-4 M solutions of Pb²⁺ and Cd²⁺, and a background electrolyte solution of 0.01 M NaNO₃. All samples were undersaturated with respect to Pb(OH)₂(s) and Cd(OH)₂(s). Samples of goethite were weighed into a 500-mL teflon lined flat-bottomed, water-jacketed reaction vessel covered with a removable glass lid containing entry ports for a mechanical stirrer, pH electrode, N₂ gas, burette tip, and pipette. The goethite was sonicated, hydrated, N₂ sparged for 24 h in 450 mL of 0.01 M NaNO₃ and adjusted to pH 6 using 0.10 M HNO₃. The Pb²⁺ and Cd²⁺ were dispensed in stepwise quantities from stock solutions to minimize local oversaturation of the suspension. The suspension pH was kept constant at 6.0 and well-stirred with the aid of an automatic titrator and mechanical stirrer. All experiments were conducted at 298 ± 0.1 K at 0.101 MPa (1 atm) pressure in a N₂ environment to eliminate CO₂ influences.

Sorption experiments were conducted for 1 wk (short-term study) and 20 wk (long-term study). Samples were taken throughout the duration of both studies. An initial 2-mL aliquot was removed from the batch reactor and filtered through a 0.10-µm Gelman metrical membrane to presaturate the membrane. An additional 10-mL aliquot was removed from the batch reactor and filtered through the same presaturate membrane into previously acid-washed polypropylene test tubes. All suspension samples were carefully removed from the batch reactor using an electronic pipette to avoid changes in the total surface area/solution ratio. The filtered samples were acidified to a pH <2 with 8 M HNO₃, sealed, and stored in a refrigerator prior to analysis. After 7 d the long-term samples were removed from the pH-stat and placed in 500 mL acid-washed high-density polyethylene centrifuge bottles. The bottles were sealed with teflon tape to prevent evaporation and placed on an environmentally controlled rotating shaker at 298 ± 0.1 K. The pH was maintained constant at 6.00 ± 0.05 through manual addition of 0.10 M HNO₃ or NaOH. Lead and Cd were analyzed using either ICP-AES or AA with graphite furnace.

Desorption Study
Samples prepared for the sorption studies were used in the desorption studies. A filter flow method (i.e., miscible displacement technique) was used to maintain a low solution/soil ratio (characteristic of natural soil environments) and to prevent readsorption of desorbed species (Sparks, 1989). Samples were injected through a weighed 47-mm Corning Nuclepore Swin-Lok filter (Corning, Corning, NJ) holder containing a 0.45-µm Gelman cellulose ester filter (Millipore, Bedford, MA). For each suspension concentration enough solution was injected to obtain a goethite mass of 0.15 g. After injection of the suspension a thin layer of goethite and a small amount of entrained solution was retained on the filter paper. The filter holder plus the sample were weighed after injection to determine the volume of entrained solution. The Pb²⁺ and Cd²⁺ concentration of the filtrate was measured to determine both the total Pb and Cd sorbed and the entrained concentration. The entrained concentration was subsequently subtracted from the first fraction collected. Lead and Cd²⁺ were desorbed by continuous piston-pumping (Fluid Metering Model RHSY) of 0.01 M NaNO₃, 0.002 M oxalate, and 0.002 M salicylate solution adjusted to pH 4.5 and 298 K. All organic acids were made from reagent grade Na salts. Samples were collected at a flow rate of 3 mL min^-1 at intervals of 300 s using an Isco Cygnet fraction collector (Isco Inc., Lincoln, NE) for a total desorption period of 8 h. Between each desorption run, all tubing was washed with copious amounts of dilute HNO₃ (0.01 M) followed by double-deionized water. Samples were acidified to a pH <2 using 8 M HNO₃, sealed and stored in a refrigerator prior to analysis. Lead and Cd were analyzed using either ICP-AES or AA with graphite furnace. All desorption studies were run in duplicate.

Miscible displacement techniques have several advantages over traditional batch techniques, but, they are not without problems (Sparks, 1989). Problems include preferential flow through the adsorbent on the filter, film, and particle diffusion, and excess adsorptive present in the entrained solution following adsorption. Therefore, flow methods such as the miscible displacement technique often measure diffusion-controlled rather than true-chemical kinetics (Sparks, 1989). The miscible displacement technique was chosen because it may better represent metal adsorption-desorption behavior under natural conditions where transport processes are rate-limiting (Sparks, 1989). Although flow through methods often measure transport or diffusion-controlled kinetics, we did not determine whether changes in flow rates affected desorption rate coefficients. In this study, many of the above problems should be minimized because of the small quantity of goethite used on the filter and the small volume of the entrained solution (McLaren et al., 1998).

Kinetic Modeling
The experimental data from the short- and long-term desorption runs were fit to several commonly used kinetic models. While it is common for complex models to be developed to more accurately describe and interpret reaction mechanisms, our primary goal was to understand the role of aging on adsorption and desorption. Apparent rate coefficients may in fact be composed of numerous chemical and diffusional reactions, making it difficult to interpret reaction mechanisms simply from time dependent data without spectroscopic evidence (Sparks, 1989). Both chemical kinetic models and diffusion-controlled transport models have been used successfully in the past to describe experimental results. The following equations were applied to the desorption kinetic data: a single first-order equation over the whole time range, two first-order equations that were optimized at apparent rate changes, and the parabolic diffusion equation. Although all models successfully fit the data, two first-order equations resulted in the best fit. Therefore we will only present the first-order equation below. The first-order rate equation (Sparks et al., 1980) was used to model the data as two first-order reactions:

[1]

where Me_t was the amount of metal sorbed at desorption time t (µmol m^-2), Me₀ was the amount of metal sorbed at time 0 (µmol m^-2), t is time (s), and k_d is the apparent desorption coefficient (s^-1). If the reaction is first-order, a graph of ln (Me_t/Me₀) vs. t should yield a straight line of slope -k_d. Two first-order rate equations were optimized by dividing the data sets consistent with an apparent rate change and fitting both data sets to the first-order rate equation. Optimized time ranges were 20 to 150 min and 155 to 480 min.

Statistical Analysis
Differences in short- and long-term rate coefficients and cumulative quantity of trace metal desorbed for each metal cation and desorbing solution (e.g., short- and long-term Cd²⁺ in the presence of oxalate) were tested using Tukey-Kramer HSD multiple comparison procedure at the 0.05 and 0.10 confidence level (Sall and Lehman, 1996). For each desorbing solution the replicates from each experiment were used to determine variance and compare differences between short- and long-term treatments. All computations were performed on a PC with JMP IN Version 3.2 for Windows, SAS Institute Inc (Sall and Lehman, 1996).

	RESULTS AND DISCUSSION

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Adsorption Edges
Adsorption edges are often used to characterize the affinity of trace-metal cations and anions for mineral surfaces as a function of pH. Lead and Cd exhibited typical S-shaped adsorption edges where sorption increased with an increase in pH (Fig. 1a) . From Fig. 1a it is clear that Pb²⁺ has a higher affinity for the goethite surface compared with Cd²⁺. The Pb²⁺ adsorption edge is shifted to a lower pH and 100% of the added Pb²⁺ is adsorbed at a pH of 6.0. In contrast, 100% adsorption of Cd²⁺ is not reached until pH 8. Furthermore, a much greater percentage of Pb²⁺ (60%) is adsorbed at pH 4.5 compared with Cd²⁺ (5%). Other investigators have observed similar results (Ainsworth et al.,1994; Benyahya and Garnier, 1999). It has been suggested that adsorption and hydrolysis are correlated in some way (McBride, 1994). Recent spectroscopic evidence has indicated that Pb²⁺ adsorbs to goethite as a hydrolysis species while Cd²⁺ does not (Spandini et al., 1994; Barger et al., 1997). Although other factors such as electrostatics and electronegativity are important for trace metal cation binding to oxide surfaces, differences in hydrolysis properties may be primarily responsible for the observed differences in affinity of Pb²⁺ and Cd²⁺ for goethite.

View larger version (14K): [in this window] [in a new window]   Fig. 1. (A) Sorption of Pb2+ and Cd2+ on goethite as a function of pH. (B) Sorption of oxalate and salicylate on goethite as a function of pH. Goethite suspension density 5 g L-1 and a background electrolyte concentration of 0.01 M NaNO3.

Short- and Long-Term Adsorption Experiments
Trace metal sorption on oxide surfaces is often characterized by an initial rapid step (<1–5 h) followed by a slow continuous adsorption step (McKenzie 1970; Bruemmer et al., 1988). The rapid reaction has been attributed to adsorption on high affinity surface sites. However, the slow reaction mechanism is not as well understood and has been attributed to diffusion into crystal defects or dead-end pores, surface precipitation, and a change in the type of surface complex (Farley et al.,1985; Ainsworth et al., 1994; Eick and Fendorf, 1998). In this study, the adsorption behavior of Pb²⁺ and Cd²⁺ were markedly different. Lead adsorption was nearly complete after 4 h, with very little additional sorption occurring during the 20-wk period (Fig. 2) . In contrast, Cd showed a slow continuous increase in the amount of adsorption over a 20-wk period (Fig. 2). Other researchers examining trace metal adsorption on Fe-oxides obtained similar results (Farley et al., 1985; Bruemmer et al., 1988). Furthermore, a greater quantity of Pb²⁺ was sorbed to the goethite surface (0.1978 µmol m^-2) compared with Cd²⁺ (0.1797 µmol m^-2). The difference in the quantity and rates of Pb²⁺ and Cd²⁺ adsorption to goethite may be attributable to the different affinities of the trace metals for the goethite surface and the type of surface complex formed. Additionally, recent spectroscopic evidence has demonstrated that both Cd²⁺ and Pb²⁺ form inner-sphere surface complexes on Fe-oxide surfaces (Spandini et al., 1994; Bargar et al., 1997). However, Pb²⁺ is adsorbed as a hydrolyzed species while Cd²⁺ is not. Research has shown that goethite particles contain defect structures and micropores related to synthesis conditions and procedures (Schwertmann et al., 1985). Diffusion of cations into dead-end or micropores created by these defects may explain the slow metal sorption over time (Backes et al., 1995). One would expect that diffusion of Pb²⁺ as Pb(OH)⁺ would be slow compared with Cd²⁺ because of its much larger size, which may be responsible for the difference in long-term adsorption (Eick, 1999).

View larger version (16K): [in this window] [in a new window]   Fig. 2. Long-term sorption of Pb and Cd on goethite at pH 6.0. Goethite suspension density 5 g L-1 and a background electrolyte concentration of 0.01 M NaNO3.

View this table: [in this window] [in a new window]   Table 1. Quantity of Pb2+ or Cd2+ adsorbed and desorbed from goethite for short- and long-term desorption experiments at pH 4.5.

View larger version (24K): [in this window] [in a new window]   Fig. 3. Effect of residence time on the desorption kinetics of Pb2+ from goethite in the presence of 0.002 M salicylate.

View larger version (22K): [in this window] [in a new window]   Fig. 4. First-order rate equation plots of Pb2+ and Cd2+ desorption from goethite in the presence of 0.01 M NaNO3 (A) k1 and (B) k2.

View larger version (21K): [in this window] [in a new window]   Fig. 6. First-order rate equation plots of Pb2+ and Cd2+ desorption from goethite in the presence of 0.002 M salicylate (A) k1 and (B) k2.

View larger version (22K): [in this window] [in a new window]   Fig. 5. First-order rate equation plots of Pb2+ and Cd2+ desorption from goethite in the presence of 0.002 M oxalate (A) k1 and (B) k2.

View this table: [in this window] [in a new window]   Table 3. First-order desorption rate coefficients describing Cd2+ desorption from goethite using two first-order equations and statistical results between short- and long-term desorption experiments for each extracting solution at pH of 4.5.

View this table: [in this window] [in a new window]   Table 4. First-order desorption rate coefficients describing Pb2+ desorption from goethite using two first-order equations and statistical results between short- and long-term desorption experiments for each extracting solution at pH of 4.5.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
We examined the influence of residence time and organic acids on the desorption kinetics of Pb²⁺ and Cd²⁺ on goethite. For all experiments (except Pb in the presence of oxalate) the total amount of trace metal removed from the goethite surface decreased with an increase in residence time. Similarly, for all experiments (except k₁ and oxalate) the desorption rate coefficients decreased with an increase in residence time. However, statistical analyses indicated that these results were not statistically significant except for Pb²⁺ in the presence of salicylate. The effectiveness of extracting solutions for desorbing Pb²⁺ and Cd²⁺ followed the order salicylate > NaNO₃ > oxalate for all experiments except long-term Pb²⁺. The difference in the effectiveness of the organic acids for desorbing the trace metals may be related to the ability of the organic acid to form bridging or ternary complexes between the metal and the goethite surface. This research suggests that residence time effects observed by researchers at near neutral pH values may be less prominent as the pH of the aqueous environment is reduced. This information is extremely important because the effectiveness of monitored natural attenuation may be reduced by pH fluctuations that can occur in natural soil environments, for example as a result of high inputs of inorganic fertilizers, increased microbial activity, or soils that have a low buffering capacity. Furthermore, the presence and ability of organic acids to desorb trace metals from oxide surfaces may also reduce or enhance the effectiveness of these processes depending on pH and the nature of the organic acid.

	ACKNOWLEDGMENTS

 
This work was supported by the United States Department of Energy under Contract #DOE-AC04-94AL85000.

Received for publication October 27, 2000.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Ainsworth, C.C., J.L. Pilon, P.L. Gassman, and W.G. Van Der Sluys. 1994. Cobalt, cadium and lead sorption to hydrous iron oxide: residence time effect. Soil Sci. Soc. Am. J. 58:1615–1623.[Abstract/Free Full Text]
• Backes, C.A., R.G. McLaren, A.W. Rate, and R.S. Swift. 1995. Kinetics of cadium and cobalt desorption from iron and manganese oxides. Soil Sci. Soc. Am. J. 59:778–785.[Abstract/Free Full Text]
• Bargar, J.R., G.E. Brown, Jr., and G.A. Parks. 1997. Surface complexation of Pb(II) at the oxide-water interfaces: II. XAFS and bond-valance determination of mononuclear Pb(II) sorption products and surface functional groups on iron oxides. Geochim. Cosmochim. Acta. 61:2639–2652.
• Benyahya, L., and J. Garnier. 1999. Effect of salicylic acid upon trace-metal sorption (Cd, Zn, Co, and Mn) onto alumina, silica, and kaolinite as a fuction of pH. Environ. Sci. Technol. 33:1398–1407.
• Bruemmer, G.W., J. Gerth, and K.G. Tiller. 1988. Reaction kinetics of the adsorption and desorption of nickel, zinc and cadium by goethite. I. Adsorption and diffusion of metals. J. Soil Sci. 39:37–52.
• Eick, M.J., J.D. Peak, P.V. Brady, and J.D. Pesek. 1999. Kinetics of lead adsorption and desorption on goethite: Residence time effect. Soil Sci. 164:28–39.
• Eick, M.J., and S.E. Fendorf. 1998. Reaction sequence of Nickel(II) with kaolinite: Mineral dissolution and surface complexation/precipitation. Soil Sci. Soc. Am. J. 62:1257–1267.[Abstract/Free Full Text]
• Farley, K.J., D.A. Dzombak, and F.M.M. Morel. 1985. A surface precipitation model for the sorption of cations on metal oxides. J. Colloid Interface Sci. 106:226–238.
• Ford, R.G., A.C. Scheinhost, K.G. Scheckel, and D.L. Sparks. 1999. The link between clay mineral weathering and the stabilization of Ni surface precipitates. Environ. Sci. Technol. 33:3140–3144.
• Geelhoed, J.S., T. Hiemstra, and W.H. Van Riemsdijk. 1998. Competitive interaction between phosphate and citrate on goethite. Environ. Sci. Technol. 32:2119–2123.
• Jardine, P.M., and D.L. Sparks. 1984. Comparison of kinetic equations to describe K-Ca exchange in pure and mixed systems. Soil Sci. 138:115–122.
• McBride, M.B. 1994. Environmental soil chemistry. Oxford University Press, New York.
• McKenzie, R.M. 1970. The reaction of cobalt with manganese dioxide minerals. Aust. J. Soil Res. 8:87–106.
• McLaren, R.G., D.M. Lawson, and R.S. Swift. 1986. Sorption and desorption of cobalt by soils and soil constituents. J. Soil Sci. 37:413–426.
• McLaren, R.G., C.A. Backes, A.W. Rate, and R.S. Swift. 1998. Cadium and cobalt desorption kinetics from soil clays: Effect of sorption period. Soil Sci. Soc. Am. J. 62:332–337.[Abstract/Free Full Text]
• Mesuere, K., and W. Fish. 1992 Chromate and oxalate adsorption on goethite. 1. Calibration of surface complexation models. Environ. Sci. Technol. 26:2357–2364.
• Naidu, R., and R.D. Harter. 1998. Effect of different organic ligands on cadmium sorption by and extractability from soils. Soil Sci. Soc. Am. J. 62:644–650.[Abstract/Free Full Text]
• Sall, J., and A. Lehman. 1996. JMP start statistics. A guide to statistical and data analysis using JMP and JMP IN software. Duxbury Press, Belmont, CA.
• Schwertmann, U., P. Cambier, and E. Murad. 1985. Properties of goethites of varying crystallinity. Clays Clay Miner. 33:369–378.[Abstract]
• Schwertmann, U., and R.M. Cornell. 1991. Iron oxides in the laboratory. VCH Publishers, New York.
• Spandini, L., A. Manceau, P.W. Schindler, and L. Charlet. 1994. Structure and stability of Cd²⁺ surface complexes on ferric oxides I. Results from EXAFS Spectroscopy. J. Colloid Interface Sci. 168:73–86.
• Sparks, D.L. 1989. Kinetics of soil chemical processes. Academic Press, New York.
• Sparks, D.L., L.W. Zelazny, and D.A. Martens. 1980. Kinetics of potassium desorption in soil using miscible displacement. Soil Sci. Soc. Am. J. 44:1205–1208.[Abstract/Free Full Text]
• Stevenson, F.J. 1994. Humus chemistry. 2nd ed. John Wiley & Sons, New York.
• Stumm, W. 1992. Chemistry of the solid-water interface. John Wiley & Sons, New York.

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