Rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium distribution coefficients of a surficial sediment at the Idaho National Engineering Laboratory, Idaho

 The rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium sorption were measured as part of an investigation to determine strontium chemical transport properties of a surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. Batch experimental techniques were used to determine the rate of strontium sorption and strontium distribution coefficients (K_ds) between aqueous and solid phases. Rate experiments indicate that strontium in solution reached an apparent equilibrium with the sediment in 26 h. K_ds were derived using the linear isotherm model at initial sodium concentrations from 100 to 5,000 mg/l and initial potassium concentrations from 2 to 150 mg/l. K_ds ranged from 56±2 to 62±3 ml/g at initial aqueous concentrations of sodium and potassium equal to or less than 300 and 150 mg/l, respectively. K_ds ranged from 4.7±0.2 to 19±1 ml/g with initial aqueous concentrations of sodium between 1,000 and 5,000 mg/l. These data indicate that sodium concentrations greater than 300 mg/l in wastewater increase the availability of strontium for transport beneath waste disposal ponds at the INEL by decreasing strontium sorption on the surficial sediment. Wastewater concentrations of sodium and potassium less than 300 and 150 mg/l, respectively, have little effect on the availability of strontium for transport. Received: 6 February 1997 · Accepted: 31 March 1997     

Chemical and physical properties affecting strontium distribution coefficients of surficial-sediment samples at the Idaho National Engineering and Environmental Laboratory, Idaho

 The U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy, conducted a study to determine strontium distribution coefficients (K_ds) of surficial sediments at the Idaho National Engineering and Environmental Laboratory (INEEL). Batch experiments using synthesized aqueous solutions were used to determine K_ds, which describe the distribution of a solute between the solution and solid phase, of 20 surficial-sediment samples from the INEEL. The K_ds for the 20 surficial-sediment samples ranged from 36 to 275 ml/g. Many properties of both the synthesized aqueous solutions and sediments used in the experiments also were determined. Solution properties determined were initial and equilibrium concentrations of calcium, magnesium, and strontium, pH and specific conductance, and initial concentrations of potassium and sodium. Sediment properties determined were grain-size distribution, bulk mineralogy, whole-rock major-oxide and strontium and barium concentrations, and Brunauer-Emmett-Teller (BET) surface area. Solution and sediment properties were correlated with strontium K_ds of the 20 surficial sediments using Pearson correlation coefficients. Solution properties with the strongest correlations with strontium K_ds were equilibrium pH and equilibrium calcium concentration correlation coefficients, 0.6598 and –0.6518, respectively. Sediment properties with the strongest correlations with strontium K_ds were manganese oxide (MnO), BET surface area, and the >4.75-mm-grain-size fraction correlation coefficients, 0.7054, 0.7022, and –0.6660, respectively. Effects of solution properties on strontium K_ds were interpreted as being due to competition among similarly charged and sized cations in solution for strontium-sorption sites; effects of sediment properties on strontium K_ds were interpreted as being surface-area related. Multivariate analyses of these solution and sediment properties resulted in r² values of 0.8071 when all five properties were used and 0.8043 when three properties, equilibrium pH, MnO, and BET surface area, were used. Received: 30 November 1998 · Accepted: 16 February 1999     

Geochemical and thermodynamic aspects of sorption of strontium on kaolinite dominated clay samples at Kalpakkam

The mobility of strontium in subsurface is largely influenced by sorption on to clay minerals. In the present study, kaolinite clay samples collected from the Kalpakkam nuclear plant site were employed to understand the sorption characteristics of strontium by batch method. The effect of several parameters such as time, strontium ion concentration, pH, temperature and ionic strength was investigated. The kinetic studies suggested pseudo-second-order mechanism. The experimental sorption data was fitted to Langmuir adsorption model for obtaining the sorption capacity of the sorbent. The maximum sorption capacity was 5.77 mg/g at 298 K and was found to increase with an increase in temperature. It was observed that the distribution coefficient (K _d) of strontium on clay increased as the pH of the solution increased. The distribution coefficient was found to decrease with an increase in concentration of Na⁺ and Ca²⁺ ions. This variation of K _d suggests that cation exchange is the predominant sorption process. It was also observed that sorption process is endothermic. The thermodynamic parameters such as ∆G ⁰, ∆H ⁰ and ∆S ⁰ were calculated. The negative values obtained for ∆G ⁰ indicated that the sorption of strontium on clay was spontaneous at all studied concentrations. ∆G ⁰ becomes more negative with an increase in temperature, suggests that the sorption process is more favorable at higher temperatures.     

Determination of variables in the prediction of strontium distribution coefficients for selected sediments

Idaho State University and the US Geological Survey, in cooperation with the US Department of Energy, conducted a study to determine and evaluate strontium distribution coefficients (K_ds) of subsurface materials at the Idaho National Engineering and Environmental Laboratory (INEEL). The K_ds were determined to aid in assessing the variability of strontium K_ds and their effects on chemical transport of strontium-90 in the Snake River Plain aquifer system. Data from batch experiments done to determine strontium K_ds of five sediment-infill samples and six standard reference material samples were analyzed by using multiple linear regression analysis and the stepwise variable-selection method in the statistical program, Statistical Product and Service Solutions, to derive an equation of variables that can be used to predict strontium K_ds of sediment-infill samples. The sediment-infill samples were from basalt vesicles and fractures from a selected core at the INEEL; strontium K_ds ranged from ~201 to 356 ml g^-1. The standard material samples consisted of clay minerals and calcite. The statistical analyses of the batch-experiment results showed that the amount of strontium in the initial solution, the amount of manganese oxide in the sample material, and the amount of potassium in the initial solution are the most important variables in predicting strontium K_ds of sediment-infill samples.     

Phosphorus Speciation in Stream Bed Sediments from an Agricultural Watershed: Solid-Phase Associations and Sorption Behavior

The sorption behavior and solid-phase associations of phosphorus (P) in fine-grained sediments (<63 μm) from two upstream tributaries and one downstream main stem site of the Spoon River in west-central Illinois were characterized to better understand phosphorus bioavailability in this agriculturally dominated watershed. The P sorption affinities, as indicated by linear distribution coefficients (K _d), of all sediments were 330–5,150 L/kg, and negatively correlated with equilibrium phosphorus concentration (EPC_o) values, which ranged between 0.2 and 2.2 μM. pH values measured at the conclusion of the sorption experiments varied only slightly (7.45–8.10) but were nonetheless strongly positively correlated to EPC_o values, and negatively correlated to K _d values, suggesting the importance of pH to the observed sorption behavior. K _d values were generally lower and EPC_o values higher at the main stem site than at the upstream tributary sites, suggesting dissolved reactive P (DRP) bioavailability (specifically orthophosphate) increased downstream. The solid phase associations of P were operationally assessed with the streamlined SEDEX (sedimentary extraction) procedure, and most sediment P (≥50%) was released during the step designed to determine iron oxide–associated P. On average, 70–90% of the total sediment P pool was potentially bioavailable, as estimated by the sum of the iron oxide-, authigenic carbonate-, and organic-associated P fractions. Considerable calcium was also extracted from some sediments during the step designed to specifically remove iron oxide–associated P. It is hypothesized that the severe drought conditions that persisted between April and October, 2005 allowed authigenic carbonates (perhaps partly amorphous) to accumulate, and that these carbonates dissolved during the iron oxide extraction step. The extensive benthic algal populations also present may have aided carbonate precipitation, which under more normal hydrologic conditions would be periodically flushed downstream and replaced by fresh sediment. This suggests antecedent hydrologic conditions played a dominant role in the P sorption and solid phase associations identified.     

The effect of groundwater seepage on nutrient delivery and seagrass distribution in the northeastern Gulf of Mexico

A hypothesis was tested to determine if a relationship exists between rates of submarine groundwater discharge and the distribution of seagrass beds in the coastal, nearshore northeastern Gulf of Mexico. As determined by nonparametric statistics, four of seven seagrass beds in the northeastern Gulf of Mexico had significantly greater submarine groundwater discharge compared with adjacent sandy areas, but the remainder exhibited the opposite relationship. We were thus unable to verify if a relationship exists between submarine groundwater discharge and the distribution of seagrass beds in the nearshore sites selected. A second objective of this study was to determine the amount of nitrogen and phosphorus delivered to nearshore areas by submarine groundwater discharge. We considered new nutrient inputs to be delivered to surface waters by the upward flux of fresh water. This upward flux of water encounters saline porewaters in the surficial sediments and these porewaters contain recycled nutrients; actual nutrient flux from the sediment to overlying waters includes both new and recycled nutrients. New inputs of nitrogen to overlying surface waters for one 10-km section of coastline, calculated by multiplying groundwater nutrient concentrations from freshwater wells by measured seepage rates, were on the order of 1,100±190 mol N d⁻¹. New and recycled nitrogen fluxes, calculated by multiplying surficial porewater concentrations by measured seepage rates, yielded fluxes of 3,600 ±1,000 mol N d⁻¹. Soluble reactive phosphate values were 150±40 mol P d⁻¹ using freshwater well concentrations and 130±3.0 mol P d⁻¹ using porewater concentrations. These values are comparable to the average nutrient delivery of a small, local river.     

Competitive sorption and desorption of cadmium and lead in paddy soils of eastern China

To assess the competitive sorption and desorption of cadmium (Cd) and lead (Pb), batch equilibrium experiments were performed using single- and binary-metal solutions in surface samples of three paddy soils from eastern China. Sorption isotherms were well fitted with one-metal and competitive Langmuir equation for single- and binary-metal system, respectively. The distribution coefficient (K _d) values were K _{d single} (Pb) > K _{d binary} (Pb) > K _{d single} (Cd) > K _{d binary} (Cd), indicating that Pb was stronger sorbed by these soils than Cd in binary metal system. Soils with high pH and clay content had the greatest sorption capacity as estimated by the maximum sorption parameter (Q). The co-existence of both metals reduces their tendency of sorption, whereas Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (b) in binary sorption system was greater than that in single sorption system for all soils (b < b ₁), indicating that competition for sorption sites promote the retention of both metals into more specific sorption sites. Sorption of Cd and Pb decreased soil pH by 1.61 U for YRS, 1.39 U for PCS, and 0.91 U for SLS. The decreases of pH in binary metal system were greater than in single-metal system for three soils. Cadmium and Pb desorption increased with increasing Cd and Pb sorption saturation for all soils; however, Cd desorption ratio in binary metal system (d _Cd*) was much greater than Pb (d _Pb*), indicating that under the competitive sorption conditions, the sorbed Cd was more readily desorbed from the soils than the sorbed Pb.     

Equation of state, elasticity, and shear strength of pyrite under high pressure

 Physical properties including the equation of state, elasticity, and shear strength of pyrite have been measured by a series of X-ray diffraction in diamond-anvil cells at pressures up to 50 GPa. A Birch–Murnaghan equation of state fit to the quasihydrostatic pressure–volume data obtained from laboratory X-ray source/film techniques yields a quasihydrostatic bulk modulus K _0T =133.5 (±5.2) GPa and bulk modulus first pressure derivative K ^′ _0T =5.73 (±0.58). The apparent equation of state is found to be strongly dependent on the stress conditions in the sample. The stress dependency of the high-pressure properties is examined with anisotropic elasticity theory from subsequent measurements of energy-dispersive radial diffraction experiments in the diamond-anvil cell. The calculated values of K _0T depend largely upon the angle ψ between the diffracting plane normal and the maximum stress axis. The uniaxial stress component in the sample, t=σ₃−σ₁, varies with pressure as t=−3.11+0.43P between 10 and 30 GPa. The pressure derivatives of the elastic moduli dC ₁₁/dP=5.76 (±0.15), dC ₁₂/dP=1.41 (±0.11) and dC ₄₄/dP=1.92 (±0.06) are obtained from the diffraction data assuming previously reported zero-pressure ultrasonic data (C ₁₁=382 GPa, C ₁₂=31 GPa, and C ₄₄=109 GPa). Received: 21 December 2000 / Accepted: 11 July 2001     

Pressure–volume–temperature equation of state of andradite and grossular, by high-pressure and -temperature powder diffraction

 The thermoelastic parameters of natural andradite and grossular have been investigated by high-pressure and -temperature synchrotron X-ray powder diffraction, at ESRF, on the ID30 beamline. The P–V–T data have been fitted by Birch-Murnaghan-like EOSs, using both the approximated and the general form. We have obtained for andradite K ₀=158.0(±1.5) GPa, (dK/dT )₀=−0.020(3) GPa K⁻¹ and α₀=31.6(2) 10⁻⁶ K⁻¹, and for grossular K ₀=168.2(±1.7) GPa, (dK/dT)₀=−0.016(3) GPa K⁻¹ and α₀=27.8(2) 10⁻⁶ K⁻¹. Comparisons between the present issues and thermoelastic properties of garnets earlier determined are carried out. Received: 7 July 2000 / Accepted: 20 October 2000     

Do carbonate liquids become denser than silicate liquids at pressure? Constraints from the fusion curve of K<Subscript>2</Subscript>CO<Subscript>3</Subscript> to 3.2 GPa

Brackets on the melting temperature of K₂CO₃ were experimentally determined at 1.86 ± 0.02 GPa (1,163–1,167°C), 2.79 ± 0.03 GPa (1,187–1,195°C), and 3.16 ± 0.04 GPa (1,183–1,189°C) in a piston-cylinder apparatus. These new data, in combination with published experiments at low pressure (<0.5 GPa), establish the K₂CO₃ fusion curve to 3.2 GPa. On the basis of these experiments and published thermodynamic data for crystalline and liquid K₂CO₃, the high-pressure density and compressibility of K₂CO₃ liquid were derived from the fusion curve. The pressure dependence of the liquid compressibility (K′₀ = dK ₀/dP, where K ₀ = 1/β₀) is between 16.2 and 11.6, with a best estimate of 13.7, in a third-order Birch–Murnaghan equation of state (EOS). This liquid K′₀ leads to a density of 2,175 ± 36 kg/m³ at 4 GPa and 1,500°C, which is ∼30% lower than that reported in the literature on the basis of the falling-sphere method at the same conditions. The uncertainty in the liquid K′₀ leads to an error in melt density of ± 2% at 4 GPa; the error decreases with decreasing pressure. With a K′₀ of 13.7, the compressibility of K₂CO₃ at 1,500°C and 1 bar (K ₀ = 3.8 GPa) drops rapidly with increasing pressure ( ), which prevents a density crossover with silicate melts, such as CaAlSi₂O₈ and CaMgSi₂O₆, at upper mantle depths.     

P–T–X relationships in the Precambrian Al–Mg-rich granulites from In Ouzzal, Hoggar, Algeria

The Al–Mg-rich granulites from the In Ouzzal craton, Algeria, show a great diversity of mineral reactions which correspond to continuous equilibria as predicted by phase relationships in the FeO–MgO–Al₂O₃–SiO₂ system. The sequence of mineral reactions can be subdivided into three distinct stages: (1) a high-P stage characterized by the growth of coarse mineral assemblages involving sapphirine and the disappearance of early corundum and spinel-bearing assemblages; (2) a high-T stage characterized by the development of Sa–Qz-bearing assemblages; and (3) a later stage, in which garnet-bearing assemblages are replaced by more or less fine symplectites involving cordierite. During the course of early mineral reactions, the distribution coefficient, K_d, between the various ferromagnesian phases decreased significantly whereas Al₂O₃ in pyroxene increased concomitantly. These observations, when combined with topological constraints, clearly indicate that the high-P stage 1 was accompanied by a significant rise in temperature (estimated at 150 ± 50° C) under near isobaric conditions, in agreement with the reaction textures. By stage 2, pressure and temperature were extreme as evidenced by the low K_d value between orthopyroxene and garnet (K_d= 2.06–1.99), the high alumina content in pyroxene (up to 11.8%) and the high magnesium content in garnet [100 Mg/(Mg + Fe) = 60.6]. Mineral thermometry based on Fe–Mg exchange between garnet and pyroxene and on Al-solubility in pyroxene gives temperatures close to 970 ± 70° C at 10 ± 1.5 kbar. These results are in agreement with the development of Sa–Qz assemblages on a local scale. Late mineral reactions have been produced during a decompression stage from about 9 to 6 kbar. Except for local re-equilibration of Mg and Fe at grain boundaries, there is no evidence for further reactions below 700° C. We interpreted the whole set of mineral reactions as due to changes in pressure and temperature during a tectonic episode located at c. 2 Ga. Because of the lack of evidence for further uplift after the thermal relaxation which occurred at c. 6 kbar, it is possible however that the exhumation of this granulitic terrane occurred in a later tectonic event unrelated to its formation.     

Surface complexation model for strontium sorption to amorphous silica and goethite

Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr²⁺ and SrOH⁺ complexes on the β-plane and a monodentate Sr²⁺complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH⁺ complexes and a tetradentate binuclear Sr²⁺ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr²⁺ and SrOH⁺ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces.     

Plutonium and radiocesium in the water column of the Hudson River estuary

Isotopes of plutonium (Pu), cesium (Cs), and cobalt (Co) introduced into the Hudson River Estuary from fallout deposition, the erosion of fallout-contaminated surface soils, and nuclear reactor effluent (isotopes of Cs and Co only) have been measured in water column samples collected from 1975 to 1980 Isotopic measurements conducted independently by two research groups utilizing different sampling and analytical techniques have been summarized. The major conclusions drawn from the work are that for water samples collected by the two laboratories over similar time periods, the mean concentrations of nonfilterable^239,240Pu (<0.45 μm) were identical at 0.13 fCi/l, mean concentrations of both¹³⁷Cs and^239,240Pu in suspended particulates were more divergent at 2,270±920 pCi/kg (±1 SD) and 1,430±430 pCi/kg for¹³⁷Cs, and 19±8 pCi/kg and 12±4 pCi/kg for^239,240Pu The behavior of^239,240Pu and¹³⁷Cs within the water column is shown to diverge within brackish waters Specifically, the magnitude of the¹³⁷Cs distribution coefficient (K _d ) can be expressed as an inverse power function of the chloride ion concentrations for chlorinities between 0.1 and 4 g Cl⁻/l No difference in the^239,240PuK _d has been observed between fresh and brackish waters Based on the expected inventories of^239,240Pu and¹³⁷Cs within watershed soils, the current downstream transport of these radionuclides represents fractional mobilization rates on the order of 1–4 (×10⁻⁴) per year     

Competitive adsorption of trace elements in calcareous soils as affected by sewage sludge,poultry manure,and municipal waste compost

The competitive adsorption of trace elements is a key issue in assessing the mobility of trace elements in calcareous soils and can be affected by disposal of sewage sludge, municipal waste, and poultry manure. The effect of municipal sewage sludge, poultry manure, and municipal waste compost on the sorption of cadmium (Cd), copper (Cu), zinc (Zn), and nickel (Ni) in surface samples of three calcareous soils was studied. As the applied concentrations increased, Cu and Cd adsorption increased, while Zn and Ni adsorption decreased in all treatments. Based on the distribution coefficient (K _d) values and proportion of increase or decrease in metal adsorption, the selectivity sequence in control and amended soils found was Cu ≫ Cd ≫ Ni > Zn and Cu ≫ Cd ≫ Zn > Ni, respectively. In general, among control and amended soils, control soils showed the highest K _d for Cd, Cu, and Ni, while sludge, poultry manure, and composted waste-amended soils had lowest K _d for Cd, Cu, and Ni, respectively. In the case of Zn, composted waste-amended and control soils had highest and lowest K _d, respectively. The present experimental results indicated that the addition of organic amendments to these calcareous soils reduced the sorption of Cd, Cu, and Ni. Thus, the effects of preferential adsorption and organic matter should be considered in assessing the risk associated with applying sewage sludge, poultry manure, and composted material to calcareous soils.     

Low-temperature thermodynamic properties of disordered zeolites of the natrolite group

 The heat capacity of paranatrolite and tetranatrolite with a disordered distribution of Al and Si atoms has been measured in the temperature range of 6–309 K using the adiabatic calorimetry technique. The composition of the samples is represented with the formula (Na_1.90K_0.22Ca_0.06)[Al_2.24Si_2.76O₁₀]·nH₂O, where n=3.10 for paranatrolite and n=2.31 for tetranatrolite. For both zeolites, thermodynamic functions (vibrational entropy, enthalpy, and free energy function) have been calculated. At T=298.15 K, the values of the heat capacity and entropy are 425.1 ± 0.8 and 419.1 ±0.8 J K⁻¹ mol⁻¹ for paranatrolite and 381.0 ± 0.7 and 383.2 ± 0.7 J K⁻¹ mol⁻¹ for tetranatrolite. Thermodynamic functions for tetranatrolite and paranatrolite with compositions corrected for the amount of extraframework cations and water molecules have also been calculated. The calculation for tetranatrolite with two water molecules and two extraframework cations per formula yields: C _p (298.15)=359.1 J K⁻¹ mol⁻¹, S(298.15) −S(0)=362.8 J K⁻¹ mol⁻¹. Comparing these values with the literature data for the (Al,Si)-ordered natrolite, we can conclude that the order in tetrahedral atoms does not affect the heat capacity. The analysis of derivatives dC/dT for natrolite, paranatrolite, and tetranatrolite has indicated that the water- cations subsystem within the highly hydrated zeolite may become unstable at temperatures above 200 K. Received: 30 July 2001 / Accepted: 15 November 2001     

Particle-solution behaviour of plutonium in an estuarine environment,Esk Estuary,UK

The particle-solution (K_d) relationships of Pu(III,IV) in the Esk Estuary are investigated, using new experimental data together with a synthesis of our earlier work. Adsorption of ²³⁶Pu(IV) by a suspension of intertidal mud (40 mg L⁻¹) from the Esk Estuary was determined after 1 h, as a function of salinity and pH, in a series of controlled laboratory experiments. Desorption of ^{239, 240}Pu(III,IV) from this environmentally contaminated sediment was determined concurrently. The short term (i.e., within a tidal cycle) non-conservative behaviour of Pu(III,IV) in both the laboratory experiments and the estuary appears to be dominated by a rapid, reversible surface complexation reaction, although only a small fraction (<5%) of the ^239,240Pu(III,IV) activity of the environmentally contaminated sediment is able to participate in the reaction. The existence of this exchangeable or labile fraction can explain the apparent dependence of Pu(III,IV) K_d on sediment concentration. Thus, a single K_d value is able to describe both the observed adsorption and desorption behaviour and the effect of sediment concentration, when desorption is expressed with respect to the labile ^239,240Pu(III,IV) fraction. For example, in R. Esk water, the adsorption of ²³⁶Pu(III,IV) and the desorption of ^236,240Pu(III,IV), over a two order of magnitude concentration range of unwashed Esk Estuary sediment, can be accounted for by a single K_d of ∼3 × 10³ L kg⁻¹. The K_d for the labile Pu(III,IV) fraction varies mainly as a function of salinity. pH is not an important factor over the pH range 4–9, although H⁺ ion exchange does occur, probably through a similar surface complexation reaction. The kinetic and equilibrium characteristics of the Pu (III,IV) sorption behaviour conform to the pattern observed by Jannasch et al. (1988) and other workers for a range of trace elements.     

Sorption Model for Dissolved Aluminium in Freshwaters

A series of aluminium speciation measurements were madein the freshwaters of the Yare and Great Ouse rivers (England). Samples were analysedfor dissolved and particulate Al, suspended particulate matter (SPM), and other alliedchemical species in order to assess the role of sorption processes on the suspended phasesin controlling dissolved Al levels. Partitioning of Al occurs between solid andsolution phases with a distribution coefficient (K_d) which varies over about one anda half orders of magnitude for suspended particle concentrations of comparablemagnitude. A sorption model is proposed for dissolved Al concentrations in thesefreshwaters with most of the data fitting the model defined by a zone with K_dvalues of 0.316 × 10⁶ and 10⁷. However, a few data points lie outside thiszone, suggesting that other processes may also influence dissolved Al distributions.Nevertheless, the model may serve as a starting point for predicting concentrations ofdissolved Al in rivers where SPM levels are moderate to high (>1 mg l^-1 but< 75 mg l^-1), and indeed, this model works reasonably well for the Conway system(Wales). Further, the empirical distribution coefficient, K_d, decreases withincreasing suspended particle concentration, which may be due in part to colloidal phenomena.     

Sorption of cesium and iodide ions onto KENTEX-bentonite

The sorption of cesium and iodide ions onto KENTEX-bentonite was investigated using batch test and in-diffusion test methods. The cesium ions were highly sorbed on the bentonite, and the experimental data fit the Freundlich isotherm well. The distribution coefficient, K _d, of the cesium ions was variably affected by the chemical conditions of the solution (initial ion concentration, pH, salinity) and temperature. An increasing pH of solution increased the K _d. However, there were different K _d values that decrease with an increase in the initial ion concentration, salinity, and temperature. The iodide ions, on the contrary, were negligibly sorptive. The K _d values obtained from the in-diffusion tests were quite lower than those from the batch tests, which could be explained by changes in the pore water chemistry and surface area available for sorption.     

Sorption of selenite in a multi-component system using the “dialysis membrane” method

⁷⁹Se is a potentially mobile long-lived fission product, which may make a dominant contribution to the long-term radiation exposure resulting from deep geological disposal of radioactive waste. Its mobility is affected by sorption on minerals. Selenium sorption processes have been studied mainly by considering interaction with a single mineral surface. In the case of multi-component systems (e.g. soils), it is difficult to predict the radioelement behaviour only from the mineral constituents. This study contributes to the understanding of multi-component controls of Se concentrations towards predicting Se behaviour in soils after migration from a disposal site. This goal was approached by measuring selenite sorption on mono and multi-phase systems physically separated by dialysis membranes. To the best of the authors’ knowledge, very few studies have used dialysis membranes to study the sorption competition of selenite between several mineral phases. Other workers have used this method to study the sorption of pesticides on montmorillonite in the presence of dissolved organic matter. Indeed, this method allows measurement of individual K_d in a system composed of several mineral phases. Dialysis membranes allowed (i) determination of the competition of two mineral phases for selenite sorption (ii) and determination of the role of humic acids (HAs) on selenite sorption in oxidising conditions. Experimental results at pH 7.0 show an average Se(IV) sorption distribution coefficient (K_d) of approximately 125 and 9410 L kg⁻¹ for bentonite and goethite, respectively. The average K_d for goethite decreases to 613 L kg⁻¹ or 3215 L kg⁻¹ in the presence of bentonite or HA, respectively. For bentonite, the average K_d decreases slightly in the presence of goethite (60 L kg⁻¹) and remains unchanged in the presence of HA. The experimental data were successfully modelled with a surface complexation model using the PHREEQC geochemical code. The drastic decrease in Se(IV) sorption on goethite in a multi-phase system is attributed to competition with dissolved silica released by bentonite. As with Si the HA compete with Se for sorption sites on goethite.     

Benthic fluxes and the cycling of biogenic silica and carbon in two southern California borderland basins

Benthic fluxes in two southern California borderland basins have been estimated by modeling water column property gradients, by modeling pore water gradients and by measuring changes in concentration in a benthic chamber. Results have been used to compare the different methods, to establish budgets for biogenic silica and carbon and to estimate rate constants for models of CaCO₃ dissolution. In San Pedro Basin, a low oxygen, high sedimentation rate area, fluxes of radon-222 (86 ± 8 atoms m⁻² s⁻¹), SiO₂ (0.7 ± 0.1 mmol m⁻² d⁻¹), alkalinity (1.7 ± 0.3 meq m⁻² d⁻¹), TCO₂ (1.9 ± 0.3 mmol m⁻² d⁻¹) and nitrate (−0.8 ± 0.1 mmol m⁻² d⁻¹) measured in a benthic chamber agree within the measurement uncertainty with fluxes estimated from modeling profiles of nutrients and radon obtained in the water column. The diffusive fluxes of radon, SiO₂ and TCO₂ determined from modeling the sediment and pore water also agree with the other approaches. Approximately 33 ± 13% of the organic carbon and 37 ± 47% of the CaCO₃ arriving at the sea floor are recycled. In San Nicolas Basin, which has larger oxygen concentrations and lower sedimentation rates than San Pedro, the fluxes of radon (490 ± 16 atoms m⁻² s⁻¹), SiO₂ (0.7 ± 0.1 mmol m⁻² d⁻¹), alkalinity (1.7 ± 0.3 meq m⁻² d⁻¹), TCO₂ (1.7 ± 0.2 mmol m⁻² d⁻¹), oxygen (−0.7 ± 0.1 mmol m⁻² d⁻¹) and nitrate (-0.4 ± 0.1 mmol m⁻² d⁻¹) determined from chamber measurements agree with the water column estimates given the uncertainty of the measurements and model estimates. Diffusion from the sediments matches the lander-measured SiO₂ and PO₄³⁻ (0.017 ± 0.002 mmol m⁻² d⁻¹) fluxes, but is not sufficient to supply the radon or TCO₂ fluxes observed with the lander. In San Nicolas Basin 38 ± 9% of the organic carbon and 43 ± 22% of the CaCO₃ are recycled. Approximately 90% of the biogenic silica arriving at the sea floor in each basin is recycled. The rates of CaCO₃ dissolution determined from chamber flux measurements and material balances for protons and electrons are compared to those predicted by previously published models of CaCO₃ dissolution and this comparison indicates that in situ rates are comparable to those observed in laboratory studies of bulk sediments, but orders of magnitude less than those observed in experiments done with suspended sediments.