Sulfate Sorption Research Articles

Competitive Sorption of Simple Organic Acids and Sulfate on Goethite

Sorption of phthalic acid, chelidamic acid, and sulfate onto goethite (α-FeOOH) was examined in single-sorbate and in sulfate−organic acid binary-sorbate systems to determine the extent of competition between the simple organic acids and sulfate. Sorption characteristics of sulfate and the organic acids were similar and resembled those reported for humic substances onto oxides. Sorption data for all three sorbates over a wide range of conditions (pH, I, sorbate/sorbent ratio) were described quantitatively by the generalized two-layer model with a unique set of surface reactions and equilibrium constants for each sorbate. Sorption affinities of sulfate and the organic acids were comparable, and sulfate effectively competed with the organic acids for surface sites on goethite, particularly at low pH. These results suggest that sulfate can significantly influence the sorption of simple organic acids and humic substances in natural aquatic systems. Predictions of sorption in binary-sorbate systems based on si...

Modelling long-term acidification trends of forested sandstone catchments in the Black Forest (SW Germany)

An extensive database from eight Triassic (Bunter) sandstone catchments in the Black Forest, SW Germany, was used to apply the MAGIC model and simulate long-term acidification trends. Using the ion ratio (Ca+Mg)/(SO4+NO3) as criterium (values< 1.5 indicate an acidified state), hindcast simulations showed that the brooks of three catchments have reached values <1.5, three catchments are approaching 1.5, and two catchments (carbonate bearing upper Bunter) are still well above this limit. The different acidification state of the catchments is mainly caused by the amount of acidic deposition and bedrock geology. Other differences (shallow or deep groundwater circulation, sulphate sorption and soil parameters) are less significant. To simulate the future evolution, three scenarios were tested: a pessimistic, an optimistic and a most probable case. The latter leads to a still progressing but decelerated acidifcation in the next 100 years. In the pessimistic case, acidification rates will be accelerated in two of the catchments. Even in the optimistic case, the initial state, prior to acidification, cannot be restored up to the year 2130. However, the forecasting of the future evolution is still markedly hampered by the significant uncertainty in the evaluation of nitrogen-driven acidification, a process which today already predominates in parts of the Black Forest.

Sulfate Sorption in Soils under Acid Deposition: Modeling Field Data from Forest Liming

AbstractSulfate sorption can modify the reaction of a soil to acid depositions. Different models of this process exist. In a preceeding paper the adsorption isotherm and the solubility product modeling approach have been compared and a solubility product model has been introduced. The latter model is tested using a forest liming experiment. Concentration data from canopy drip and seepage covering a 20‐yr observation period are used as 3‐yr moving averages. The model assumes a steady seepage flow and uses only one 1‐m compartment. The model considers joint chemical equilibria for gibbsite, jurbanite, cation exchange, and complexation. The seepage pH and concentrations of Al and sulfate under the unlimed reference plot can be modeled if a reduced CEC and a free parameter function for alkalinity production are used. The sulfate desorption caused by liming can be explained by the model. It is concluded that sorbed sulfate contributes to the lime requirement of an acidified soil.

Sorption of Sodium Dodecyl Sulfate on Amberlite XAD-2 Resin

Sorption of Sodium Dodecyl Sulfate on Amberlite XAD-2 Resin

Sulfate Sorption in Soils under Acid Deposition: Comparison of Two Modeling Approaches

AbstractSoil acidification under the impact of acid deposition is often modeled by adsorption isotherms. The assumption of solubility equilibria for basic Al sulfates is an alternative modeling approach. Similarities and differences between both concepts are discussed. A simple solubility equilibrium model is defined and used to demonstrate that the second model can explain results that are well described by typical adsorption isotherms. The same model can also explain a pH dependency of adsorption isotherms that has been widely reported. In the application to assumed soil acidification scenarios, predictions are presented that could not be described by an adsorption isotherm approach.

Sorption of calcium and sulfate by sandy soils from flue‐gas desulfurization gypsum and phosphogypsum

Abstract Increasing concern on sulfur dioxide (SO2) pollution has prompted many coal‐fired electric power generating plants to install SO2 scrubbing units which generate large amounts of flue‐gas desulfurization gypsum (FGDG). This source of gypsum can be an excellent amendment to supply calcium (Ca) and/or sulfate (SO4) to sandy soils which are deficient in these nutrients. In this study, reactions of FGDG, phosphogypsum (PG), reagent grade calcium sulfate (CaSO4), and calcium chloride (CaCl2) were investigated using a Candler fine sand (uncoated, hyperthermic, Typic Quartzipsamment), a typical well‐drained deep sand, and a Pineda fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf), a typical shallow poorly drained sand. Concentrations of various water‐soluble elements were similar in FGDG as well as PG, except the latter contained 11 and 15 g/kg phosphate (PO4) and fluoride (F), respectively, while these ions were undetectable in the former. In batch‐equilibration (4 h) technique using soilrsolution ratio of 1:2, pH of equilibrium solution decreased by 0.2 and 0.8 units, while ionic strength increased by 5‐ and 15‐fold in the Pineda and Candler sand, respectively, when using FGDG or PG solution as compared to using water for equilibration. Sorption of Ca by the two soils varied from 0.56 to 0.71 Cmolc/kg regardless of source of gypsum. As compared to sorption of SO4, that of Ca was greater by 2.5‐ and 2.6 to 4.3‐fold by the Candler and Pineda sand, respectively. With the exception of SO4 sorption by the Pineda sand, this study demonstrated that the reactions of FGDG with these sandy soils were very similar to those of PG or reagent grade CaSO4. Since much of the past research on agricultural use of gypsum was done using PG and CaSCU, we could conclude that similar response could be expected with use of FGDG.

The dynamics of sulfur, phosphorus and iron in flooded soils as affected by changes in Eh and pH

The dynamics of Fe, P and S were studied in three soils (prairie, podzolic and krasnozem) with varying S sorption capacity (13, 32 and 132 �g S sorbed g soil-1 at 5 �g S mL-1). The soils were incubated as suspensions for 14 days at 25�C and the pH and Eh adjusted independently to four levels in the range of pH 4-8-70 and Eh from + 350 to -150 mV. In the prairie and krasnozem soils, the concentration of S in the soil solution at high pH increased as Eh was lowered to +200 mV and then decreased as Eh was lowered further. At low pH, Eh changes did not affect the concentration of S in the soil solution. The changes in the concentration of sorbed S extracted by KH2PO4 were generally similar to those for S in the soil solution. Sulfate sorption increased with a decrease in pH, with the pH effect being greater at higher Eh. At high pH and Eh, the soils released S into the solution but sulfate sorption capacity increased when Eh was lowered. At low pH, the sulfate sorption capacity of the prairie soil first increased with a lowering in Eh from +350 to about +200 mV, but then decreased with a further lowering of Eh. In the krasnozem soil, sulfate sorption capacity increased with a lowering in Eh from the highest (+350 mV) to the lowest (-150 mV) level only at the lowest pH (4.8). In the podzolic soil, the effect of pH on sulfate sorption capacity was similar at all Eh levels. The Eh effects on sulfate sorption capacity of the three soils were different.

Relationships between soil chemical properties and sulfate sorption kinetics in Podzolic soils from Quebec

The relationships between the slope of three kinetic equations (Elovich, first-order and parabolic diffusion) and commonly measured soil chemical properties were investigated. Twenty-six horizons covering a variety of vegetation types, parent materials and topographic positions were sampled in 18 soil profiles of southern Quebec. A miscible displacement technique in which soils were leached with a 250 μmol SO4 L−1 solution (pH = 4.40) was used to determine time-dependent sulfate sorption. The sum of crystalline plus amorphous inorganic Fe (dithionite-pyrophosphate extraction) was the soil property most closely related to the slope parameters of the Elovich (r = 0.797) and of the parabolic (r = 0.808) equations. Amorphous Al (r = − 0.546) and soil pH measured in CaCl2 (r = − 0.588) were most strongly correlated to ln − k′a. Organic carbon was not directly related to sulfate sorption as an individual variable but it improved the multiple regression equations used to estimate 1/β and K0 for the 26 horizons. The Elovich equation was found to give the best representation (average R2 = 0.978) of sulfate sorption kinetics. Good results were also obtained using the first-order equation (average r2 = 0.976) although a marked deviation of experimental data from linearity was observed at high surface coverage. The relatively close relationship between predicted and calculated values confirmed the potential of equations based upon commonly measured soil properties to estimate the slope parameter of kinetic equations describing sulfate sorption by Podzolic soils. Key words: Podzols, sulfate, sorption, kinetics, sesquioxides

Irreversibility of sulfate sorption on goethite and hematite

Sulfate ion adsorption and desorption experiments carried out on synthetic goethite and hematite and natural hematite show adsorption to be a highly irreversible reaction. All oxides showed an increase in sulfate ion adsorption with decrease in pH. Only a small fraction of sorbed sulfate was desorbable after 48 hr, and only at a pH of 3. Extreme irreversibility of sulfate sorption on these common soil minerals suggests that adsorbed sulfate is more immobile in watersheds than previously considered and that recovery models which inherently assume reversibility may need to be modified.

Effect of changes in pH on sulphate and phosphate retention in soils

Abstract Soils with differing capacities to sorb anions were incubated with lime, each to a range of pH values (4.5-6.8), and characterised for their ability to sorb phosphorus (P) and sulphur (S) by sorption isotherms, and “Quick Test” sulphate retention, and phosphate retention methods. Although both phosphate and sulphate sorption changed with pH, the effects of lime were much more significant for sulphate than for phosphate. Sulphate sorption was reduced in the soils studied as pH was increased, and this was also reflected in sulphate retention Quick Test results. In contrast, phosphate retention values showed little dependence on pH. These findings have implications for the mobility of sulphate in soils, the correlation between P retention and S retention values, and the methodology of sulphate retention tests.

SULFATE RETENTION AND RELEASE IN SOILS AT PANOLA MOUNTAIN, GEORGIA

Inorganic sulfate pools, sulfate sorption characteristics, and Fe and Al fractions were determined on soils at Panola Mountain, a 41-ha forested watershed in the Georgia piedmont. Sulfate adsorption was measured in batch solutions that bracketed the range of ambient sulfate concentrations and soil solution acidity. The slope and intercept of the initial mass (IM) isotherms, formed from plots of sulfate retained against sulfate added, were used to compare sorption behavior among soils. The reversibility of sulfate adsorption was determined by measuring desorption of soluble sulfate from soil before and after equilibration with a concentrated sulfate solution. Sulfate sorption properties of soils at Panola Mountain fall along a continuum between two end members. The “low-adsorbing” end member comprises shallow soils (0–10 cm), with high water-soluble sulfate (Sw), low phosphate-extractable sulfate (Sp-w), high organic matter, low sulfate retention ability (IM isotherm slope near 0.0), and high sulfate adsorption reversibility. The “high-adsorbing” end member comprises deeper soils (>10 cm), with higher total native sulfate (mostly as Sp-w), low organic matter, high sulfate retention ability (isotherm slope near 1.0), and low sulfate adsorption reversibility. Sulfate retention was only weakly related to Fe and Al fractions, possibly because of inhibition of adsorption by organic matter. Sulfate concentrations in surface waters reflect the spatial distribution of soil sulfate retention properties; baseflow, representing water which has equilibrated with the mineral subsoil, has sulfate concentrations near 10 μeq/L, whereas stormflow, which is dominated by water flowing through shallow horizons, has sulfate concentrations near 100 μeq/L.

Sulphate sorption by variable charge soils

SUMMARYThe sorption of sulphate (SO2−4) by three variable charge soils from the Canary Islands (Spain) was studied. Sulphate sorption decreased with increasing pH. Only negligible amounts of SO2−4 were sorbed above pH 6.5. When the soils were washed with an indifferent electrolyte (0.01 M KCl), more SO2−4 was recovered than had been sorbed. This indicated a release of native SO2−4 Sulphate replaced hydroxyl ions (OH) and co‐ordinated H2O molecules, as well as very small amounts of silicate (Si). No measurable amount of phosphate (P) was released. On average hydroxyl release accounted for 50% of SO2−4 sorbed, the rest being accounted for by the increase in negative charge as measured by K+ adsorption. The results presented here are consistent with the sorption of SO2−4 through a ligand exchange mechanism, but in a different plane of sorption to that of phosphate.

Electrolyte Concentration and Composition Effects on Sulfate Sorption by Two Spodosols

AbstractFew reports exist on the influence of electrolyte concentration and composition on SO4 retention, although sorption experiments have been conducted with a variety of supporting electrolytes. Sulfate sorption by the B horizon of two forest Spodosols from Quebec was measured as a function of supporting electrolyte concentration and cationic composition, solution pH, and reaction time. The solutions had an ionic strength (I) of ≈0 (deionized H2O), 0.001, 0.01, 0.1, and 1.0 M NaCl, 0.01 M KCl, and 0.01 M CaCl2. Increasing the ionic strength of the electrolyte (NaCl) always decreased SO4 sorption at pH 4.25. It was proposed that increased Cl‐ ion competition for sorption sites and the formation of NaSO‐4 aqueous complexes (2.8, 14, and 55% of total SO4 at 0.01, 0.1, and 1.0 M NaCl) contributed to the observed trend. Increasing electrolyte concentration also lowered SO4 sorption by both horizons in the range of pH 3.0 to 5.2. Moreover, the influence of pH on sorption was more pronounced at low electrolyte concentration. At a constant I value, the cationic composition of the electrolyte also had an impact on SO4 sorption. The presence of Ca2+ and K+ favored sorption, compared with Na+. A mechanism involving the formation of a surface complex between Ca2+ or K+ and SO2‐4 is proposed to explain the experimental data. The results of this study support the hypothesis that the composition and concentration of the electrolyte influence SO4 sorption by Spodosols and that both should be considered when comparing the SO4‐sorption capacity of soil materials from distinct experiments or when projecting laboratory results to field conditions.

Air‐Drying and Pretreatment Effects on Soil Sulfate Sorption

AbstractDrying, freezing, and refrigeration are commonly employed to facilitate the handling and storage of soil samples on which chemical, biological, and physical analyses are to be performed. These laboratory protocol have the potential to alter soil chemical characteristics and may result in unrealistic estimates of in situ chemical processes. We determined the effect of air drying, storage temperature, and time on SO4‐sorption characteristics. Sulfate‐sorption experiments were conducted in the field on moist samples and compared with laboratory results for the same soils that had been kept frozen (−5 °C), refrigerated (4 °C) for 14 or 60 d, or air dried. Only air drying significantly altered SO4‐sorption characteristics. The impact of air drying on SO4‐sorption capacities was then determined on 29 pedons (84 horizons) from four northeastern USA (NE) and three southern Blue Ridge province states. A suite of physico‐chemical properties of soils whose sorption capacities were affected by drying were also measured. The SO4‐sorption capacity increased as much as 320% when dried soils were compared with field‐moist samples. Soils whose sorption capacities were most affected by air drying included the NE soils group, which had a higher percentage of the clay fraction in the form of amorphous minerals and were high in exchangeable acidity and total organic C. Air drying caused significant decreases in ethylenediaminetetraacetic acid (EDTA) extractable Fe and Al, oxalate‐extractable Al, and KCl‐extractable Al. This suggests the formation of new solids on drying, which increase SO4 sorption. Development of a multivariate model, however, indicated that total organic C, change in Fe extracted by pyrophosphate, dry minus moist; change in Fe extracted by oxalate, dry minus moist; and H+ solution concentration in 0.01 M CaCl2, dry minus moist were the best predictors of the change in SO4 sorption capacity with drying.

Fractionation of sulfur and oxygen isotopes in sulfate by soil sorption

Both field and laboratory data indicate that there is no significant isotope fractionation of sulfate during sorption in upland forest Podzols. The dominant sulfate sorption process in these soils is adsorption onto mineral surfaces. In the Plastic Lake watershed, Dorset, Ontario, Canada, fractions of sulfate from Podzol B-horizons have the following mean isotope (%.) compositions: water soluble sulfate, δ 34 S = +6.4; δ 18 O = −5.3; bicarbonate-exchanged sulfate by two methods, δ 34 S = + 4.5 and + 3.4; δ 18 O =−6.2 and −5.6; dissolved sulfate in B-horizon soilwater seepage, δ 34 S = + 4.8; δ 18 O = −5.4. These data indicate that soil sorption enriches dissolved sulfate in 34S by approximately 1 ± 1%. and in 18O by 0 +- 1 %. relative to sorbed sulfate. Similar results were obtained by laboratory sorption of sulfate by prepared goethite, which is a mineral representative of soil sorption sites in acidic Podzols like the one at Plastic Lake. The mean fractionation between sorbed and dissolved sulfate was found to be − 0.3%. for 34S and 0.1 %. for 18O. Earlier literature has confused the term adsorption; in many cases the more general term sorption, or retention, should be used. Pronounced fractionation of S and O isotopes in sulfate by lake and ocean sediments has been attributed to “adsorption” or “retention” but is more likely the result of sulfate reduction. Apparently, at Earth-surface conditions the only substantial isotope shifts in sulfate occur during microbial processes.

Sorption of various drugs in polyvinyl chloride, glass, and polyethylene-lined infusion containers

The sorption of chloroquine sulfate, diazepam, isosorbide dinitrate, lorazepam, midazolam, nitroglycerin, promethazine hydrochloride, thiopental sodium, and warfarin sodium to three types of containers was studied. Appropriate amounts of the drugs were added to 500 mL of 0.9% sodium chloride injection in polyvinyl chloride (PVC) bags, glass bottles, and Clear-Flex bags composed of a laminate of polyethylene, nylon, and polypropylene. The containers were stored in the dark at room temperature for 24 hours. Samples were taken at various intervals and assayed for drug concentration by high-performance liquid chromatography. There were no appreciable changes in pH after 24 hours, and all the admixtures remained clear and colorless. The potency of chloroquine sulfate, lorazepam, midazolam, promethazine hydrochloride, and thiopental sodium remained unchanged in glass, PVC, and Clear-Flex containers. Diazepam, isosorbide dinitrate, nitroglycerin, and warfarin sodium did not show any sorption to glass bottles and Clear-Flex bags. In PVC bags, however, up to 55% of diazepam, 23% of isosorbide dinitrate, 51% of nitroglycerin, and 24% of warfarin sodium was lost during the 24-hour study period. Diazepam, isosorbide dinitrate, nitroglycerin, and warfarin sodium in 0.9% sodium chloride injection showed a loss of potency when stored in PVC containers for 24 hours at room temperature, but none of the drugs studied lost potency when stored in glass bottles and Clear-Flex bags.

Distribution of aluminum in black spruce saplings growing on two New Brunswick forest soils with contrasting acid sulfate sorption

Two adjacent soils with contrasting sulfate sorption were examined in terms of (i) water-soluble and ion-exchangeable Al, Fe, Ca, Mg, K, Mn and Zn, (ii), water- and bicarbonate-extractable sulfate, (iii) Truog-extractable P, (iv) dithionite-extractable Al, Mn and Fe and (v) treatment response to irrigation with simulated acid precipitation. The biomass of 8 year old black spruce saplings growing on the soils, and the distributions of Al, Fe, Ca, Mg, K, Mn, P and Zn within these plants, were also examined. The soils were well to moderately-well drained, with the mineral soil exposed by site preparation prior to planting. The exposed soil underneath individual saplings was treated with acid sulfate solutions (75 mm containing 2 to 50 mg L−1 H2SO4) applied during each of three consecutive growing seasons. The results indicate that Al, much like Fe, Ca, Mn and Zn, accumulated with time in the foliage, but K, Mg and P were highest in young plant tissues. Much of Al and Fe taken up remained in the fine roots. Aluminum uptake increased with the amount of dithionite-extractable Al (free Al oxide) in the soil. Growth of the black spruce saplings was not visibly affected by readily accessed Al in each soil, or by acid irrigation.Instead, growth was restricted by factors other than soil Al and acid irrigation in spite of (i) low soil pH, (ii) high levels of exchangeable Al, and (iii) high levels of Al in fine roots. Sulfate retention across and within the two soils was positively correlated with free Al oxide. The two soils responded to acid irrigation by accelerated silicate weathering and enhanced ion leaching. Sulfate sorption reduced these effects.

SULFATE RETENTION IN SOME PODZOLIC SOILS OF THE SOUTHERN LAURENTIANS, QUEBEC

Sulfate sorption and desorption as a function of pH were measured for six podzolic horizons from two forested watersheds of the southern Laurentians. The results showed a rapid increase in sulfate sorption with decreasing pH to a maximum sorption capacity at pH values between 3.8 and 4.2 depending on the horizon considered. Below this pH retention decreased except for the Coniferous (Con) B horizon where sorption remained almost constant. This drop in the sorption capacity of the soils is related to the partial dissolution of Al, and possibly Fe, surface coatings. Levels of up to 15.9 mmol L−1 of total dissolved Al were measured at pH 3.0 for the Herminc (Her) B horizon. The amount of sorbed and total native sulfate and the maximum sorption during the experiment are positively correlated (R2 = 0.986, 0.982 and 0.800) with the oxalate extractable Al content of the soils. Except for the Con B horizon, amorphous plus crystalline Fe make up the bulk of the inorganic coatings in all six horizons. For the Con B horizon, which has the highest sorption capacity of the horizons tested, the composition of these coatings is dominated by Al materials. In all soils, the variations in sulfate sorption as a function of solution concentration are best described by the Gunary equation in the range of pH values tested. Key words: Sulfate, pH-dependent sorption, dissolution, Podzol

A generalized soft water acidification model

A generalized soft water acidification model has been developed. The enhanced trickle‐down (ETD) model is driven by precipitation, evaporation, acidity, sulfate, and chloride loading time series daily input data. The hydrologic component simulates snowmelt, interflow, overland flow, groundwater flow, frozen ground processes, seepage, and evapotranspiration. Physicochemical and biological processes that affect the alkalinity or sulfate balance and are included in the formulation are cation exchange, chemical weathering, sulfate sorption, and sulfate reduction. The system of 20 ordinary differential equations is solved by using a variable time step fourth‐order predictor‐corrector numerical scheme. Shown here is calibration of the ETD model for two lakes in the Adirondack Park of New York. ETD is relatively simple and requires limited input data, and yet it accounts for the predominant hydrologic and biochemical processes of the ecosystem.

Capacity of soils for sorption of sulfur dioxide

Abstract Studies with 41 soils selected to obtain a wide range in properties showed that air‐dry and moist soils have substantial capacities for sorption of SO2from air (averages, 1.80 and 9.98 g S kg‐1soil, respectively). Soil properties influencing the capacities of air‐dry soils for sorptlon of SO2included clay content, surface area, DCB‐soluble Mn, CaCO3equivalent, dpH, acid‐titratable basicity, and sulfate sorption capacity. The corresponding capacities of moist soils were influenced by surface area and soil properties associated with CaCO3equivalent. It was possible to closely predict the SO2sorption capacities of both air‐dry and moist soils (R2‐ 0.913 and 0.939, respectively) from consideration of their properties