Soil Science Society of America Journal 65:1101-1108 (2001)
© 2001 Soil Science Society of America
DIVISION S-2—SOIL CHEMISTRY
Alkaline Fly Ash Effects on Boron Sorption and Desorption in Soils
T. Matsi* and
V. Z. Keramidas
Laboratory of Soil Science, Faculty of Agriculture, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece
* Corresponding author (theomats{at}agro.auth.gr)
 |
ABSTRACT
|
|---|
Application of alkaline fly ash to soils is expected to result in an increase in B sorption capacity. If fly ash is B-rich, B phytotoxicity might occur depending not only on B loads and magnitude of soil sorption capacity for B, but also on the strength of B retention by sorption surfaces of the fly ash amended soils. This strength determines the ease through which B releases into the soil solution. Aged-alkaline fly ash was applied to one calcareous and two acid soils at rates equal to 0, 5, 20, and 50 g kg-1 of soil, and the impact of fly ash addition on B sorption in these soils was characterized, by means of the parameters (affinity and maximum) obtained through fitting B sorption data to the nonlinear Freundlich, Langmuir isotherms, and the phenomenological equation of Keren et al. Boron was added to the untreated and the fly ash-treated soils, left in contact for 30 d, and its desorbability was studied. It was observed that although B sorption maximum of soils tended to increase upon fly ash addition, the affinity of B to sorption sites remained practically unaltered in most of the cases. Boron sorption was an exothermic reaction and the greatest part (more than 60%) of sorbed B in the fly ash-treated soils could be easily desorbed within 24 h, reaching 80% for the acid soils and 100% for the calcareous soil after 120 h of desorption time. It was concluded that although there was a tendency of an increase in B sorption capacity in most cases upon fly ash addition, this increase was not generally accompanied by an increase in strength of B retention by soil surfaces. A major part of added B in the fly ash-treated soils remained labile enough to be released in the soil solution in a short time.
Abbreviations: CEC, cation-exchange capacity • ECse, electrical conductivity • SE, standard error of the estimate
|
INTRODUCTION
|
|---|
FLY ASH, a byproduct of lignite-fired electric power stations, is produced in large quantities in many countries and is partially disposed of in soils. Fly ash can enhance soil fertility, improve the soil's physical properties, and raise the pH of acid soils if it is alkaline in reaction. However, it may result in undesirable environmental consequences such as salinity and B toxicity. The latter can become a severe problem because fly ashes are reported to contain elevated concentrations of B (Carlson and Adriano, 1993). On the other hand, application of alkaline fly ash would raise soil pH and consequently increase soil sorption capacity for B and possibly the strength of B retention, resulting in low levels of B in the soil solution. Since it is established that plants respond only to the activity of B in the soil solution and that sorbed B is not toxic to plants (Goldberg, 1997), B sorption capacity of a soil and the strength of B retention by soil surfaces are important factors for attenuating the impact of heavy loads of B added to soils. This means that upon addition of fly ash to soils, high amounts of B in it or added to soils from another source are less likely to become phytotoxic if the subsequent increase in the soil sorption capacity for B is accompanied by an increase in the binding strength of B to soil solids. If, however, addition of fly ash to soils does not increase B binding strength onto soil solids and sorbed B is easily released into the soil solution, the risk of B phytotoxicity cannot be overlooked.
Comparison of B sorption characteristics between soils untreated and treated with fly ash can be made by obtaining B sorption data in each case, fitting them to sorption equations, and deriving empirical parameters characterizing B sorption. These parameters can be used for the comparisons because they are related either to the B sorption capacity of the sorbent or the affinity of the sorbent for the sorbate. Thus, they provide a quantitative measure of any changes occurring upon treatment of the sorbent.
Certain sorption models with molecular features that can be given thermodynamic significance are the surface complexation models, which have been used recently to describe B adsorption on soils and soil minerals (Toner and Sparks, 1995; Goldberg, 1999). The role of such models is to predict and quantify accurately B concentration in the soil solution and to provide a better understanding of the mechanisms involved in B adsorption on soils. If, however, the role of a sorption model is to summarize information about a given soil by providing a few empirical parameters useful for comparing the effects of a particular treatment on a certain soil, then simpler models are preferable (Barrow, 1978). In this respect, simple adsorption equations that describe B sorption by soils in pragmatic rather than in mechanistic terms have been used with variable success. Such models include the Freundlich and the Langmuir equations (Elrashidi and O'Connor, 1982; Goldberg and Forster, 1991). The Langmuir model has enjoyed wider applicability because its parameters are related to the maximum sorption capacity and affinity of the sorbate for the sorbent. Keren et al. (1981) have put forward a quasi-mechanistic model, which they called a phenomenological equation, to describe B sorption by soils. Their model takes into account the influence of pH on B sorption and assumes that three species are involved in the reaction, namely B(OH)3, B
-4, and OH-. The presence of the former two species on the surface of an amorphous Fe oxide has been verified by Su and Suarez (1995), using Attenuated Total Reflectance Fourier Transformed Infrared Spectroscopy. Therefore, the importance of each competing species on boron sorption can be evaluated, thus providing indirect evidence on the effect of fly ash addition on B sorption maximum and its strength of retention by soil solids.
The objectives of the present work were to: (i) evaluate changes in B sorption characteristics of three soils, imposed by the addition of fly ash, through the empirical parameters derived from the application of three sorption equations, i.e. the Freundlich, the Langmuir and the phenomenological equation to B sorption data, and (ii) study the desorbability of externally added B from the fly ash-treated soils.
|
MATERIALS AND METHODS
|
|---|
Soils and Fly Ashes
Surface samples (0–30 cm) were collected from three different locations representing three different soil types of northern Greece. Soil 1 was a sandy loam, acidic, developed on mica schist (Ultic Haploxeralf), Soil 2 was a sandy clay loam, acidic, developed on unconsolidated calcareous deposits (Typic Haploxeralf), and Soil 3 was a clay, calcareous, developed on limestone (Vertic Calcixeroll). The soils differed in their physicochemical properties and in the mineralogy of the clay fraction (Table 1). The soil samples were air-dried, and the material that passed through a 2-mm sieve was used for all subsequent experiments and analyses. Two samples of alkaline fly ash were collected from the electrostatic precipitators of two lignite-fired electric power plants operating in northern Greece, namely St Dimitrios and Filotas (the fly ashes will be designated as Fly ash I and Fly ash II, respectively, henceforth). The fly ash samples were artificially aged for 6 mo by maintaining them in the open air and leaching periodically with distilled water. This treatment was an attempt to simulate actual conditions in which fly ash, after its collection from the electrostatic filters, is transported to open storage areas where it remains exposed to atmospheric conditions prior to its use for any purpose. After aging, the ashes were air-dried and passed through a 2-mm sieve. This material was used for subsequent analyses and for addition to soils at rates equal to 5, 20, and 50 g kg-1 of soil. These rates are equivalent to 10, 40, and 100 Mg ha-1. They were selected to represent the usual rates of fly ash additions to soils and not to increase soil pH beyond 8.4. The fly ash-soil mixtures (treated soils), after equilibration for 20 d at field capacity, were air-dried and the material < 2 mm was used in the sorption–desorption experiments.
The original soils (untreated soils), the fly ashes, and the treated soils were assayed for their basic physicochemical characteristics. All analyses were run in duplicate and average values are reported (Tables 1, 2, and 3). Calcium carbonate content was determined volumetrically using a calcimeter and organic C by the wet oxidation method of Walkley and Black (1934). Particle-size analysis of soils was performed by the hydrometer method and cation-exchange capacity (CEC) was determined according to the method of Polemio and Rhoades (1977). Electrical conductivity (ECse) was measured in the saturation extract. In all treatments, soil pH did not exceed the value of 8.2, and ECse did not exceed the value of 0.25 S m-1 (Table 3). Boron was extracted with hot water and determined by the azomethine–H method (Keren, 1996). Water soluble Si and P of the fly ashes were extracted by a 1:4 soil/water ratio combined with a 2-h shaking, and determined colorimetrically. The mineralogy of the clay fraction of the original soils was determined by obtaining x-ray diffractograms of parallel oriented clay specimens, by a Philips (Wavre, Belgium) diffractometer, model PW 1830, equipped with a Cu target operated at 45 kV and 30 mA and a graphite crystal monochromator. Inorganic phases predominant in both fly ashes were identified by obtaining x-ray diffraction patterns of randomly oriented powder specimens of the material. The major components of both ashes were hydrous aluminosilicates (ettringite), quartz, calcite, and anhydrite. Neither fly ash contained high amounts of Si, P, and B or excessive amounts of soluble salts (Table 2).
Boron Sorption Experiments
Boron sorption data for the untreated and treated soils were obtained by a slight modification of the technique used by Mezuman and Keren (1981). Two and one-half–gram subsamples of each untreated and treated soil, in three replicates, were placed in 50-mL polypropylene centrifuge tubes with 10 mL of 0.01 M CaCl2 solution, containing varying concentrations of B, as H3BO3. Boron concentration of the initial solutions ranged from 2 to 100 mg L-1. The suspensions were equilibrated for 24 h at constant temperature with intermittent shaking. After equilibration, the tubes were centrifuged, and B was determined in the supernatant liquid employing the azomethine-H method. The amount of sorbed B was calculated by the difference between the amount added and that found in solution at equilibrium. No correction for native surface B was made because of its low level (Table 1). Sorption data were obtained at two temperatures, namely, 27 and 37 ± 1°C.
Sorption Equations
The following nonlinear equations were used to fit the obtained B sorption data: The Freundlich equation,
 | (1) |
The Langmuir equation,
 | (2) |
where x is the amount of B sorbed (mg kg-1 of soil); C is B concentration in the equilibrium solution (mg L-1); k and n constants; K (L mg-1) is a parameter related to the affinity of the sorbent for the sorbate, and M (mg kg-1 of soil) is the maximum B sorption capacity of the sorbent. Boron sorption data were fit to the above equations by nonlinear regression using the Levenberg–Marquardt algorithm.
The phenomenological equation of Keren et al. (1981),
 | (3) |
where QBT (mol g-1) is the total amount of sorbed B; KHB, KB, and KOH (L mol-1) are affinity coefficients related to the binding strength of the species B-3, B-4, and OH-, respectively, with the sorbent; (HB), (B), and (OH) (mol L-1) are equilibrium solution activities of the previous species, respectively; and TS is the maximum sorption capacity (mol g-1) of the sorbent.
Keren et al. (1981) based their equation on the assumption that B(OH)3, B-4, and OH- participate in B sorption having different affinities for the sorbent, and compete for the same sorption sites, while the sorption capacity of the sorbent for the sorbed species is pH dependent. The form of the phenomenological equation is analogous to a competitive Langmuir equation but differs from it and other purely empirical equations in that, it can describe B sorption as a function of both the equilibrium B concentration and the pH. Estimation of the constants was made by nonlinear regression using Levenberg–Marquardt's algorithm. The computer code used was the PROC NLIN of the SAS package (SAS Institute, 1988). The fitting of the phenomenological equation, Eq. [3], requires the acquisition of sorption data for at least two different pH values for the same soil (Keren et al., 1981). In the present study, since each treatment with fly ash changed soil pH, sorption data for different treatments of the same soil were used for fitting them to the phenomenological equation.
Boron Desorption Experiments
Since both fly ashes did not contain appreciable amounts of B, this element was externally added to the treated soils in the form of a solution of H3BO3, and at amounts equal to 2.5, 10, and 25 mg B kg-1 of fly ash–soil mixture for the treatments of 5, 20, and 50 g of fly ash kg-1 of soil, respectively. The same B additions were made to the untreated soils, for comparison. After B addition, the samples were equilibrated at field capacity for 30 d, air-dried, and used for the desorption experiment.
Desorption of B was studied, according to Elrashidi and O'Connor (1982), by placing 5 g of the B spiked samples and 20 mL of 0.01 M CaCl2 boron-free solution into 50 mL polypropylene centrifuge tubes and equilibrating the suspensions for 24 h at 25 ± 1°C, shaking them periodically. After equilibration, the tubes were centrifuged, a 10-mL aliquot of the supernatant was removed and analyzed for B, employing the azomethine–H method. The 10-mL aliquot removed was replaced with 10 mL of the 0.01 M CaCl2 solution, the mixtures were resuspended by vigorous agitation and equilibrated for 24 h at 25 ± 1°C. This procedure was repeated until B concentration in the supernatant reached undetectable levels, resulting in a total of four to five desorption steps for the different samples. This represents a maximum of 120 h desorption time. The amount of B desorbed at each step was corrected for the amount of B transferred from the previous step.
|
RESULTS AND DISCUSSION
|
|---|
The Freundlich and Langmuir Equations
Boron sorption data for the untreated and the treated soils conformed satisfactorily to the nonlinear forms of both the Freundlich and Langmuir equations, the latter being slightly superior, as judged by the low standard errors of the estimate (SE), which were used as the criterion of goodness of fit (Table 4). Figures 1 and 2 also show the good agreement between the observed and the predicted values of sorption data. In both figures, for reasons of simplicity, only one treatment of the three soils with one fly ash is shown, namely 20 g kg-1 of Fly ash I. For the rest of the treatments the goodness of fit can be deduced from the data of Table 4 and the parameters shown in Tables 5 and 6. The nonlinear Freundlich and Langmuir isotherms was also used successfully by Goldberg and Forster (1991) to describe B adsorption on two calcareous and one noncalcareous soils, over a wide range (1–250 mg L-1) of B concentration in the external solution. Performance of a t-test, to evaluate the significance of the parameters k and n of the Freundlich; and K and M of the Langmuir equations, revealed that in all cases the parameters were significant at the 0.05 probability level. Therefore, their use as a means to compare the effects of fly ash treatment on the three soils seems justified with a reasonable degree of confidence.
View this table:
[in this window]
[in a new window]
|
Table 4. Standard errors of the estimate (SE) for the two sorption equations, used for the untreated and treated soils.
|
|
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 1. Freundlich isotherm, x = kCn, for (a) B sorption on the untreated soils and those (b) treated with 20 g Fly ash I kg-1 soil.
|
|
View larger version (19K):
[in this window]
[in a new window]
|
Fig. 2. Langmuir isotherm, x = KMC/(1 + KC), for (a) B sorption on the untreated soils and (b) those treated with 20 g Fly ash I kg-1 soil.
|
|
The parameters, k and n, of the Freundlich equation (Table 5) are rather obscure in their interpretation although certain researchers argue that k can be visualized as a quantity term, since it corresponds to the amount of B sorbed when C equals 1, whereas n can be considered a measure of sorption intensity (Adamson, 1967). The data of Table 5 shows that the parameter, k, of the two acid soils (Soil 1 and 2) increased upon fly ash addition. This increase was statistically significant (P 
0.05) in several cases. The parameter, k, of the calcareous soil (Soil 3) tended to decrease, but the decrease was not significant. The parameter, n, however, did not change significantly upon fly ash addition, except in two cases for Soil 3, where it increased significantly (Table 5). This particular behavior of Soil 3, as evidenced by the changes of k and n cannot be explained under the light of the present findings.
The situation is better depicted through the use of the Langmuir equation, whose parameters, K and M, are related to the affinity and maximum sorption, respectively (Table 6). Upon fly ash addition, M tended to increase in all treatments of the three soils and this increase was significant in several cases. On the contrary, the affinity parameter, K, seemed to remain unaffected by fly ash addition in the two acid soils and decreased significantly in half of the treatments of the calcareous soil (Table 6).
These findings supported the idea that, in general, fly ash additions to the three soils tended to increase their B sorption capacity. This was more pronounced in the acid soils whose pH was appreciably raised upon addition of alkaline fly ash. Soil pH is a major factor controlling B sorption and a positive correlation between soil pH and B sorption maximum has been established clearly by many researchers (e.g., Okazaki and Chao, 1968; Evans, 1987). On the contrary, the strength of B retention by soil solids did not seem to be altered considerably and in some cases it seemed to be reduced upon fly ash addition to soils. This might be due to the strong competition of OH ions (see below) or to the presence of other competing ions in the fly ash.
The Phenomenological Equation
Equation [3] described successfully B sorption on soils as a function of B concentration in the soil solution and soil pH (Fig. 3). The fitting of B sorption data to Eq. [3] was more satisfactory for Soils 1 and 2 in comparison to Soil 3, as judged by the value of the SE (Table 7). Fitting of the phenomenological equation to B sorption data requires the acquisition of sorption data for at least two different pH values. The greater the difference between the pH values, the better the fit. In Soil 3, there was no great difference between the pH values upon fly ash addition and this explains the poor fitting of Eq. [3] to B sorption data relative to Soils 1 and 2. The solid lines in Fig. 3 were drawn by means of Eq. [3] using the coefficients TS, KHB, KB, KOH, given in Table 7, which were calculated from the experimental data. The agreement of the theoretical lines (solid lines) and the experimental results indicates that the calculated coefficients do describe B sorption on these three soils as a function of pH. Boron sorption maximum increased as the pH of the soils increased, as expected, and was the highest in the calcareous soil (Table 7). The values of the coefficients KHB, KB, KOH, which represent the binding strength of the species B(OH)3, B-4, and OH-, respectively, increased in order. The same order was found for soils (Mezuman and Keren; 1981, Yermiyahu et al., 1995), clay minerals (Keren and Mezuman, 1981) and composted organic matter (Yermiyahu et al., 1988). This implies that the OH ions compete strongly with the two B species for the same sorption sites and that the higher their activity—up to the pH where maximum B sorption occurs—following fly ash addition, the smaller the possibility of B to be sorbed on the soil solid phase. The above mentioned observations manifest the strong effect of OH- on B sorption. An increase in soil pH results in an increased activity of B-4, with a corresponding increase in B sorption capacity, but at the same time in an increased activity of OH-, which compete strongly with B species for the same sorption sites and probably reducing the affinity of the sorbate to them.
View larger version (15K):
[in this window]
[in a new window]
|
Fig. 3. Boron sorption on the three soils as a function of B concentration in solution and pH (Solid lines predict sorption according to Eq. [3]; open symbols are the observe sorption). Sorption data for all treatments of each soil were used for fitting the Keren et al. (1981) equation.
|
|
View this table:
[in this window]
[in a new window]
|
Table 7. Parameters for fitting the phenomenological equation to B sorption data of the three soils and the standard errors of the estimate (SE).
|
|
Effect of Temperature on Boron Sorption
Plotting B sorption isotherms for the three soils (untreated and treated) at the two temperatures, revealed the exothermic character of the reaction; since the isotherms at the higher temperature were always located below the isotherm at the lower temperature (Fig. 4 shows an example for Soil 3). In addition, the Langmuir adsorption maximum, M, calculated from the isotherms obtained at the two temperatures, decreased as the temperature increased, in almost all cases. The exothermic character of the reaction in all cases (treated and untreated soils) can lead one to speculate a physical or highly specific ion adsorption mechanism for B sorption by soil, which is not altered by fly ash addition. The nature of B sorption reaction and the effect of equilibration time are issues that depend on the experimental conditions. Biggar and Fireman (1960) and Goldberg et al. (1993) reported that B sorption on soils and clay minerals was an exothermic reaction, while Bingham et al. (1971) reported an endothermic one in soils where amorphous clays were dominant. Obviously, clay mineralogy makes the difference. In addition, it has been established that the rate of B sorption by clay minerals is a two-step process, consisting of a fast adsorption reaction (within 24 h) followed by a slow fixation reaction that continues for several months. The general consensus is that the initial adsorption of B is exothermic while the subsequent B fixation reaction is endothermic (Goldberg, 1997). Since in the present study B sorption isotherms were obtained after a short equilibration time (24 h), the results and any deductions thereof cannot be extrapolated to field conditions where B reacts with soil colloids for considerably longer period of time. The experiment of B release, however, where B remained in contact with the soil for 30 d, would give a more realistic picture of the situation in the field (see following discussion on B desorption).
View larger version (13K):
[in this window]
[in a new window]
|
Fig. 4. Boron sorption isotherms for Soil 3 at two temperatures. (a) untreated; (b) and (c) treated with 20 and 50 g Fly ash  kg-1 soil, respectively.
|
|
Boron Desorption
The B desorption experiment, in which added B was left to equilibrate with the soil solid phase for a considerable time (30 d), gave a more realistic picture about the effect of fly ash addition on B desorption from soils in the case where B was added from sources other than the fly ash. At all rates of B addition and for all soils (untreated and treated with fly ash), the greatest part of total desorbable B was released during the first desorption step (24 h). The amount of desorbable B continued to increase in the subsequent steps reaching a cumulative amount of 80 to 100% of B added, at the end of the last desorption step (120 h). An example of the cumulative amounts of desorbed B for the untreated and the treated with 50 g of fly ash kg-1 of soil, when B was added at 25 mg kg-1 soil, is shown in Fig. 5 and the total amounts of desorbed B for all soils and all B additions are shown in Table 8.
View larger version (12K):
[in this window]
[in a new window]
|
Fig. 5. Cumulative amounts of desorbed B from treated and untreated soils, after addition of 25 mg B kg-1 soil and 30 d equilibration. Each step represents a 24-h desorption interval.
|
|
View this table:
[in this window]
[in a new window]
|
Table 8. Total amount of desorbed B (mg kg-1 soil) from treated and untreated with fly ash soils, at the end of the desorption period (120 h). All samples had received the shown quantities of B and left for equilibration for 30 d, before starting the desorption experiment.
|
|
Griffin and Burau (1974) and Sharma et al. (1989) suggested that soils are multisite systems and postulated the existence of three types of B sorption sites: (i) low-affinity, high capacity which release B at a very fast rate; (ii) high-affinity, low capacity which release B at an intermediate rate; and (iii) a third type of sites which release B at a very slow rate. It is obvious in the present desorption experiment that the low-affinity, high capacity sorption sites were operating in all cases since more than 60% of the total desorbable B was released in the first desorption step. In Soil 3 (calcareous, smectitic), the recovery of added B approached 100% (Fig. 5 and Table 8) for all B additions. Whereas, for Soils 1 and 2 (acidic, illitic), the recovery of B was between 64 to 82% for the fly ash-treated soils and between 44 to 70% for the untreated soils (Table 8). In some cases, B desorption exceeds 100%, apparently due to some native B release. The differences between soils can be attributed to the mineralogy of the clay fraction. In Soils 1 and 2, illite dominated the clay fraction, while in Soil 3, smectite was prevalent (Table 1). Previous studies have shown that illites have a higher capacity of B retention than smectites (Hingston, 1964; Fleet, 1965). In addition, it has been postulated that the initially sorbed B at the edge of the mineral can diffuse into the lattice and replace either silica or tetrahedral aluminum (illites normally have large amounts of tetrahedral aluminum), the latter being preferentially displaced, because of a certain degree of lattice distortion (Griffin and Burau, 1974). Boron emission from these sites is governed by diffusion out of the crystal lattice, thus explaining the relatively small amounts of B and the very slow rate of its release into the soil solution from soils of illitic mineralogy.
The above observations imply that fly ash addition to soils will certainly create new sites for B sorption, as evidenced from the increase of B sorption maximum. However, these sites are of low-affinity and will release B easily into the soil solution, whereas the initial, native sites are of much stronger affinity for B, particularly if they are located on illitic clay minerals. These are corroborated by the previous findings, based on the Langmuir coefficients, which showed that the strength of B retention was not generally altered by fly ash addition and consequently B could be easily removed from the soil solid phase.
|
CONCLUSIONS
|
|---|
Boron soprtion on fly ash amended two acid and one calcareous soil conformed satisfactorily to the nonlinear Freundlich, Langmuir, and Keren et al. (1981) isotherms. Boron sorption capacity of fly ash amended soils showed a tendency to increase relative to the untreated soils, whereas the strength of B retention by soil solids remained practically unaltered in most of the cases.
When B was added to the untreated and treated with fly ash soils and its desorbability was studied, it became evident that 80 to 100% sorbed B could be easily released into the soil solution within 120 h of desorption period. Higher amounts of B were desorbed from the fly ash treated soils. This can be attributed to the strong competition of OH ions as the pH is raised or to the presence of competing ions such as silicate or phosphate present in the fly ash. The above findings suggested that fly ash addition to soils did not generally increase the strength of B retention and added B remained in a loosely held condition onto soil solids. Consequently, it could be easily released into the soil solution.
|
ACKNOWLEDGMENTS
|
|---|
The funding for this work provided by the Greek State Scholarships Foundation is gratefully appreciated.
|
NOTES
|
|---|
Research supported by the Greek State Scholarships Foundation.
Received for publication May 24, 2000.
|
REFERENCES
|
|---|
- Adamson, A.W. 1967. Physical chemistry of surfaces. 2nd ed. John Wiley & Sons, New York, NY.
- Barrow, N.J. 1978. The description of phosphate adsorption curves. J. Soil Sci. 29:447–462.
- Biggar, J.W., and M. Fireman. 1960. Boron adsorption and release by soils. Soil Sci. Soc. Am. Proc. 24:115–119.
- Bingham, F.T., A.L. Page, N.T. Coleman, and K. Flach. 1971. Boron adsorption characteristics of selected amorphous soils from Mexico and Hawaii. Soil Sci. Soc. Am. Proc. 35:546–550.
- Carlson, C.L., and D.C. Adriano. 1993. Environmental impacts of coal combustion residues. J. Environ. Qual. 22:227–247.
- Elrashidi, M.A., and G.A. O'Connor. 1982. Boron sorption and desorption in soils. Soil Sci. Soc. Am. J. 46:27–31.[Abstract/Free Full Text]
- Evans, L.J. 1987. Retention of boron by agricultural soils from Ontario. Can. J. Soil Sci. 67:33–42.
- Fleet, M.E.L. 1965. Preliminary investigation into the sorption of boron by clay minerals. Clay Miner. 6:3–16.
- Goldberg, S. 1997. Reactions of boron with soils. Plant Soil 193:35–48.
- Goldberg, S. 1999. Reanalysis of boron adsorption on soils and soil minerals using the constant capacitance model. Soil Sci. Soc. Am. J. 63:823–829.[Abstract/Free Full Text]
- Goldberg, S., and H.S. Forster. 1991. Boron sorption on calcareous soils and reference calcites. Soil Sci. 52:304–310.
- Goldberg, S., H.S. Forster, and E.L. Heick. 1993. Temperature effects on boron adsorption by reference minerals and soils. Soil Sci. 156:316–321.
- Griffin, R.A., and R.G. Burau. 1974. Kinetic and equilibrium studies of boron desorption from soil. Soil Sci. Soc. Am. Proc. 38:892–897.
- Hingston, F.J. 1964. Reactions between boron and clays. Aust. J. Soil Res. 2:83–95.
- Keren, R. 1996. Boron. p. 603–626. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. SSSA Book Ser. 5. SSSA and ASA., Madison, WI.
- Keren, R., R.G. Gast, and B. Bar-Yosef. 1981. pH-dependent boron adsorption by Na-montmorillonite. Soil Sci. Soc. Am. J. 45:45–48.[Abstract/Free Full Text]
- Keren, R., and U. Mezuman. 1981. Boron adsorption by clay minerals using a phenomenological equation. Clays Clay Miner. 29:198–204.[Abstract]
- Mezuman, U., and R. Keren. 1981. Boron adsorption by soils using a phenomenological adsorption equation. Soil Sci. Soc. Am. J. 45:722–726.[Abstract/Free Full Text]
- Okazaki, E., and T.T. Chao. 1968. Boron adsorption and desorption by some Hawaiian soils. Soil Sci. 105:255–259.
- Polemio, M., and J.D. Rhoades. 1977. Determining cation exchange capacity: A new procedure for calcareous and gypsiferous soils. Soil Sci. Soc. Am. J. 41:524–528.[Abstract/Free Full Text]
- SAS Institute. 1988. SAS/STAT user's guide, release 6.03 ed., SAS Inst., Cary, NC.
- Sharma, H.C., N.S. Pasricha, and M.S. Bajwa. 1989. Comparison of mathematical models to describe boron desorption from saltaffected soils. Soil Sci. 147:77–84.
- Soil Survey Staff. 1996. Keys to soil taxonomy. USDA-SCS. U.S. Gov. Print. Office, Washington DC.
- Su, C., and D.L. Suarez. 1995. Coordination of adsorbed boron: A FTIR spectroscopic study. Environ. Sci. Technol. 29:302–311.
- Toner, C.V., and D.L. Sparks. 1995. Chemical relaxation and double layer model analysis of boron adsorption on alumina. Soil Sci. Soc. Am. J. 59:395–404.[Abstract/Free Full Text]
- Walkley, A., and I.A. Black. 1934. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci. 37:29–38.
- Yermiyahu, U., R. Keren, and Y. Chen. 1988. Boron sorption on composted organic matter. Soil Sci. Soc. Am. J. 52:1309–1313.[Abstract/Free Full Text]
- Yermiyahu, U., R. Keren, and Y. Chen. 1995. Boron sorption by soil in the presence of composted organic matter. Soil Sci. Soc. Am. J. 59:405–409.[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
I. A. M. Yunusa, V. Manoharan, D. L. DeSilva, D. Eamus, B. R. Murray, and S. P. Nissanka
Growth and Elemental Accumulation by Canola on Soil Amended with Coal Fly Ash
J. Environ. Qual.,
May 1, 2008;
37(3):
1263 - 1270.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Communar and R. Keren
Rate-Limited Boron Transport in Soils: The Effect of Soil Texture and Solution pH
Soil Sci. Soc. Am. J.,
April 19, 2006;
70(3):
882 - 892.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
