Published online 9 January 2007
Published in J Environ Qual 36:298-304 (2007)
DOI: 10.2134/jeq2006.0050
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORTS
Waste Management
Influence of Soil pH and Application Rate on the Oxidation of Calcium Sulfite Derived from Flue Gas Desulfurization
Y. B. Leea,*,
J. M. Bighama,
W. A. Dickb,
F. S. Jonesa and
C. Ramsierc
a School of Environment and Natural Resources, The Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210
b School of Environment and Natural Resources, The Ohio State Univ., 1680 Madison Ave., Wooster, OH 44691
c Ag Spectrum Company, 428 East 11th St., DeWitt, IA 52742
* Corresponding author (lee.2306{at}osu.edu)
Received for publication February 3, 2006.
 |
ABSTRACT
|
|---|
Calcium sulfite hemihydrate (CaSO3·0.5H2O), a common byproduct of coal-fired utilities, is fairly insoluble and can decompose to release toxic SO2 under highly acidic soil conditions; however, it can also oxidize to form gypsum. The objective of this study was to examine the effects of application rate and soil pH on the oxidation of calcium sulfite under laboratory conditions. Oxidation rates measured by release of SO4–S to solution decreased with increasing application rate. Leachate SO4–S from soils amended with 1.0 to 3.0 g kg–1 CaSO3 increased over a 21 to 28 d period before reaching a plateau. At 4 g kg–1, maximum SO4–S release was delayed until Week 7. Oxidation and release of SO4–S from soil amended with 3.0 g kg–1 calcium sulfite increased markedly with decreasing soil pH. After only 3 d incubation, the concentrations of SO4–S in aqueous leachates were 77, 122, 170, 220, and 229 mg L–1 for initial soil pH values of 7.8, 6.5, 5.5, 5.1, and 4.0, respectively. At an initial soil pH value of 4.0, oxidation/dissolution did not increase much after 3 d. At higher pH values, oxidation was maximized after 21 d. These results suggest that autumn surface applications of calcium sulfite in no-till systems should permit ample time for oxidation/dissolution reactions to occur without introducing biocidal effects related to oxygen scavenging. Soil and annual crops can thus benefit from additions of soluble Ca and SO4 if calcium sulfite is applied in advance of spring planting.
Abbreviations: CEC, cation exchange capacity • EC, electrical conductivity • FGD, flue gas desulfurization • XRD, X-ray diffraction
|
INTRODUCTION
|
|---|
CALCIUM sulfite hemihydrate (CaSO3·0.5H2O), also known as the mineral hannebachite, is a major component of flue gas desulfurization (FGD) residues produced by the lime-based scrubbing processes employed at many coal-fired electric utilities in the Ohio River Valley (Dick et al., 2000; Bigham et al., 2005). FGD-CaSO3 is sometimes an intermediate product in forced oxidation units that generate agricultural-quality or wallboard-quality gypsum (CaSO4·2H2O) as a value-added material. More commonly, it is treated as an end waste product and is stockpiled in lagoons or mixed with fly ash for storage in landfills or for service as mine grout (Laperche and Bigham, 2002). Statistics from the American Coal Ash Association (2004) show that of the 12 million tons of FGD-gypsum produced in 2004, 9 million tons or 75% was used for beneficial purposes. In contrast, an estimated 17.5 million tons of wet scrubber material (mostly FGD-CaSO3) were produced but only 1.2 million tons or 6.8% were effectively utilized. The use of FGD-CaSO3 as a soil amendment in production agriculture would provide an attractive alternative to disposal if agronomic benefits and environmental safety can be demonstrated.
Whereas gypsum, a natural oxidation product of hannebachite, is widely employed as a soil amendment to improve physical and chemical properties and to provide a soluble source of Ca and S for plant nutrition (Shainberg et al., 1989), CaSO3·0.5H2O has not been seriously tested for its impact on soil properties or biological activity. Questions exist because the bisulfite ion (HSO3–) is a strong chemical reductant that is employed as a disinfectant in brewing vats, as a preservative for fruit juices, and as a scavenger of oxygen in the stabilization of pharmaceutical and other food products (Windholz, 1976) as demonstrated by the sequential reactions:
 | [1] |
 | [2] |
A competing process, especially at pH < 2.0, is the decomposition of bisulfite to produce SO2 gas:
 | [3] |
Reaction [3] is a concern because sulfur dioxide is quite soluble and has been found toxic to plant root tissues (Ritchey et al., 1995).
Unlike other sulfite salts (e.g., Na2SO3, K2SO3), CaSO3·0.5H2O has a relatively low solubility in water (0.054 g L–1 at room temperature). The rate of conversion to more soluble CaSO4·2H2O (solubility = 2.1 g L–1) is therefore important because a rapid oxidation rate would tend to mitigate any potential long-term biocidal effects while producing soluble Ca and SO4 for plant uptake and soil stabilization.
Gypsum applications to combat surface sealing in corn-soybean rotations in the Midwest are commonly made at rates of 2.2 to 4.4 Mg ha–1 on an alternate year schedule under no-till management (Norton et al., 1993; Dontsova et al., 2005). In contrast, previous laboratory studies demonstrating serious phytotoxic effects from CaSO3·0.5H2O applications to soils have involved incorporated loadings of up to 110 Mg ha–1 (Ritchey et al., 1995). The work of Hao and Dick (2000) has also demonstrated that the dissolution rate of CaSO3·0.5H2O in aqueous solutions is highly dependent on pH, as would be predicted from reaction [1]. Because a need clearly exists to define practical boundary conditions if FGD-CaSO3 is to be used in production agriculture, the objectives of this study were to determine the effects of soil pH and application rate on the oxidation of FGD-CaSO3 in bench-scale experiments designed as precursors to greenhouse and field tests.
|
MATERIALS AND METHODS
|
|---|
Synthesis of Calcium Sulfite
Synthetic CaSO3·0.5H2O was prepared for use as a chemical and mineralogical standard by mixing 6% sulfurous acid with powdered, reagent-grade Ca(OH)2. Excess sulfurous acid was removed by heating the solution gradually in a water bath to a temperature of 90°C. The resulting precipitate of CaSO3·0.5H2O was washed with deionized water and dried at 60°C for at least 12 h.
Flue Gas Desulfurization Calcium Sulfite and Calcium Sulfate
Bulk samples of wet FGD-CaSO3 and CaSO4 were obtained from the Zimmer Station Power Plant operated by CINERGY Corporation near Cincinnati, OH. The FGD-CaSO4 was taken from a stream directed to wallboard manufacture, whereas the precursor CaSO3 was destined to be land-filled. Subsamples were dried at 60°C for 12 h before study.
Mineralogy
The mineralogical purity of the FGD byproducts and synthetic CaSO3·0.5H2O was determined by X-ray diffraction (XRD). Diagnostic data were collected using CuK
radiation and a Philips PW 1316/90 diffractometer equipped with a theta-compensating slit, a 0.2-mm receiving slit, and a diffracted-beam monochromator. Randomly-oriented powder mounts were scanned from 10 to 70° 2
using a step interval of 0.05° 2 and a counting time of 4 s/step.
Chemistry
Total Ca and Mg were determined by atomic absorption spectrometry using a Varian SpectrAA5 instrument following complete dissolution of the samples in an acid digest prepared according to Kost et al. (2005). Total S was measured using a LECO Model 521 induction furnace and Model 518 semi-automatic titrator with K iodate titration of SO2 evolved by combustion of a 10-mg sample at 900°C. A standard curve was constructed using BaSO4. The SO3–S contents were measured by using an iodometric method (Hao and Dick, 2000). Trace element concentrations were obtained from samples digested according to Method 3050B (USEPA, 1996) with subsequent analysis of the digests using a Varian VISTA-AX inductively coupled plasma–atomic emission spectrometer (ICP–AES).
Soil Characterization
The soil material used in this study was collected from the surface horizon (0 to 20 cm) of a Platea soil (fine-silty, mixed, active, mesic Aeric Fragiaqualfs). The bulk sample was dried for 12 h at 60°C and crushed to pass a 2-mm sieve before analysis. Soil pH was measured in deionized water (1:1 v/v), and total C was determined by dry combustion (Nelson and Sommers, 1982). Exchangeable Ca, Mg, and K were extracted with 1 M NH4OAc (pH 7.0) and analyzed by atomic absorption and flame emission spectrometry (Holmgren et al., 1977). Exchangeable acidity was determined by the BaCl2–triethanolamine titrimetric method of Peech et al. (1947). Cation exchange capacity (CEC) was calculated from the sum of exchangeable cations (K, Ca, Mg) and exchangeable acidity. Soil texture was analyzed using the pipette method (Kilmer and Alexander, 1949), and water content at field capacity was measured according to Gardner (1986).
Oxidation of Flue Gas Desulfurization-Calcium Sulfite in Soils with Different pH
Subsamples (1 kg) of the acid soil material were dry-mixed with 0, 2.0, 4.0, 6.0, and 10.0 g of Ca(OH)2 and equilibrated with 100 mL of deionized water for 6 wk in a closed container (vented weekly) to adjust the soil reaction. Twenty g of each pH-adjusted material (pH 4.0, 5.0, 5.6, 6.5, and 7.8) were then blended with FGD-CaSO3 at application rates of 0 and 3 g kg–1 (
6.6 Mg ha–1). These preparations were loaded onto 1.0 g of compressed, ashless filter pulp inside 50 mL extraction syringes and covered with 0.5 g of compressed filter pulp to facilitate liquid and gas exchange. The loaded samples were initially adjusted to field capacity with deionized water and weighed periodically to determine how much deionized water must be added to compensate for water loss over time. At the end of each incubation period (0.5, 1, 2, 3, 5, 7, and 10 wk), the syringes were extracted at a constant rate with 50 mL of deionized water over a 12-h extraction time using a variable-rate mechanical leaching device (Model 24–01, Centurion International, Lincoln, NE) (Fig. 1). The leachates were retained for analysis of pH with an ion specific electrode, Ca by atomic absorption spectrometry, and SO42– by ion chromatography using a Dionex DX 120 instrument. All experiments were conducted using three replications. The combination of soil pH (5x), application rate (2x), incubation time (7x), and replication (3x) involved the preparation and analysis of 210 samples.
Effect of Application Rate on the Oxidation of Flue Gas Desulfurization Calcium Sulfite
Calcium Sulfite Oxidation in Water
The solubility of FGD-CaSO3 and CaSO4 in water were compared in a simple dissolution experiment involving a single rate of FGD-CaSO4 (2.1 g L–1) and multiple rates of CaSO3 (1.0, 2.0, 3.0, and 4.0 g L–1) without pH adjustment. The solids were transferred to bottles containing 1000 mL of deionized water with 78.5 cm3 head space. The resulting suspensions were stirred for 5 min every day using a magnetic stir assembly, and any loss of water by evaporation was compensated gravimetrically. Because CaSO4·xH2O solubility is approximately 40 times greater than CaSO3·0.5H2O, the oxidation of FGD-CaSO3 was determined by monitoring the electrical conductivity (EC). The oxidation end point was identified when the change in EC was <0.03 dS m–1 over a 3-d period. At that point, the solution was filtered through a 0.2-µm membrane filter, and the Ca concentration was determined using an atomic absorption spectrophotometer.
Calcium Sulfite Oxidation in Soil
For this experiment, two soil materials with pH adjusted to 5.5 and 6.5 were prepared as described previously. Subsamples (20 g) of both materials were then mixed with four levels of FGD-CaSO3 equivalent to application rates of 0, 1.0, 2.0, and 4.0 g kg–1 (0, 2.2, 4.4, and 8.8 Mg ha–1), and one level of FGD-CaSO4 equivalent to an application rate of 1.0 g kg–1 (2.2 Mg ha–1). The method of batch incubation (7 equilibration times), leachate collection, and analysis of the solutions was as described previously. This experiment was also conducted with three replications for a total of 210 samples.
|
RESULTS
|
|---|
Characterization of Soil and Byproduct Materials
The soil material selected for this study was a strongly acid (pHHOH = 4.0) silt loam (20.1% clay, 64.5% silt, and 15.4% sand) with a relatively high organic C content (33.0 g·kg–1) and a very low base saturation (12% with CEC = 24.7 cmol+ kg–1)). Liming with Ca(OH)2 at rates defined in the Materials and Methods produced subsamples with equilibrium pH values of 5.1, 5.6, 6.5, and 7.8 in water and thus provided a broad range of soil reaction over which to evaluate the oxidation of admixed FGD-CaSO3.
The FGD-CaSO3 gave an XRD pattern that compared well with that of synthetic hannebachite (Fig. 2), but its total Ca and S contents were slightly less than those of the synthetic sample or values predicted from the stoichiometry of CaSO3·0.5H2O (Table 1). Likewise, the SO3–S content was less than ideal and suggested that partial oxidation of the byproduct material had occurred during processing. The FGD-CaSO4 contained no detectable SO3–S and was identified as bassanite (Plaster of Paris or CaSO4·0.5H2O) rather than gypsum (Fig. 2; Table 1). Bassanite rapidly rehydrates and recrystallizes to form gypsum when water is added, as in the manufacture of wallboard.
View larger version (24K):
[in this window]
[in a new window]
|
Fig. 2. X-ray powder diffraction patterns from FGD (flue gas desulfurization)-CaSO4, FGD-CaSO3, and synthetic CaSO3·0.5H2O (hannebachite). Peak positions (numerical values) are in Å units.
|
|
Concentrations of both minor (Al, B, Fe, Mn) and trace elements were 5 to 10 times greater in the FGD-CaSO3 as compared with CaSO4 because of less complete washing of the former in the FGD waste stream. However, land application of either byproduct should not be an environmental issue because the contents of regulated trace metals in both materials were much lower than concentration limits established through government 40 CFR 503 regulations for land application of excellent quality biosolids (USEPA, 1993).
Dissolution of Flue Gas Desulfurization-Calcium Sulfate and the Oxidation of Flue Gas Desulfurization-Calcium Sulfite in Water
The dissolution of 2.1 g L–1 FGD-CaSO4, the reported equilibrium solubility concentration of gypsum, was complete within 12 h, and the resulting Ca concentration was 585 mg L–1. This value was near the 578 mg L–1 expected for a saturated solution of CaSO4·0.5H2O. By contrast, EC values for FGD-CaSO3 suspensions increased linearly over time to the apparent endpoint of oxidation, at which time no further change in EC (or Ca concentration) occurred (Fig. 3). For suspension concentrations of 2.0 g L–1 or greater, the oxidation process required approximately 21 d under unbuffered conditions.
View larger version (19K):
[in this window]
[in a new window]
|
Fig. 3. Electrical conductivity (EC) and Ca concentration in aqueous suspensions of FGD (flue gas desulfurization)-CaSO3 and FGD-CaSO4 over time.
|
|
Calcium sulfite spontaneously oxidizes to CaSO4 because it is thermodynamically unstable (Windholz, 1976). The HSO3– ion is the major sulfur oxyanion in solution between pH 1.9 and 7.2, and during the conversion of CaSO3 to CaSO4 in aerated water, the solution pH decreases as a result of the oxidation of weakly acidic HSO3– to strongly acidic HSO4– (Eq. [2]). In this study, the initial pH of the solution equilibrated with 4.0 g L–1 of FGD-CaSO3 was 9.0 and subsequently fell to 8.0, 7.9, and 7.6 at 3, 10, and 20 d, respectively. The equilibrium concentration of Ca in suspension was 546 mg L–1 for 2.0 g L–1 FGD-CaSO3 and was 97% of the total Ca content in the FGD-CaSO3 (Table 1).
Oxidation of Flue Gas Desulfurization-Calcium Sulfite as a Function of Soil pH
The pH values of leachates from soils admixed with 3.0 g kg–1 (6.6 Mg ha–1) FGD-CaSO3 were lower than those from unamended soils after 0.5 to 10 wk equilibration at near field capacity (Fig. 4). The pH difference was approximately 0.5 units for samples with the lowest initial pH values of 4.0 and 5.1. The disparity decreased at intermediate pH values, and there was little or no divergence in leachate pH with and without FGD-CaSO3 when the initial soil pH was 7.8 (Fig. 4). The observed decrease in leachate pH could be partially due to protons released from HSO3– oxidation (Eq. [2]) but more likely reflects a salt and cation exchange effect caused by the high concentration of soluble Ca arising from FGD-CaSO3 oxidation/dissolution. This Ca would displace Al from cation exchange sites and thereby facilitate acid hydrolysis reactions occurring at low soil pH (Chang and Thomas, 1963).
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 4. Change of leachate pH over time from soil materials of differing initial pH with and without addition of 3 g kg–1 FGD (flue gas desulfurization)-CaSO3.
|
|
Hao and Dick (2000) reported that decreasing the pH of an aqueous suspension of CaSO3 from 6.5 to 5.0 dramatically increased the dissolution/oxidation rate, which was accompanied by increases in EC and the concentrations of water-soluble Ca and SO4. Our EC data clearly show the effect of FGD-CaSO3 treatment on the ionic strength of the soil solution with a strong separation in conductivity between treated and most untreated samples (Fig. 5). The untreated material at pH 7.8 gave intermediate values, presumably due to the presence of unreacted liming agent (i.e., Ca(OH)2). Using either EC or water-soluble SO4–S (Fig. 5, 6a) as indicators, our results also show that the oxidation of FGD-CaSO3 in treated soils was strongly affected by soil pH. After only 3 d incubation, the concentrations of SO4–S in the aqueous leachates were 77, 122, 170, 220, and 229 mg L–1 for initial soil pH values of 7.8, 6.5, 5.5, 5.1, and 4.0, respectively. At an initial soil pH value of 4.0, oxidation/dissolution did not increase much after 3 d. Oxidation rates decreased with increasing soil pH, but oxidation was essentially complete after 21 d in all cases and was therein consistent with results obtained from aqueous suspensions of CaSO3 at concentrations approaching the solubility limits of the material (Fig. 3). The final SO4–S concentrations were similar among all soils, irrespective of pH, and indicated recovery of 75% of the total S added as FGD-CaSO3 (Fig. 6b). The S fraction not recovered in a single leaching of the sample presumably reflected material remaining in the soil pore water and/or a small quantity of unreacted CaSO3.
View larger version (28K):
[in this window]
[in a new window]
|
Fig. 5. Change in leachate EC (electrical conductivity) over time from soil materials with different initial pH after equilibration with 3 g kg–1 FGD (flue gas desulfurization)-CaSO3 for up to 10 wk.
|
|
View larger version (15K):
[in this window]
[in a new window]
|
Fig. 6. Change in leachate composition (SO4–S) over time from soil materials with different initial pH after equilibration with 3 g kg–1 FGD (flue gas desulfurization)-CaSO3 for up to 10 wk. Results expressed as (a) soluble SO4–S concentrations and (b) SO4–S as a percentage of total S added.
|
|
Effect of Flue Gas Desulfurization-Calcium Sulfite Application Rates
The influence of application rate on oxidation of FGD-CaSO3 was examined using soil samples adjusted to pH 5.5 and 6.5. The equilibrium pH and concentration of SO4–S released were compared both to a control and a sample receiving 1.0 g kg–1 (2.2 Mg ha–1) FGD-CaSO4, which is the annual or biennial rate commonly used for surface applications of gypsum to agricultural lands in the Midwest. As in previous experiments, the leachate pH from treated soils was less than that of the control and also decreased with increasing application rate of FGD-CaSO3 from 0 to 4.0 g kg–1 (0 to 8.8 Mg ha–1) (Fig. 7a and 7b). The pH at a given rate initially increased and then decreased over the course of the 10 wk incubation period in a manner similar to that noted with aqueous suspensions of FGD-CaSO3. Overall lower pHs with applications of FGD-CaSO3 were, once again, attributed to a salt/ion exchange effect because there was little or no difference in pH between equal rates of FGD-CaSO3 and CaSO4.
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 7. Change in leachate chemistry over time from soils with initial pH values of 5.5 and 6.5 after equilibration with FGD (flue gas desulfurization)-CaSO4 and variable rates of FGD-CaSO3 for up to 10 wk. (a) and (b) pH; (c) and (d) SO4–S.
|
|
The oxidation rate of FGD-CaSO3 was affected by the amount of applied byproduct. As observed previously, the concentration of SO4–S in leachates from soils amended with 1.0 to 2.0 g kg–1 CaSO3 increased over a 3 to 4 wk period before reaching a plateau. At 4 g kg–1, maximum oxidation was delayed through Week 7. Whereas the SO4–S concentrations in all FGD-CaSO3 treatments were greater at pH 5.5 than at pH 6.5 after 3 d equilibration, concentrations were similar after 7 wk incubation. The concentration of SO4–S in the leachates was slightly greater with FGD-CaSO4 treatment as compared with an equivalent rate of FGD-CaSO3 even though the stoichiometric S content was somewhat greater in CaSO3·0.5H2O than in CaSO4·0.5H2O. The data suggest, as in earlier experiments, that some FGD-CaSO3 remained unreacted throughout the incubation period.
|
DISCUSSION
|
|---|
At least one previous laboratory study has demonstrated phytotoxic effects from the addition of coal combustion byproducts enriched with CaSO3 to agricultural soils (Ritchey et al., 1995). The effects were temporary and were observed when FGD-CaSO3 was applied at moderate to high rates (>10 Mg ha–1) and incorporated into acidic soils (pH < 6.0). The phytotoxic effects were attributed to release of gaseous SO2 brought about by the decomposition of the HSO3– ion under acidic soil conditions. The results of the current study indicate that any such chemical limitations can be overcome by adopting simple management practices, such as autumn applications of CaSO3 to soils that have had their pH adjusted to 6.0 or greater.
Hannebachite (CaSO3·0.5H2O) spontaneously oxidizes to CaSO4·2H2O (gypsum) at pH values associated with most agricultural soils. Because of its relatively high solubility, gypsum subsequently releases Ca and SO4 that can be leached through the plow layer to benefit the physicochemical properties of both topsoil and subsoil horizons (Pavan et al., 1982; Farina and Channon, 1988; Carvalho and van Raij, 1997). The CaSO3–CaSO4 conversion rate was found in this study to be pH-dependent and increased with decreasing soil pH (Fig. 5). At loadings typical for land application of gypsum in the Midwest (i.e., 2.2 to 4.4 Mg ha–1yr–1), oxidation was mostly complete within 3 wk at room temperature, circumneutral soil pH (where SO2 release is not an issue), and a water content approaching field capacity. Hao and Dick (2000) observed that oxidation rates in water were also temperature-dependent, but the rates were not significantly different between 25 and 15°C. Autumn applications of FGD-CaSO3 should thus permit ample time for oxidation/dissolution reactions to occur before crops are planted.
It was noted in our pH experiment that recovery of total S added as FGD CaSO3 was 75% complete based on soluble SO4–S concentrations in soil leachates (Fig. 6b). Moreover, the recovery of SO4–S from FGD-CaSO3 was somewhat less than from an equivalent rate of FGD-CaSO4 (Fig. 7c and 7d). Collectively, these results suggest that oxidation of added FGD-CaSO3 may have been oxygen-limited even though attempts were made to maintain adequate air exchange with the amended soil samples. Unfortunately, no direct measurements of O2 were attempted. Under no-till management conditions, FGD-CaSO3 would be surface-applied without incorporation. Thus, oxygen should not be limiting during the several months between fall application and spring planting.
Although additional greenhouse and/or field testing is clearly appropriate, it appears that other issues related to processing, handling characteristics, and trace element composition have greater potential to influence the adoption of FGD-CaSO3 as a soil amendment on agricultural lands than slow oxidation rates to SO42–. Synthetic FGD-CaSO4 has been observed to have superb handling characteristics in field applications (Dontsova et al., 2005), but high water contents (10 to 15 wt%) prohibit long distance transport. Without additional processing (i.e., washing and de-watering), FGD-CaSO3 can be expected to have greater trace element and water contents than FGD-CaSO4. Most available data (e.g., Table 1) indicate that trace elements are not sufficiently high to become limiting, but processing costs and spreading characteristics of byproduct FGD-CaSO3 await further evaluation.
|
ACKNOWLEDGMENTS
|
|---|
This work was supported by the Post-doctoral Fellowship Program of Korea Science & Engineering Foundation (KOSEF). The authors thank CINERGY Corporation for supplying samples of FGD-CaSO3 and CaSO4.
|
REFERENCES
|
|---|
- American Coal Ash Association. 2004. 2004 coal combustion product (CCP) production and use survey. Am. Coal Ash Assoc., Aurora, CO. Available at http://www.acaa-usa.org/CCPSurveyShort.htm (verified 10 Oct. 2006).
- Bigham, J.M., D.A. Kost, R.C. Stehouwer, J.H. Beeghly, R. Fowler, S.J. Traina, W.E. Wolfe, and W.A. Dick. 2005. Mineralogical and engineering characteristics of dry flue gas desulfurization products. Fuel 84:1839–1848.[CrossRef]
- Carvalho, M.C.S., and B. van Raij. 1997. Calcium sulphate, phosphogypsum, and calcium carbonate in the amelioration of acid subsoil for root growth. Plant Soil 192:37–48.[CrossRef]
- Chang, M.L., and G.W. Thomas. 1963. A suggested mechanism for sulfate adsorption by soils. Soil Sci. Soc. Am. Proc. 27:281–283.
- Dick, W.A., Y. Hao, R.C. Stehouwer, J.M. Bigham, W.E. Wolfe, D. Adriano, J.H. Beeghly, and R.J. Haefner. 2000. Beneficial uses of flue gas desulfurization by-products: Examples and case studies of land application. p. 505–536. In J.F. Power and W.A. Dick (ed.) Land application of agricultural, industrial, and municipal byproducts. SSSA Book Ser. 6. SSSA. Madison, WI.
- Dontsova, K., Y.B. Lee, B.K. Slater, and J.M. Bigham. 2005. Gypsum for agricultural use in Ohio–sources and quality of available products. The Ohio State University Extension, Columbus, OH. Available at http://ohioline.osu.edu/anr-fact/pdf/0020.pdf (verified 10 Oct. 2006).
- Farina, M.P.W., and P. Channon. 1988. Acid-subsoil amelioration: II. Gypsum effects on growth and subsoil chemical properties. Soil Sci. Soc. Am. J. 52:175–180.[Abstract/Free Full Text]
- Gardner, W.H. 1986. Water content. p. 493–544. In A. Klute (ed.) Methods of soil analysis. Physical and mineralogical methods. Part 1, 2nd ed. Agronomy 9. ASA, Madison, WI.
- Hao, Y., and W.A. Dick. 2000. Potential inhibition of acid formation in pyritic environments using calcium sulfite byproduct. Environ. Sci. Technol. 34:2288–2292.[CrossRef]
- Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled variable rate leaching device. Soil Sci. Soc. Am. J. 41:1207–1208.[Abstract/Free Full Text]
- Kilmer, V.J., and L.T. Alexander. 1949. Methods of making mechanical analyses of soils. Soil Sci. 68:15–24.
- Kost, D.A., J.M. Bigham, R.C. Stehouwer, J.H. Beeghly, R. Fowler, S.J. Traina, W.E. Wolfe, and W.A. Dick. 2005. Chemical and physical properties of dry flue gas desulfurization products. J. Environ. Qual. 34:676–686.[Abstract/Free Full Text]
- Laperche, V., and J.M. Bigham. 2002. Quantitative chemical and mineralogical characterization of flue gas desulfurization byproducts. J. Environ. Qual. 31:979–988.[Abstract/Free Full Text]
- Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. p. 539–579. In A.L. Page, R.H. Miller, and D.R. Keeney (ed.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agronomy 9. ASA, Madison, WI.
- Norton, L.D., I. Shainberg, and K.W. King. 1993. Utilization of gypsiferous amendments to reduce surface sealing in some humid soils of eastern USA. p. 77–92. In J.W.A. Poesen and M.A. Nearing (ed.) Soil surface sealing and crusting. Catena Supplement 24. Catena Verlag, Cremlingen-Destedt.
- Pavan, M.A., F.T. Bingham, and P.F. Pratt. 1982. Toxicity of aluminum to coffee in Ultisols and Oxisols amended with CaCO3, MgCO3, and CaSO4·2H2O. Soil Sci. Soc. Am. J. 46:1201–1207.[Abstract/Free Full Text]
- Peech, M., L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for soil fertility investigations. USDA Circ. No. 757. US Gov. Print. Office, Washington, DC.
- Ritchey, K.D., T.B. Kinraide, and R.R. Wendell. 1995. Interactions of calcium sulfite with soils and plants. Plant Soil 173:329–335.[CrossRef]
- Shainberg, I., M.E. Sumner, W.P. Miller, M.P.W. Farina, M.A. Pavan, and M.V. Fey. 1989. Use of gypsum on soils: A review. p. 1–111. In B.A. Stewart (ed.) Advances in soil science. Vol. 9. Springer-Verlag, NY.
- USEPA. 1993. Standards for the disposal of sewage sludge: Proposed rule 40 CFR parts 503. Fed. Regist. 58:9284–9415 USEPA, Washington, DC.
- USEPA. 1996. Method 3050B. Acid digestion of sediments, sludges, and soils. SW-846. USEPA, Washington, DC.
- Windholz, M. 1976. The merck index, 9th ed. Merck and Co., Rahway, NJ.
TOP
ABSTRACT
INTRODUCTION
