Flue Gas Desulfurization By-products Research Articles

97/03288 Macroscopic to microscopic studies of flue gas desulfurization byproducts for acid mine drainage mitigation

The use of flue gas desulfurization (FGD) systems to reduce SO{sub 2} emissions has resulted in the generation of large quantities of byproducts. These and other byproducts are being stockpiled at the very time that alkaline materials having high neutralization potential are needed to mitigate acid mine drainage (AMD). FGD byproducts are highly alkaline materials composed primarily of unreacted sorbents (lime or limestone and sulfates and sulfites of Ca). The American Coal Ash Association estimated that approximately 20 million tons of FGD material were generated by electric power utilities equipped with wet lime-limestone PGD systems in 1993. Less than 5% of this material has been put to beneficial use for agricultural soil amendments and for the production of wallboard and cement. Four USGS projects are examining FGD byproduct use to address these concerns. These projects involve (1) calculating the volume of flue gas desulfurization (FGD) byproduct generation and their geographic locations in relation to AMD, (2) determining byproduct chemistry and mineralogy, (3) evaluating hydrology and geochemistry of atmospheric fluidized bed combustion byproduct as soil amendment in Ohio, and (4) analyzing microbial degradation of gypsum in anoxic limestone drains in West Virginia.

Growth of forages on acid soil amended with flue gas desulfurization by-products

To assess beneficial or detrimental plant growth effects when flue gas desulfurization by-products (FGD-BPs) are applied to acid soil, experiments were conducted in a greenhouse to determine growth of forages (orchardgrass, tall fescue, switchgrass, eastern gamagrass, white clover and alfalfa) on an acid pH 4.6 soil with different levels of three FGD-BPs and chemical-grade calcium carbonate (limestone), calcium sulfate and calcium sulfite. The FGD-BPs tested were high-CaSO 4, high-CaSO 4 enriched with Mg, and high-CaSO 3. Maximum total plant dry matter (DM) was obtained when ∼25% of high-CaSO 4 FGD-BP or ∼2.5% of high-CaSO 4 FGD-BP + Mg was incorporated into soil mixes; DM decreased at higher levels of addition. High-CaSO 3 FGD-BP benefited growth of all species when added at levels up to ∼3.0% in soil mixes. Beneficial plant responses were higher for the high-CaSO 4 FGD-BPs than for the high-CaSO 3 FGD-BP. Maximum beneficial plant responses for limestone were at ∼0.25–0.50% and for CaSO 4 at 50–75% in soil mixes, which were comparable with the high-CaSO 4 FGD-BP and high-CaSO 4 FGD-BP + Mg responses. Chemical-grade CaSO 3 gave no beneficial growth effects on any of the plant species. The FGD-BPs used in this study benefited forage growth when added at appropriate levels.

Use of clean coal combustion by-products in highway repairs

A dry flue gas desulfurization (FGD) by-product was used to reconstruct the failed portion of a highway embankment. A wall was constructed through the failure plane to stop further slippage. To evaluate the suitability of FGD by-products in this type of project, the site of the repair was divided into three test sections. In the first section, the soil removed from the slide area was recompacted and replaced according to standard construction practices. In the second section, the embankment consisted of a field-compacted mixture of soil and FGD ash in approximately equal proportions. The third section was constructed of compacted FGD by-product. All three test sections were capped by a layer of compacted boiler ash or crushed stone to provide a temporary wearing surface. Measurements of slope movement as well as water quality and levels are being made at the site to evaluate long-term embankment performance. The completion of this experiment should lead to increased acceptance of FGD by-products in construction projects. Monetary savings will be realized in avoiding some of the disposal costs for the material, as well as in the reduced reliance on alternative engineering materials.

Amendment of Acidic Coal Refuse with Yard Trimmings Compost and Alkaline Materials: Effects on Leachate Quality and Plant Growth

Establishment of vegetative cover on coal refuse stabilizes the pile surface and reduces off site deposition of acidic sediments and drainage water. Direct revegetation through the use of by-product amendments would eliminate the need for topsoil cover and provide a beneficial use for by-product materials. This 8 month greenhouse study investigated yard trimmings compost, flue gas desulfurization (FGD) by-product, and agricultural limestone (ag-lime) amendments for direct revegetation of hyper-acidic coal refuse and their effects on leachate and plant quality. Pots (30 cm tall × 15 cm diam) of coal refuse were amended with five rates of compost (0 to 200 g kg−1), with and without sufficient agricultural limestone (ag-lime) to raise refuse pH to 7, and planted with orchardgrass (Dactylis glomerata). Compost increased leachate pH from <2 to 4.4, decreased specific conductance from >17 to <5 mmho cm−1 (due to large decreases in Al, Fe, and S), and decreased leachate concentrations of several trace elements. The pH increase from ag-lime greatly reduced leachate Al, Fe, and S and largely masked any effects of compost addition. Because no plant growth occurred with compost only, after 2 months FGD (200 g kg−1) was added to the upper 1/3 depth of compost-amended coal refuse. The FGD increased refuse pH to the range 4.2 (no compost) to 5.7 (200 g kg−1 compost), decreased leachate Al and Fe, increased leachate B, and allowed vigorous growth of orchardgrass. When combined with FGD, compost increased downward movement of Ca and Mg. Although compost addition decreased plant growth at the first harvest due to N immobilization, application of mineral N fertilizer alleviated this problem in subsequent harvests. Compost did not increase orchardgrass growth when combined with ag-lime. With FGD, however, compost increased orchardgrass growth to levels above that for ag-lime and compost, in spite of increased plant tissue B.

97/01942 Transport and plant uptake of soil-applied dry flue gas desulfurization by-products

97/01942 Transport and plant uptake of soil-applied dry flue gas desulfurization by-products

High‐Calcium Flue Gas Desulfurization Products Reduce Aluminum Toxicity in an Appalachian Soil

An acid Appalachian soil was amended with two flue gas desulfurization (FGD) by-products, one consisting of wallboard-quality gypsum (CaSO4·2H2O) and the other containing CaSO3·0.5H2O as a major component. Soil columns treated with FGD by-products were leached with deionized H2O under unsaturated conditions. Aluminum amounts leached increased 25-fold over the control when CaSO4·2H2O FGD by-product was incorporated into the soil. Leachate pH decreased with FGD product treatment, but bulk soil pH increased, and exchangeable Al and total soil acidity decreased. Mean 4-d root lengths of sudangrass (Sorghum bicolor L. Moench) seedlings grown in the leached soils were as much as 440 and 310% the value of the control for CaSO3·0.5H2O and CaSO4·2H2O treatments, respectively. Mechanisms by which mitigation of Al toxicity occurs with addition of high-Ca FGD by-products to acid soils are discussed.

TRANSPORT AND PLANT UPTAKE OF SOIL-APPLIED DRY FLUE GAS DESULFURIZATION BY-PRODUCTS

Clean air legislation has resulted in increased production of flue gas desulfurization (FGD) by-products by coal-fired boilers. Use of FGD by-products as substitutes for agricultural limestone represents a potential beneficial use alternative to landfill disposal of these materials. To determine the efficacy and potential for environmental impact of such use, an 8-month greenhouse study was conducted in which three dry FGD by-products were mixed with Wooster silt loam at rates of 0, 3.5, 7, 14, and 28 g kg−1. Separate pots were planted with alfalfa (Medicago sativa, L) and tall fescue (Festuca arundinacea, Schreb). Following a 3-month growth period, plants were harvested monthly for a total of six harvests. Pots were leached at the beginning and end of the experiment. All three FGD by-products increased soil pH from 4.5 to approximately 7.5. Leachate concentrations of Ca, Mg, and S were increased by FGD, indicating a potential for transport of these solutes to subjacent soil. Leachate Mn and Zn concentrations were decreased by FGD amendment of alfalfa, and leachate Al was decreased with both crops. Leachate trace element concentrations were not increased by FGD with the exceptions of B and Cu. Alfalfa yield was increased by FGD, although the largest amendments suppressed yields of the first two harvests. Fescue yield was also increased by FGD amendment although the response was less than with alfalfa. Plant tissue contents of Ca, Mg, and S were increased by FGD. There were no increases in tissue concentrations of any trace elements except B and Mo. Dry FGD by-products appear to be effective substitutes for agricultural limestone with little potential for adverse environmental impacts.

Chemical properties of acid soil treated with coal combustion by‐products and leached

Abstract Application of coal combustion by‐products (CCBs) to acid soils can have beneficial or detrimental effects. A column study was conducted to determine the effects of CCBs on mitigating acid soil properties after leaching with 138 cm deionized water. Columns containing 105 cm acidic Lily soil (Typic Hapludult) had mixed in the top 15 cm the following treatments (g/kg soil): no CCB or limestone (check); dolomitic limestone (lime) at 3.98; high‐calcium sulfate (CaSO4) flue gas desulfurization (FGD) by‐product (BP) at 15.88; combination of lime+FGD at rates given; high‐CaSO4 FGD BP enriched with Mg (FGD+Mg) at 15.88; and fluidized bed combustion (FBC) BP at 6.45. After being leached for 39 days, the columns of acid soil treated with high‐CaSO4 by‐products showed higher subsurface pH, calcium (Ca), and sulfur (S) and lower aluminum (AI) and manganese (Mn). In contrast, the lime alone treatment had little effect on subsurface soil properties. Use of dolomitic limestone to supply magnesium (Mg) in conjunction with the CaSO4 treatments was more effective than supplementation with Mg(OH)2, where97% of the added Mg leached from the top layer. Substances leached from the CCBs studied were effective in reducing problems associated with subsurface soil acidity.

Growth, Photosynthesis, and Water Relations of Wheat Grown on Acid Soil Amended with Coal Combustion By‐Products

Aluminum toxicity often reduces plant growth on acid soils, and coal combustion by‐product (CCBPs) can partially mitigate acid soil effects. Columns containing acidic (pH 4.7) Lily soil (Typic Hapludult) were amended in the upper 15 cm with CCBPs, lime, or both. Amendments were, in grams per kilogram, (i) none (Check); (ii) 3.98 dolomitic limestone (Lime); (iii) 15.88 high‐gypsum flue gas desulfurization by product (FGD); (iv) 3.98 + 15.88 combination of Lime + FGD; (v) 15.88 high‐gypsum FGD by‐product containing −6% Mg(OH)2 (FGD + Mg); and (vi) 6.45 fluidized bed combustion by‐product (FBC). The soil columns were leached with 138 cm of deionized water. Wheat (Triticum aestivum L., ‘Arthur’) was grown in the columns for 34 d with no additional water. Plants grown in Check and FGD treatments had lowest and similar shoot and root dry matter (DM) and leaf area. Leaf areas and DM for FBC, FGD + Mg, Lime, and Lime + FGD plants were similar and 13 to 17 times higher than for Check plants. Total root length (RL) was highest for FBC plants, which was about six‐fold higher than FGD plants, while total RL of plants grown with other amendments was about half that of FBC plants. Specific RL was highest for FGD plants. Plants grown on Lime, Lime + FGD, FGD + Mg, and FBC treatments had higher leaf photosynthetic rates, chlorophyll, and ET and lower leaf temperatures than Check and FGD plants. Even though DM of FGD plants was low, they had the highest leaf relative water content (RWC) and leaf water potential (LWP). Amendments increased soil pH and reduced acid soil stress. Higher mineral nutrient concentrations were noted in shoots of plants grown on amended soil, except for the FGD plants, which had lower Mg and higher B than considered optimal. Some but not all CCBPs benefitted plants grown on acid soil.

96/03301 - Plant growth and soil properties responses to additions of dry flue gas desulfurization byproducts

96/03301 - Plant growth and soil properties responses to additions of dry flue gas desulfurization byproducts

Flue gas desulfurization gypsum improves orchardgrass root density and water extraction in an acid subsoil

In Appalachia, many soils are acidic, high in exchangeable aluminium, and low in calcium. Large amounts of high gypsum flue gas desulfurization (FGD) by-products are currently disposed of into landfills, although they have potential value as a soil amendment for the region. This study was conducted to determine if leaching an acid subsoil with a saturated solution of a FGD by-product can improve the subsoil as a rooting media for orchardgrass (Dactylis glomerata L.) which is widely used for pasture in the region. Orchardgrass was grown in soil from a pHc 3.8 (in 0.01 M CaCl2) Lily loam Bt horizon (fine loamy siliceous, mesic, Typic Hapludult) leached with two different rates of a saturated FGD by-product aqueous solution, as well as in soil that was limed, and an unamended soil. Water use by a clipped and partially enclosed vegetative canopy was measured in a growth chamber during two drying cycles. Small but consistent increases in water use were correlated with decreases in aluminium saturation of the soil. The effect was greatest during the second drying cycle. Increases in root biomass were also correlated with decreases in aluminium saturation. The effect of treatment on the pattern of water use altered after the first drying cycle when water uptake became most restricted in the unamended treatment. The manganese content of leaf tissue increased from 208 mg kg-1 to 570 mg kg-1 between the unaltered and highest leaching rate treatment. The highest level was still below the 2000 mg kg-1 that is considered toxic to grazing animals. These results suggest that the application of high gypsum FGD by-products to pastures in Appalachia has the potential to improve root growth and functioning in subsoil horizons, but some care may be needed to monitor forage quality.

Dry Flue Gas Desulfurization Byproducts as Amendments for Reclamation of Acid Mine Spoil

Dry Flue Gas Desulfurization Byproducts as Amendments for Reclamation of Acid Mine Spoil

Dry Flue Gas Desulfurization Byproducts as Amendments for Acid Agricultural Soils

Dry Flue Gas Desulfurization Byproducts as Amendments for Acid Agricultural Soils

Mine Spoil Reclamation with Sewage Sludge Stabilized with Cement Kiln Dust and Flue Gas Desulfurization Byproduct (N-Viro Soil Process)

Mine Spoil Reclamation with Sewage Sludge Stabilized with Cement Kiln Dust and Flue Gas Desulfurization Byproduct (N-Viro Soil Process)

Mine Spoil Reclamation with Sewage Sludge Stabilized with Cement Kiln Dust and Flue Gas Desulfurization Byproduct (N-Viro Soil Process)

Mine Spoil Reclamation with Sewage Sludge Stabilized with Cement Kiln Dust and Flue Gas Desulfurization Byproduct (N-Viro Soil Process)