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Journal of Environmental Quality 32:1122-1129 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORTS
Waste Management

Sequestration of Phosphorus by Acid Mine Drainage Floc

Paul R. Adler and Philip L. Sibrell

National Center for Cool and Cold Water Aquaculture, USDA Agricultural Research Service, 11876 Leetown Rd., Kearneysville, WV 25430

Received 28 Apr. 2002. *Corresponding author (pra10{at}psu.edu)



   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Solubilization and transport of phosphorus (P) to the water environment is a critical environmental issue. Flocs resulting from neutralizing acid mine drainage (AMD) were tested as a possible low-cost amendment to reduce the loss of soluble P from agricultural fields and animal wastewater. Flocs were prepared by neutralizing natural and synthetic solutions of AMD with limestone, lime, ammonium hydroxide, and sodium hydroxide. Phosphorus sequestration was tested in three distinct environments: water, soil, and manure storage basins. In water, flocs prepared from AMD adsorbed 10 to 20 g P kg-1 dry floc in equilibrium with 1 mg L-1 soluble P. Similar results were observed for both Fe-based and Al-based synthetic flocs. A local soil sample adsorbed about 0.1 g P kg-1, about two orders of magnitude less. The AMD-derived flocs were mixed with a high-P soil at 5 to 80 g floc kg-1 soil, followed by water and acid (Mehlich-1) extractions. All flocs performed similarly. About 70% of the water-extractable P was sequestered by the floc when applied at a rate of 20 g floc kg-1 soil, whereas plant-available P only decreased by about 30%. Under anaerobic conditions simulating manure storage basins, all AMD flocs reduced soluble P by greater than 95% at a rate of 0.2 g floc g-1 rainbow trout (Oncorhynchus mykiss) manure. These findings indicate that AMD flocs could be an effective agent for preventing soluble P losses from soil and manure to the water environment, while at the same time decreasing the costs associated with AMD treatment.

Abbreviations: AMD, acid mine drainage • RTM, rainbow trout manure


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
EUTROPHICATION HAS been identified as the most common cause of water quality impairment in the USA (United States Geological Survey, 1999) and this process can be accelerated by phosphorus (Sharpley, 2000). As P releases from municipal and industrial sources have decreased through mandated water treatment and reduction of P in cleaning products, agricultural sources have increased in significance (Litke, 1999). Erosion control can significantly reduce runoff losses of particulate P; however, loss of dissolved P from overapplication of animal manure to soils can be significant even when erosion is controlled (Sharpley and Rekolainen, 1997). Overflow water from primary treatment units for animal manure can contain significant levels of P. Therefore, identifying and evaluating management practices to remove dissolved P from water and to reduce losses of soluble P from soils and manure storage basins are critical.

Excess P typically is removed from water in municipal wastewater systems by adding alum or ferric iron salts (Metcalf and Eddy, Inc., 1991). Depending on the water pH and alkalinity, P reacts directly with these compounds to form a precipitate, or adsorbs on the aluminum or iron hydroxide precipitate formed by hydrolysis. In either case, P is removed from solution with the solids. One drawback to the application of these water treatment chemicals for fixation of agricultural P loads is the cost. Recent pricing information shows the cost of these compounds to be $160 to $330 per metric ton, not including shipping, depending on physical form and location (Chemical Market Reporter, 2001). Citing low P removal efficiency with alum and related compounds, Kioussis et al. (1999) investigated using a synthetic polymer gel to remove P from aquaculture wastewater. The gel could reversibly remove P, and thus could be reused. However, the production cost of the gel was estimated to be from $10 to $40 per kg, which could be an economic barrier to implementation.

Soils with higher vs. lower P sorption capacity release less dissolved P to the water environment. The P sorption capacity of soils can be increased by adding Fe and Al oxides, and by Ca compounds such as limestone and gypsum. These compounds are the natural chemical components that account for the P sorption capacity of soils (Lindsay et al., 1989). Some researchers have proposed the addition of alum or other chemical amendments directly to animal manure to prevent release of excess P (Moore and Miller, 1994; Shreve et al., 1995). The cost of chemical amendments makes using waste materials an attractive option for reducing P runoff. Several investigators have looked at using regional waste materials as soil amendments to control P runoff. These included materials containing iron oxides, such as steelmaking slags and dusts (Lee et al., 1996) and residues from processing bauxite ores (Summers et al., 1996), and materials rich in aluminum oxides, such as coal combustion by-products (O'Reilly and Sims, 1995; Stout et al., 1998, 2000), and water treatment residuals (Haustein et al., 2000).

Before land application, animal manure is often stored in settling basins where it continues to mineralize and release P under anaerobic conditions. For rainbow trout production, off-line settling basins are used to settle and store solids that are vacuumed from raceways. The overflow water is discharged to surface water, carrying with it the mineralized P. A 50% reduction in the P content of rainbow trout manure (RTM) has been measured between RTM in the raceway and that in settling basins (Idaho Division of Environmental Quality, 1996). Reduction of leaching losses of dissolved P under anaerobic conditions in off-line settling basins could significantly decrease the discharge of P from aquaculture, since most P is contained in the solids (Heinen et al., 1996).

In some locations, solid wastes have been stabilized by adding calcium hydroxide or lime to limit mineralization and reduce pathogens. A rate of 0.2 g lime g-1 RTM is commonly recommended for lime stabilization of aquaculture manure (Bergheim and Cripps, 1998). Although the high pH causes loss of ammonia N, carbon and organic N and P are conserved because microbial mineralization of the organic matter is inhibited (Adler, 2000). Lime stabilization also has the benefit of reducing pathogens due to the elevated pH (Metcalf and Eddy, Inc., 1991). Although lime stabilization is effective, the use of regional waste products for P sequestration and stabilization could result in lower treatment costs and a significant reduction in the discharge of P from aquaculture and other facilities that store submerged solid wastes.

Acid mine drainage (AMD) flocs contain many of the same compounds effective in P removal as some of the previously described materials. Acid mine drainage is widespread in the Appalachian region due to decades of coal mining activities predating regulation of acid discharge. Acid mine drainage is generated when sulfide minerals such as pyrite are exposed to air and moisture. The sulfur is oxidized to sulfuric acid, which then solubilizes metals such as iron, manganese, and aluminum (Evangelou and Zhang, 1995). Chemical reactions involved in AMD formation are as follows:

[1]

[2]

[3]

[4]

These reactions are discussed in detail by Stumm and Morgan (1996). The abiotic oxidation of pyrite by air (Reaction 1) is slow; however, bacterial action can accelerate the rate of AMD formation by catalyzing the oxidation of iron from the ferrous to the ferric state (Reaction 2). The ferric iron acts as an alternative oxidation agent for the pyrite (Reaction 4) and is regenerated by bacterial action. The sulfur oxidation (Reactions 1 and 4) and iron hydrolysis (Reaction 3) both generate acidity. The resulting acidity and metal content is harmful to aquatic life and degrades stream quality until diluted to innocuous levels. The states of Pennsylvania and West Virginia alone have more than 7000 km of streams affected by AMD (USEPA, 1995). The most common methods used for AMD treatment include neutralization with limestone (CaCO3), lime [Ca(OH)2], sodium hydroxide (NaOH), or ammonia (NH3) (Skousen et al., 2000). When AMD is treated by neutralization with alkaline substances, a precipitate or floc is formed, consisting mainly of base metal hydroxides, sulfate salts, and unreacted alkaline material. Depending on the host rock composition, the AMD and resulting floc may have a high iron or aluminum content, or a mixture of the two, in addition to other base metals that may be present. The floc is usually pumped to a pond for settling, then removed and trucked to a landfill for disposal. Handling and disposal costs of the floc can be as much as one-half of the total operating cost for a treatment facility. Use of neutralized AMD flocs for P sequestration could contribute to the resolution of both the disposal of AMD floc and eutrophication problems.

The objective of this paper was to evaluate the use of flocs produced from neutralizing AMD with different chemicals for sorption of P in water, high-P soils, and anaerobic manure storage environments (e.g., off-line settling basins, lagoons, and clarifiers). Since the composition of the AMD floc may have a significant effect on its P sorption capacity, the effects of the neutralization reagent, the initial AMD solution composition, and the physical form of the floc on P uptake were tested. The effect of neutralization agent was tested by neutralizing AMD with limestone, sodium hydroxide, lime, and ammonia. Synthetic flocs were prepared by neutralizing solutions of pure iron or aluminum sulfate with limestone or sodium hydroxide to investigate the efficacy of Fe and Al compounds separately, since many AMD sources contain both metals. The effect of the physical state of the floc was tested by measuring P absorption of both wet and dry flocs.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Floc Preparation
Acid mine drainage was collected from the portal of an abandoned coal mine at the Friendship Hill National Historic Site, near Point Marion, PA. The AMD from this source typically has a pH of 2.8 and an acidity of more than 1000 mg L-1 as CaCO3. An 8000-L sample of AMD was collected at the site in April 1999 to be used for preparation of floc material. A subsample was analyzed by inductively coupled plasma (ICP) emission spectrometry (Department of Horticulture Nutrient and Elemental Analysis Laboratory, Cornell University, Ithaca, New York) and found to contain 145 mg L-1 Fe, 53 mg L-1 Al, and 226 mg L-1 Ca. This analysis also demonstrated the absence of toxic metals (each less than 0.5 mg L-1), including arsenic, cadmium, chromium, lead, and selenium. Equal volumes of AMD were neutralized with limestone, lime, sodium hydroxide, or ammonium hydroxide. Limestone is not normally effective for AMD neutralization at elevated metal levels due to the formation of armor coatings that decrease the reactivity of the limestone. Therefore, a proprietary process using pulsed fluidized limestone beds was used (Sibrell et al., 2000). The AMD was neutralized to pH 7 and mixed for 24 h, and then the suspended floc was allowed to settle. The clarified water was decanted and the floc collected and air-dried in plastic-lined troughs. A final drying step at 105°C was used to drive off excess moisture. The dried floc formed clumps, which were broken up by grinding until all particles passed a 1-mm screen. The Al, Fe, and Ca content of the flocs was determined by ICP analysis following digestion using USEPA Method 3050B (USEPA, 1986). Surface areas of selected floc and soil samples were determined by a nitrogen adsorption BET (Brunauer–Emmett–Teller) analysis. These analyses were performed by the Materials Characterization Laboratory, The Pennsylvania State University, University Park, PA.

Since iron or aluminum may or may not be equally effective at removing P under some conditions, the individual contributions of each of these elements were tested by preparing synthetic AMD flocs derived from pure iron or aluminum solutions. Synthetic metal hydroxides were prepared by neutralizing pure solutions of aluminum sulfate [Al2(SO4)3·14H2O] and ferric sulfate [Fe2(SO4)3·5H2O] with sodium hydroxide or limestone. The solids were filtered from solution, washed to remove soluble salts, dried at 105°C, and ground to pass a 1-mm screen. The composition of the synthetic flocs was determined as described earlier.

It has been shown that the crystallinity of amorphous Fe(III) flocs increases as a function of time, and proceeds much more rapidly at elevated temperatures (Flynn, 1984). Therefore, the effect of drying of the AMD floc was checked by testing P sorption using a sample of filtered floc that was not dried. A control sample of the same floc was dried for comparison of P removal efficiency.

Water Sorption Tests
Since P removal by alum or ferric salts is a standard operation for wastewater treatment, aluminum and ferric sulfate were tested as a baseline from which to measure the effectiveness of other materials. Also, calcium carbonate and calcium sulfate are present in AMD flocs, and may have some P uptake capacity; therefore, their effect was quantified before proceeding directly to floc testing.

Phosphorus adsorption capacity of AMD flocs was determined by mixing 0.5 g of dried floc with 25 mL of solution containing from 250 to 4000 mg L-1 P (added as KH2PO4) using a reciprocating shaker. Floc P sorption capacity was determined by the procedure of Nair et al. (1984). After 24 h, the floc suspensions were centrifuged (3570 x g for 15 min) and filtered (0.45 µm) and the solution P concentration determined (Murphy and Riley, 1962). The amount of P sorbed was calculated by the difference between P added and P remaining in solution. For purposes of comparison, similar P sorption tests were conducted for a local soil, a Hagerstown loam (residuum from limestone; fine, mixed, semiactive, mesic Typic Hapludalf) from Jefferson County in West Virginia.

Regression coefficients were obtained for each replicate with SAS using PROC GLM (SAS Institute, 1999). Means for the slope and intercept of the regression equations of P adsorbed over a range of P in solution for the different types of flocs were separated by Bonferroni LSD (P <= 0.05).

Soil Amendment Tests
The effectiveness of AMD floc as a soil amendment was also tested. The AMD floc was mixed with a high P-containing (1318 ± 135 mg P kg-1 soil) Sassafras sand (fine-loamy, siliceous, semiactive, mesic Typic Hapludult) from a feedlot on the Eastern Shore of Maryland in Caroline County. Six amendment rates of the AMD floc (0, 5, 10, 20, 40, and 80 g kg soil-1) were mixed with three 250-g replicate soil samples in sealed polyethylene bags. The water content was brought to 0.1 MPa and treatments were incubated at ambient temperature (about 26°C) for 1, 7, or 21 d. After incubation, duplicate samples were taken for analysis and stored frozen (-20°C) for P analysis. Water-extractable and Mehlich 1–extractable P analyses were performed on the soil samples. Mehlich-1 P (Kuo, 1996) was determined by shaking 5 g soil with 20 mL of 0.05 M HCl and 0.0125 M H2SO4 for 5 min in 50-mL graduated conical-bottom polypropylene centrifuge tubes on an end-over-end shaker. Water-extractable P was determined by shaking 1 g soil with 25 mL of double deionized water for 1 h (Pote et al., 1996).

Manure Amendment Tests
The capacity of AMD flocs to sequester P in an anaerobic environment was also tested, to simulate the environment of RTM stored in off-line settling basins. Rainbow trout manure was collected and settled, and a subsample was dried at 105°C to determine the moisture content. A 1-g dry weight basis sample of RTM was placed in 50-mL graduated conical-bottom polypropylene centrifuge tubes and total water content brought to 25 mL. Three rates of floc were added (0.05, 0.20, or 0.5 g) and then the tubes were shaken on an end-over-end shaker for 1 h. After a 30-d incubation, samples were shaken for 1 h, and then centrifuged (3570 x g for 15 min). A subsample of supernatant was analyzed for pH and dissolved reactive P.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Water Sorption Tests
Initial P removal tests were conducted using alum, ferric sulfate, calcium carbonate, and calcium sulfate. The efficacy of alum and ferric sulfate was confirmed in our tests. For alum [Al2(SO4)3·14H2O] and ferric sulfate [Fe2(SO4)3·5H2O], when the molar ratio of Al or Fe to P was >1, P removal was >99%. However, once the molar ratio fell below one, some P remained in solution. A typical dosage ratio of 2.1 to 2.6 Al to P is recommended for 95% removal of P in the industry (Metcalf and Eddy, Inc., 1991), probably because industrial waste waters contain P in many different forms that may be less amenable to removal than the orthophosphate salts tested here. Calcium carbonate removed as much as 73% of the soluble P at a molar Ca to P ratio of 13.3, but was less effective than alum or ferric sulfate when the ratio of Ca to P decreased. The capacity of calcium sulfate was even more limited, removing no more than 30% of the soluble P even at a molar Ca to P ratio of 15.1.

Table 1 shows the composition of AMD-derived and synthetic flocs. For the flocs made from AMD, the Fe (CV = 11.6%) and Al (CV = 5.2%) contents were roughly similar. Calcium content was elevated for those flocs prepared by neutralization with limestone or lime, as would be expected. In contrast to the AMD-derived flocs, synthetic flocs contained either Fe or Al, but not both. The synthetic flocs prepared by neutralization with sodium hydroxide showed greater Fe or Al content than the corresponding synthetic flocs prepared using limestone, indicating the dilution effect of the insoluble calcium compounds in the limestone flocs. Elemental analysis of the Hagerstown loam (Ciolkosz et al., 1993) is included in Table 1 for comparison, and shows much lower Fe and Al contents.

Surface areas of selected flocs and soils are also shown in Table 1. All of the flocs had much greater specific surface areas than the Hagerstown loam. Flocs produced by the neutralization of Fe and Al solutions are known to be amorphous to poorly crystalline (Nordstrom and Alpers, 1999), which leads to the high surface areas observed. The link between P sorption and amorphous Fe and Al content in a soil is well known. Brady et al. (1986) found that precipitates from acid mine drainage sites were almost totally soluble in acid ammonium oxalate, indicating that most of the Fe and Al oxides in AMD flocs are amorphous. In contrast, Ciolkosz et al. (1989) found that less than 3% of the Hagerstown soil was ammonium oxalate extractable.

The P uptake of the AMD flocs was plotted in the form of a Freundlich plot, with log of adsorbed P as a function of log of P remaining in solution (Fig. 1) . The linearity of the plots was consistent with an adsorption mechanism rather than chemical precipitation. The intercept of the fitted line to the Freundlich isotherm is a measure of the adsorption capacity of the solid (Weber, 1972). Since the equilibrium solution concentration was plotted in terms of mg L-1, the intercept is the P sorption capacity of the solids in equilibrium with 1 mg P L-1. The adsorption capacities of the AMD flocs ranged from 10 to 20 g P kg-1 floc. The Hagerstown loam gave an adsorption capacity of 0.07 g kg-1, about two orders of magnitude less than the floc samples. Other investigators have reported similar values for soil samples. For example, Nair et al. (1984) analyzed 12 different soil samples for P sorption, and reported maximum adsorptions of 0.05 to 0.25 g kg-1. Mozaffari and Sims (1994) reported maximum sorption capacities of 0.1 to 2.6 g kg-1 for several mid-Atlantic soils. The high Fe and Al content linked with the high surface area and amorphous nature of the flocs make them capable of much greater P sorption capacity compared with typical soil samples. Linear regression coefficients for the adsorption plots are given in Table 2. Statistical analysis of the regression coefficients revealed that the fitted P sorption lines were significantly different for each of the AMD-derived flocs. Although the compositions of the flocs were all very similar, surface areas were different (Table 1). In general, higher areas corresponded with higher P sorption. This indicates that both composition and surface area affect P sorption.



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  		Fig. 1. Phosphorus sorption isotherms for acid mine drainage (AMD) flocs.

 
Regression coefficients for P sorption by the synthetic flocs are shown in Table 2. The adsorption capacities of the synthetic flocs were very similar to the AMD flocs. Synthetic flocs prepared by neutralization with sodium hydroxide adsorbed greater amounts of P than those made using calcium carbonate. The higher adsorption capacity of sodium hydroxide flocs may be related to the higher Al and Fe content of those materials (Table 1), although surface area effects (not measured for the synthetic flocs) may be important as well. The calcium carbonate flocs had significant amounts of calcium sulfate and unreacted calcium carbonate, which were shown to have less affinity for P under the conditions tested. This was not the case for the sodium hydroxide flocs, where the unused reactant and reaction byproducts were soluble, and were washed out of the flocs during filtration. Iron- and aluminum-based flocs performed similarly under the conditions tested, demonstrating that both compounds were equally effective at sorbing P.

The effect of the physical state of the floc on P uptake was tested by comparing floc in the wet versus oven-dried forms. Regression coefficients for these materials are given in Table 2. Both flocs were generated by neutralizing AMD with CaCO3; however, one portion of the floc was dried. The adsorption capacities of the wet floc were about double that of the dry floc. Since both samples were derived from the same source, this increased capacity must be related to the more amorphous structure of the wet floc. As stated earlier, crystallization of the amorphous precipitates in the floc is accelerated at elevated temperatures. However, it is also possible that other factors in the drying process, such as caking, may have affected the floc particles. These results show that flocs can be used to sequester P in either the wet or dry state. The moisture state of the flocs at the point of use will depend on economics and facilities present at both the sites of generation and utilization.

Soil Amendment Tests
The AMD-derived flocs were tested as a soil amendment for a high-P soil. The unamended soil had an initial water-extractable P level of about 110 mg kg-1, which increased over time, as organic P mineralized, to 180 mg kg-1. All of the flocs reduced water-extractable P in the soil, even with additions as low as 5 g floc per kg soil (Fig. 2) . In contrast to the earlier floc absorption tests, the differences in P absorption capacity for each of the flocs were not great. Little change was observed between 1, 7, and 21 d, indicating that most of the reduction occurred within the first 24 h after addition. About 70% of the water-extractable or environmentally available P was sequestered at a rate of 20 g floc kg-1 soil. This is in contrast to about a 30% reduction in acid-extractable (Mehlich-1) P (Fig. 3) . Therefore, these waste byproduct amendments could be used to mitigate high source P soils immediately, to reduce the short-term runoff P losses while allowing for plant removal to reduce soil P levels over the long term.



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  		Fig. 2. Effect of acid mine drainage (AMD) floc amendments on water-extractable P from a high-P Sassafras sand. Flocs produced by neutralizing AMD with different compounds shown separately. Vertical bars denote ± SD.

 


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  		Fig. 3. Effect of acid mine drainage (AMD) floc amendments on Mehlich 1–extractable P from a high-P Sassafras sand. Flocs produced by neutralizing AMD with different compounds shown separately. Vertical bars denote ± SD.

 
Manure Amendment Tests
Figure 4 shows the effect of AMD floc amendments on the release of P from RTM under anaerobic conditions. Lime stabilization was also tested for comparison. All AMD floc amendments reduced P from 90 mg L-1 to less than 2 mg L-1 at a rate of 0.2 g floc g-1 RTM (Fig. 4). At the lower amendment rate of 0.05 g g-1 RTM, differences were found between treatments. Statistical analysis of the data at this treatment level (means separated by Bonferroni LSD, P <= 0.05) showed that the Ca(OH)2 and CaCO3 flocs removed a significantly greater amount of P than the NaOH floc. No other differences were significant, indicating that each of the AMD flocs were statistically indistinguishable from lime. Synthetic flocs derived from iron- and aluminum-based solutions were also tested as manure amendments. Since iron-based compounds are known to be sensitive to the oxidation–reduction potential in their environment (Moore and Reddy, 1994), it was expected that the flocs prepared from ferric sulfate might be less effective at P sorption than aluminum-based flocs. However, the iron compounds were actually more effective at P sorption than the aluminum compounds (data not shown). It may be that conditions were not reducing enough to affect the iron compounds. The redox potential (Eh) of the samples ranged from 0 to 250 mV (after correction of the potential of the reference electrode) at a pH of 4 to 6. This is considered to be in a transitional zone between oxidized and anaerobic waters (Garrels and Christ, 1965), which may account for the lack of difference in adsorption between Al and Fe compounds. However, those same redox conditions may be present in off-line settling basins.



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  		Fig. 4. Sorption of phosphorus mineralized from rainbow trout manure (RTM) under anaerobic conditions by acid mine drainage (AMD) flocs and Ca(OH)2. Vertical bars denote ± SD.

 
These results demonstrate that AMD flocs effectively prevented release of P from manures under submerged storage conditions. Blending the flocs with alkaline waste products could add the other benefits of lime stabilization, such as pathogen destruction and organic matter stabilization. Byproducts such as cement kiln dust, lime kiln dust, or coal combustion ash have been blended with biosolids for this purpose (Wright et al., 1998). The combination of AMD flocs for P removal and alkaline byproducts for pathogen destruction could result in a lower-cost alternative to commercial lime stabilization processes now in use.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Flocs derived from neutralizing AMD were tested for P removal from water and soil under aerobic and anaerobic conditions. These flocs are a waste product of AMD neutralization and are widely available in certain regions of the USA. Under aerobic conditions in water, the flocs were found to have adsorption densities two orders of magnitude higher than typical soils. Similar absorption densities were noted for synthetic flocs derived by neutralizing solutions of Fe and Al, indicating that both metals formed flocs that effectively removed P. The flocs were then tested as an amendment to a high-P soil. At an amendment rate of 20 g kg-1 soil, the flocs decreased water-soluble P by more than 70%. Plant-available P, as measured by the Mehlich-1 method, was decreased by a lesser degree, by about 30%. Although flocs prepared from AMD using different neutralization reagents showed some differences in the water adsorption tests, the differences in the soil environment were minor to insignificant. In the anaerobic water environment, the flocs were as equally effective as lime stabilization for the sequestration of P from RTM. These findings indicate that AMD-derived flocs could be effectively used for P sequestration in soils and in water, thus preventing loss of P to the environment, while at the same time, decreasing the cost of AMD treatment.


   ACKNOWLEDGMENTS
 
We thank Bill Blake, Dan Heatherly, Holly Lohman, and Renee Yost for their technical assistance in chemical analysis of samples. Samples of AMD were obtained at the Friendship Hill National Historic Site with the assistance of Mark Grant and Connie Ranson.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Current address USDA-ARS, Building 3702, Curtin Road, University Park, PA 16802-3702. P.L. Sibrell, U.S. Geological Survey, Leetown Science Center, 11700 Leetown Rd., Kearneysville, WV 25430.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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JEQ 2003 32: 745-750. [Full Text]  




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