No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Flue Gas Desulfurization By-Product Weathering by Acidic Mine Drainage
Abstract
The authors examined the suitability using a flue gas desulfurization grout (FGDG) for the attenuation and abatement of acidic mine drainage (AMD). The FGDG used was a mixture of fly ash (FA) and filter cake (FC) with a FA/FC ratio of 1:1 to improve handling. Five percent of lime (CaO) was added to improve strength development and allow the use of this FGDG as a hydrologic seal for underground mines. Acidic mine drainage solutions collect from wells located within mine voids were reacted with samples of FGDG for up to 168 d, to evaluate the potential for grout dissolution subsequent to subterranean implacement. Shortly upon reaction with AMD, FGDG released a number of ions into solution (As, B, Ca, K, Na, Se, SOâ), a concomitant with a rapid increase in solution pH (8.5), causing decreases in the solubility of most cations (Al, Fe, Mn, Zn). Significant increases in dissolved As and B concentrations were noted. Both elements were present in solution at levels below respective regulatory limits for drinking water. Of the original quantities of As and B present in FGDG, 1.3 and 45.6%, respectively, were released to solution over a 168-d reaction period. Concomitant with changes in solution composition, reaction of FGDG with AMD resulted in a loss of ettringite and hannebachgite and a growth of gypsum. Additional changes in mineralogy were observed as FGDG equilibrated with AMD solutions. From these reactions, the long-term stability of FGDG in underground acidic mine environments is questionable and warrants study in situ.
... But the release of major (Ca and S) and trace elements (As, B, Cd, Cu, Ni, Pb, and Se) in neutral or acidic aqueous environments was also found (Stehouwer et al., 1995;Lamminen et al., 2001). For example, the dissolution of mineral components, especially ettringite (Myneni et al., 1997;Laperche and Traina, 1999), can release immobilized contaminants and affect the structural integrity of fixated FGD material (Laperche and Traina, 1999). ...
... But the release of major (Ca and S) and trace elements (As, B, Cd, Cu, Ni, Pb, and Se) in neutral or acidic aqueous environments was also found (Stehouwer et al., 1995;Lamminen et al., 2001). For example, the dissolution of mineral components, especially ettringite (Myneni et al., 1997;Laperche and Traina, 1999), can release immobilized contaminants and affect the structural integrity of fixated FGD material (Laperche and Traina, 1999). ...
... Understanding the leaching characteristics of fixated FGD material is, therefore, important with respect to the use, as well as disposal of this material. While numerous studies have examined the leaching of fly ash, comparatively much fewer studies have studied the leaching properties of FGD material (Zhou and Dayal, 1990;Ibanez et al., 1998;Laperche and Traina, 1999;Kost et al., 2005). In most of these studies, leaching experiments were performed at equilibrium or near-equilibrium conditions. ...
A flow-through-rotating-disk system was applied to study the pH effect on the leaching kinetics of fixated FGD material. The objectives of this study were (1) to determine if the leaching kinetics are surface- or transport-controlled, (2) to elucidate the role of pH in controlling the leaching kinetics, and (3) to propose pH-dependent leaching models for specific elements. The independence of leaching rates of selected elements on various hydrodynamic conditions indicated a surface-controlled reaction mechanism. The leaching rates of major and minor elements including Ca, S, Al, Si, Mg, and Fe all increased with decreasing pH. Leaching rates of divalent and trivalent cations at acidic leaching conditions increased 3.2 and 5.2 times, respectively, as pH decreased 1 unit.
... But the release of major (Ca and S) and trace elements (As, B, Cd, Cu, Ni, Pb, and Se) in neutral or acidic aqueous environments was also found (Stehouwer et al., 1995;Lamminen et al., 2001). For example, the dissolution of mineral components, especially ettringite (Myneni et al., 1997;Laperche and Traina, 1999), can release immobilized contaminants and affect the structural integrity of fixated FGD material (Laperche and Traina, 1999). ...
... But the release of major (Ca and S) and trace elements (As, B, Cd, Cu, Ni, Pb, and Se) in neutral or acidic aqueous environments was also found (Stehouwer et al., 1995;Lamminen et al., 2001). For example, the dissolution of mineral components, especially ettringite (Myneni et al., 1997;Laperche and Traina, 1999), can release immobilized contaminants and affect the structural integrity of fixated FGD material (Laperche and Traina, 1999). ...
... Understanding the leaching characteristics of fixated FGD material is, therefore, important with respect to the use, as well as disposal of this material. While numerous studies have examined the leaching of fly ash, comparatively much fewer studies have studied the leaching properties of FGD material (Zhou and Dayal, 1990;Ibanez et al., 1998;Laperche and Traina, 1999;Kost et al., 2005). In most of these studies, leaching experiments were performed at equilibrium or near-equilibrium conditions. ...
A number of agricultural and engineering uses for fixated flue gas desulfurization (FGD) material exist; however, the potential for leaching of hazardous elements has limited widespread application and the processes controlling the leaching of this material are poorly understood. In this study, a flow-through rotating-disk system was applied to elucidate the relative importance of bulk diffusion, pore diffusion, and surface chemical reaction in controlling the leaching of fixated FGD material under pH conditions ranging from 2.2 to 6.8. Changing the hydrodynamics in the rotating disk system did not affect the leaching kinetics at both pH 2.2 and 6.8, indicating that bulk diffusion was not the kinetic-limiting step. Application of the shrinking core model (SCM) to the data suggested a surface reaction-controlled mechanism, rather than a pore diffusion mechanism. The leaching of fixated FGD material increased with decreasing pH, suggesting it can be described by a combination of an intrinsic hydration reaction and a proton-promoted dissolution reaction. X-ray diffraction (XRD) and elemental composition analyses before and after leaching suggests that for most elements a number of solid phases controlled the leaching process.
... A negative impact from the deterioration of FSS as a capping material would be the potential release of trace metals sequestered in the FSS. Previous studies have documented the occurrence of trace metals in the FSS components of FGD filter cake, fly ash and lime as well as the final product (Laperche & Traina, 1999;Cheng et al., 2007;Lee et al., 2007). And though trace element concentrations can vary significantly between FSS components (Sanchez et al., 2008), in most cases there are sufficient concentrations of constituents of potential concern (COPC) to warrant some apprehension regarding their use as a capping material in AML reclamation. ...
... The mineralogical changes observed at the top of the FSS where calcite and gypsum are more abundant while hannebachite and ettringite decrease coincides with the mineral transformation described in reaction 2 above along with the carbonation of ettringite (Laperche and Traina, 1999): ...
In 1996 an abandoned mine site containing a coal refuse pile, ash-filled highwall lake, and spoil was capped with fixated scrubber sludge (FSS) obtained from a nearby coal-fired power generation station. The FSS is a blend of flue-gas desulfurization sludge from an oxygen-inhibited scrubber unit, fly ash, and lime. Core samples of the FSS cap were collected and lysimeters were placed above and below the cap near monitoring wells screened in the refuse and ash fill. Mineral compositions of cores were determined, and samples of weathered and unweathered FSS were subjected to laboratory leaching experiments of 3-week duration. The experiments employed ultrapure water, synthetic regional groundwater, and synthetic acid mine drainage. Mineralogical analysis of core samples determined that the primary weathering indicators are increases in gypsum and calcite coinciding with decreases in hannebachite (CaSO 3 • 0.5H 2 O), the dominant sulfur-capture mineral phase generated in an oxygen-inhibited flue gas scrubber from which the bulk of the FSS is derived. Weathering appears to be minimal since the 1996 emplacement and confined to the top of the capping material. Laboratory studies demonstrate that weathered FSS leachate generated more sulfate, boron, molybdenum, and arsenic than unweathered FSS leachate, and less aluminum, barium, nickel, and selenium. Both synthetic solutions enhanced calcium, sulfate, nickel, and boron, and suppressed aluminum, arsenic, and selenium in leachate. Weathering characteristics observed for the FSS cap after 15 years suggest negligible water interaction based on comparisons of field data with laboratory leaching potential from continuous exposure to synthetic equivalents of locally present water.
... Understanding the leaching characteristics of fixated FGD material is therefore important with respect to the re-use and disposal of this material. However, most leaching studies of fixated FGD material have been performed in batch systems following regulatory leaching procedures (e.g., TCLP, SPLP) [11][12][13][14]. While these leaching tests have provided useful information about leachate quality with respect to regulatory standards, they provide little information about the mechanisms controlling leaching. ...
The presence of organic ligands, including oxalate, citrate, maleate and Pahokee peat humic acid (PPHA), influenced the leaching kinetics of fixated flue gas desulfurization (FGD) material in acidic solution (pH 2.9-5.0). In the presence of oxalate, the leaching was inhibited at all pH values examined. XRD and SEM analyses demonstrated that formation of a calcium oxalate mineral phase on the fixated FGD material surface created a surface layer which reduced the extent of leaching. Maleate and PPHA inhibited leach-ing at pH 2.9, but either promoted, inhibited, or had no effect on leaching, depending on the particular element, at pH 5.0. ATR-FTIR analysis indicated maleate and PPHA formed both inner-and outer-spherically bound species at pH 2.9, whereas at pH 5.0 only outer-sphere complexes seemed evident. These surface species likely inhibited the leaching process at pH 2.9 through a surface blocking mechanism. At pH 5.0, the ligand surface complexes either promoted or inhibited leaching, depending on the element, through a combination of direct and indirect mechanisms. Citrate significantly promoted the leaching process at all pH values examined.
... Although the elemental composition of the material was not determined upon delivery, extensive testing of stabilized FGD from the same source has been carried out previously [77,78] fly ash (FA) with a dry weight ratio of 1:1.5. Milli-Q water and an additional 6% quicklime were added to produce a final mixture with 30% moisture content. ...
This study combines field monitoring and laboratory experiments to investigate the environmental impacts associated with the re-use of coal combustion by-products (CCPs). The monitoring data obtained from two full-scale CCP applications (i.e., re-use of fixated flue gas desulfurization (FGD) material as a low permeability liner for a swine manure pond and portland cement concrete pavements containing CCPs) allowed environmental impacts to be evaluated under real or simulated in-service conditions. A complimentary laboratory leaching study elucidated fundamental physical and chemical mechanisms that determine the leaching kinetics of inorganic contaminants from CCPs. In the first field study, water quality impacts associated with the re-use of FGD material as a low permeability liner for a swine manure pond were examined by monitoring the water quality of water samples collected from the pond surface water and a sump collection system beneath the liner over a period of 5 years. Water samples collected from the sump and pond surface water met all Ohio non-toxic criteria, and in fact, generally met all national primary and secondary drinking water standards. Furthermore it was found that hazardous (i.e., As, B, Cr, Cu, and Zn) and agricultural pollutants (i.e., phosphate and ammonia) were effectively retained by the FGD liner system. The retention might be due to both sorption and precipitation. In the second field study, the release of metals and metalloids from full-scale portland cement concrete pavements containing CCPs was evaluated by laboratory leaching tests and accelerated loading of full-scale pavement sections under controlled loading and environmental conditions. Three types of portland-cement-concrete driving surfaces were tested, including a control section (i.e., ordinary portland cement (OPC) concrete) containing no fly ash and two sections in which fly ash was substituted for a fraction of the cement; i.e., 30% fly ash (FA30) and 50% fly ash (FA50). None of the leachate concentrations for fluids collected from laboratory leaching tests exceeded the OhioEPA's non-toxic criteria. Surface runoff monitoring showed the highest release rates of inorganic elements from the FA50 concrete pavement, while there were no significant differences in release rates between OPC and FA30 concretes. The release of elements generally decreased with increasing pavement loading. Except for K and Cr, the release of elements was associated with the particulate (>0.45 micron) phase rather than the dissolved phase. (Abstract shortened by UMI.)
... Moreover, secondary minerals formed at CCR disposal sites can adsorb trace elements and thus alleviate downward leaching and reduce phytoavailability (Barton et al., 2005b). However, the drop in pH associated with CCR aging may result in enhanced solubility of As, Se, and Sb (Fig. 2), probably due to the dissolution of the respective adsorbing/immobilizing mineral phases (Laperche and Traina, 1999). ...
The world's ever-growing energy demand will lead to the installation of new coal-fired power plants. At least part of the coal combustion residue (CCR) generated in the coming years will be disposed of, adding to the large number of CCR disposal sites generated in the past and reinforcing the need for sound assessment and management of associated risks. Physical and chemical composition of CCR varies considerably depending on the quality of the feed coal, the combustion technology, fraction considered, and the method of disposal. Related risk pathways include (i) aerial routes, i.e., dust resuspension (Cr(VI)), emanation of radioactivity (Rn associated with U and Th series), and Hg volatilization threatening animal and human health; (ii) phytoaccumulation (B, Se, Mo, As) and plant toxicity (B) with subsequent effects on animals (e.g., Mo-induced hypocuprosis, As and Se toxicity) and humans (e.g., selenosis; food chain); and (iii) effluent discharge and percolation to groundwater and rivers (suspended solids, unfavorable pH, high Se, B, Hg, and As(III) concentrations). Recent and projected changes of CCR composition due to emerging clean coal technologies require close monitoring as the concentration of volatile elements such as Hg and Se, solubility (Hg, Cd, Cu) and volatilization (Hg, NH(3)) of some pollutants are likely to increase because of higher retention in certain fractions of CCRs and concurrent changes in pH (e.g., by mineral carbonation) and NH(3) content. These changes require additional research efforts to explore the implications for CCR quality, use, and management of risk associated with disposal sites.
... L5 (30% LKD) exhibits a similar trend but at a lower concentration range (1.63-25 mg/L and then down to 1 mg/L) due to the presence of relatively lower free lime content. These findings are consistent with the observations made by Laperche and Traina [27]. During remediation of AMD from Roberts-Dawson mine in Ohio, they reported a similar trend, a peak and a subsequent decrease in sulfate concentration with flue gas desulfurization grout. ...
Acid mine drainage (AMD) from abandoned coal mines continues to be one of the most significant environmental problems. Remediation of AMD requires an addition of lime source to decrease the acidity, and grouting the entire mine and encapsulating the pyrite by calcium-rich additives is often employed. Utilization of alkaline coal combustion by-products (CCBs) has gained acceptance in such remediation applications because of their cost-effectiveness. A study was conducted to investigate the effectiveness of CCBs to abate acid mine drainage by encapsulation of pyrite. Geomechanical, hydraulic, and environmental tests were performed on grouts prepared with various ratios of CCBs as well as an alternative free lime source, lime kiln dust (LKD). The results indicated that the mechanical properties of grouts were dependent on their free lime contents. Hydraulic conductivities of pyrite-grout columns were relatively high due to the coating of the pyrite rock with the grout rather than the filling of all of the void spaces, as commonly experienced in field applications. The leaching tests indicated that the presence of high amounts of lime in a grout is not solely sufficient to improve the quality of AMD, since the rate of dissolution of a high lime content grout may be slow due to its rapid hardening. Therefore, it is recommended that grouts be selected with consideration of their hardening capacities, as well as the percentage of lime content present in the mixture.
The objective of this study was to demonstrate that simple fractionation and selective dissolution techniques can be used to provide detailed chemical and mineralogical analyses of flue gas desulfurization by‐products. The material studied was a mine grout prepared as a 1:1 mixture (wt./wt.) of fly ash (FA) and filter cake (FC) with hydrated lime (50 g kg ⁻¹ ) added to improve handling. The hydrated lime was composed mostly of calcite (CaCO 3 ), portlandite [Ca(OH) 2 ], lime (CaO), and brucite [Mg(OH) 2 ] (515, 321, 55, and 35 g kg ⁻¹ , respectively) and had low (<6 g kg ⁻¹ ) concentrations of most trace elements. The FC contained hannebachite (CaSO 3 ·0.5H 2 O) (786 g kg ⁻¹ ) with smaller quantities (<10 g kg ⁻¹ ) of calcite, quartz (SiO 2 ), brucite, and gypsum (CaSO 4 ·2H 2 O). Except for B and Cu, trace element concentrations were comparable to those in the hydrated lime. The FA contained both magnetic (222 g kg ⁻¹ ) and nonmagnetic (778 g kg ⁻¹ ) fractions. The former was composed mostly of hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and glass (272, 293, and 287 g kg ⁻¹ , respectively), whereas the latter was enriched in glass, quartz, and mullite (Al 6 Si 2 O 13 ) (515, 243, and 140 g kg ⁻¹ , respectively). Etching with 1% HF showed that 60 to 100% of trace elements were concentrated in the glass, although some metals (Co, Cr, and Mn) were clearly enriched in the magnetic phase. The aged grout contained 147 g kg ⁻¹ ettringite [Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O] in addition to 314 g kg ⁻¹ hannebachite and 537 g kg ⁻¹ insoluble phases (mullite, quartz, hematite, magnetite, and glass).
In this paper, we examine the water quality impacts associated with the reuse of fixated flue gas desulfurization (FGD) material as a low permeability liner for agricultural applications. A 0.457-m-thick layer of fixated FGD material from a coal-fired power plant was utilized to create a 708 m² swine manure pond at the Ohio Agricultural Research and Development Center Western Branch in South Charleston, Ohio. To assess the effects of the fixated FGD material liner, water quality samples were collected over a period of 5 years from the pond surface water and a sump collection system beneath the liner. Water samples collected from the sump and pond surface water met all Ohio nontoxic criteria, and in fact, generally met all national primary and secondary drinking water standards. Furthermore it was found that hazardous constituents (i.e., As, B, Cr, Cu, and Zn) and agricultural pollutants (i.e., phosphate and ammonia) were effectively retained by the FGD liner system. The retention of As, B, Cr, Cu, Zn, and ammonia was likely due to sorption to mineral components of the FGD liner, while Ca, Fe, and P retention were a result of both sorption and precipitation of Fe- and Ca-containing phosphate solids.
In this research, we examine the long-term (4 years behavior of fixated flue gas desulfurization FGD material grout following placement within the Roberts–Dawson underground coal mine. Surface water and groundwater samples were collected to examine the impact of grouting on water quality, and core samples were obtained to assess the geochemical stability of the grout material. Surface water samples collected from the main seep at the Roberts–Dawson mine indicated that 4 years after grout placement the long-term fluxes of acidity, iron, sulfur, and calcium were slightly elevated compared to pregrout conditions. The long-term discharge of these constituents was likely due to continued dissolution of grout material for Ca and S as well as changes in flow paths and subsequent solubilization of metal salts accumulated within the mine voids for acidity, Fe, Al, and S. Although the fluxes of these elements were elevated, no measurable deleterious impact was observed for the underlying groundwater or adjacent surface water reservoir. Groundwater samples collected from monitoring wells installed within the grout material indicated that acid mine drainage waters were neutralized by the grout material. Mineralogical analyses demonstrated minimal penetration of mine drainage water into the high strength fixated FGD material grout, and little weathering of the material was observed. These data indicate that the high strength fixated FGD material grout injected into the Roberts–Dawson mine was geochemically stable and could locally neutralize mine drainage waters. However, more complete grouting and more extensive mine flooding is likely needed in order to bring about significant improvements in seep water quality.
Long term monitoring of the physical and chemical effects of using coal-combustion residues (CCRs), in particular fixated flue gas desulfurization (FGD) sludge, as a major component in the reclamation of a pyritic refuse deposit was undertaken to determine the beneficial and detrimental consequences of placing these controversial materials in an unrestricted environment. Monitoring wells, neutron probe access tubes, and weirs were installed before and after reclamation to observe hydrologic conditions and determine how the use of FGD sludge as a recharge barrier was affecting hydrochemical response to ambient weather conditions. Data were collected for six months prior to reclamation and then for an additional 13 years (more intensively during the first 5 years). Statistical analyses of water levels in the pyritic refuse deposit indicate a shift from precipitation- to barometric-controlled fluctuations. These findings, along with minimal variability in soil moisture within the CCR cap and transient perching of groundwater above the cap, are evidence that recharge of the refuse aquifer has been minimized. Statistically significant improvements in the quality of groundwater on-site and surface water leaving the site include long-term declines in acidity, As, and Fe concentrations within the refuse aquifer, attributed to a decrease in recharge of oxygenated water as supported by an analysis of calculated mineral saturation indices. Long-term declines in acidity and associated trace metals discharging from the site are attributed to the post-reclamation loss of sulfate salts brought to the surface by capillary forces. The results of this study indicate that strategic usage of CCRs in reclamation programs can produce beneficial effects, including acid drainage reductions, that are beyond those achieved using traditional reclamation approaches such as the utilization of mine spoil as capping and fill material.
In this paper, a field study was carried out to examine the effect of flue gas desulfurization (FGD) by-product on water quality at an underground coal mine in central-eastern Ohio. Flue gas desulfurizalion by-product was injected into the down-dip portions of the Robert-Dawson mine in an attempt to seal major seeps exiting the mine and to coat exposed pyritic surfaces. Immediately following grout injection, significant increases in acidity, iron, aluminum, sulfur, and calcium were observed at most surface and ground water locations near where grouting was carried out. Following this initial flush of elements, concentrations of most constituents have decreased to near pre-grouting levels. Data from the site and geochemical modeling suggest that an increase in water level or rerouting of drainage flow resulted in the dissolution of iron and aluminum sulfate salts and ferrihydrite. Dissolution of the FGD grout material resulted in increases in calcium and sulfate concentrations in the drainage waters. Water within the mine voids was saturated with respect to calcium sulfate and gypsum immediately following grout injection. Based on an analysis of core samples obtained from the site, acid mine drainage (AMD) was in contact with at least some portions of the grout and this resulted in grout weathering. Subsequent transport of calcium and sulfate to the underclay, perhaps by fracture flow, has resulted in the deposition of gypsum and calcium sulfate solids.
The objective of this study was to demonstrate that simple fractionation and selective dissolution techniques can be used to provide detailed chemical and mineralogical analyses of flue gas desulfurization by-products. The material studied was a mine grout prepared as a 1:1 mixture (wt./wt.) of fly ash (FA) and filter cake (FC) with hydrated lime (50 g kg(-1)) added to improve handling. The hydrated lime was composed mostly of calcite (CaCO3), portlandite [Ca(OH)2], lime (CaO), and brucite [Mg(OH)2] (515, 321, 55, and 35 g kg(-1), respectively) and had low (<6 g kg(-1)) concentrations of most trace elements. The FC contained hannebachite (CaSO3 x 0.5H2O) (786 g kg(-1)) with smaller quantities (<10 g kg(-1)) of calcite, quartz (SiO2), brucite, and gypsum (CaSO4 x 2H2O). Except for B and Cu, trace element concentrations were comparable to those in the hydrated lime. The FA contained both magnetic (222 g kg(-1)) and nonmagnetic (778 g kg(-1)) fractions. The former was composed mostly of hematite (Fe2O3), magnetite (Fe3O4), and glass (272, 293, and 287 g kg(-1), respectively), whereas the latter was enriched in glass, quartz, and mullite (Al6Si2O13) (515, 243, and 140 g kg(-1), respectively). Etching with 1% HF showed that 60 to 100% of trace elements were concentrated in the glass, although some metals (Co, Cr, and Mn) were clearly enriched in the magnetic phase. The aged grout contained 147 g kg(-1) ettringite [Ca6Al2(SO4)3(OH)12 x 26H2O] in addition to 314 g kg(-1) hannebachite and 537 g kg(-1) insoluble phases (mullite, quartz, hematite, magnetite, and glass).
Disposal of highly saline industrial by-products in landfills is not permitted in member states of the European Union, such as Germany. Large amounts of such by-products thus have to be disposed of in alternative ways. In many countries bare potash mining residue mounds, consisting almost entirely of rock salt (NaCl), pose environmental problems. Covering such mounds with soil or soil-like material could help to reduce the yearly amount of briny runoff. A fine-granular saline aluminum recycling by-product (ALRP) has been proposed as a soil substitute to cover rock salt residue mounds. Use of this by-product as a combined soil substitute and surface barrier is not considered to be a landfill disposal, but as a beneficial by-product reuse. To judge the feasibility of ALRP for this purpose, its properties must be known. In this study physical characteristics of an industrially produced ALRP, mixed with the flue gas desulfurization by-product (FGDP) of a coal combustion power plant, were determined. It was found that the texture of both ALRP and ALRP-FGDP mix was silt loam. Bulk densities of ALRP and ALRP-FGDP were 0.93 and 0.88 Mg x m(-3) and the corresponding salt contents were 50.0 and 35.5%, respectively. The erodibility factor K of pure ALRP was estimated as 0.65 Mg h x ha (-1)N(-1). Because of the stabilizing effect of FGDP, this factor was reduced considerably in ALRP-FGDP. The water-holding capacity of unwashed ALRP was 44.5% and of washed ALRP-FGDP 61.8%. In view of its physical properties, ALRP-FGDP seems to be suitable as an evaporation enhancing, runoff reducing cover material for potash mine residue mounds, even on steep slopes. Use of ALRP, mixed with FGDP, as a soil substitute in a surface barrier, thus seems to be environmentally meaningful. However, the high salt content initially prevents plant growth. With time, after the salt has been leached, the material seems able to support plant growth, which would further reduce runoff. The physical and hydraulic parameters determined in this study may serve future users of similar by-products.
Most ochre deposits are mineralogically complex and require a combination of selective chemical extraction procedures and instrumental techniques for proper characterization. Pathways leading to the formation of minerals are strongly influenced by both biological and geochemical parameters.
The solubility and weathering reactions of ettringite, (Ca6Al2(SO4)3(OH)12·26H2O), were used to study the geochemical equilibria of the Ca(OH)2–Al2(SO4)3–H2O system at environmental pH conditions. Ettringite is a stable mineral above a pH of 10.7 and dissolved congruently with a log Ksp of −111.6 (±0.8). Between pH 10.7 and 9.5, ettringite underwent incongruent dissolution to gypsum and Al-hydroxides and controlled Ca2+, Al3+, and SO42− activities. At near neutral pH, Al-hydroxy sulfates precipitated in addition to gypsum and Al-hydroxide. These Al-hydroxy sulfate phases exhibited prismatic and anhedral shapes and had variable Al/S ratios. In addition, some new poorly crystalline Ca–Al-hydroxy sulfate phases were identified in microscopic studies when the pH was acidic (pH∼5). The activities of Ca2+, Al3+, and SO42− suggest that the geochemistry of the Ca(OH)2–Al2(SO4)3–H2O system in the pH range of 7 to 10 is simple and its component Ca(OH)2–SO3–H2O and Al2(SO4)3–H2O systems behave independently of each other. The precipitation of Al-hydroxy sulfates below pH 7.0 significantly influenced Ca2+ and SO42− activities. This effect was pronounced when Ca–Al-hydroxy sulfate phases started precipitating (pH<5.0). The lack of thermodynamic data on the newly identified Al, and Ca–Al-hydroxy sulfates makes it difficult to interpret the geochemistry of Ca(OH)2–Al2(SO4)3–H2O system for pH≤5.0. Reaction path calculations conducted using the EQ6 computer code predicted ion activities close to the experimental values above pH 5.0. The observed differences between thermodynamic modelling and actual experimental data below this pH can be explained by the formation of Al–/Ca–Al-hydroxy sulfate phases in the system, as detected by electron microscopy and X-ray elemental analysis. These reactions are relevant and useful to the prediction of Al, and Ca geochemistry in natural systems.
One potential use for alkaline, dry flue gas desulfurization (FGD) by- products is in reclamation of acidic minespoils. Greenhouse column studies of 8-mo duration investigated growth and tissue composition of plants grown on three acidic minespoils amended with two dry FGD by-products (lime injection multistage burners, LIMB; and, pressurized fluidized bed combustion, pFBC). Amendment amounts ranged from 0 to 320 g kg -1 by dry weight. Two minespoils also were amended with sewage sludge at 60 g kg -1 by dry weight. Column mixes were planted with Kentucky 31 tall fescue (Festuca arundinacea Schreb.). After 92 d of growth, fescue was harvested every 30 d for a total of six harvests. Tissue composition was determined on material from the sixth harvest. Root growth was measured at the end of the experiment. Fescue growth was improved by FGD amendments of 30 to 120 g kg -1, but larger amendments caused high pH and cementation, which decreased rescue growth and limited rooting volume. Plant tissue composition was generally within sufficiency ranges for the elements analyzed. Tissue Ca, Mg, and S were increased by FGD amendment, while tissue concentrations of most trace elements were decreed. There was no increase in tissue B from PFBC, however, LIMB application caused B concentrations >100 mg kg -1, which could be toxic to less tolerant species. These results indicate that when applied in amounts equivalent to spoil neutralization needs, dry FGD by-products can benefit acidic spoil revegetation with little potential for introduction of toxic elements into the food chain.
Solid solutions of ettringites containing SO42−, B(OH)4− and CrO42− were investigated. The compositions of the solid solutions under different synthesis conditions are represented by paste reaction (1) and “saccharate method” (2):1.1: [Ca6Al2 (OH)12·24H2O]6+ [(3−3x) (SO4)·(3x) (Cro4)·2H2O]6− 0≤x≤12.2: [Ca6Al2 (OH)12·24H2O]6+ [(x) (SO4)·(3−x) (Cro4)·2H2O]6− 0≤x≤13.3: [Ca6Al2 (OH)12·24H2O]6+. [(3−3x) (SO4)·(2x) (OH)·(4x)B (OH)4·yH2O]6− 0≤x≤14.4: [Ca6Al2 (OH)12·24H2O]6+. [(3−3x) (SO4)·(4x) (OH)·(2x)B (OH)4·yH2O]6− 0≤x≤1The crystallographic properties of the different solid solution series were determined. An interpretation of the ternary solid solutions is given.
Arsenate sorption by ettringite [Ca6Al2(SO4)3(OH)12·26H2O] is examined as adsorption and coprecipitation systems at alkaline pH (10.0−12.5) and for a wide range of As(V) concentration (<1 μM−15 mM). The mode of sorption and sorbate and sorbent concentrations controlled the nature of solid-phase As(V) speciation. Although high pH increased ettringite stability in concentrated As(V) solutions, it did not influence total As(V) sorption. During adsorption, ettringite exposure to concentrated As(V) solutions (>2.0 mM) precipitated new unidentified microcrystalline minerals at the expense of ettringite. Concentrated As(V) solution exposure to coprecipitating ettringite poisoned ettringite crystal growth, with precipitation of some microcrystalline minerals. Sorbed As(V) was also not desorbable in the presence of concentrated sulfate and high ionic strength solutions. Details of As(V) adsorption and coprecipitation systems and inferences on As(V) molecular interactions are proposed.
Degradation of water quality related to oxidation of iron disulfide minerals associated with coal is a naturally occurring process that has been observed since the late seventeenth century, many years before commencement of commercial coal mining in the United States. Disturbing coal strata during mining operations accelerates this natural deterioration of water quality by exposing greater surface areas of reactive minerals to the weathering effects of the atmosphere, hydrosphere, and biosphere.
Degraded water quality in the temperate eastern half of the United States is readily detected because of the low mineralization of natural water. Maps are presented showing areas in the eastern United States where concentrations of chemical constituents in water affected by coal mining (pH, dissolved sulfate, total iron, total manganese) exceed background values and indicate effects of coal mining. Areas in the East most affected by mine drainage are in western Pennsylvania, southern Ohio, western Maryland, West Virginia, southern Illinois, western Kentucky, northern Missouri, and southern Iowa.
Effects of coal mining on water quality in the more arid western half of the United States are more difficult to detect because of the high degree of mineralization of natural water. Normal background concentrations of constituents are not useful in evaluating effects of coal mine drainage on streams in the more arid West.
Three approaches to reduce the effects of coal mining on water quality are: (1) exclusion of oxygenated water from reactive minerals, (2) neutralization of the acid produced, (3) retardation of acid-producing bacteria population in spoil material, by application of detergents that do not produce byproducts requiring disposal. These approaches can be used to help prevent further degradation of water quality in streams by future mining.