The isomorphic substitution (IS) of Al for Fe can alter many properties of Fe oxide minerals, including their aqueous solubility. The resistance of these minerals to dissolution in soils can, in turn, influence the availability of Fe and the formation of new Fe oxides. In this study, the dissolution kinetics of synthetic, Al-substituted maghemites (γ-Fe2−xAlxO3) were investigated in 2 M HCl. The IS values varied from 0.0 to 14.3 mol% Al, and the dissolution reaction was conducted under controlled temperature (20°C ± 1) over a period of 288 h. Successive, 5-mL aliquots of suspension were withdrawn after set times, and Fe and Al were analyzed by ICP–MS. The overall dissolution rates of Fe and Al were similar throughout the experiment, indicating congruent dissolution. The resulting data were described equally well by using the Kabai and Avrami-Erofejev equations. Dissolution rates considering the specific surface area (SSA), as k2 = k/SSA, were the most efficient for describing the influence of IS on mineral dissolution and demonstrated that the maghemites became more resistant to dissolution with increasing Al substitution. Observations from transmission electron microscopy (TEM) supported isotropic dissolution of individual particles.
Sulfate-reducing bacteria (SRB) play a major role in the precipitation of metal sulfides in the environment. In this work, biogenic copper sulfide formation was examined in cultures of SRB and compared to chemically initiated Cu sulfide precipitation as a reference system. Mixed cultures of SRB were incubated at 22, 45, and 60°C in nutrient solutions that contained copper sulfate. Abiotic reference samples were produced by reacting uninoculated liquid media with Na2S solutions under otherwise identical conditions. Precipitates were collected anaerobically by centrifugation, frozen in liquid N2, and freeze-dried, followed by analysis using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy. Covellite (CuS) was the only mineral found in the precipitates. Covellite was less crystalline in the biogenic precipitates than in the abiotic samples based on XRD peak widths and peak to background ratios. Poor crystallinity may be the result of slower precipitation rates in bacterial cultures as compared to the abiotic reference systems. Furthermore, bacterial cells may inhibit the nucleation steps that lead to crystal formation. Incubation at elevated temperatures improved the crystallinity of the biotic specimens.
The purpose of this study was to assess the weathering of biotite under conditions simulating an active bioleaching environment. Finely ground biotite was contacted with Acidithiobacillus ferrooxidans culture solutions for up to 120 days. Biotite was altered under these conditions to interstratified structures comprised of mixed layers of biotite and vermiculite. Interlayer K in biotite was released upon weathering and precipitated with ferric iron and sulfate to form jarosite. Substantial dissolution of biotite was also associated with weathering. The data demonstrate that exposed, biotite-rich rocks in mine tailings and heap and dump leaching systems can undergo acid mediated solubilization and structural changes, which are coupled with the formation of expansive, vermiculite-like minerals and jarosite precipitation.
Mine lands are an environmental concern worldwide because of their potential strong negative impact on water and soil quality. A field study was conducted to assess the use of a dry flue gas desulfurization (FGD) product for reclamation of an abandoned surface coal mine in Ohio. The FGD product was an atmospheric fluidized bed combustion residue and was applied to the graded mine site at 280 Mg ha-1, both alone and in combination with 112 Mg ha-1 yard waste compost, and was compared with conventional reclamation with 20 cm of borrow soil plus 157 Mg ha-1 of agricultural limestone. A grass-legume sward was planted, and soil physical and chemical properties and β-glucosidase activity were measured over both short- (1–4 yr) and long-term (15–17 yr) periods following reclamation. Soil pH at 0- to 20-cm depth increased from 3.1 to approximately neutral and was sustained at this level for 15 yr. Compared with the conventional reclamation, extractable Ca, S, B, and Zn concentrations at 0- to 20-cm depth were generally increased by the treatments with FGD product, while other extractable trace metals measured were generally not increased in short- or long-term measurements. Seventeen years after reclamation, β-glucosidase activity had increased in all three treatments at 0- to 5- and 5- to 10-cm depths compared with an adjacent untreated area. Furthermore, β-glucosidase activity more than doubled in the treatments with FGD product compared with the conventional soil treatment at 0- to 5-cm depth. These results suggest that the use of high lime FGD products for reclamation of acid coal mine lands can provide effective long-term reclamation.
The influence of chemical and textural discontinuities on soil development has not been well documented. In this study, weathering and clay accumulation in a thin (43 to 66 cm), Late Wisconsinan loess mantle underlain by different materials (dolomite, siltstone, sandstone, and shale residua; Illinoian and Wisconsinan glacial tills) were assessed in six pedons from southcentral Ohio. Lithological and micro-morphological evidence suggested that mixing of underlying materials with the loess was limited to the basal portion of the mantle. Chemical analyses indicated greater weathering of loess deposited over low base status or clayey materials relative to that deposited over those with high base status or loamy textures. Particle size and micromorphological and reconstructional analyses also indicated greater pedogenic clay accumulation in loess deposited over clayey materials. Apparently, the presence of acidic materials beneath the initially calcareous loess accelerated acidification and weathering within the loess mantle. In addition, fine-textured underlying materials may have impeded water movement, resulting in a wetter environment in the loess that accelerated in situ clay formation or promoted deposition of clay from suspension. We propose that enhanced weathering of parent materials just above, and as a result of contact with, a contrasting material be referred to as basal weathering.
Natural gypsum has been used as a soil amendment in the United States. However, flue gas desulfurization (FGD)-gypsum has not traditionally been used for agricultural purpose although it has potential benefit as a soil amendment. To expand use of FGD-gypsum for agricultural purpose, the effect of FGD-gypsum on soil chemical properties was investigated in the field scales. Application rates for this study were 0( control), 1.1, and 2.2 Mg ha -1 of FGD-gypsum. After two year application, the soil samples were taken to 110 cm depth and sub-sampled at 10 cm intervals. The heavy metal contents in FGD-gypsum were lower than ceiling levels allowed by regulations for land-applied biosolids. Soil pH was not largely affected by FGD-gypsum application. Although degree of calcium (Ca) saturation in surface horizons increases only slightly with respect to the control, there is a clear decrease in exchangeable aluminum (Al). FGD-gypsum clearly increases the soil electrical conductivity (EC) with increasing application rate. Water-soluble Ca and sulfate is increased with FGD-gypsum application and these ions moved to a depth of at least 80 cm after only 2 years. We conclude that surface application of FGD-gypsum can mitigate toxicity of Al and deficiency of Ca in subsoil of acid soil.
Abstract Schwertmannite is a new oxyhydroxysulphate of iron from the Pyhäisalmi sulphide mine, Province of Oulu, Finland. It occurs there, and elsewhere, as an ochreous precipitate from acid, sulphate-rich waters. Associated minerals at other localities may include jarosite, natrojarosite, goethite and ferrihydrite. Schwertmannite is a poorly crystalline, yellowish brown mineral with a fibrous morphology under the electron microscope. A high specific surface area in the range of 100 to 200 m 2 /g, rapid dissolution in cold, 5 M HCl or in ammonium oxalate at pH 3, and pronounced X-ray diffraction line broadening are consistent with its poorly crystalline character. Colour parameters for the type specimen as related to CIE illuminant C are L* = 53.85, a* = + 15.93, and b* = +47.96. Chemical analysis gives Fe 2 O 3 , 62.6; SO 3 , 12.7; CO 2 , 1.5; H 2 O − , 10.2; H 2 O + , 12.9; total 99.9 wt.%. These data yield an empirical unit cell formula of Fe 16 O 16 (OH) 9.6 (SO 4 ) 3.2 ·10H 2 O after exclusion of CO 2 and H 2 O − . The most general simplified formula is Fe 16 O 16 (OH) y (SO 4 ) z · n H 2 O, where 16 − y = 2 z and 2.0 ⩽ z ⩽ 3.5. Schwertmannite has a structure akin to that of akaganéite (nominally β-FeOOH) with a doubled c dimension. Its X-ray powder diffraction pattern consists of eight broad peaks [d obs in (I obs ) ( hkl )] 4.86(37)(200,111); 3.39(46)(310); 2.55(100)(212); 2.28(23)(302); 1.95(12)(412); 1.66(21)(522); 1.51(24)(004); and 1.46(18)(204,542), giving a = 10.66(4), c = 6.04(1) Å, and V = 686(6) Å 3 for a primitive, tetragonal unit cell. The probable space group is P4/m . Upon heating, schwertmannite transforms to hematite with Fe 2 (SO 4 ) 3 occurring as an intermediate phase. Bidentate bridging complexes between Fe and SO 4 are apparent in infrared spectra. Mössbauer data show the Fe in schwertmannite to be exclusively trivalent and in octahedral coordination; it has a Néel temperature of 75 ± 5 K and a saturation magnetic hyperfine field of about 45.6 T. Pronounced asymmetry of the Mössbauer spectra indicates different locations for Fe atoms relative to SO 4 groups in the structure. The name is for Udo Schwertmann, professor of soil science at the Technical University of Munich.
The loss of N and P by leaching is an important issue, especially on agricultural fields with subsurface tile drainage. The objective of this study was to evaluate how gypsum amendment and soil exchangeable Ca2+ and Mg2+ could affect the movement of P, NH4–N, and NO3–N in infiltrated water and soil. A column experiment was performed using a Miami silt loam soil, and the treatments were (i) control, (ii) gypsum applied at the surface, (iii) gypsum mixed into the 2.5-cm depth, and (iv) alteration of five different target exchangeable Ca/Mg ratios. A clear Plexiglas cylinder was filled with a 15-cm layer of soil; N, P, and K were applied in solution at the surface after the soil had been wetted and drained. Deionized water at a flow of 0.5 mL min−1 was applied and eight leachate fractions, totaling about five pore volumes, were collected. Gypsum (5000 kg ha−1) applied at the surface and mixed into the 2.5-cm depth significantly decreased P and increased NH4–N concentration but had no significant effect on NO3–N leaching. Exchangeable Ca/Mg ratio treatments did not affect soluble nutrient losses; however, leaching of particulate P was significantly less in the Ca-treated soil than the Mg-treated soil. The overall practical conclusion of this study is that to control P transport, it is necessary to add gypsum even with a high soil exchangeable Ca/Mg ratio. The application of gypsum to the soil could be recommended as a best management practice to avoid water pollution by P; on the other hand, this could cause environmental problems by increasing the NH4 soil mobility.
