Jerry M. Bigham’s research while affiliated with The Ohio State University and other places

The purpose of this study was to characterize a series of (Na, NH4, H3O)-jarosites produced with various combinations of NH4⁺ + Na⁺ in cultures of Acidithiobacillus ferrooxidans that simulated acid solutions from bioleaching systems. The solution concentrations utilized were 6.1, 80, 160 and 320 mM for NH4⁺ and 0, 50, 100, 250 and 500 mM for Na⁺ as their respective sulfates. Media at pH 2.2 were inoculated with iron-oxidizing A. ferrooxidans and incubated in shake flasks at 22 ± 2 °C. As the bacteria oxidized ferrous sulfate, ferric iron hydrolyzed and precipitated as schwertmannite (idealized formula Fe8O8(OH)6(SO4).nH2O) and/or as solid solution jarosites [(Na, NH4, H3O)-Fe3(SO4)2(OH)6)] depending on the relative and absolute concentrations of NH4⁺ and Na⁺. The precipitates were characterized by elemental analysis, X-ray diffraction, specific surface area, and Munsell color. Schwertmannite was the dominant mineral product at low combinations of Na⁺ (≤50 mM) and NH4⁺ (≤80 mM) in the media after 2 weeks of aging. At higher single or combined concentrations and with aging for 6 and 11 weeks, the formation of yellowish, solid solution jarosites was enhanced. Precipitation of jarosite-group minerals was favored by NH4⁺ relative to Na⁺. Color (Munsell hue) was a useful tool for assessing sample mineralogy after extended aging, but the presence of abundant, poorly crystalline schwertmannite tended to mask the color of admixed jarosite-group minerals after only 2 weeks of contact with the culture media. The purest samples of jarosite-type minerals had specific surface areas <1.0 m²/g. Unit cell edge lengths and cell volume calculations from powder XRD data indicated that the jarositic phases produced were ternary (Na, NH4, H3O)-solid solutions. Most products also appeared to be deficient in structural Fe, especially at low NH4 contents. Thus, ferric iron precipitation from the simulated bioleaching systems yielded solid solutions of jarosites with chemical compositions that were dependent on the relative concentrations of Na⁺ and NH4⁺ in the synthesis media. No phase separations involving discrete, end-member Na-, NH4-, or H3O-jarosites were detected.

Although particles >2 mm are not considered soil material, gravels composed of resistant secondary minerals can be useful records of past soil environments. We investigated gravels (2–8 mm) from a Plinthic Haplustox in central Brazil in order to assess their composition, fabric and genesis. Gravels were initially grouped into six macromorphological types, and investigated by mineralogical, micromorphological and microprobe analyses. The results suggest that gravels can be classified as pedogenic or lithopedogenic. Pedogenic gravels comprise indurated soil materials and include black magnetic gravels, black non-magnetic gravels and red earthy gravels. Magnetic gravels contained mostly quartz, hematite and magnetite–maghemite and were poor in kaolinite, gibbsite and goethite, whereas non-magnetic and red earthy gravels had the same minerals as in the surrounding soil. Lithopedogenic gravels are fragments of resistant rocks impregnated by iron (Fe), aluminium (Al) and manganese (Mn) oxides, including platy shales, quartzites and coarse quartz. The latter two showed oxide impregnations around internal pores, whereas the shale fragments included considerable mica, which contributed illite and potassium to the soil clays and, thus, the pedogenic gravels. These results point to multiple cycles of formation and incorporation of cemented materials into the soil, as well as their later impregnation by Fe, Mn and Al oxides. Thus, the conventional classification of all such gravels as ‘ironstone’ is questionable, and their potential role as indicators of past and present soil environments is demonstrated, which deserves further investigation.

The purpose of this study was to synthesize a series of solid solution jarosites by biological oxidation of ferrous iron at pH 2.2 – 2.4 and ambient temperature in media containing mixtures of K+ (0, 1, 4, 6, 12, 31 mM) and NH4+ (6.1, 80, 160, 320 mM). The starting material was a liquid medium for Acidithiobacillus ferrooxidans comprised of 120 mM FeSO4 solution and mineral salts at pH 2.2. Following inoculation with A. ferrooxidans, the cultures were incubated in shake flasks at 22°C. As bacteria oxidized ferrous iron, ferric iron hydrolyzed and precipitated as jarosite-group minerals (AFe3(SO4)2(OH)6) and/or schwertmannite (idealized formula Fe8O8(OH)6(SO4)•nH2O). The precipitates were characterized by X-ray diffraction (XRD), elemental analysis, and Munsell color. Schwertmannite was the dominant mineral product at low combinations of K+ (< 4 mM) and NH4+ (< 80 mM) in the media. At higher single or combined concentrations, yellowish jarosite phases were produced, and Munsell hue provided a sensitive means of detecting minor schwertmannite in the oxidation products. Although the hydrated ionic radii of K+ and NH4+ are similar, K+ greatly facilitated the formation of a jarosite phase compared to NH4+. Unit cell and cell volume calculations from refinements of the powder XRD patterns indicated that the jarosite phases produced were mostly ternary (K, NH4, H3O) solid solutions that were also deficient in structural Fe, especially at low NH4 contents. Thus, ferric iron precipitation from the simulated bioleaching systems yielded solid solutions of jarosite with chemical compositions that were dependent on the relative concentrations of K+ and NH4+ in the synthesis media. No phase separations involving discrete, end-member K-jarosite or NH4-jarosite were detected in the un-aged precipitates.

Arsenic in soil is an important public health concern, but risk-based toxicity regulatory standards derived from laboratory studies should also consider concentrations measured away from obvious contamination (i.e., baseline concentrations that approximate natural background) to avoid unnecessary remediation burdens on society. We used soil and stream sediment samples from the USGS National Geochemical Survey to assess the spatial distribution of As over a 1.16 × 10 km area corresponding to the state of Ohio. Samples were collected at 348 soil and 144 stream sites at locations selected to minimize anthropogenic inputs. Total As was measured by sodium peroxide fusion with subsequent dissolution using concentrated HCl and analysis using hydride-generation atomic absorption spectrometry. Arsenic in the soil and streambed samples ranged from 2.0 to 45.6 mg kg. Sequential Gaussian simulation was used to map the expected concentration of As and its uncertainty. Five areas of elevated concentration, greater than the median of 10 mg kg, were identified, and relationships to geologic parent materials, glacial sedimentation, and soil conditions interpreted. Arsenic concentrations <4 mg kg were rare, >10 mg kg common, and >20 mg kg not unusual for the central and west central portions of Ohio. Concentrations typically exceeded the soil As human generic screening level of 0.39 mg kg, a value corresponding to an increase in cancer risk of 1 in 1,000,000 for soil ingestion. Such results call into question the utility of the USEPA and similarly low soil screening levels. The contrast between laboratory screens and concentrations occurring in nature argue for risk assessment on the basis of baseline concentrations. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Synthetic aluminum-substituted maghemites were characterized by total chemical analysis, powder X-ray diffraction (XRD), Mössbauer spectroscopy (ME), and vibrating sample magnetometry (VSM). The aim was to determine the structural, magnetic, and hyperfine properties of γ-Fe2-xAlxO3 as the Al concentration is varied. The XRD results of the synthetic products were indexed exclusively as maghemite. Increasing Al for Fe substitution decreased the mean crystalline dimension and shifted all diffraction peaks to higher °2θ angles. The a0 dimension of the cubic unit cell decreased with increasing Al according to the equation ao = 0.8385 - 3.63 x 10-5 Al (R2= 0.94). Most M̈ssbauer spectra were composed of one sextet, but at the highest substitution rate of 142.5 mmol mol-1 Al, both a doublet and sextet were obtained at ≈ 300 K. All hyperfine parameters from the sub-spectra were consistent with high-spin Fe3+ (0.2 a 0.7 mms-1) and suggested a strong superparamagnetic component associated with the doublet. The magnetic hyperfine field of the sextets decreased with the amount of Al-substitution [Bhf (T) = 49.751 - 0.1202Al; R2 = 0.94] while the linewidth increased linearly. The saturation magnetization also decreased with increasing isomorphous substitution.

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 beta-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, b-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, beta-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 purpose of the work was to examine the co-precipitation of Fe(III) and Pb(II) in Acidithiobacillus ferrooxidans cultures under ambient temperature conditions. The competitive formation of plumbojarosite (PbFe6(SO4)4(OH)12) and anglesite (PbSO4) was of particular interest with respect to defining the phase(s) controlling Pb solubility. The medium contained no K+ and a low level of 6.06 mM NH4+. Precipitates were prepared in two phases. In the first phase (8 days), A. ferrooxidans cultures oxidized ferrous iron to ferric iron (pH 2.4), which partially precipitated as schwertmannite (Fe8O8(OH)5.5(SO4)1.25). In the second phase, lead nitrate (up to 100 mmol Pb/l) was added to the schwertmannite-containing culture solutions, and the suspensions were held for an additional 22 days. X-ray diffraction analysis indicated that lead precipitated as anglesite, and ferric iron was associated with schwertmannite and hydronium jarosite. No characteristic X-ray diffraction peaks for plumbojarosite were evident.