Synthesis of argentojarosite with simulated bioleaching solutions produced by Acidithiobacillus ferrooxidans.

Argentojarosite (AgFe3(SO4)2(OH)6) is formed as a secondary phase in Ag-catalyzed bioleaching of chalcopyrite (CuFeS2), but to date very little is known about the paragenesis or characteristics of this silver-containing compound. The purpose of this study was to synthesize argentojarosite via biological oxidation of 120mM ferrous sulfate by Acidithiobacillus ferrooxidans. Because of its toxicity to A. ferrooxidans, Ag(+) (as AgNO3) was added to spent culture media (pH2) after complete oxidation of ferrous sulfate. Schwertmannite (ideally Fe8O8(OH)6(SO4)) was precipitated during the iron oxidation phase, and subsequent Ag(+) addition resulted in the formation of argentojarosite. Contact time (8h, 5d, and 14d) and Ag(+) concentration (0, 5, 20, and 40mM) were used as variables in these experiments. Synthesis of argentojarosite, schwertmannite and other mineral phases was confirmed through X-ray diffraction analysis. Additional analyses of solid-phase oxidation products included elemental composition, color and specific surface area. The sample synthesized in the presence of 40mM Ag(+) and with 14d contact time yielded an X-ray diffraction pattern of well crystallized argentojarosite, and its elemental composition closely matched the calculated Ag, Fe, and S contents of ideal argentojarosite. The color and surface area of the remaining samples were influenced by the presence of residual schwertmannite. This phase remained stable over the time course of 14d when no Ag(+) was present in the system. When equilibrations were extended to 42d, partial conversion of reference schwertmannite to goethite was noted in the absence of Ag. In the presence of 20mM or 40mM Ag over the same time course, some formation of argentojarosite was also noted. In this case, schwertmannite was the only source of Fe and SO4 for argentojarosite formation.

Surface coal mine land reclamation using a dry flue gas desulfurization product: Short-term and long-term water responses.

Abandoned coal-mined lands are a worldwide concern due to their potential negative environmental impacts, including erosion and development of acid mine drainage. A field study investigated the use of a dry flue gas desulfurization product for reclamation of abandoned coal mined land in USA. Treatments included flue gas desulfurization product at a rate of 280 Mg ha(-1) (FGD), FGD at the same rate plus 112 Mg ha(-1) yard waste compost (FGD/C), and conventional reclamation that included 20 cm of re-soil material plus 157 Mg ha(-1) of agricultural limestone (SOIL). A grass-legume sward was planted after treatment applications. Chemical properties of surface runoff and tile water (collected from a depth of 1.2m below the ground surface) were measured over both short-term (1-4 yr) and long-term (14-20 yr) periods following reclamation. The pH of surface runoff water was increased from approximately 3, and then sustained at 7 or higher by all treatments for up to 20 yr, and the pH of tile flow water was also increased and sustained above 5 for 20 yr. Compared with SOIL, concentrations of Ca, S and B in surface runoff and tile flow water were generally increased by the treatments with FGD product in both short- and long-term measurements and concentrations of the trace elements were generally not statistically increased in surface runoff and tile flow water over the 20-yr period. However, concentrations of As, Ba, Cr and Hg were occasionally elevated. These results suggest the use of FGD product for remediating acidic surface coal mined sites can provide effective, long-term reclamation.

Synthesis and properties of ternary (K, NH4, H3O)-jarosites precipitated from Acidithiobacillus ferrooxidans cultures in simulated bioleaching solutions.

The purpose of this study was to synthesize a series of solid solution jarosites by biological oxidation of ferrous iron at pH2.2-4.4 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 pH2.2. 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.

Modeling spatial patterns in soil arsenic to estimate natural baseline concentrations.

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.

Formation of Fe-sulfides in cultures of sulfate-reducing bacteria.

The purpose of this study was to synthesize Fe-sulfides produced with sulfate-reducing bacteria under experimental laboratory conditions. Fe-sulfides were precipitated with biologically produced sulfide in cultures growing at 22, 45, and 60 degrees C for up to 16 weeks. Abiotic controls were prepared by reacting liquid media with Na(2)S solutions. Precipitates were collected anaerobically, freeze-dried and analyzed by X-ray diffraction. Additional analyses included total Fe and S content, magnetic susceptibility, specific surface area, and scanning electron microscopy. Mackinawite (FeS) and greigite (Fe(3)S(4)) were the dominant iron sulfide phases formed in sulfate-reducing bacterial cultures. An increase in the incubation temperature from 22 to 60 degrees C enhanced the crystallinity of the Fe-sulfides. Generally, greigite was more prevalent in abiotic samples and mackinawite in biogenic materials. Pyrite (FeS(2)) was also found in abiotic precipitates. Abiotic samples had a higher magnetic susceptibility because of the greigite and displayed improved crystallinity compared to biotic materials.

Metal release from bottom sediments of Ocoee Lake No. 3, a primary catchment area for the Ducktown Mining District.

Ocoee Lake No. 3 is the first reservoir receiving suspended sediments contaminated with trace metals discharged by acid mine effluents from the Ducktown Mining District, Tennessee. Bottom sediments (0-5 cm) from the lake were sampled to assess the potential for future adverse environmental effects if no remediation controls or activities are implemented. The sediments were found to include a major component (173 +/- 19 g kg(-1)) that dissolved in 6 mol L(-1) HCl within 24 h. This acid-soluble and relatively labile fraction contained high concentrations of Fe (460 +/- 40 g kg(-1)), Al (99 +/- 11 g kg(-1)), Mn (10 +/- 8 g kg(-1)), Cu (2000 +/- 700 mg kg(-1)), Zn (1300 +/- 200 mg kg(-1)), and Pb (300 +/- 200 mg kg(-1)). When the pH of water in contact with the sediment was decreased experimentally from 6.4 to 2.6, the concentrations of dissolved trace metals increased by factors of 2200 for Pb, 160 for Cu, 21 for Zn, 9 for Cd, 8 for Ni, and 5 for Co. The order in which metals were released with decreasing pH was the reverse of that reported for pH-dependent sorption of these metals in upstream systems. Substantial release of trace metals from the sediment was observed even by a modest decrease of pH from 6.4 to 5.9. Therefore, the metal-rich sediment of the lake should be considered as potentially hazardous to bottom-dwelling aquatic species and other organisms in the local food chain. In addition, if the reservoir is dredged or if the dam is removed, the accumulated sediment may have to be treated for recovery of sorbed metals.

Mechanisms controlling the leaching kinetics of fixated flue gas desulfurization (FGD) material under neutral and acidic 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.

Experimental oxidative dissolution of sphalerite in the Aznalcollar sludge and other pyritic matrices.

After the collapse on 25 Apr. 1998 of the Aznalcóllar mine tailings dike in southwestern Spain, 45 km2 of the Guadiamar valley were covered by a pyritic sludge containing up to 2% sphalerite (ZnS). Later, the sludge was mechanically removed and calcium carbonate was plowed into the soil to immobilize heavy metals. By June 2001 more than 60% of the sulfides in the residual sludge had oxidized and soil Zn contents reached locally phytotoxic levels. Therefore, the oxidative dissolution of sphalerite in the sludge and other pyritic samples was examined. Flow-through oxidation experiments showed that: (i) about 5 and 17% of the sludge Fe and Zn were in soluble form, respectively, because the sludge sample had been partly oxidized in the field; (ii) the oxidation rates of the residual pyrite and sphalerite were similar; (iii) the overall sulfide oxidation rate was relatively unaffected by the addition of calcite; and (iv) poorly crystalline Fe (hydr)oxides containing Zn in occluded form and Zn (hydroxi)carbonates were formed in the presence of calcite. The rate of oxidation of reference sphalerite greatly increased when it was incorporated in the sludge or in a reference pyrite matrix. This enhancement was due to galvanic interaction because pyrite oxidation was depressed in the presence of sphalerite. Oxidation by Fe3+ ions was less important because the oxidation rates of native sphalerite were not greater at low than at high pH. The fast oxidation rate of sphalerite in the Aznalcóllar sludge indicates a need for quick adoption of remediation measures in similar accidents elsewhere. The use of calcite amendments has little influence on the oxidation rate but does result in the accumulation of Zn in relatively insoluble forms.

Chemical and physical properties of dry flue gas desulfurization products.

Beneficial and environmentally safe recycling of flue gas desulfurization (FGD) products requires detailed knowledge of their chemical and physical properties. We analyzed 59 dry FGD samples collected from 13 locations representing four major FGD scrubbing technologies. The chemistry of all samples was dominated by Ca, S, Al, Fe, and Si and strong preferential partitioning into the acid insoluble residue (i.e., coal ash residue) was observed for Al, Ba, Be, Cr, Fe, Li, K, Pb, Si, and V. Sulfur, Ca, and Mg occurred primarily in water- or acid-soluble forms associated with the sorbents or scrubber reaction products. Deionized water leachates (American Society for Testing and Materials [ASTM] method) and dilute acetic acid leachates (toxicity characteristic leaching procedure [TCLP] method) had mean pH values of >11.2 and high mean concentrations of S primarily as SO(2-)4 and Ca. Concentrations of Ag, As, Ba, Cd, Cr, Hg, Pb, and Se (except for ASTM Se in two samples) were below drinking water standards in both ASTM and TCLP leachates. Total toxicity equivalents (TEQ) of dioxins, for two FGD products used for mine reclamation, were 0.48 and 0.53 ng kg(-1). This was similar to the background level of the mine spoil (0.57 ng kg(-1)). The FGD materials were mostly uniform in particle size. Specific surface area (m2 g(-1)) was related to particle size and varied from 1.3 for bed ash to 9.5 for spray dryer material. Many of the chemical and physical properties of these FGD samples were associated with the quality of the coal rather than the combustion and SO2 scrubbing processes used.

Sonolytic desorption of mercury from aluminum oxide.

As discrete particles and/or as coatings on other mineral surfaces in natural systems, aluminum (hydr)oxides are efficient sinks for Hg(II). Ultrasound at 20 kHz was applied to enhance the desorption of Hg(II) from aluminum oxide particles (5.0 micromol of Hg g(-1)). Results showed that at short times ultrasound enhanced Hg(II) release at pH 4.0 compared to both that from hydrodynamic mixing and that expected on the basis of the Hg(II) sorption isotherm. The higher the input power of sonication, the higher the desorption of Hg(II). However, with longer times, much less desorption occurred by ultrasound than by hydrodynamic mixing, with mass balance measurements demonstrating that the desorbed Hg(II) was resorbed back to the particles. The particles were characterized to explore the mechanism for resorption of Hg(II) by prolonged sonication. No surface area change was observed even though ultrasound dramatically reduced the particle size and changed the surface morphology. Although a decrease in the point of zero charge (PZC) due to sonication was observed, it was excluded as the primary mechanism for Hg(II) resorption. Hg(II) occlusion by aluminum hydroxide precipitation was supported by X-ray photoelectron spectroscopy results and the formation of solutions supersaturated with AI. Experiments on presonicated particles verified the occlusion theory by ruling out the effects of the surface area and PZC.

Weathering of phlogopite by Bacillus cereus and Acidithiobacillus ferrooxidans.

The purpose of this study was to assess the weathering of finely ground phlogopite, a trioctahedral mica, by placing it in contact with heterotrophic (Bacillus cereus) and acidophilic (Acidithiobacillus ferrooxidans) cultures. X-ray diffraction analyses of the phlogopite sample before and after 24 weeks of contact in B. cereus cultures revealed a decrease in the characteristic peak intensities of phlogopite, indicating destruction of individual structural planes of the mica. No new solid phase products or interlayer structures were detected in B. cereus cultures. Acidithiobacillus ferrooxidans cultures enhanced the chemical dissolution of the mineral and formed partially weathered interlayer structures, where interlayer K was expelled and coupled with the precipitation of K-jarosite [KFe3(SO4)2(OH)6].

Quantitative, chemical, and mineralogical characterization of flue gas desulfurization by-products.

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).

Relationships among plant available phosphorus, fertilizer sales, and water quality in northwestern Ohio.

Soluble reactive phosphorus (SRP) in northwestern Ohio river water has declined over the past 20 yr in response to decreased applications of fertilizer P. Our objective was to evaluate changes in soluble P (Bray-1 P) levels in the soil over time as influenced by fertilizer P management, cultivation practice, soil properties, and landscape factors. Because soil is the intermediary between added P and SRP measured in river water, we examined the relationship between fertilizer P, soluble soil P, and SRP. Using historical soil survey sample sites as a baseline for original soluble P concentrations (Por), we resampled Ap horizons to establish current levels of soluble P (Pcu). The Por baseline extended from 1953-1982 and Pcu from 1996-1998. Thirty percent of the Pcu values and 17% of the Por values were > or = 40 mg kg(-1). Log-transformed means for Pcu were significantly higher than for Por. The principal determining factors for Por were physiography, soil texture, and soil series. Current P is affected by present tillage practice and drainage class. Change in soluble P in the soil is not as responsive to fertilizer P sales as is SRP in river water. This suggests that as fertilizer P sales decline, a declining percentage of P added as fertilizer is annually dissolved and transported into the drainage system. Soluble P in soil is governed by a combination of fertilizer and tillage management, soil properties, and landscape factors interacting over time.