Samuel J. Traina

Schwertmannite and the chemical modeling of iron in acid sulfate waters

Abstract Analyses of ochreous sediments and associated solutions from twenty-eight mine drainage sites showed that precipitates formed at pH 6.5 or higher were composed of ferrihydrite (nominally Fe5HO8 · 4H2O) or a mixture of ferrihydrite and goethite (α-FeOOH), whereas those precipitated from waters having pH values in the range of 2.8 to 4.5 were predominantly schwertmannite (ideally Fe8O8(OH)6SO4) with trace to minor amounts of goethite. Solutions of intermediate pH values produced mixtures of ferrihydrite and schwertmannite. Only one sample, formed at pH 2.6, contained a significant amount of jarosite (H, K, Na)Fe3(OH)6(SO4)2. A solubility window of log IAPSh = 18.0 ± 2.5 was calculated for schwertmannite from selected mine drainage solutions with pH values in the range of 2.8 to 3.2. The relationship between pH and log αFe3 over the full range of drainage waters was consistent with published results from other sources, and the combined mineralogy-chemistry data were used to compute a new pe-pH diagram for the system FeSKOH that included a field of metastability for schwertmannite. The metastable nature of schwertmannite was confirmed in a long-term (1739 d) aqueous equilibrium study wherein a pure, synthetic specimen was completely transformed to goethite over a period of 543 days. The pH and computed activity of Fe 3+ in the final equilibrium solutions yielded a log KGT = 1.40 ± 0.01 for goethite. Additional field data supporting a paragenetic relationship between jarosite, schwertmannite, ferrihydrite, and goethite were obtained from a naturally acid alpine stream. Similar results were predicted from the water chemistry using a nonequilibrium reaction path model that included appropriate solubility data for the mineral phases of interest.

Lead Immobilization from Aqueous Solutions and Contaminated Soils Using Phosphate Rocks

This research investigated the effectiveness of phosphate rocks in immobilizing Pb from aqueous solutions and contaminated soils. Different amounts of phosphate rocks were reacted with aqueous solutions containing Pb or with Pb-contaminated soils. The results show that phosphate rocks were effective in immobilizing Pb from aqueous solutions with a minimum Pb removal of 38.8-100%. The reaction time had less effect on Pb immobilization than the quantity of phosphate rocks used. Selected phosphate rocks reduced water-soluble Pb from a contaminated soil by 56.8-100%. The primary mechanism of Pb immobilization was via dissolution of phosphate rocks and precipitation of a fluoropyromorphite-like mineral. Different methods of mixing phosphate rocks and soil and incubation time had little effect on Pb immobilization. Our results strongly demonstrate that phosphate rocks may provide a cost-effective way to remediate Pb-contaminated water, soils, and wastes.

Effects of Aqueous Al, Cd, Cu, Fe(II), Ni, and Zn on Pb Immobilization by Hydroxyapatite

The effects of aqueous Al, Cd, Cu, Fe(II), Ni, or Zn on Pb immobilization by hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] were studied. Lead was removed mainly via hydroxyapatite dissolution and hydroxypyromorphite [Pb 10 (PO 4 ) 6 (OH) 2 ] precipitation in the presence of these metals with a Pb removal efficiency of 37-100%. These metals inhibited Pb immobilization by hydroxyapatite in the order. Al>Cu>Fe(II)>Cd>Zn>Ni and Cu>Fe(II)>Cd>Zn>Al>Ni at high and low initial Pb concentrations, respectively. The inhibition was probably through the precipitation of amorphous to poorly crystalline metal phosphates, decreasingthe amountofdissolved P available for precipitation with dissolved Pb ions

Sorption of zn2+ and cd2+ on hydroxyapatite surfaces.

This study examines the mechanisms and kinetics of Zn 2+ and Cd 2+ sorption onto hydroxyapatite surfaces. The concentrations of Zn 2+ and Cd 2+ in the study rage from 0 to 2.5 mmol/L. Although the sorption data follow Langmuir isotherms, a detailed examination reveals that surface complexation and coprecipitation are the most important mechanisms with possibly ion exchange and solid diffusion also contributing to the overall sorption process. pH-controlled experiments point to significant deprotonation of hydroxyapatite surface and sorption by metal complexation with surface functional groups such as ≡POH. The major metal surface species are likely to be ≡POZn + and ≡POCd + .

Experimental and theoretical vibrational spectroscopic evaluation of arsenate coordination in aqueous solutions, solids, and at mineral-water interfaces

Arsenate (AsO43−) is a common species in oxidizing aquatic systems and hydrothermal fluids, and its solubility and partitioning into different mineral phases are determined by the nature of AsO43− coordination, solution pH, type of soluble cations, and H2O structure at the mineral-fluid interfaces. While the vibrational spectroscopy has been widely used in examining the AsO43− coordination chemistry, insufficient knowledge on the correlation of AsO43− molecular structure and its vibrational spectra impeded the complete spectral interpretation. In this paper, we evaluated the vibrational spectroscopy of AsO43− in solutions, crystals, and sorbed on mineral surfaces using theoretical (semiempirical, for aqueous species) and experimental studies, with emphasis on the protonation, hydration, and metal complexation influence on the As-O symmetric stretching vibrations. Theoretical predictions are in excellent agreement with the experimental studies and helped in the evaluation of vibrational modes of several arsenate-complexes and in the interpretation of experimental spectra. These vibrational spectroscopic studies (IR, Raman) suggest that the symmetry of AsO43− polyhedron is strongly distorted, and its As-O vibrations are affected by protonation and the relative influence on AsO43− structure decreases in the order: H+ ≫ cation ≥ H2O. For all AsO43− complexes, the As-OX symmetric stretching (X = metal, H+, H2O; ≤820 cm−1) shifted to lower wavenumbers when compared to that of uncomplexed AsO43−. In addition, the As-OH symmetric stretching of protonated arsenates in aqueous solutions shift to higher energies with increasing protonation (<720, <770, <790 cm−1 for HAsO42−, H2AsO4−, and H3AsO40, respectively). The protonated arsenates in crystalline solids show the same trend with little variation in As-OH symmetric stretching vibrations. Since metal complexation of protonated AsO43− does not influence the As-OH vibrations significantly, deducing symmetry information from their vibrational spectra is difficult. However, for metal unprotonated-AsO43− complexes, the shifts in As-OM (M = metal) vibrations are influenced only by the nature of complexing cation and the type of coordination, and hence the AsO43− coordination environment can be interpreted directly from the splitting of As-O degenerate vibrations and relative shifts in the As-OM modes. This information is critical in evaluating the structure of AsO43− sorption complexes at the solid-water interfaces. The vibrational spectra of other tetrahedral oxoanions are expected to be along similar lines.

VIBRATIONAL SPECTROSCOPY OF FUNCTIONAL GROUP CHEMISTRY AND ARSENATE COORDINATION IN ETTRINGITE

The functional group chemistry and coordination of AsO43−-sorption complexes in ettringite [Ca6Al2(SO4)3(OH)12·26H2O] were evaluated as a function of sorption type (adsorption, coprecipitation) and pH using Raman and Fourier Transform infrared (FTIR) spectroscopies. The reactive functional groups of ettringite, ≡Al-OH, ≡Ca-OH2, and ≡Ca2-OH exhibit broad overlapping OH bands in the range 3600–3200 cm−1, prohibiting separation of component vibrational bands. The SO42− polyhedra of the channels are present in three crystallographically different sites and exhibit weakly split S-O asymmetric stretch at 1136 cm−1 (with several components) and symmetric stretch at 1016, 1008, and 989 cm−1. During AsO43− adsorption, the vibrational spectra of SO42− were least affected, and the OH stretching intensities around 3600 cm−1 decreased with an increase in AsO43− sorption. In contrast, the S-O symmetric stretch at 1016 and 1008 cm−1 were almost completely removed, and the OH vibrations were relatively unaffected during AsO43−-coprecipitation. The As-O asymmetric stretch of sorbed AsO43− are split and occur as overlapping peaks around 870 cm−1. The As-Ocomplexed stretching vibrations are at ∼800 cm−1. The low pH samples (pH = 10.3–11.0) exhibit distinct As-OH stretching vibrations at 748 cm−1, indicating that some of the sorbed AsO43− ions are protonated. These spectral features demonstrate that AsO43− directly interacts with ettringite surface sites during adsorption and substitute inside the channels during coprecipitation (preferentially for two of the three sites). The energy position of the As-O symmetric stretch vibrations suggest that the AsO43− polyhedra interacts predominantly with ≡Ca-OH2 and ≡Ca2-OH sites rather than with ≡Al-OH sites. Sorption of more than one type of As species was evident in low pH (<11.0) samples.

Effects of NO3-, Cl-, F-, SO42-, and CO32- on Pb2+ Immobilization by Hydroxyapatite.

Remediation of Pb-contaminated wastes has received considerable attention recently. We have previously shown that hydroxyapatite [Ca 5 (PO 4 ) 3 OH] can reduce Pb 2+ concentrations below the EPA action level (72.4 nmol L -1 ) and, thus, has the potential for in situ Pb 2+ immobilization against leaching. This research investigated the effects of NO 3 - , Cl - , F - , SO 4 2- , and CO 3 2- on hydroxyapatite-Pb 2+ interactions. Solutions containing initial Pb 2+ concentrations of 24.1-482 μmol L -1 were reduced to below 72.4 nmol L -1 after reaction with hydroxyapatite, except in the presence of high levels of CO 3 2- and Pb 2+

Adsorption of (poly)maleic acid and an aquatic fulvic acid by geothite

The adsorption of Suwannee River fulvic acid (SRFA) and a synthetic organic polymer, polymaleic acid (PMA) by geothite was studied. The adsorption density of the sorbates decreased with increasing pH, and the data could best be described by the Langmuir adsorption equation. The number- and weight-averaged molecular weights, Mw and Mn, of the sorbates in the solution phase before and after adsorption by geothite were measured by high-pressure size exclusion chromatography. The observed decreases in the Mn and Mw of SRFA in the solution phase after adsorption demonstrated that fractionation of SRFA on the basis of molecular size occured. UV molar absorptivities measured at 280 nm also decreased, which suggests that the more aromatic moieties are preferentially adsorbed. Potentiometric titrations conducted on SRFA revealed changes in the conditional acidity constants (expressed as the negative logarithm, pKa) of the fulvic acid after adsorption. The increased pKa value of the humic material remaining in the solution after adsorption implies that the strongly sorbing compounds possessed stronger acidic functional groups. Fractionation of PMA after adsorption, however, did not occur to the same extent compared to SRFA because PMA is relatively homogeneous. The experimental results confirm that molecular weight, aromaticity, and organic acidity are major factors controlling the fractionation of natural organic matter (NOM) by adsorption onto hydrous mineral oxides. PMA, a relatively uniform and less polydisperse organic polymer, may serve as an endmember material characteristic of NOM that exhibits the least amount of fractionation upon adsorption.

Significance of earthworms in stimulating soil microbial activity

Abstract The stimulatory effect of earthworms (Lumbricus terrestris L.) on soil microbial activity was studied under microcosm-controlled conditions. The hypothesis was tested that microbial stimulation observed in the presence of a soil invertebrate would be due to the utilization of additional nutritive substances (secretion and excretion products) that it provides. Changes in microbial activity were monitored by measuring simultaneously CO2 release and protozoan population density. The increase in CO2 released in the presence of earthworms was found to result from both earthworm respiration and enhanced microbial respiration. The stimulation of microbial activity was confirmed by a significant increase in protozoan population density, which was 3–19 times greater in the presence of earthworms. The respiratory rate of L. terrestris was estimated to be 53 μl O2 g–1 h–1. Earthworm respiration significantly correlated with individual earthworm weight, but there was no correlation between the increase in microbial respiration and earthworm weight. This finding does not support the hypothesis given above that enhanced microbial respiration is due to utilization of earthworm excreta. A new hypothesis that relationships between microbial activity and earthworms are not based on trophic links alone but also on catalytic mechanisms is proposed and discussed.

Role of lumbricus terrestris (L.) burrows on quality of infiltrating water

Abstract Long-term watershed studies at the North Appalachian Experimental Watershed, Coshocton, Ohio have shown that when corn ( Zea mays L.) is planted in soil covered by the residue of the previous crop (i.e. no-tillage management), surface runoff from summer storms is greatly reduced. In addition, the residue cover provides a favorable environment for various soil invertebrates, especially earthworms. During high-intensity rainstorms, some of the water that infiltrates in no-till corn fields moves rapidly downward in burrows made by the earthworms Lumbricus terrestris L. Samplers were developed for collecting infiltrating rain water flowing in L. terrestris burrows at a depth of 45cm below the soil surface. With annual surface applications of 175 kg N ha −1 as NH 4 NO 3 , concentrations of NO 3 -N in water flowing in individual burrows during growing season storms ranged up to 152 mg l −1 . Concentrations of NO 3 -N tended to be lowest after prolonged wet soil conditions and highest after intermittent warm, dry periods. Distilled water poured directly into the surface openings of L. terrestris burrows and immediately collected as it drained into samplers, contained up to 40 mg of NO 3 -N I −1 , a value greater than that measured in many of the samples resulting from natural rain storms. Water and herbicide mixtures poured through L. terrestris burrows showed that the linings of the burrow, or drilosphere, may contribute nitrogen to the infiltrating water while greatly reducing the concentrations of atrazine and alachlor.