Ronald S. Sletten

Sorption and filtration of metals using iron-oxide-coated sand

Abstract Iron oxides are good adsorbents for uncomplexed metals, some metal-ligand complexes, and many metal oxyanions. However, the adsorbent properties of these oxides are not fully exploited in wastewater treatment operations because of difficulties associated with their separation from the aqueous phase. This paper describes experiments in which iron oxides were coated onto the surface of ordinary filter sand, and this composite media was used in a fixed bed configuration for simultaneous filtration of particulate matter and sorption of dissolved metals. The process was successful in removing uncomplexed and ammonia-complexed cationic metals (Cu, Cd, Pb, Ni, Zn), as well as some oxyanionic metals (SeO 3 , AsO 3 ), from simulated and actual waste streams over a wide range of metal concentrations. The adsorbent was stable during backwashing and regeneration operations, releasing most metals quantitatively; the exception was AsO 3 , which was not efficiently recovered by regeneration with either acid or base. The composite media is inexpensive to prepare and could serve as the basis of a useful metal removal and possibly metal recovery process in a variety of settings.

N isotope fractionation and measures of organic matter alteration during decomposition

Most soil organic matter (SOM) derives from plant material, but there are substantial gaps in our understanding of its transformation mechanisms. Alterations that occur as SOM decays and is stabilized have proved difficult to study owing largely to its diverse initial chemical composition and stable isotope values. We examined SOM stable isotope ratios in relation to composition using solid-state 13C Cross Polarization Magic Angle Spin (CPMAS) nuclear magnetic resonance (NMR) in sequentially deeper organic and mineral horizon soil samples collected from an unpolluted ecosystem in southeast Alaska, USA, dominated by C3 vegetation. We found that, as humified carbon (C not respired as CO2 during decomposition) increased in aliphaticity (ratio of unsubstituted aliphatics to carbohydrates), it also increased in 15N but showed no clear trend in 13C. These results imply that humification (and the concomitant stabilization of soil C) at our site resulted from microbial alteration of organics rather than from accu...

Adsorption of natural organic matter (NOM) on iron oxide: Effects on NOM composition and formation of organo-halide compounds during chlorination

A large fraction of the natural organic matter (NOM) in potable water sources can be extracted by adsorption onto iron-oxide-coated sand (IOCS). In this research, two water sources were characterized with respect to their hydrophobic/hydrophilic fractionation, their 13C NMR and UV absorbance spectra and their reactivity with chlorine, before and after the waters were contacted with IOCS. The IOCS preferentially adsorbs acidic fractions of NOM and NOM molecules that are enriched in aromatic and carboxylic carbon. The yield of chloro-organic compounds (quantified as total organo-halide) produced upon chlorination of the NOM or its major fractions correlates with the specific absorbance (As) at 254 nm. IOCS may be useful for removing disinfection by-product (DBP) precursors from potable waters and/or as a medium for NOM accumulation.

SEQUENTIALLY EXTRACTED ARSENIC FROM DIFFERENT SIZE FRACTIONS OF CONTAMINATED SOILS

Five soils from Austria that have high contents of arsenic (As)due to anthropogenic and/or geogenic sources were separated intosand, silt, and clay fractions. The distribution of As among theparticle-size fractions was clay >> silt > sand. Theparticle-size fractions were analysed according to an 8-stepsequential extraction procedure (SEP) designed to assess theprimary reservoirs and extractability of As. Steps 1 and 2,(i.e. NH4NO3 and (NH4)2SO4) extractedthe least As, while considerably greater amounts were extractedin steps 3, 4 and 5 (i.e. NH4H2PO4,NH2OH-HCl, and NH4F). The greatest amounts of As wereextracted in steps 6 and 7, both NH4-oxalate extractantstargeting the amorphous and crystalline oxide fractions. Theresidual fraction (step 8) was typically low. The extraction ofthe clays contained generally more As in steps 3 to 8, while Asrelease in the first two steps was typically highest in the sandand silt fractions. These findings are in accord with factoranalysis indicating that the extractants of the SEP areseparated into weak (steps 1 and 2) and strong (steps 3 to 8)extractants. SEP data along with microprobe analyses (X-raymicroanalyses) indicate that most As is associated with Fe andis therefore not readily mobile. Anyhow, As could be releasedupon changes in redox potential or pH. The greaterextractability of As from sand fractions using weak extractantsmay explain the higher toxicity of As in coarse-textured soils,as found in previous studies.

Arsenic adsorption by soils and iron‐oxide‐coated sand: kinetics and reversibility

Arsenic has recently received increasing attention due to its high toxicity and to the possible risks for human and environmental health associated with As-polluted soils. The present work deals with the kinetics and reversibility of As sorption by Fe-oxide-coated sand (IOCS) and soils with different chemical and physical characteristics. Soils and IOCS were equilibrated for five different periods of time with solutions containing As (III) and/or (V) in order to study the kinetics of As adsorption. After 1, 10 and 30 days of equilibration soils and IOCS were sequentially extracted to assess the effect of aging on the binding forms of As. The kinetics of arsenite and arsenate adsorption varied among the soils as a result of differential soil characteristics. The conversion of As to less mobile forms was demonstrated using a sequential extraction. The amount of As extracted with weaker extractants decreased with time whereas the amount of As in more recalcitrant fractions increased. This conversion is expected to render As less mobile and toxic with time after addition to the soil. Arsenadsorption an Boden und Eisenoxid-ummanteltem Sand: Kinetik und Reversibilitat Erhohte Gehalte von Arsen in Boden sind wegen seiner Toxizitat und den damit verbundenen Risiken fur die menschliche Gesundheit und die Umwelt zunehmend Gegenstand von Untersuchungen. Die vorliegende Arbeit befast sich mit der Kinetik und Reversibilitat der Bindung von Arsen in Boden mit unterschiedlichen Eigenschaften und an mit Eisenoxid umhulltem Sand (IOCS). Die Boden und der als Modellsubstanz verwendete IOCS wurden zur Erfassung der Adsorptionskinetik uber funf verschieden lange Perioden mit Losungen equilibriert, die As(III), As(V) bzw. beide Arsenspezies enthielten. Nach 1, 10 und 30 Tagen wurden die Materialien einer sequentiellen Extraktion unterzogen, um die Reversibilitat der Reaktion zu untersuchen. Die Reaktionskinetik der Adsorption war von den Bodeneigenschaften abhangig. Durch sequentielle Extraktion konnte gezeigt werden, das adsorbiertes Arsen mit der Zeit in weniger losliche Formen umgewandelt wurde. Daraus kann man folgern, das die Mobilitat und somit die Toxizitat von Arsen, das in den Boden gelangt, mit der Verweildauer abnimmt.

Soil carbon dynamics across a windthrow disturbance sequence in southeast Alaska

Few studies have examined the influence of natural disturbances, such as windthrow, on soil organic matter formation, stabilization, and loss in soils. In shallow (<1 m) mountain forest soils, windthrow activity may result in the redistribution and mixing of mineral and organic soil horizons down to bedrock. We studied the patterns of soil carbon, the dominant constituent of soil organic matter, in watersheds along a windthrow disturbance sequence in a mountainous temperate rain forest in southeast Alaska. Our objectives were (1) to evaluate the influence of windthrow and illuviation on the accumulation of soil organic carbon in mineral horizons and (2) to compare the forms of soil organic matter that have accumulated. Soils were described, and the thickness of the major organic and mineral horizons was measured, every 5 m along transects in three watersheds with contrasting windthrow histories. A subset of the soil description sites was randomly selected and then sampled to determine the quantity and qua...

Fast-growing till over ancient ice in Beacon Valley, Antarctica

We analyze published cosmogenic 3He depth profiles through the till that covers relict glacier ice in Beacon Valley, Antarctica, in order to derive rigorous constraints on the till thickness history, and on the amount and rate of ice loss by sublimation. The till is a residue of debris-laden ice that sublimed. The 3He profiles show that the lower 80% of the till formed in the past 310–43 k.y. under sublimation rates averaging >7 m·m.y.−1 (meters per million years). Such rapid recent growth of the till contradicts previous interpretations that it is older than 8.1 Ma at an adjacent site, where it encloses volcanic ash of this age. We question whether the ash provides a valid age constraint for the ice. Cosmogenic nuclide analysis of the till where the ash was collected for dating should resolve this question.

Physical-chemical treatment of landfill leachate for metals removal

Abstract A detailed treatability study investigating metals removal from leachates collected from a sanitary landfill is presented. Experiments investigated treatment of raw leachate from younger and older zones of the landfill and of a mixture of the two leachates (representing an average leachate from the landfill). The metal concentrations and COD in leachate from the older area were approximately one order of magnitude greater than in leachate from the active area. The leachates contained significant quantities of reduced iron and manganese that, upon aeration and base addition, were precipitated and served as sorbents for trace metals that were present at much lower concentrations. Most trace metals in the younger zone leachate and in the leachate mixture were removed by adjusting solution pH to 9.0, but in leachates collected from the older landfill area, even raising the pH to 11.0 did not remove all the trace metals efficiently. Various options for treating a blend of leachate from the older and younger areas (20%:80% by volume) were evaluated. One of the key design decisions was whether to aerate the leachate prior to pH adjustment. Trace metals could be removed efficiently from the leachate with or without aeration. Benefits of aeration include increased formation of iron oxide adsorbent and a significant reduction in the amount of base required to raise the pH, since aeration strips large amounts of CO2 from the leachates. Drawbacks include decreased sludge settleability and the cost of the aeration process itself. The settleability of the aerated sludge could be increased 5–10 fold by the addition of anionic polymer. Sludge produced was not toxic as determined by TCLP. Trade-offs implicit in these results are addressed both experimentally and theoretically.

Diversity and potential sources of microbiota associated with snow on western portions of the Greenland Ice Sheet

Snow overlays the majority of the Greenland Ice Sheet (GrIS). However, there is very little information available on the microbiological assemblages that are associated with this vast and climate-sensitive landscape. In this study, the structure and diversity of snow microbial assemblages from two regions of the western GrIS ice margin were investigated through the sequencing of small subunit ribosomal RNA genes. The origins of the microbiota were investigated by examining correlations to molecular data obtained from marine, soil, freshwater and atmospheric environments and geochemical analytes measured in the snow. Snow was found to contain a diverse assemblage of bacteria (Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria) and eukarya (Alveolata, Fungi, Stramenopiles and Chloroplastida). Phylotypes related to archaeal Thaumarchaeota and Euryarchaeota phyla were also identified. The snow microbial assemblages were more similar to communities characterized in soil than to those documented in marine ecosystems. Despite this, the chemical composition of snow samples was consistent with a marine contribution, and strong correlations existed between bacterial beta diversity and the concentration of Na(+) and Cl(-) . These results suggest that surface snow from western regions of Greenland contains exogenous microbiota that were likely aerosolized from more distant soil sources, transported in the atmosphere and co-precipitated with the snow.

The rock abrasion record at Gale Crater: Mars Science Laboratory results from Bradbury Landing to Rocknest

Ventifacts, rocks abraded by wind-borne particles, are found in Gale Crater, Mars. In the eastward drive from “Bradbury Landing” to “Rocknest,” they account for about half of the float and outcrop seen by Curiositys cameras. Many are faceted and exhibit abrasion textures found at a range of scales, from submillimeter lineations to centimeter-scale facets, scallops, flutes, and grooves. The drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow. This upwind direction is inconsistent with predictions based on models and the orientation of regional dunes, suggesting that these ventifact features formed from very rare high-speed winds. The absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today.