Suchergebnisse

AbstractTreatment of aqueous leachate from acid mine tailings with pristine biochar (BC) resulted in the removal of more than 90% of the dissolved arsenic with an attendant rapid and sustained pH buffering from 3 to 4. Pine forest waste BC was transformed to a highly effective adsorbent for arsenic remediation of acid mine drainage (AMD) because the dissolved iron induced "activation" of BC through accumulation of highly reactive ferric hydroxide surface sites. Physicochemical properties of the BC surface, and molecular mechanisms of Fe, S, and As phase transfer, were investigated using a multi-method, micro-scale approach (SEM, XRD, FTIR, XANES, EXAFS, and STXM). Co-located carbon and iron analysis with STXM indicated preferential iron neo-precipitates at carboxylic BC surface sites. Iron and arsenic X-ray spectroscopy showed an initial precipitation of ferrihydrite on BC, with concurrent adsorption/coprecipitation of arsenate. The molecular mechanism of arsenic removal involved bidentate, binuclear inner-sphere complexation of arsenate at the surfaces of pioneering ferric precipitates. Nucleation and crystal growth of ferrihydrite and goethite were observed after 1 h of reaction. The high sulfate activity in AMD promoted schwertmannite precipitation beginning at 6 h of reaction. At reaction times beyond 6 h, goethite and schwertmannite accumulated at the expense of ferrihydrite. Results indicate that the highly functionalized surface of BC acts as a scaffolding for the precipitation and activation of positively charged ferric hydroxy(sulf)oxide surface sites from iron-rich AMD, which then complex oxyanion arsenate, effectively removing it from porewaters.

Transport and reactivity of carbon in the critical zone are highly controlled by reactions of dissolved organic matter (DOM) with subsurface soils, including adsorption, transformation and exchange. These reactions are dependent on frequent wet–dry cycles common to the unsaturated zone, particularly in semi-arid regions. To test for an effect of wet–dry cycles on DOM interaction and stabilization in subsoils, samples were collected from subsurface (Bw) horizons of an Entisol and an Alfisol from the Catalina-Jemez Critical Zone Observatory and sequentially reacted (four batch steps) with DOM extracted from the corresponding soil litter layers. Between each reaction step, soils either were allowed to air dry (wet–dry treatment) before introduction of the following DOM solution or were maintained under constant wetness (continually wet treatment). Microbial degradation was the dominant mechanism of DOM loss from solution for the Entisol subsoil, which had higher initial organic C content, whereas sorptive retention predominated in the lower C Alfisol subsoil. For a given soil, bulk dissolved organic C losses from solution were similar across treatments. However, a combination of Fourier transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic analyses revealed that wet–dry treatments enhanced the interactions between carboxyl functional groups and soil particle surfaces. Scanning transmission X-ray microscopy (STXM) data suggested that cation bridging by Ca2+ was the primary mechanism for carboxyl association with soil surfaces. STXM data also showed that spatial fractionation of adsorbed OM on soil organo-mineral surfaces was diminished relative to what might be inferred from previously published observations pertaining to DOM fractionation on reaction with specimen mineral phases. This study provides direct evidence of the role of wet–dry cycles in affecting sorption reactions of DOM to a complex soil matrix. In the soil environment, where wet–dry cycles occur at different frequencies from site to site and along the soil profile, different interactions between DOM and soil surfaces are expected and need to be considered for the overall assessment of carbon dynamics. ; Binational Agricultural Research and Development (BARD) program [FI-534-2015]; National Science Foundation [EAR 13-31408]; Canadian Foundation for Innovation; Natural Sciences and Engineering Research Council of Canada; University of Saskatchewan; Government of Saskatchewan; Western Economic Diversification Canada; National Research Council Canada; Canadian Institutes of Health Research ; Open access journal. ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.

Abstract
Mine tailings contain multiple toxic metal(loid)s that pose a threat to human health via inhalation and ingestion. The goals of this research include understanding the speciation and molecular environment of these toxic metal(loid)s (arsenic and lead) as well as the impacts particle size and residence time have on their bioaccessibilty in simulated gastric and lung fluid. Additionally, future work will include smaller size fractions (PM10 and PM2.5) of surface mine tailings, with the goal of increasing our understanding of multi-metal release from contaminated geo-dusts in simulated bio-fluids. This research is important to environmental human health risk assessment as it increases the accuracy of exposure estimations to toxic metal(loid)s.

Intro -- Series Editor's Preface -- Contents -- 1 An Introduction to Biogeochemistry of the Critical Zone -- References -- 2 Hot Spots and Hot Moments in the Critical Zone: Identification of and Incorporation into Reactive Transport Models -- 2.1 Introduction -- 2.1.1 Definition of Terms -- 2.1.2 Scope and Overall Impact -- 2.2 Capturing Scales and Complexity Using Models -- 2.2.1 Hot Spots Within the Hyporheic Zone-The Redox Microzone Concept -- 2.2.2 HSHMs at the Floodplain Scale -- 2.2.3 HSHMs Along River Corridors -- 2.3 Current Understanding and the Path Forward -- 2.3.1 A Conceptual Take on HSHMs Using a Trait-Based Framework -- 2.3.2 Improvements in Field-Scale Characterization of Hyporheic Zones -- 2.3.3 Recent Developments in Observation and Modeling of Hot Spots Featuring the Sediment Water Interface -- 2.4 How Can Models Contribute? -- 2.4.1 Scale Aware Modeling/Parameterization -- 2.4.2 A Preemptive Prioritization of HSHMs -- 2.5 Concluding Remarks -- References -- 3 Constraints of Climate and Age on Soil Development in Hawai'i -- 3.1 Understanding Critical Zone Functioning Through State Factor Analysis -- 3.2 Physiographic Setting -- 3.3 Analytical Approach -- 3.4 Development of Critical Zone Properties Across the Hawaiian Islands -- 3.4.1 Weathering Depth and Chemical Denudation -- 3.4.2 Conditioning Lava Flows for Critical Zone Development -- 3.5 Biogeochemical Properties of Hawaiian Critical Zone -- 3.5.1 Weathering and Soil Properties -- 3.6 Soil Process Domains and Pedogenic Thresholds in Hawai'i -- 3.6.1 Process Domains -- 3.6.2 Transitions Among Process Domains -- 3.7 Conclusions -- References -- 4 Biofilms in the Critical Zone: Distribution and Mediation of Processes -- 4.1 Introduction -- 4.2 Documenting Environmental Biofilms Using the Scanning Electron Microscope -- 4.3 Biofilms in the Critical Zone.