Understanding the influence of soil development on contaminant reactivity along a fluvial chronosequence in the Oregon Coast Range

Weathering processes are recognized as drivers of soil and water resource sustainability, but how pedogenesis stage impacts contaminant reactivity and mobility in soils has been minimally investigated. The primary goal of this study was to quantify how soil development influences contaminant reactivity. To achieve this goal, soils from two depths (30 and 100 cm) across a chronosequence (ages 3.5, 20, 69, 140, 200, and 908 ky) in the Oregon Coast Range were subjected to arsenic (As) adsorption isotherms, with As removal from solution serving as a proxy for soil-contaminant reactivity. Langmuir models were applied to isotherm data to quantify relationships between contaminant retention capacity, soil age and soil physicochemical properties, and data revealed that 20 ky soils from a 30-cm-depth had the greatest affinity for As sorption (8,474.5 mg kg-1). Chemical extractions revealed that amorphous (oxy)hydroxides were the dominant mineral phases governing As sorption, even in the presence of abundant crystalline oxides. Micro-X-ray fluorescence spectroscopy revealed a strong spatial correlation between As and Fe in reacted soils. The abundance of amorphous minerals within soils is controlled by the balance between their production from weathering of primary minerals and their loss from ripening to crystalline minerals, and because the mode, extent and minerals governing contaminant sorption determine solid-aqueous phase partitioning, this knowledge will assist in improving models for predicting Critical Zone processes that govern the sustainability of soil and water quality.

Pyrogenic Carbon Promotes Anaerobic Oxidation of Methane Coupled with Iron Reduction via the Redox-Cycling Mechanism

Pyrogenic carbon (PC) can mediate electron transfer and thus catalyze biogeochemical processes to impact greenhouse gas (GHG) emissions. Here, we demonstrate that PC can contribute to mitigating GHG emissions by promoting the Fe(III)-dependent anaerobic oxidation of methane (AOM). It was found that the amendment PCs in microcosms dominated by Methanoperedenaceae performing Fe(III)-dependent AOM simultaneously promoted the rate of AOM and Fe(III) reduction with a consistent ratio close to the theoretical stoichiometry of 1:8. Further correlation analysis showed that the AOM rate was linearly correlated with the electron exchange capacity, but not the conductivity, of added PC materials, indicating the redox-cycling electron transfer mechanism to promote the Fe(III)-dependent AOM. The mass content of the C═O moiety from differentially treated PCs was well correlated with the AOM rate, suggesting that surface redox-active quinone groups on PCs contribute to facilitating Fe(III)-dependent AOM. Further microbial analyses indicate that PC likely shuttles direct electron transfer from Methanoperedenaceae to Fe(III) reduction. This study provides new insight into the climate-cooling impact of PCs, and our evaluation indicates that the PC-facilitated Fe(III)-dependent AOM could have a significant contribution to suppressing methane emissions from the world's reservoirs.

Experimental Investigation of Oxide Leaching Methods for Li Isotopes

To examine the applicability of different leaching methods used to extract secondary oxides from silicate solids for lithium isotope (δ⁷Li) measurement, this study has conducted leaching experiments on five different types of silicate solids, including a fresh basalt, two weathered basalts, a Yellow River sediment (loess-dominated) and a shale. Four factors were assessed in the experiments: the concentration of the leaching reagent hydroxylamine hydrochloride (HH), the leaching temperature (20 °C vs 95 °C), the leaching time and the reagent/solid ratio. Based on elemental concentrations and Li isotopes, 0.04 mol l^-1 hydroxylamine hydrochloride (HH) in 25% v/v acetic acid at room temperature for 1 h with 40 ml g^-1 reagent/solid ratio is recommended. At high temperatures, low δ⁷Li and high magnesium/iron ratios indicate that minerals other than secondary oxides are dissolved. With increased leaching time, there is no evidence for Li isotopic fractionation at room temperature. However, longer leaching time or increased reagent/solid ratios may increase the risk of leaching from non-oxide phases. Meanwhile, results suggest that low concentrations of HH are not sufficient to target the secondary oxides evenly, while high concentrations of HH can leach out more non-oxides. We also examined the optimal oxide leaching method within a full sequential leaching procedure (i.e., exchangeable, carbonate, oxide, clay and residual phases). Elemental concentrations show that no elements exist exclusively in oxides, so it is essential to analyse multi-elemental concentrations to verify that the leaching has accessed this phase in a given sample. Comparing secondary oxides with their corresponding solutions, we estimate the isotopic fractionation (Δ⁷Li_{oxide-solution}) is -16.8‰ to -27.7‰.

Direct identification of hazardous elements in ultra-fine and nanominerals from coal fly ash produced during diesel co-firing

This study has provided an initial assessment of the environmental impacts and potential health effects associated with coal fly ash produced during diesel co-firing. Many hazardous elements that are typically detected by multifaceted chemical characterization by XRD, petrology, FE-SEM/EDS, and HR-TEM/SEAD/FFT/EDS in ultra-fine compounds and nanominerals from the co-fired coal fly ashes (CFAs). It provided an in-depth understanding of coal ash produced during diesel co-firing. Several of the neoformed ultra-fine compounds and nano-minerals found in the coal ashes are the same as those commonly associated with oxidation/transformation of aluminosilicates, carbonates, sulphides and phosphates.