The synergistic effect of calcium on organic carbon sequestration to ferrihydrite

作者：Tyler D. Sowers, Jason W. Stuckey, Donald L. Sparks · 发表于：Geochemical Transactions · 年份：2018 · DOI：10.1186/s12932-018-0049-4 · 被引用次数：121 · 研究领域：Iron oxide chemistry and applications、Clay minerals and soil interactions、Arsenic contamination and mitigation

Sequestration of organic carbon (OC) in environmental systems is critical to mitigating climate change. Organo-mineral associations, especially those with iron (Fe) oxides, drive the chemistry of OC sequestration and stability in soils. Short-range-ordered Fe oxides, such as ferrihydrite, demonstrate a high affinity for OC in binary systems. Calcium commonly co-associates with OC and Fe oxides in soils, though the bonding mechanism (e.g., cation bridging) and implications of the co-association for OC sequestration remain unresolved. We explored the effect of calcium (Ca 2+ ) on the sorption of dissolved OC to 2-line ferrihydrite. Sorption experiments were conducted between leaf litter-extractable OC and ferrihydrite at pH 4 to 9 with different initial C/Fe molar ratios and Ca 2+ concentrations. The extent of OC sorption to ferrihydrite in the presence of Ca 2+ increased across all tested pH values, especially at pH ≥ 7. Sorbed OC concentration at pH 9 increased from 8.72 ± 0.16 to 13.3 ± 0.20 mmol OC g −1 ferrihydrite between treatments of no added Ca 2+ and 30 mM Ca 2+ addition. Batch experiments were paired with spectroscopic studies to probe the speciation of sorbed OC and elucidate the sorption mechanism. ATR-FTIR spectroscopy analysis revealed that carboxylic functional moieties were the primary sorbed OC species that were preferentially bound to ferrihydrite and suggested an increase in Fe-carboxylate ligand exchange in the presence of Ca at pH 9. Results from batch to ...