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Publication . Article . 2016

Molecular-level understanding of malic acid retention mechanisms in ternary kaolinite-Fe(III)-malic acid systems: The importance of Fe speciation

Jianjun Yang; Jin Liu; Yongfeng Hu; Cornelia Rumpel; Nanthi Bolan; Donald L. Sparks;
Closed Access
Published: 13 Mar 2016 Journal: Chemical Geology, volume 464, pages 69-75 (issn: 0009-2541, Copyright policy )
Publisher: Elsevier BV

International audience; Multivalent cation interaction and mineral association play a vital role in organic carbon (OC) stability in tropical soils. However, the retention mechanisms of OC in mineral-cation-OC systems remain largely unclear at the molecular level. Of all OC forms, low molecular weight organic acids (LMWOAs) are readily biodegradable. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of malic acid (MA) in kaolinite-Fe(III)-MA systems with various Fe/MA molar ratios at pH similar to 3.5 using Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. Our results indicated the formed ferrihydrite mainly contributed to the enhanced MA retention through adsorption and/or coprecipitation at high Fe/MA molar ratios in kaolinite-Fe(III)-MA systems relative to kaolinite-MA systems. With the decrease of Fe/MA molar ratios, ternary complexation of MA with kaolinite via a tetrahedral Fe bridge occurred in kaolinite-Fe(III)-MA systems. This study highlighted the significant impact of Fe speciation on MA retention mechanisms in kaolinite-Fe(III)-MA systems under acidic conditions, and clearly showed the impact of ferrihydrite-induced adsorption/coprecipitation and Fe-bridged ternary complexation on MA retention in ternary kaolinite-Fe(III)MA systems, which will enhance our understanding of the dynamics of MA and other LMWOAs in tropical soils.

Subjects by Vocabulary

Microsoft Academic Graph classification: Adsorption Absorption (chemistry) Ferrihydrite Coprecipitation Extended X-ray absorption fine structure Kaolinite Malic acid chemistry.chemical_compound chemistry Ternary operation Inorganic chemistry


Geochemistry and Petrology, Geology, Carbon sequestration, Mineral-OC interaction, LMWOAs, Iron speciation, RAY-ABSORPTION SPECTROSCOPY, DISSOLVED ORGANIC-MATTER, EXAFS SPECTROSCOPY, CARBON, ALUMINUM, EXAFS, SOIL SOLUTION CONCENTRATIONS, FOREST SOILS, SURFACE COMPLEXES, SORPTION, [SDV]Life Sciences [q-bio], [SDE]Environmental Sciences, [SDV] Life Sciences [q-bio], [SDE] Environmental Sciences, carbon sequestration, EXAFS, iron speciation, LMWOAs, mineral-OC interaction