†Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, United States.
‡Department of Environmental Geosciences, University of Vienna, 1010 Vienna, Austria.
Environ Sci Technol. 2015 Jun 16;49(12):7236-44. doi: 10.1021/acs.est.5b01191. Epub 2015 May 22.
Ligand-promoted dissolution and reductive dissolution of iron (hydr)oxide minerals control the bioavailability of iron in many environmental systems and have been recognized as biological iron acquisition strategies. This study investigated the potential synergism between ligands (desferrioxamine B (DFOB) or N,N'-Di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED)) and a reductant (ascorbate) in goethite dissolution. Batch experiments were performed at pH 6 with ligand or reductant alone and in combination, and under both oxic and anoxic conditions. Goethite dissolution in the presence of reductant or ligand alone followed classic surface-controlled dissolution kinetics. Ascorbate alone does not promote goethite dissolution under oxic conditions due to rapid reoxidation of Fe(II). The rate coefficients for goethite dissolution by ligands are closely correlated with the stability constants of the aqueous Fe(III)-ligand complexes. A synergistic effect of DFOB and ascorbate on the rate of goethite dissolution was observed (total rates greater than the sum of the individual rates), and this effect was most pronounced under oxic conditions. For HBED, macroscopically the synergistic effect was hidden due to the inhibitory effect of ascorbate on HBED adsorption. After accounting for the concentrations of adsorbed ascorbate and HBED, a synergistic effect could still be identified. The potential synergism between ligand and reductant for iron (hydr)oxide dissolution may have important implications for iron bioavailability in soil environments.
配体促进的溶解和还原溶解铁（氢）氧化物控制着许多环境系统中铁的生物利用度，并被认为是生物获取铁的策略。本研究考察了配体（去铁胺 B（DFOB）或 N，N'-二（2-羟基苄基）乙二胺-N，N'-二乙酸（HBED））和还原剂（抗坏血酸）在针铁矿溶解中可能存在的协同作用。在 pH 6 下进行了批实验，单独使用配体或还原剂，以及在有氧和无氧条件下进行了实验。单独使用还原剂或配体时，针铁矿的溶解遵循经典的表面控制溶解动力学。由于 Fe(II) 的快速再氧化，抗坏血酸单独在有氧条件下不会促进针铁矿的溶解。配体对针铁矿的溶解速率系数与水溶液中 Fe(III)-配体络合物的稳定常数密切相关。DFOB 和抗坏血酸对针铁矿溶解速率有协同作用（总速率大于单个速率之和），这种作用在有氧条件下最为明显。对于 HBED，由于抗坏血酸对 HBED 吸附的抑制作用，宏观上协同作用被隐藏。在考虑到吸附的抗坏血酸和 HBED 的浓度后，仍能识别出协同作用。配体和还原剂对铁（氢）氧化物溶解的潜在协同作用可能对土壤环境中铁的生物利用度有重要影响。
