New publication in Chemosphere: Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

19.11.2020

Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5e15 min) accelerate the dissolution of iron(hydr) oxides by ligands during subsequent dark periods under anoxic conditions.

Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 mM EDTA or DFOB were illuminated with UV-A light of com-parable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10e40 and dissolved Fe(III) reached 50 mM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3e5 only during illumination. With DFOB dissolved Fe(III) reached 35 mM after 10 h of illumination, while with EDTA it peaked at 15 mM and then decreased to below 2 mM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled

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