Synthesis, morphological–structural characterization and magnetic properties of amorphous iron (III)-oxyhydroxy-phosphate nanoparticles

Enhanced immobility of Pb(II) during ferrihydrite-Pb(II) coprecipitates aging impacted by malic acid or phosphate

Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging.

Thermal Stability and Decomposition Products of P-Doped Ferrihydrite

This work aimed to determine the effect of various amounts of P admixtures in synthetic ferrihydrite on its thermal stability, transformation processes, and the properties of the products, at a broad range of temperatures up to 1000 °C. A detailed study was conducted using a series of synthetic ferrihydrites Fe5HO8·4H2O doped with phosphates at P/Fe molar ratios of 0.2, 0.5, and 1.0. Ferrihydrite was synthesized by a reaction of Fe2(SO4)3 with 1 M KOH at room temperature in the presence of K2HPO4 at pH 8.2. The products of the synthesis and the products of heating were characterized at various stages of transformation by using differential thermal analysis accompanied with X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. Coprecipitation of P with ferrihydrite results in the formation of P-doped 2-line ferrihydrite. A high P content reduces crystallinity. Phosphate significantly inhibits the thermal transformation processes. The temperature of thermal transformation increases from below 550 to 710-750 °C. Formation of intermediate maghemite and Fe-phosphates, is observed. The product of heating up to 1000 °C contains hematite associated with rodolicoite FePO4 and grattarolaite Fe3PO7. Higher P content greatly increases the thermal stability and transformation temperature of rodolicoite as well.

Phosphate inhibits in vitro Fe3+ loading into transferrin by forming a soluble Fe(III)-phosphate complex: a potential non-transferrin bound iron species

In chronic kidney diseases, NTBI can occur even when total iron levels in serum are low and transferrin is not saturated. We postulated that elevated serum phosphate concentrations, present in CKD patients, might disrupt Fe(3+) loading into apo-transferrin by forming Fe(III)-phosphate species. We report that phosphate competes with apo-transferrin for Fe(3+) by forming a soluble Fe(III)-phosphate complex. Once formed, the Fe(III)-phosphate complex is not a substrate for donating Fe(3+) to apo-transferrin. Phosphate (1-10mM) does not chelate Fe(III) from diferric transferrin under the conditions examined. Complexed forms of Fe(3+), such as iron nitrilotriacetic acid (Fe(3+)-NTA), and Fe(III)-citrate are not susceptible to this phosphate complexation reaction and efficiently deliver Fe(3+) to apo-transferrin in the presence of phosphate. This reaction suggests that citrate might play an important role in protecting against Fe(III), phosphate interactions in vivo. In contrast to the reactions of Fe(3+) and phosphate, the addition of Fe(2+) to a solution of apo-transferrin and phosphate lead to rapid oxidation and deposition of Fe(3+) into apo-transferrin. These in vitro data suggest that, in principle, elevated phosphate concentrations can influence the ability of apo-transferrin to bind iron, depending on the oxidation state of the iron.