Photoreductive dissolution of Fe-containing mineral dust particles in acidic media

In this study, the photoreductive dissolution of Fe-containing mineral dust particles in acidic media is investigated. Photolysis experiments were performed using a solar simulator to irradiate acidic mineral dust suspensions prepared from source materials of Inland Saudi sand (IS), Saharan sand (SS) and one commercial sample, Arizona test dust (AZTD). The results show that Fe dissolution is a pH-dependent process, and total Fe solubility decreases with the solution pH increasing. Comparing iron dissolution from different source materials, Fe(II)-containing AZTD is more soluble than IS and SS samples, irrespective of the presence or absence of light. Experiments performed at three different temperatures of 278, 293, and 308 K show that both total dissolved Fe and dissolved Fe(II) increase with temperature and upon light exposure. Results of dissolution studies with AZTD performed at low pH also illustrate that the nature of the acid strongly influences iron solubilization. Fe solubility decreases in the suspensions of H2SO4 and HNO3 in the presence of light, whereas Fe solubility increases in the HCl solution under the irradiation compared to the dark reaction. Finally, our results confirm earlier work showing that photoreductive dissolution of Fe is very sensitive to dissolved oxygen. Results from this laboratory study show that mineralogy and speciation of iron, as well as environmentally relevant factors including pH, light, O-2, and nature of the inorganic anion, NO3-, SO42 -, and Cl-, must be considered when modeling the input of iron to the oceans.