Abiotic Generation of Floating Iron (Fe) Hydroxide Film with Rainbow Reflection: A Preliminary Hypothesis Testing Study

Abstract

Iron (Fe) is special. It is the last stable element generated in stars. Fe is also at the center of many chemical dramas involving ferric Fe (Fe(III)) and ferrous Fe (Fe(II)) and their reduction/oxidation (redox) staged in our environments. In a separate study, naturally occurring floating film with rainbow reflection observed on the surface of some natural waters was successfully regenerated in a laboratory setting (see the poster of Zac Rush and Zoe Penn). Here we report a laboratory study to test the hypothesis proposed in the separate study that the floating film is Fe(III) hydroxide polymer film generated by oxidation of Fe(II) (microbially produced at water/soil interface and released to water surface) to Fe(III) at water/air interface. Our study showed that the floating rainbow reflection film was successfully generated using inundated sand particles mixed with an Fe(II) salt in a beaker (as a simulation of the inundated soil systems). The study further demonstrated that the floating film was successfully generated even in a simplest system of a beaker with the Fe(II) salt and water only. We also found that the amount of the floating film generated was dependent on the level of the Fe(II) salt and the level of free oxygen present in the water and headspace of the beaker. The evidences collected in this preliminary study jointly support the hypothesis on the natural phenomenon of the floating film involving a fascinating environmental redox drama.