Dr Ellen Moon

My research focusses on heavy metals in the environment: how they move through landscapes, the risk they pose, and how to clean them up.

My research combines

• Field- and lab-based chemistry
• Advanced spectroscopic and scattering techniques
• Geochemical modelling

to understand the molecular-scale processes that underpin landscape-scale geochemistry. Research highlights include:

Mineral transformations in coastal acid sulfate soils

The formation and persistence of the meta-stable iron sulfide mineral greigite is an important step in the remediation of coastal acid sulfate soils, but the response of greigite to periods of oxygenation (for example, during a neap tide) is poorly understood. In this study, we employed X-ray absorption spectroscopy to identify the Fe and S speciation and mineralogy resulting from the oxidative disintegration of synthetic greigite under neap tide conditions. Results indicate divergent Fe and S mineralization pathways culminating in elemental sulfur and iron (hyr)oxide minerals. No sulfate-containing minerals were identified, and under all conditions tested, residual greigite remained. The oxidation products, and the presence of sulfur reducing bacteria, provide the right chemical environment for the reformation of greigite during the sub-oxic conditions of the rest of the tidal cycle. This likely explains the persistence of greigite in the intertidal zone, and implies that the oxidation of greigite is not detrimental to the long term stability of the acid sulfate soil remediation process.

Bushfires mobilize arsenic in Australian soils

Fires in iron-rich seasonal wetlands can thermally transform soil minerals and alter their crystallinity. However, the fate of As associated with thermally transformed iron minerals is unclear. We subjected As(V)-coprecipitated schwertmannite to thermal transformation (200-800 °C). Heating to >400 °C caused transformation of schwertmannite to a nanocrystalline hematite with greater surface area and smaller particle size. Higher temperatures also caused the initially structurally incorporated As to become progressively more exchangeable, increasing surface-complexed As by up to 60-fold, thereby triggering enhanced As mobilization upon reflooding. Further research is warranted to unravel the wider implications for water quality in natural wetlands.

Adapting uranium mineral processing circuits to tolerate seawater

Using X-ray absorption spectroscopy, we identified the mechanism by which chloride impacts the extraction of U(VI) by a weak base anion exchange resin from acidic sulfate solutions. The amount of chloride present affects U(VI) speciation both in the feed solutions and adsorbed by the resin, and we find three distinct U(VI) species taken up by the resin across the salinity gradient, directly corresponding to changes in levels of U(VI) extraction. These findings are integral to the effective design of mineral processing circuits incorporating seawater—a cheaper and more sustainable water source than fresh water.

SET111 - Environmental Design

SEV201 - Environmental Health Engineering