Postgraduate Profiles

Nian Xu

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Thesis: Assessing effects of acid sulfate processes on behavior of rare-earth elements from river catchment to estuary

Acid sulfate soils (ASSs) is the common name for soils which contain metal sulfides (such as pyrite and iron monosulfide) and occur worldwide on coastal plains (McKenzie et al. 2004; Australian Government Department of the Environment 2014). In Australia, ASSs commonly occur in coastal areas and extensively stretch extensively along the eastern and northern coastline of Australia, while smaller areas exist in southern Western Australia, South Australia, Victoria and Tasmania (McKenzie et al. 2004; Dent & Pons 1995; Sullivan 2004). Exposure of sediments to oxygen during anthropogenic drainage, excavation, sea level changes and tectonic uplift has the potential to generate acidity by oxidation of the sulfidic minerals in acid sulfate soils (Edward D. Burton et al. 2008). The oxidation of acid sulfate soils commonly triggers the release of sulfide-associated trace elements (including REEs), which is of concern because of the potential toxicity of many trace elements (Edward D. Burton, Richard T. Bush & Leigh A. Sullivan 2006; Dent & Pons 1995; Degens 2009). Additionally, dredging of aquatic sediments and disposal of dredged material in aerobic environments is also known to oxidise sulfidic materials and release trace element contaminants (Morse, Presley & Taylor 1993).

Rare earth elements (REEs, the fifteen lanthanide series of elements La to Lu), plus the associated elements of scandium and yttrium, are known to have similar chemical properties. These elements are very important geochemically because their chemical behaviour is very similar, with minor systematic differences across the lanthanide series (e.g., solubility of mineral phases). Consequently a subset of the REE may become enriched or depleted during the geochemical process such as weathering or oxidation. This fractionation allows for REE to be used as geochemical tracers based on recognition and analysis of their fractionation patterns.

Why my research is important

The South Yunderup Main drain is directly affected by the disposal spoils from housing construction and dredging boat channels. Soil and water are contaminated by receiving acid sulfate soil drainage. Samples of drain & estuarine surface water, drain & estuarine sediments, and soils will be collected to study a complete ‘life cycle’ of REEs and metal chalcogenides.

This project will study on the behaviour of rare earth and associated elements during geo-chemical processes by investigating fractionation and distribution pattern of REEs in acid sulfate soils and receiving sediments. We aim to use an understanding of REE fractionation and redistribution to trace the origins and fate of acidity and contaminants in estuarine environments influenced by oxidised acid sulfate soil.

Funding

Aug 2013

Aug 2017

Contact

Supervisors