Laura Wegner, University of Bayreuth

Re-aeration of iron(III)-reducing environments: Exploring the coupling of
antimony mobility and iron mineral precipitation

Antimony (Sb) is a suspected carcinogenic substance and listed as a pollutant of priority interest. Despite its toxicity, it is used and mined in increasing quantities. This has resulted in a steadily growing legacy of environmental Sb contamination. What follows is a significant risk to environmental and human health, particularly in areas where drinking and agricultural irrigation water is sourced from Sb-impacted sediments. The environmental behavior of the two environmentally relevant Sb species Sb(OH)6- (antimonate) and Sb(OH)3 (antimonite) has been shown to be tightly linked to sorption or co-precipitation reactions with iron(III) oxides that originate from Fe(II) oxidation. While our knowledge of the coupling between Fe mineralogy and Sb mobility in anaerobic, in particular Fe(III)-reducing environments has greatly improved in the past 10 years, our understanding of Sb-Fe interactions upon Fe(II) re-aeration of such environments is surprisingly poor. A preliminary study demonstrated that Sb(V) presence can change the Fe mineral assemblage following the oxidation of Fe(II)-containing solutions and therefore alter the mobility of Sb, which may also affect the behavior of frequently occurring co-contaminants like arsenic (As). Understanding the processes controlling Sb mobility in the environment is essential for the development of adequate remediation practices for Sb-contaminated soils and sediments, especially in environments with fluctuating redox conditions. Here, we propose to investigate the influence of Sb speciation, pH, co-occurring contaminants (arsenic) and the fluctuation of redox conditions on Fe(III) oxide mineralogy and contaminant sequestration. The experimental work will be organized in three work packages. The first two will use dissolved Sb(III) or Sb(V) and Fe(II) in oxygen-saturated solutions that will undergo abiotic Fe(II) oxidation. The third one will build on the knowledge gained from these experiments and add another level of complexity by including repeated Fe(III) reduction and Fe(II) oxidation cycles. In addition, the last work package will use natural Sb- and As-contaminated mining soil that will undergo a similar suite of reduction and oxidation cycles. While the experiments with dissolved Fe(II) and pure Fe(III) oxides are well defined, easy to manipulate and enable the identification of the effect of single factors, the experiments with natural soil will allow for better transferability of the results to real- world environments. The experimental work will be combined with highly advanced solid- and liquid-phase analytical techniques.