The release of arsenic from biologically formed arsenic-containing FeS under aerobic environment: Implications for the stability and species variation of nano-sized iron sulfide in remediation

Abstract

Biologically formed nano-FeS is a potential and low-cost adsorbent and soil remediation agent. Remediation of arsenic from contaminated groundwater and soil by biological FeS is promising, however, the fate and transport of arsenic associated with nano-FeS in the natural environment are poorly understood. To investigate the fate of adsorbed arsenic on nano-FeS under aerobic conditions, static and dynamic experiments were carried out at different pH values and different oxidants. Batch and column sets showed that arsenic(V)-loaded FeS could release arsenic into solutions at pH 3.0 and 9.0. Especially noteworthy is the release of arsenic sustained at pH 9.0. Introducing Fe3+ and H2O2 at pH 3.0 showed that Fe3+ and a high concentration of H2O2 could reduce the release of arsenic, which might be ascribed to the oxidants promoting secondary Fe mineral phases to form on the arsenic(V)-FeS solid surface. X-ray diffraction patterns indicated that elemental S(0) and arsenic(V)-bearing Fe(II)/Fe(III) minerals formed as the main products. The generated secondary parasymplesite and FeAsO4 were mainly responsible for dissolved arsenic retention. The performance of hydraulic conductivity followed the sequence pH 7.0 > 50 mg/L Fe3+ > 1 mg/L Fe3+ > pH 9.0 > pH 3.0. In addition, H2O2 always kept good hydraulic conductivity. XPS analysis demonstrated that arsenic(III) and arsenic(V) were the main arsenic speciation on the surfaces of the solids, implying that lower valence arsenic was oxidized to arsenic(III/V) during the oxidation processes. The present study facilitates a better understanding of the stability of arsenic-loaded FeS in aerobic environment.

Keywords

• Arsenic mobility
• Biological nano-FeS particles
• Arsenic speciation
• Hydraulic conductivity