Antimony leaching from contaminated soil under manganese- and iron-reducing conditions: column experiments

Abstract

Environmental context. Contamination of shooting range soils by antimony (Sb) released from corroding ammunition has become an issue of public environmental concern. Because many of these sites are subject to waterlogging and consequently limited aeration, we performed column experiments with contaminated shooting range soil to investigate Sb mobility under such conditions. The results are important for our understanding of the risks arising from Sb-contaminated soils, and also for the derivation of appropriate management strategies for such sites.Abstract. Despite the environmental risks arising from antimony-contaminated sites, critical factors controlling the mobility of Sb in soils have still not been fully identified to date. We performed column experiments to investigate how reducing conditions affect Sb leaching from a calcareous shooting range soil, with a special focus on the relationship between Sb release and mineral dissolution processes. After eluting the columns for 5 days with 15 mM lactate solution at a flow rate of 33 mm day À1 , the flow was interrupted for 37 days and then resumed for another 5 days. With the transition to moderately reducing conditions (,300 mV) after 1 day of flow, effluent Sb V and manganese (Mn) concentrations showed a concomitant increase, providing evidence that Sb V associated to these phases was released by the reductive dissolution of Mn minerals. The release of Sb V was counteracted by the reduction to Sb III , which was first scavenged by iron (Fe) (hydr) oxides and then slowly liberated again when the redox potential further decreased to Fe-reducing conditions. Laser ablation-inductively coupled plasma-mass spectrometry revealed the presence of an initial pool of Sb associated with Mn-containing, Fe-free phases, underpinning the important role of the latter in addition to Fe (hydr)oxides as Sb sorbents.

Seasonal Temperature Oscillations Drive Contrasting Arsenic and Antimony Mobilization in a Mining‐Impacted River System

“…However, as the magnitude of Fe(III) reduction increases (i.e., above ~6%), Sb is subsequently released due to more extensive dissolution of Fe(III) oxide host phases and via increased competitive desorption from HCO 3 − produced via Fe(III) reduction. This complex biphasic trend (initial Sb retention, followed by Sb release) as reducing conditions develop is consistent with the result of Hockmann, Tandy, et al (2014), who found Sb mobilization occurred under reducing conditions via (1) initial reduction of Sb(V) producing Sb(III), which was first scavenged by Fe(III) oxides, and then (2) slow liberation of the newly produced Sb(III) when Eh further decreased to enable extensive reductive dissolution of Fe(III) oxides.…”

Antimony Sorption to Goethite: Effects of Fe(II)-Catalyzed Recrystallization

“…As a consequence, there is very little tendency for Fe atom exchange with the aqueous phase, and, as a result, goethite recrystallization is exceptionally slow under such conditions . Reducing conditions, however, are common in waterlogged soils, benthic sediments, and shallow groundwater systems. ,− ,,, Reducing conditions also commonly occur within anoxic microenvironments in otherwise oxic systems (e.g., within the aggregate structure of upland soils) . Under reducing conditions, Fe­(III) within minerals such as goethite can act as a terminal electron acceptor in microbial respiration, thereby leading to the generation of aqueous Fe­(II) …”

“…Antimony is a toxic and carcinogenic metalloid, and its release into the environment threatens soil and water quality, ecosystem processes, and human health. − Particularly severe environmental contamination has been reported in relation to Sb mining and ore-processing activities. − Antimony is also released during mining of many other metals (e.g., copper, gold, lead, and zinc) due to its common enrichment in metal sulfide ores. − Other major sources of Sb release to the environment include shooting range soils (leaching of Sb during weathering of bullets) − and disposal of plastic waste (especially Sb-rich E-waste such as computer plastics and consumer electronics). ,, …”

Soil organic matter affects arsenic and antimony sorption in anaerobic soils

“…due to waterlogging, is typically associated with mobilisation of As, however exceptions and reverse trends have been documented (Frohne et al, 2011;Hamon et al, 2004;Stroud et al, 2011;Williams et al, 2011). In contrast, anaerobic conditions typically immobilise Sb and, again, some exceptions have been noted (Frohne et al, 2011;Hockmann et al, 2014bHockmann et al, , 2014aMitsunobu et al, 2006;Okkenhaug et al, 2012). The mechanisms behind mobilization or immobilization of As and Sb upon reducing conditions are rather complex, because changing redox conditions not only affects the speciation of As and Sb, but also the properties of their sorbents which, in turn, influences strongly As and Sb mobility.…”

“…The mechanisms behind mobilization or immobilization of As and Sb upon reducing conditions are rather complex, because changing redox conditions not only affects the speciation of As and Sb, but also the properties of their sorbents which, in turn, influences strongly As and Sb mobility. For example, reductive dissolution of Fe(III) and Mn (III, IV) hydroxides can release previously bound As and Sb (Frohne et al, 2011;Hamon et al, 2004;Hockmann et al, 2014b;Lovley, 1997). In contrast, Fe(II)-induced transformation of ferrihydrite to more crystalline feroxyhyte and goethite under mild reducing conditions can immobilize Sb, likely by structural incorporation of Sb(V) into the freshly formed Fe(III) hydroxide crystal lattice (Burton et al, 2019).…”