THE MOBILITY AND SPECIATION OF ANTIMONY IN CONTAMINATED SOILS AND WATERS

Abstract

Total element concentrations, solid state partitioning and leaching characteristics of antimony are examined in surface soils at two contrasting field sites contaminated by former mining activities. These parameters are compared in each soil and related to selected soil properties and leachant solution pH to identify factors that influence the mobilisation of antimony in soils. Total element concentrations are determined in soils using an evaluated Mg(N03)2 ashing technique and highly elevated concentrations (up to 8202 mg kgˉ¹ antimony) are measured in soils formed on the surface of spoil heaps at these sites. A stream system bisects a spoil heap at one of these sites and elevated antimony concentrations (up to 22.5 ng mlˉ¹) are observed in these waters suggesting the influence of leaching processes. Antimony's solid state partitioning is investigated in soils using a previously reported five-step low temperature sequential chemical leaching method. Largest proportions of antimony are extracted in the 'Ca-associated' (6.1-11.6% of the total) soil fraction and the 'Fe- and Organic-Fe associated' soil fraction (5.0-8.7 % of the total). However, low extraction efficiency is observed for the sum of the five leaching steps and 73.8-83,3 % of the total antimony is partitioned in the residual soil fraction. Short term, long term and pH-dependant antimony leaching is investigated in selected contaminated soils using laboratory-based batch tests. Antimony leaching is shown to be influenced significantly by the total antimony soil concentration, leachant solution pH and L:S leaching ratio and these observations are apparent despite notable variations in soil pH and organic matter content. Antimony leaching is most significant in soils that contain highest total antimony concentrations although increased antimony leaching is observed as the L:S ratio is increased and/or the leachant solution pH is increased from pH 4.0 to pH 10. Aqueous antimony speciation is determined in soil leachates and surface waters using HPLC-ICP-MS methodologies and the influence of selected soil properties is examined with respect to the resultant leachate antimony speciation. Novel HPLC separations are developed using Phenomenex SAX-SB and Alltec HAAX stationary phases in conjunction with ammonium tartrate mobile phases to facilitate the simultaneous separation and quantification of inorganic SbIII, inorganic SbV and organic SbV species. These methodologies achieve detection limits for species in the pg mlˉ¹ to low ng mlˉ¹ range to enable quantitative analysis of contaminated leachates and surface waters. Inorganic SbV species are found to be predominant in the surface water and soil leachate samples despite notable variations in soil pH and organic matter content. These data show good agreement with thermodynamic predictions. Inorganic SbV species are generally accepted to exhibit 10 times lower toxicity than inorganic SbIII species and potential for antimony toxicity at these sites may be reduced due to the intrinsic elemental speciation. Three unidentified antimony species are 9etected in selected soil leachates although inorganic SbIII and organic SbV species are not detected in surface waters and soil leachates in this study.