Quantitative method for determining the concentration of mercury(II) sulphide in soils and sediments

Abstract

A method for extracting mercury from soil sequentially using HNO₃ and a saturated solution of sodium sulphide (ss-Na₂S) is described. Most chemical forms of mercury are soluble in HNO₃, with the exception of HgS. Because HgS is soluble in Na₂S solution, a sequential extraction procedure was developed to determine the distribution of HgS in soil. To determine the efficiency of this sequential extraction procedure, soil samples were spiked with either ²⁰³HgS or ²⁰³HgCl₂ and extracted sequentially with HNO₃ and ss-Na₂S. For samples spiked with ²⁰³HgCl₂, HNO₃ extracted 95 and ss-Na₂S 1% of the added ²⁰³HgCl₂. In contrast, for soil spiked with ²⁰³HgS, HNO₃ extracted 1 and ss-Na₂S 98% of the added ²⁰³HgS. When this sequential extraction procedure was applied to mercury-contaminated soil, the mercury concentrations in the combined HNO₃ and ss-Na₂S extracts accounted for 99% of the total mercury present. Further, of the total mercury present, 74–100% was HgS as determined by the concentration of mercury in the ss-Na₂S extract. These results suggest that the proposed sequential extraction procedure can selectively differentiate HgS from other species and compounds of mercury in soil.