Adsorption of Mercury(II) by Soil: Effects of pH, Chloride, and Organic Matter

Abstract Effects of pH, Cl − , and organic matter on Hg(II) adsorption from 10 −7 M solution by 15 New Jersey soils were examined to understand the factors responsible for Hg partitioning to soils under different environmental conditions. Maximum adsorption ranged from 86 to 98% of added Hg and occurred at pH 3 to 5. Further increasing the pH significantly decreased adsorption of the added Hg, for example, from 89 ± 8% at pH 4.0 to 39 ± 11% at pH 8.5. An important factor was the complexation of Hg by dissolved organic matter whose concentration increased with increasing pH. When organic matter was removed from the soil samples, adsorption decreased under acidic conditions, but increased under alkaline conditions. The effect of Cl − on Hg(II) adsorption by soil depended on both pH and the soil organic matter content. At circumneutral and higher pH, addition of Cl − did not affect adsorption by any soil. The standard deviation of Hg adsorption for all soils was <4% for Cl − concentrations from about 1 × 10 −6 to 1 × 10 −2 M . At about pH 3, the effect of Cl − on Hg(II) adsorption by soil depended on the soil organic matter content. When the Cl − concentration increased from about 1 × 10 −6 to 1 × 10 −2 M , adsorption by the lowest organic matter soil (1.2 g C kg −1 ) decreased from 93 to 40%, whereas the measured adsorption by the largest organic matter soil (49.9 g C kg −1 ) decreased only from 95 to 91%.