Sorption of inorganic mercury on soils from Ankobra basin in the south - western part of Ghana

Abstract

Understanding the adsorption of mercury on soil from aqueous solution is necessary for tracing the fate of mercury in the environment. This study was undertaken to predict the fate of mer- cury emitted from artisanal gold mining activities within the Ankobra basin. Total mercury (THg) concentrations were determined in soils close to River Ankobra and its major tributaries in the south-western part of Ghana by Cold Vapour Atomic Absorption Spectrophotometry. THg content of the soils ranged from 0.051 µgg-1 to 0.366 µgg-1 with an average of 0.15 µgg-1 which was below the level (200 µgg-1) set by US EPA. THg correlated positively (r = 0.57) with the or- ganic matter content of the soil. Sorption of Hg (II) onto the soils had an L - type isotherm and the distribution coefficient (Kd) ranged from 41.4 µgg-1 to 182.2 µgg-1. The Freundlich model showed a better fit followed by Langmuir model and linear. The superiority of Freundlich model to the other models could be attributed to the heterogeneous surface energies and exponential distribution of active sites which are characteristics of such soils. All the soils had adsorption intensity (n) lower than one, indicating the soils could be good sorbent for Hg (II). This suggests that Hg fate and availability in soil for runoff and leaching could be low for soils with such characteristics.