Surface Complexation Modelling of Arsenic and Copper Immobilization by Iron Oxide Precipitates Derived from Acid Mine Drainage

Resumen

Acid mine drainage
(AMD) constitutes a serious environmental problem in mining areas
due to the acidification of soils and aquatic systems, and the
release of toxic metals. Many of the pollutants that occur in AMD
display a high affinity for the surfaces of the aluminium and iron
oxides that are typically present in systems affected by AMD. This
binding affinity reduces the mobility of trace metals and
metalloids, such as copper and arsenic, thus helping to mitigate
contamination of aquatic systems. In the present study, water
samples and iron-rich bed sediments were collected in areas affected
by copper mining activities. A loose ochre-coloured precipitate
occurring on the banks of a river close to an abandoned tungsten and
tin mine was also sampled. The composition of the precipitate was
established, and adsorption experiments were performed with copper
and arsenate ions to determine the ability of natural iron
precipitates to reduce the concentration of these ions in solution.
Surface complexation models provided a good description of the
behaviour of natural iron oxides in terms of copper and arsenate
retention. Use of this type of model enables prediction of the
distribution of pollutants between the solid and solution phases and
analysis of their mobility in relation to environmental conditions
(pH, ionic strength, presence of competing species, etc.).