Arsenic mobility in soils contaminated with metallurgical wastes as a function of variable chemical conditions

Arsenic is a pervasive contaminant of natural aqueous systems, such as groundwater and soils, its sources being both natural and anthropogenic. The present investigation was performed on soils contaminated with residues from ore processing activities and revealed the presence of arsenate [As(V)] species with a very low mobility, through natural attenuation processes. The stability of this attenuation was investigated by varying two specific equilibrium chemical conditions: pH and presence of bicarbonate ions. One-unit changes in equilibrium pH generally caused small increases in As mobility, whereas the presence of bicarbonate ions considerably increased this mobility. The results were compared to thermodinamic simulations of equilibrium conditions using the total elemental composition of each individual soil, but excluding sorption reactions. Close matches between experimental data and simulations revealed the predominance of solubility-controlled As mobility via heavy-metal arsenate solid formation. Bicarbonate ions were found to be highly unsuitable for extraction of sorbed arsenate fractions due to indirect As release from solid arsenates, via heavy-metal carbonate precipitation processes.