Dynamic flow-through sequential extraction for assessment of fractional transformation and inter-element associations of arsenic in stabilized soil and sludge

A dynamic flow-through extraction system was applied for the first time to ascertain the fractional transformation and inter-element associations of arsenic in stabilized environmental solids, as exemplified by the partitioning of soil and sludge stabilized with three additives, namely MnO2. Ca(OH)(2) and FeSO4. The extraction system used not only gave fractionation data, but also the extraction profiles (extractograms) which were used for investigation of the breaking down of phases, kinetic releasing of As and elemental association between As and inorganic additives. Five geochemical fractions of As were elucidated by accommodation in the flow manifold of a modified Wenzel's sequential extraction scheme, well established for fractionation of arsenic. The results revealed that MnO2 and FeSO4 have a slight effect on As phase transformation for soil and sludge samples amended for one week whereas the addition of Ca(OH)(2) increases As mobility due to the desorption of As from the solid Fe-oxides phase. The significant change in fractional transformation after 8 weeks of incubation can be seen in MnO2-treated soil. There was an increase of 17% in the non-mobilizable As fraction in MnO2-treated soil. From extractograms, arsenic in untreated soil was found to be rapidly leached and concurrently released with Fe. This may be evidence that the release of As is dependent on the dissolution of amorphous Fe oxides. In MnO2-treated soil, a strong affinity was observed between Mn and As in the amorphous Fe/Al oxides fraction, and this plays an important role in slowing down the kinetics of As releasing. (C) 2010 Elsevier B.V. All rights reserved.