Mobility of Manganese in a Compacted Residual Gneissic Soil Under Laboratory Conditions

Given the shortage of information available in the literature on transport parameters of heavy metals in Brazilian tropical soils, the mobility of manganese (Mn2+) in a residual gneissic compacted soil is studied in this work. Manganese can be found in toxic concentrations in landfill leachate, besides being one of the main contaminants from acid mine drainage. Column tests were performed in two groups of compacted soil samples to determine the manganese retardation factor. The sample groups presented slightly different soil compaction degrees and water contents. Soil samples were initially saturated by upward percolation of distilled water without applied counter pressure. A multi-species contaminant solution was then percolated through the soil columns. A different behavior of the hydraulic conductivity along time was observed between the two groups, during water as well as solution percolation. Manganese mobility was observed to be independent of soil hydraulic conductivity, k, for the range of k-values attained in this investigation, emphasizing the importance in evaluating the mobility of this metal in compacted soil barriers. Even when these barriers present low hydraulic conductivity values, this cation high mobility may cause it to reach soil layers below the compacted layer resulting in groundwater contamination.