Transport of Cd, Cu and Pb in an acid soil amended with phosphogypsum, sugar foam and phosphoric rock

Metal pollution in soils is a world-wide problem requiring new tools for environmental management. This study investigated the transport processes of metals (Cd, Cu and Pb) in undisturbed soil columns of an acid soil amended with phosphogypsum, sugar foam, and phosphoric rock (PG, SF and PR). Sorption mechanisms have been examined in a companion paper using sequential extraction methods. This investigation focused on how these sorption mechanisms relate to transport parameters estimated from metal breakthrough curves using temporal moment analysis. The application of the 3 soil amendments significantly reduced the total metal mass leached from all the columns. Metal travel times were also longer with the addition of the amendments, although retardation values were much lower than those reported in batch studies. Retardation (R) values for Cd, Cu and Pb averaged 1.6, 1.8 and 1.7, respectively, for all treated columns. These R values for the control columns were 1.2, 1.3 and 1.4 for Cd, Cu and Pb, respectively. Additional observations of Al, Ca and image leaching from the columns revealed the existence of fast exchange and precipitation–dissolution reactions included in the transport of metals through the soil. Under the conditions of this study, it is estimated that the mass of Cd, Cu and Pb leached from the soil would be reduced by more than 60–99% with the addition of the amendments. Therefore, all 3 amendments (PG, SF, and PR) appear to have reasonable potential to be applied to reduce metal leaching in polluted agricultural soils.