SOIL FLUSHING WITH EDTA SOLUTIONS - A MODEL FOR CHANNELED FLOW

A 1-D model for the flushing of metal contaminated soils with extracti ng aqueous solutions is presented. Previous experimental results of th e flushing of carbonatic soil contaminated with lead with EDTA solutio ns showed the formation of channels of preferential flow as well as su bstantial rebounds in effluent lead concentration after periods of no pumping, indicating an important kinetic limitation for lead removal. This limitation is associated with the presence of a stagnant aqueous phase in addition to the mobile aqueous phase running through the chan nels. The model assumes an initial homogeneous distribution of lead in the soil, mainly present as small spheres of a solid carbonate which must dissolve. If the spheres are far from the channels, after solutio n the lead must diffuse through the stagnant aqueous phase until it re aches the channels and is washed out of the column. The model is able to simulate the rebound curves as well as the effluent concentration d uring the course of the operation. The importance of the way the chann els arise is established by sensitivity studios performed for differen t mechanisms of the solution circulation and the formation of channels . More experimental results are needed to discriminate which of the al ternatives studied is operative.