A series of interaction experiments were carried but between different
substrata (soils and sewage sludge) with the aim of assessing Cd rete
ntion in these substrata. We also studied the effect that the presence
of Ca can have in Cd retention process. The data obtained were adjust
ed to different adsorption isotherms (Langmuir's, Brunauer's and Freun
dlich's), which led to different characteristic parameters. Langmuir's
isotherm is the one that best describes the data obtained, with Freun
dlich's model for the acid soil used. Increasing ionic strength with C
a seems to promote a decrease in Cd adsorption.