The present work aimed to characterize an aluminum industry by-product in natura (LA nat) and after phosphate and thermal pretreatments; evaluate the adsorption/desorption capacity of Cd and Pb by this LA nat form and after the aforementioned pretreatments, comparing them with an in natura iron mining by-product (LF nat). The LA nat presented a high pH as well as a high Na concentration and also an oxide-rich mineralogy. Pretreatment of the by-product had no significant effect upon Cd and Pd adsorption/desorption. The LA nat performed better than the LF nat as an Cd and Pb adsorbent.