Depression of pyrite flotation by dextrin has been investigated through adsorption, electrokinetic and microflotation studies in systems open to the atmosphere. Adsorption of dextrin takes place through specific interaction with ferric oxyhydroxide species that result from the oxidation of pyrite surface. Dextrin shows an isoelectric point at pH 4 and pyrite does at pH 6.4. Within this pH range adsorption is suggested to be promoted by electrostatic interactions. Coadsorption of dextrin and isopropyl xanthate occurs on the surface of pyrite and is explained to happen through distinct mechanisms taking into account the heterogeneous nature of the surface. It is likely that dextrin depresses pyrite by enveloping the dixanthogen resulting from adsorption of xanthate ions. It is shown that dextrin is as effective depressant of pyrite as cyanide. (C) 2004 Elsevier Ltd. All rights reserved.