Physicochemical properties for the arsenopyrite-Acidithiobacillus ferrooxidans system were studied to evaluate different factors involved in bacterial adhesion. The system was evaluated for electrokinetics and hydrophobicity of the bacteria/mineral/solution interface in an acid M2 culture medium. At the optimum pH for bacterial growth (pH = 1.8), adhesion of Acidithiobacillus ferrooxidans should be favored according to hydrophobic and electrostatic interactions. While for pyrite this holds true, in the arsenopyrite case that does not seem to occur and a bacterial adhesion delay is observed. This effect is explained in terms of an acid dissolution process affecting the surface characteristics of arsenopyrite. To further support the acid dissolution effect, results from an electrochemical study of the phenomena involved in this process as well as a surface characterization of arsenopyrite are presented. (c) 2005 Elsevier Ltd. All rights reserved.