Batch biosorption experiments were carried out with binary synthetic solutions and specific masses of the dead fungus Aspergillus niger. Solutions with known concentrations of gold or platinum and some of the metals copper, calcium, titanium, or aluminum were placed in contact with the fungus for 120 min at pH 4. The variables monitored were electrical conductivity, pH, and oxidation-reduction potential (ORP). At the end of the contact, aliquots of the residual aqueous medium were collected to analyze them using atomic absorption spectroscopy and UV-Vis techniques. The biomass was analyzed by FT-IR before and after contact with the solution. The experimental results show that the bioadsorption is generally selective for gold and platinum. In the case of gold, almost 100% is adsorbed, while platinum observes a recovery limit of 71%. Iron recovery is less than 10%, up to 30% for calcium and aluminum, and 60% for copper. It is concluded that the extent of adsorption does not depend on the amount of biomass included in this work but rather on the active sites or functional groups related to metals in the solution. The infrared spectra indicate that the functional groups of positive or neutral charge (N–H, C–H, and C–H2) on the surface of the biomass trap the ionic compounds in the form of chlorides (PtCl62−, AuCl4−), identified by the UV-Vis technique and the respective Pourbaix diagrams.