Arthrospira (Spirulina) platensis was tested for biosorption properties. Preliminary experiments concerning biosorption kinetics were performed on Cr(III) ions. Equilibrium of biosorption was tested for Cr(III), Mn(II) and Mg (II) ions, since these elements are crucial for animals with metabolic disorders. In our study, Spirulina was proposed as a feed additive for animals suffering from diseases characterized by insulin dysregulation, abnormal adipose distribution and a high risk for laminitis. Maximum biosorption capacity of A. platensis, determined from Langmuir equation, was 45.2 for Cr(III), 44.3 for Mn(II) and 42.0 mg/g for Mg(II) ions. Biosorption of Mg(II) ions by microalga has never been studied so far. Finally, the raw and enriched microalgal biomass was examined by ICP-OES to determine its multielamental analysis before and after biosorption, FTIR to indicate functional groups that participated in biosorption and SEM-EDX to illustrate the binding of metal ions on the surface of algal biomass. ICP-OES showed that the content of elements significantly increased in the enriched A. platensis. FTIR spectroscopy evidenced that biosorption of metal ions was mainly due to carboxylate groups present on the microalgal cell wall. SEM analysis clearly showed that biosorption occurred. Arthrospira platensis turned out to be a good biosorbent of metal ions.