This contribution is part of an international research project on prospecting uses for soluble bio-organic substances (BOS) obtained from urban biomasses. BOS are humic-like substance that can be used as surfactant, detergent and adsorbents. In the present work, mathematical models for the adsorption of N2 in pure BOS and of violet crystal in BOS-magnetite nanoparticles are developed.The models were fitted to experimental data. The N2 in BOS adsorption isotherm (Allera, 2012) is of type 2. Initially, the linear form of BET equation was used. Later, the number of multilayer was estimated as well. It is about 81 for concentrations of 0.01 mg/L of BOS and 46 layers for 0.01 mg of BOS. In the study of the adsorption of violet crystal in Fe3O4-BOS particles, the data was divided in four groups. Each group was analyzed individually and the Langmuir and Freundelinch equations were fitted for each. Finally, a model to represent global adsorption kinetic was proposed and fitted to the data.