The behavior of an isothermal and non-reaction solid-liquid system can be model using a mathematical model based on the Mixtures' Theory of Continuum Mechanics. The knowledge of the constitutive equations of this phenomenon, as pressure on the solids and medium permeability, is very important in the design and performance evaluation of the continuous thickeners or filters. In this work the batch sedimentation phenomena of a kaolin aqueous suspensions was investigated. The technique consists on measuring of the gamma rays attenuation when they cross the physical media as a function of the local concentration at several vertical positions in a reservoir. Using the experimental data and local concentration as a function of the attenuation curve, it is possible to determine the constitutive equations. The results were satisfactory, allowing simulations of this phenomenon for steady and transient regimes in future papers.