T he present study includes solubility measurements, density, and refractive indices of saturated solutions of the systems As(2)O(5) + Fe(OH)(3) + H(2)O and As(2)O(5) + CaCO(3) + H(2)O. The experimental study was carried out at (323.15 and 343.15) K and for different mass fractions of arsenic, iron, and calcium. With the experimental results obtained, phase diagrams at these two temperatures and their regions were determined. The most important precipitated salt for the first system was FeAsO(4)center dot 2H(2)O (scorodite) and for the second system CaHAsO(4)center dot H(2)O (haidingerite). The experimental data on solubility and physical properties as a function of the mass fraction of iron and calcium were correlated for both systems. These equations allowed determination of the invariant points (double saturation equilibrium) of both systems for the two temperatures studied in this work and verified by scanning electron microscopy by the second system. This work is a contribution to the mining industry, to fix arsenic to solid matrices from industrial liquid residues.