The dissolution process of the low-grade natural phosphate ores from the Epirus Area (Greece) using dilute acetic was studied by X-ray diffraction (XRD) and thermal analyses of remained solid after dissolution for an appropriate time from 1 to 80 min. There were three kinds of carbonates present in the phosphorite. The first one was the laminas of pure calcite, which primarily dissolved from acetic acid solutions. The second kind was the calcite in phosphopelloids particles, which was protected from a phosphorite cover. The third type was the carbonates in the francolite lattice. The two last kinds did not react with acetic acid solutions. A rate equation of the general form ln[1/(1-X)] = kt(m) (where X is the conversion fraction, k is a rate constant, t is times, and m is a constant) was found to represent these data.