The rate of the crud formation was determined experimentally for a pilot plant solvent extraction settler. The results show that the rate of accumulation of crud decreases slightly with time and that the thickness of the crud in the settler increases with time. The empirical correlation between the thickness of the crud (h(c)) in centimeter and time (t) in hour can be expressed as h(c)(t) = 21.39(1-e(-0.004t)) It was determined that the average rate of increase of the crud thickness for the studied pilot settler is approximately 0.04 cm/h over a period of 14 days.