An experimental investigation was carried out in order to analyze the drop size distributions of liquid-liquid dispersion in a horizontal mixer-settler. Two aqueous chemical systems were studied: synthetic gold solution and gold solution prepared from the leaching of copper anode slimes. The dependency of the drop size distributions on impeller speed, 335-600 rpm, and phase fraction, 0.167-0.54, were studied for gold chloride-DBC system. The Sauter mean diameter, D-32, was correlated for both systems in the frame of classical Hinze-Kolmogorov theory. The results showed that, for each volume fraction in the studied range, D-32 is decreasing as a power function of Weber number with an exponent equal to -0.73 and -0.65 for leach and synthetic solution, respectively. This corroborates that the mentioned theory may not be the most adequate to correlate drop size diameters, particularly when reaction occurs in the system. Also such a variation of the exponent may be interpreted as a different combination of the continuous phase. However, for both systems studied, correlation to show the effect of reaction on D-32 has been represented. By comparing the results, the prediction of mean drop size diameter in the leach solution is possible by using synthetic solution data with AARD <10%. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.