The solid-liquid equilibria data of the ternary system consisting of tert-butanol (A), m-chlorophenol (B), and p-chlorophenol (C) and the three constituent binary systems were experimentally studied by means of the solid-disappearance method. The binary system consisting of m-chlorophenol and p-chlorophenol was observed to exhibit one eutectic point. However, the tert-butanol + m-chlorophenol and tert-butanol + p-chlorophenol mixtures behave differently, each exhibiting two eutectic points and one congruent melting point; the mole fraction of tert-butanol in the congruent melting complexes, which are represented, respectively, by the formula A(2)B and A(2)C, are 0.6602 and 0.6690. All the experimental melting temperature data can be satisfactorily represented by the empirical equations of Ott and Goates. Several ternary mixtures with specified mole ratios of m-chlorophenol to p-chlorophenol (pseudo-binary mixtures) were also studied. They all exhibit two eutectic points and one congruent melting point near the tert-butanol mole fraction of 0.6667. This implies that the mixtures of the congruent melting complexes A(2)B and A(2)C were formed during freezing. A ternary phase diagram showing the projections of all eutectic and congruent melting points is prepared. Based on the information contained in this diagram, a conceptually feasible process using tert-butanol as an adductive agent is proposed to separate the eutectic mixture of m-chlorophenol and p-chlorophenol. (c) 2005 Elsevier B.V. All rights reserved.