A thermodynamic description is given of the irreversible process of zone melting of a mixture of solids, and equations of its thermodynamic balances in matter, energy, and entropy are written. The dependence of the productivity of zone melting of the mixture on the energy used has been obtained, and it is shown that the productivity of this process is bounded from above. Estimation of the maximum productivity of zone melting of the mixture depending on the external parameters of the process has been made.