Abstract: In the hydrometallurgical treatment of metal-bearing ores and particularly the beneficiation of iron-containing titaniferous ores wherein the ore is subjected to leaching with a dilute aqueous acid solution in a digestion zone, there is provided an improvement which comprises initiating and maintaining the mixture of ore and acid in a state of boiling. Initiation and maintenance of the mixture in a state of boiling is accomplished through the venting of the digestion zone to remove process vapors substantially in the form of water vapor. Initiation of the boiling of the mixture of ore and acid solution in the digestion zone is commenced when the temperature of the mixture and consumption of the free acid solution in said mixture have reached predetermined values. The initiation and maintenance of the mixture in a state of boiling results in an increased rate of dissolution of the contaminant values in the metal-bearing ore.