The first works on hydrometallurgy of molybdenum were started by the Leningrad Mining Institute in 1932 and were carried out on poor raw materials of the Takhtarvumchorr deposit, extremely far from the usual conditions. During the next two years the results of these works were discussed and approved at the broad meetings held by Academician A.E. Fersman in Kirovsk and Leningrad, but they were used in practice later, in connection with the problem of extraction of molybdenum contained in the Balkhash copper ores. In October 1941, a shop was put into operation at the Balkhash plant for processing of substandard molybdenum products using a method developed at the Leningrad Mining Institute.