In the work on the extraction of molybdenum from ores, carried out by the Research Institute of the Leningrad Mining Institute, we had to face the issue of isolating molybdenum from leaching solutions. In view of the fact that electrolytic deposition, with greater simplicity of operations, provides a product in the form of an oxygen compound of molybdenum, free from other metals and characterized by greater purity, it is of great practical interest to study the process of cathodic deposition of molybdenum hydroxide from its solutions. In the tests described below, we experimentally studied the process of electrolytic deposition of hydroxide from solutions of ammonium molybdate. The influence of various factors, such as the concentration of molybdenum in solution, current density, temperature, concentration of salts of other metals, on the process of hydroxide deposition was studied. The results presented show that for satisfactory cathodic deposition of molybdenum hydroxide, a number of conditions must be met (see article).
In this work, we used a method of direct measurement of the magnitude of the transition resistance, as well as the thickness of the gas film creating it, using an alternating current superimposed on a polarizing direct current. This work allows us to draw the following conclusions: 1) the existence of transition resistance on the mercury cathode is undoubtedly, transition resistance is not the only cause of hydrogen overvoltage; 2) the formation of a hydrogen film, which gives the transition resistance, begins at very low cathodic polarization; 3) the maximum film resistance corresponds to the beginning of an increase in current strength on the current density - potential curve; 4) as the direct current density increases, the value of the transition resistance decreases.
