Title: Mechanisms of Tungsten and Molybdenum Retention in Solid Residues during Hydrometallurgical Processing of Oxidized Industrial Materials
Authors: Khojiev Sh.T., Boltayev O.N., Javliev S.S., Abilkasimova M.S., Usmonova Z.B.
Volume: 9
Issue: 12
Pages: 162-171
Publication Date: 2025/12/28
Abstract:
Tungsten and molybdenum are strategic metals widely used in high-technology and energy-intensive industries; however, their hydrometallurgical recovery from oxidized industrial residues remains incomplete in many practical systems. This study investigates the physicochemical reasons for tungsten and molybdenum retention in solid residues formed during ammoniacal leaching of oxidized molybdenum concentrates and autoclave carbonate leaching of oxidized tungsten materials. A systematic analysis of literature data, combined with chemical, mineralogical, and microstructural interpretation, was conducted to identify the dominant mechanisms controlling metal losses. The results show that molybdenum residues typically contain 0.3-2.0 wt% Mo after ammoniacal leaching, whereas tungsten residues formed during carbonate autoclave leaching may retain 0.5-4.0 wt% W despite elevated temperature and pressure. In both systems, metal retention is governed by the formation and persistence of sparingly soluble calcium molybdate and calcium tungstate phases, re-precipitation driven by calcium activity, encapsulation within silica-iron passivation layers, incomplete oxidation of primary phases, and diffusion-controlled leaching kinetics. SEM and TEM evidence reported in the literature confirms the stabilization of Mo and W as micro- and nanocrystalline phases embedded in amorphous or poorly crystalline gangue matrices. Mechanistic graphical abstracts were developed to integrate chemical reactions, phase transformations, and microstructural evolution, providing a unified explanation for the formation of unreacted cores surrounded by compact product layers. The findings demonstrate that conventional leaching intensification alone is insufficient to achieve complete metal recovery. Instead, effective extraction requires integrated process strategies involving calcium control, disruption of passivation layers, and targeted pretreatment approaches. The results contribute to improved understanding of refractory behavior in hydrometallurgical systems and support the development of more efficient and sustainable technologies for tungsten and molybdenum recovery from technogenic wastes.