Molybdenum is a crucial element in many industrial catalysts used in the production of steels, alloys and specialty chemicals. Much of the global supply chain for molybdenum relies on mining operations in China and Russia, so various efforts are underway to establish avenues for more localized sources. Researchers from Luleå University of Technology (LTU; Sweden; www.lte.se) have demonstrated an integrated hydrometallurgical process that effectively recovers molybdenum from spent iron-molybdate catalysts using less energy and fewer processing steps than conventional methods.
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The new technology brings together an ammonia-leaching system with antisolvent crystallization (ASC). ASC is a precise crystallization technique that adds a secondary solvent to help reduce solubility for metal ions and accelerate precipitation and recovery. According to the research team, this work is the first to employ ASC for recycling molybdenum from spent catalysts. A key difference between LTU’s leaching approach and conventional ammonia-leaching methods is the use of an ammonia-ammonium buffer system that significantly reduces the required ammonia concentration of the system from around 5 mol/L to just 2 mol/L. This not only decreases reagent consumption, but also aids in scalability, since the system can be designed for more benign chemical conditions. Other recovery methods also require high temperatures, but LTU’s system operates at ambient temperatures, eliminating external heating demands. The ASC portion of the process uses ethanol as the antisolvent since its low dielectric constant relative to the ammonia solution “disrupts the hydration shell surrounding dissolved metal ions,” thereby reducing molybdate solubility.
With pellets of iron-molybdate catalyst waste from a chemical-industry end-user, the research team demonstrated over 95% molybdenum recovery with product purity over 99.9%. Details about this research were first published in the journal Scientific Reports.