Trans. Nonferrous Met. Soc. China 28(2018) 2368−2374 Selective leaching and recovery of V as iron vanadate from industrially generated Mo−V residue P. C. ROUT, G. K. MISHRA, D. MOHAPATRA, B. PADH, B. R. REDDY Technology Centre, R&D Department, Rubamin Ltd., Halol-389350, India Received 27 November 2017; accepted 10 May 2018 Abstract: A commercial process was developed to treat a Ca-based Mo−V residue generated in Mo processing plant. Vanadium was selectively leached using acetic acid and recovered as iron vanadate by hydro process. Process conditions for selective V leaching and iron vanadate precipitation were investigated. V recovery efficiency of 90.3% was achieved with a V content of 26.5% and an Fe content of 29% in the iron vanadate cake suitable for ferrovanadium industry. The overall Mo recovery in the whole process was 98.6%. The obtained leach residue containing 14.3% Mo with negligible impurities can be used as a feed material for the Mo production process or ferromolybdenum industry. This simple and economical process generates two product streams from a single operation and has the potential to solve a long standing problem of handling such a mixed Mo−V residue. Key words: iron vanadate; leaching; acetic acid; precipitation; ferrovanadium 1 Introduction Vanadium is mainly used as an alloying element in the steel industry as ferrovanadium, accounting for about 85% of the total V production. Other major applications are in nonferrous alloys, mostly V-containing titanium alloys and Ni-based super-alloys for aerospace industry, as catalyst in the manufacture of sulphuric acid by the contact process, ceramics and batteries [1,2]. The major secondary sources of V are sludges generated during processing of bauxite ore by alumina industry, waste catalyst of H 2 SO 4 manufacturing industry, steel making slag, oil and coal residues, spent catalysts, and uranium co-products. In addition to these, V is also present in deposits of heavy crude oil produced in countries like Canada, Venezuela, USA and its content varies widely from 1 to 1500 mg (V)/kg (crude) [3,4]. Hydro-treating of heavy crude oil using molybdenum- based catalyst for the removal of impurities such as V, Ni, Fe, S and N compounds by the oil producing industries worldwide, generates waste catalyst materials after prolonged usage. Such waste catalyst materials generally contain 8%−12% Mo, 0.5%−3% V, 1%−3% Ni/Co, 4%−8% S, 25%−30% Al 2 O 3 and rest hydrocarbons depending on the crude oil origin and are considered to be hazardous due to the presence of toxic elements. At the same time, these are considered as valuable sources due to the presence of Mo, V and Ni/Co metal ions in high concentrations. These waste catalysts are commercially used by different industries to recover Mo as catalyst/chemical grade molybdenum compounds, sulphur as sodium sulphate and finally alumina to cement industry application. Various methods such as leaching, precipitation, ion exchange and solvent extraction (SX) are reported for the treatment of such waste catalysts [5−9], in which two solutions are generated: one is V-free but Mo-rich solution for further processing to Mo compounds and the other is the solution containing V and Mo. Further treatment of the above Mo and V solution with lime generates mixed cake containing 2%−5% V, 10%−15% Mo, 12%−17% Ca and other impurities such as As, Co, Ni, P, SiO 2 , Al and Pb in variable quantities. At present, this type of residue is not saleable due to the presence of V as impurity for certain molybdenum applications. So, this type of material is stockpiled in the plant, thereby increasing the inventory cost. Processing of such a source of V is of considerable interest in the catalyst recycling industry to produce high-valued V and Mo products. However, due to unpredictable composition of such materials, technology and cost Corresponding author: B. R. REDDY; Tel: +91-9687605535; E-mail: ramachandra.reddy@rubamin.com, drbrcreddy_iict@yahoo.com DOI: 10.1016/S1003-6326(18)64882-4