Recovery of Vanadium from Acid and Basic Leach Solutions of Spent Vanadium Pentoxide Catalysts

Abstract

The vanadium pentoxide catalysts are used in the sulfuric acid manufacture, but as an inherent consequence of the process, they are deactivated or poisoned, because of that they need to be renewed. In Ecuador, the increase of environmental pollution concerns and the legislation related with the final dispose of hazardous residues is forcing to companies to process their waste products and residues. For the present investigation, catalysts samples were characterized using AAS (atomic absorption spectroscopy), XRD (X-ray diffraction), surface area (BET) and SEM-EDS (scanning electron microscopy). Results show presence of 6-5% w/w of vanadium pentoxide (V2O5), 10-11% w/w of potassium oxide (K2O) and 55-60% w/w of silicon oxide (SiO2). The material presents a pore size of 3 nm and a specific surface area of 200 m²/s. The spent catalyst was firstly pulverized in a powder mill until 200 µm was attempted, then a calcination at 450 °C was made. Different leaching agents were used: nitric, sulfuric, hydrochloric acid and sodium hydroxide with variation of percentage of solids, particle size, leaching agent concentration and leaching time. Sodium carbonate was added to the solution to obtain a precipitate. A final calcination step was made at 450 °C to obtain vanadium pentoxide. The best results were obtained by using sulfuric acid at 75 g/L, 20 w/w percentage solids, environmental temperature, agitation speed was maintained 750 rpm and 30 minutes leaching, the recovering vanadium rate was 94.41%. In the precipitation stage 92.2% of sodium meta vanadate, for that a pH 7 was required. Finally, precipitation was calcinated getting vanadium pentoxide at 97% purity and it costs is $104.5 per 500 grams.