A process for converting molybdenum technical oxide, partially oxidized MoS2 or off-spec products from MoS2 oxidation processes into a purified molybdenum trioxide product is provided, generally comprising the steps of: combining molybdenum technical oxide with an oxidizing agent and a leaching agent in a reactor under suitable conditions to effectuate the oxidation of residual MoS2, MoO2 and other oxidizable molybdenum oxide species to MoO3, as well as the leaching of any metal oxide impurities; precipitating the MoO3 species in a suitable crystal form; filtering and drying the crystallized MoO3 product; and recovering and recycling any solubilized molybdenum.