Preparation of High Grade Ammonium Metatungstate (AMT) as Precursor for Industrial Tungsten Catalyst

The increasing demand for pure tungsten and its compounds due to their high tensile strength makes them a versatile material in catalyst, heavy alloy, cemented carbide, among others. This exceptional property makes it to be of high interest by industrialists for use in the engineering and manufacturing industries. Thus, preparation of ammonium metatungstate (AMT) from a Nigerian wolframite ore by hydrometallurgical technique was examined in sulphuric and phosphoric acid. During leaching, parameters such as leachant concentration, reaction temperature, and particle size on ore dissolution were examined. At optimal conditions (2.0M H2SO4 + 0.15M H3PO4, 75 °C, −63 µm), 93.7% of the ore dissolved within 120 min. The calculated activation energy of 6.93 kJ/mol supported the proposed diffusion mechanism. The leachate at optimal conditions was treated to obtain a pure tungstate solution. The purified solution was beneficiated to prepare a high grade AMT ((NH4)6[H2W12O40]·4H2O: 96-901-3322, m.p.: 98.7 °C, density: 2.16 g/cm3), which serves as an intermediate for some defined industries.