Ammonium Paratungstate (NH4)[H2W12O42].4H2O is the most important precursor for the majority of tungsten products. Exceptions are only products of melting metallurgy and Menstrum WC produced directly from ore concentrates.
All other intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid and ammonium metatungstate can be derived from APT, either by thermal decomposition or chemical conversion.
APT is a white crystallized powder having average crystal size between 30 and 100 µm. Especially crucial for the quality is the purity. Typical levels of todays commercial APT are (upper limits in µg/g):
Al 1-7, As 5-10, Bi 0.5-1, Ca 1-10, Co 1-10, Cr 1-10, Cu 1-3, Fe 3-10, K 2-10, Mg 1-7, Mn 1-10, Mo 5-30, Na 5-10, Ni 1-7, P 5-7, Pb 1-5, S 5-7, Si 1-10, Sn 1-10, Ti 3-10, and U 3-10. APT is packaged in polyethylene-lined drums or woven bags up to 1 ton.