Effluent-Free Manufacture of Ammonium Paratungstate (APT) by Recycling the Byproducts

Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O.

Ammonium paratungstate is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.

Within the framework of a review of the fundamental processes applied for the manufacture of ammonium paratungstate (APT) the main byproducts and wastes generated in these processes and their environmental impact are summarized. A subsidiary process based on the electrodialytic recovery of NaOH for the elimination of the salt byproduct, which is generated in the largest quantities, is outlined together with the main aspects to be taken into account for large-scale industrial implementation.The present stage of development and implementation of an APT production line for the processing of typical scrap material from the lighting filament industry is shown, as well as the oxidizing and dissolving process of compact and lumpy tungsten alloy scrap (Cu-W, Fe-Ni-W) and hard metal scrap (Co-WC, Co-WC-Ta(Nb)C-TiC).Several as yet unexploited potentials are sketched which could, from scientific and engineering standpoints, be interesting for the development of more efficient intermediate manufacturing processes for APT and tungsten or process operations for a wide variety of raw materials.

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