From Roast to Paints

How to Use Pyrohydrolysis for Inorganic Oxide Prime Material for Ceramics

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Hydrochloric acid pickling is often applied during mild steel (normal steel) production. In contrast to this, high alloyed steel (special steel) needs a more rigid procedure of pickling, using mixed acids like hydrofluoric/nitric acid mixtures (HF/HNO3). Those solutions of mixed acids can also be recycled by thermal methods of a spray roast process, using a different construction and different materials like the above mentioned ones.

The process was originally developed by the Andritz company during the 1980´ies and is now successfully applied in steel industries. The resulting materials, usually mixtures of iron oxide together with nickel and cobalt oxides, are usually being reduced to the proper metals to get then recycled for the processing of high alloyed steels.

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Besides steel, also titanium metal is being pickled with hydrofluoric acid (alone). The resulting liquid mix of titanium fluorides can be spray roasted to give hydrogen fluoride (HF) as well as TiO2. This material may be used to make pigments, however in most cases will be returned back into the titanium production route.

On academic scale there were some developments to make mixed ferrites from HNO3 solutions containing together with manganese and iron nitrates to produce mixed oxides for ferrite applications and further to make aluminium titanate AlTiO5, a prime material for the corresponding ceramics, which are of industrial importance for use in engineering ceramics.

Pyrohydrolysis Has Come a Long Way From Acid Recycling

Pyrohydrolysis which is a process originally developed as a revolutionary method to recycle pickling acids based on hydrochloric acid to modernize steel manufacturing and to result in much higher pickling velocities, better surface properties of pickled steel and beneficial for environmental protection combined with added profit, has now turned into new processing routes for inorganic oxide production. The big and ever rising demand in prime material for ceramics, electro ceramics, refractories and pigments has been completed by process routes which were described here. Some 800 plants using this technology have been established world wide producing millions of tons of oxide materials or acids for steel pickling.

And yet, the development has not stopped at this point: Meanwhile, a big number of engineering companies in the world enlarge this list of accomplishments of better and more economic process routes. In that aspect the original developments by this technology, starting from its homeplace in Austria, have met international reputation. Reason enough for optimism: Given the current speed of development, further growth can be expected for pyrohydrolysis

* The author is a technological and scientific specialist.