From Roast to Paints
How to Use Pyrohydrolysis for Inorganic Oxide Prime Material for Ceramics
Titanium Dioxide — Pigments from the Reactor
Titanium dioxide ores, which are processed to make TiO2 pigments, start mostly from ilmenites, Fe2O3.TiO2, or natural rutile or slags from the titanium production. Besides the conventional routes like the sulfate or chlorine processes, also the leachings of ilmenites with hydrochloric acid is used. The solution then containing iron chloride FeCl2, will be further pyrohydrolyzed to recycle the acid (HCl) for further processing during ore leachings, whilst the residual impure titanium dioxide , TiO2, will be further cleaned by washing, followed by drying, calzining and milling, to finally produce pure rutile (TiO2).
In pigment production, the crystal parameters such as purity, crystal form and size, grain size and the contents of trace impurities are of great importance and are prerequisites for the proper chosen production route.
Further applications of titanium dioxide include the use for catalysts, which mostly are used in de-NOxing catalysts or also for use in solar cells.
A Niche Product of Pyrohydrolysis: Chromium Oxide
Chromium(III) oxide (Cr2O3) is an important prime material for colorants, as well as in its use in refractories. Further applications are in leather making and in catalysis. Producing Cr2O3 by spray roasting uses hydrochloric solutions of ClCl3, which can be made by HCl solvation of chromium scrap. The process requires temperatures and concentrations in hydrochloric solutions, similar to the iron oxide process, i.e. around 200 g/l. The result is a dark green powder, with particle forms and of sizes of 0,1 – 3 mm. There is no industrial production on big scale known to make chromium oxide by the spray roasting route, in contrast to the above mentioned routes.