Method for oxidizing trivalent titanium in solid titanium oxide-containing materials

摘要

An oxidic titanium-containing material comprising trivalent titanium oxide is agglomerated and then partly oxidised by means of an oxidising gas containing free oxygen in the presence of water and an electrolyte below 100 DEG C. and thereafter oxidising with a similar gas at a temperature, preferably gradually increasing, in the range 250-400 DEG C. such that autoxidation and consequent glowing is avoided. The process is particularly applicable to titanium oxide concentrates produced by thermal reduction in a rotary furnace, which have a particle size of 1-5 microns and are pyrophoric at 150 DEG C. and above. The agglomeration preferably consists of pelleting to a particle diameter of 3-15 mm. using, e.g. dilute sulphuric acid. The first oxidation stage may be conducted as described and claimed in Specification 809,753, to which reference is made. It is preferred in the second oxidation step to pass a hot gas through a layer of the material at such a velocity that the heat of reaction is substantially immediately removed, but the temperature may be controlled, e.g. in a rotary furnace, multiple-hearth furnace or tunnel kiln, by restricting the access of air. The oxidising gas may also be passed counter-currently through a moving layer of pellets. Where air is used to cool the oxidised material, the warmed air may be used in an oil burner and/or in admixture with the oxidising gases. In the examples, the first oxidation is performed by supporting a layer of pellets on an open wire screen and exposing to the air: in the second oxidation a stationary grate in an oil-fired chamber is employed and a preheated mixture of air and combustion gases passed therethrough. Specifications 754,453 and 791,366 also are referred to.