Titanium Dioxide Pigment Production Line

Product Specification

There is a high demand for titanium dioxide in the global market, which is expected to continue growing. Additionally, there is a constant increase in the worldwide need for inorganic pigments. According to experts’ estimates, in recent years, titanium dioxide pigment accounted for 65-70% of the total consumption of inorganic pigments and over 90% of the consumption of white pigments.

In producing pigmentary titanium dioxide by the nor mal sulfate process, objectionable quantities of iron, chromium, vanadium and/or niobium impurities are car ried over into the final product. By effecting precipitation of the titanium values from sulfuric acid solution in the form of a titanyl sulfate slurry or discrete titanyl sulfate particles, and separating and redissolving the titanyl sul fate in an aqueous liquid, a solution is provided from which hydrous titanium dioxide can be precipitated by hydrolysis with increased purity of product. Precipitation of titanyl sulfate as a solid mass is avoided by adding sulfuric acid to the titanyl sulfate solution shortly after initiation of precipitation.

The present invention relates to a process for the pro duction of pigmentary titanium dioxide. Pigmentary titanium dioxide is commonly made by the sulfate process wherein an impure iron-containing titani ferous material, for example ilmenite, is digested with a limited amount of hot concentrated sulfuric acid and the resulting solid is then dissolved, normally in water or dilute sulfuric acid. The solution thus formed is then subjected to various treatments such as reduction of the iron content to the ferrous state; removal of undissolved solids by clarification and of some of the dissolved iron, for exam ple by concentration and cooling. Ultimately a substan tially clear solution is obtained having acceptable iron/ titanium and acid/titanium ratios. To this solution are added or are formed in situ, rutile- or anatase-inducing nuclei and the resulting mixture is heated to hydrolyze the titanium sulfate in solution and to precipitate hy drous titanium dioxide. The latter is filtered off and subjected to various wash ing procedures to remove excess acid and various color forming impurities such as iron or chromium compounds. To the purified hydrous titanium hydroxide are added various conditioning agents, for example compounds of zinc, antimony or tin, if rutile titanium dioxide is to be produced and heat-decomposable alkali metal salts or phosphates (e.g. as the ammonium salt). The titanium dioxide is then calcined, for example at a temperature in the range of about 800 to 1100° C., wet and/or dry milled, classified following which it may be coated, dried and finally milled. It may also be coated with hydrous oxides or other metals or metalloids, for example of aluminum, titanium, silicon, zirconium and/ or cerium at some stage before recovery. Titanium dioxide pigment produced by the above proc ess frequently contains coloring impurities which prevent the development of the maximum brightness of which titanium dioxide pigments are capable. It is believed that this inferior brightness is due, at least in part, to the presence of small amounts of elements such as chromium, vanadium, niobium and/or iron in the pigment derived from impurities in the iron-containing titaniferous mate rial. It has proved impossible to remove all the coloring impurities and to de