Scour medium for titanium dioxide production
A blend of anatase and rutile titanium dioxides is calcined to a crush strength and density meeting the requirements for an acceptable scour medium in a chloride process for producing rutile titanium dioxide pigments. By using such a blend, a greater conversion of the anatase titanium dioxide can be realized than would be observed under the same calcination conditions were only anatase titanium dioxide calcined, so that a significant proportion of the less costly and less valuable anatase titanium dioxide can be used and the scour medium employed at customary rates of addition, without requiring separation of the scour medium from the produced rutile titanium dioxide and while keeping the rutile content of the combined spent scour medium and produced rutile titanium dioxide at about 99 percent and greater by weight.
1 . A method for reducing titanium dioxide buildup in equipment used for the production of titanium dioxide, comprising the steps of:
calcining a blend of anatase and rutile titanium dioxides to produce a scour medium;
and introducing the scour medium into the equipment used for the production of titanium dioxide.
2 . The method of claim 1 , wherein the calcining step takes place at a temperature greater than about 1025° C.
3 . The method of claim 1 , wherein the blend is calcined to a crush strength between about 15 percent and about 30 percent.
4 . The method of claim 1 , wherein the blend is calcined to a density of from about 1.55 g/cm3 to about 1.71 g/cm3.
5 . The method of claim 1 , wherein the calcined blend is introduced into an oxidation reactor.
6 . The method of claim 1 , wherein the calcined blend is introduced into a cooling conduit.
7 . The method of claim 1 , wherein the blend is at least about 10 percent anatase by weight.
8 . The method of claim 1 , wherein the blend is at least about 50 percent anatase by weight.
9 . The method of claim 1 , wherein the blend is at least about 75 percent anatase by weight.
10 . The method of claim 1 , wherein the blend is at least about 90 percent anatase by Case No. weight.
11 . The method of claim 1 , wherein the proportions of the anatase and rutile titanium dioxides in the blend are selected and calcinations conditions employed to effect at least that degree of conversion of the anatase titanium dioxide in the blend which enables an anatase content of less than about 1 percent by weight of the combined produced titanium dioxide and spent scouring medium, when the scour medium is used to an extent whereby it comprises from about 2 to about 10 percent of the mass flow through the production equipment for producing said titanium dioxide.
12 . The method of claim 11 , wherein the anatase content of the produced titanium dioxide and spent scouring medium is maintained at less than about 0.5 percent by weight.
13 . The method of claim 11 , wherein the anatase content of the produced titanium dioxide and spent scouring medium is maintained at less than about 0.2 percent by weight.