Method for making composite titanium dioxide rutile pigment

Claim 1

A PROCESS FOR THE MANUFACTURE OF A COMPOSITE PIGMENT MATERIAL COMPRISING TITANIUM DIOXIDE IN RUTILE FORM AND AN EXTENDER WHICH INCLUDES: HEATING A MIXTURE OF TITANIFERROUS ORE AND HYDROCHLORIC ACID IN THE RATIO OF ABOUT 1:2.25 TO PRECIPITATE A SUBSTANTIALLY IRON-FREE HYDROCHLORIC ACID LEACHED ORE RESIDUE DIGESTING A MIXTURE OF TITANIFEROUS ORE AND SAID ACID LEACHED ORE RESIDUE IN THE PRESENCE OF CONCENTRATED SULFURIC ACID TO FORM A DISGESTION CAKE, SAID ACID LEACHED ORE RESIDUE BEING PRESENT IN SAID ADMIXTURE IN AN AMOUNT WITHIN THE RANGE OF FROM 4% TO 20% ON A TITANIUM DIOXIDE BASIS AND THE RATIO OF SULFURIC ACID TO THE ADMIXED ORE AND ACID LEACHED ORE RESIDUE BEING IN THE RANGE PF FROM 1.6 TO 1.8; SOLUBILIZING SAID DIGESTION CAKE IN WATER TO FORM AN AQUEOUS LEACHED ORE SULFATE SOLUTION; MIXING AN EXTENDER SELECTED FROM THE GROUP CONSISTING OF THE SULFATES OF BARIUM, CALCIUM AND STRONTIUM WITH SAID LEACHED ORE SULFATE SOLUTION; HYDROLYZING SAID ADMIXTURE TO PRECIPITATE OUT A HYDRATE OF TIO2 AND AN ALKALINE EARTH SULFATE, AND THEN CALCINING SAID HYDRATE AT A TEMPERATURE WITHIN THE RANGE OF FROM 925-975*C.