Combined production of synthetic rutile in the sulfate TiO2 process

Abstract

Abstract This paper describes a novel process for preparation of synthetic rutile using an intermediate, sulfated ilmenite from the sulfate TiO 2 process as the feedstock. The synthetic rutile can be obtained by selective thermal decomposition of the sulfated ilmenite, followed by targeted leaching for removal of various impurities. The results of the decomposition unit showed that almost all the TiOSO 4 in the sulfated ilmenite decomposed to TiO 2 , while the iron component mainly existed in the form of sulfates in the optimal thermal decomposition conditions, i.e., a roasting temperature of 540 ° C and a roasting time of 120 min under air flow or in stagnant air or a roasting temperature of 510 ° C and a roasting time of 120 min under nitrogen flow. The thermal decomposition can be divided into three stages. The sulfates of titanium and iron in the sulfated ilmenite were first decomposed to TiO 2 and water-insoluble FeOHSO 4 , respectively, at a temperature less than 500 ° C. The FeOHSO 4 was further converted into water-soluble Fe 2 O(SO 4 ) 2 at 500–560 ° C. Finally, the Fe 2 O(SO 4 ) 2 was decomposed to Fe 2 (SO 4 ) 3 and Fe 2 O 3 at a temperature above 560 ° C. The water-soluble metal sulfates, the water-insoluble FeOHSO 4 /Fe 2 O 3 and the SiO 2 in the TiO 2 -containing slag can be removed through leaching by using water, dilute sulfuric acid and sodium hydroxide, respectively. The results showed that 70–85% of the iron, as well as a majority of the magnesium, calcium, etc. impurities, could be leached by water, and up to 92% of the total iron could be removed after the subsequent acid leaching in a 15 wt% H 2 SO 4 solution, while the silicon removal reached 65% in a 5 wt% NaOH solution. A synthetic rutile with a TiO 2 content over 90 wt% and total MgO + CaO less than 1 wt% was obtained under the optimal conditions listed above. The present process can be integrated with the sulfate TiO 2 process, producing titania pigment and synthetic rutile simultaneously. The advantages of the TiO 2 beneficiation process include the moderate reaction conditions, the capability of recycling the H 2 SO 4 completely and the recovery of a large part of the iron, as well as comprehensive utilization of the waste sulfuric acid discharged from the sulfate TiO 2 production process.