Influence of redox pretreatment on the pulverization of panzhihua ilmenite during hydrochloric acid leaching

The influence of oxidation-reduction (redox) pretreatment on the pulverization of Panzhihua ilmenite during hydrochloric acid leaching to obtain synthetic rutile was investigated in detail. We observed the dissociation of incompact TiO2 products formed via the dissolution-hydrolysis of Ti ions, which was caused by the fast dissolution of FeTiO3 during the leaching process and was the fundamental reason for pulverization for the raw Panzhihua ilmenite. A stirring operation during the acid leaching aggravated the pulverization phenomenon. The formation and consumption of insoluble rutile grains during the redox pretreatment played a key role in preventing the pulverization of pre-treated ilmenites. The rutile network formed during the pre-oxidation was retained and served as a nucleus for the hydrolyzed product during the successive leaching process, providing the leaching products of the pre-oxidized ilmenite with less hydrolyzed TiO2, higher mechanical strength, and thus an excellent resistance to pulverization, even with stirred leaching. Because the following weak reduction process (reduction of ferric iron to ferrous state) at relatively low temperatures (e.g., 873 K) did not destroy the rutile network that was formed by the pre-oxidation, it did not change the ability of the pre-oxidation to prevent the pulverization of ilmenite. However, the weak reduction process at high temperatures (e.g. 1023 K) weakened the effect of pre-oxidation because most of the rutile grains that were formed by the pre-oxidation were consumed and formed FeTiO3.