(397c) Low Temperature Hydrothermal Crystallization for a New TiO2 Process

Hutchenson, K. W., DuPont Central Research and Development
Corbin, D. R., DuPont Central Research and Development
McCarron, E. M., DuPont Company
Torardi, C. C., DuPont CR&D
Li, S., Princeton University

This presentation summarizes the development and optimization of a novel low temperature hydrothermal route to recover base TiO2 product from an intermediate titanyl hydroxide species formed in the TiO2 process following digestion of the iron titanate ore feed material. This work was part of an effort to develop a new TiO2 production process based on ammonium hydrogen oxalate digestion that can process low-grade ilmenite ores with lower energy and capital investment intensity and a smaller environmental footprint than conventional processes.

Statistically designed experiments have illustrated the feasibility of producing both pigment-grade and nano-size TiO2 base materials at mild hydrothermal process conditions. Small scale screening experiments on synthetic intermediates were carried out to examine the effects of various reaction variables on the final TiO2 properties. The screening study identified reaction time, hydrochloric acid to titanium ratio, and the concentration of a particular mineralizing salt as the three key factors most influential to the formation and growth of rutile TiO2. Based on the results of the screening experiments, empirical process models, which express TiO2 product properties as a function of the critical process variables, were developed using statistical response surface design techniques. The models were used to optimize the reaction conditions for the production of either pigmentary or nano rutile base products. The predicted reaction conditions were then validated at the same 10mL scale.

The empirical model results identified a relatively narrow operating window for the production of pigmentary rutile TiO2 at relatively low temperature (235-250C) hydrothermal crystallization conditions. The process was successfully repeated on a 1L reactor scale and resulted in the production of pigmentary rutile base. This material was then successfully surface treated via the standard chloride wet treatment technology. Subsequent work validated the application of this process to an authentic ore-derived titanyl hydroxide intermediate and demonstrated the formation of pigmentary rutile TiO2.