(519d) Low Temperature Hydrothermal Crystallization for a New TiO2 Process

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 10 mL scale.

The empirical model results identified a relatively narrow operating window for the production of pigmentary rutile TiO₂ at relatively low temperature (235-250 C) 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.