Optimization of the reactive silica quantification method applied to Paragominas-type gibbsitic bauxites

This study presents an optimization of the method used to quantify reactive silica (RxSiO2) in gibbsitic bauxites, specifically those which contain no (or insignificant) quartz. In this work they are named as Paragominas-type Bauxites. A factorial design of experiments was used. The variables included the temperature, caustic concentration and time for two cases: bauxites with low and high RxSiO2 contents. Temperature is the most important factor and has a positive influence on RxSiO2. First-order empirical models were properly obtained to predict the amount of RxSiO2 as a function of temperature, caustic concentration and time, which responded to the following optimal conditions: (1) without significant amount of quartz - 180 °C, NaOH 10% w/v and 60 min for low RxSiO2 and 25 min for high RxSiO2, and (2) with significant amount of quartz - 150 °C, NaOH 20% w/v and 60 min for both situations.