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.