Estudo da contaminação de sílica na alumina em processo bayer.

Abstract

The demand for aluminum has grown considerably in recent years as well as the requirement for high purity metals, since the use of this type of product is intended for nobler applications and higher value-added market. Silica content is one of the main impurities of the aluminum metal and alumina, as raw material, presents an important contribution. Therefore, this research aimed to comprehend the influence of certain variables, like alumina concentration , temperature and surface area, previously unknown, in the alumina contamination process of silica by DSP (dessilication product), focusing on Precipitation area in order to avoid contamination events. Through laboratory tests and case studies using plant historical data to evaluate the correlation of some variables was possible to know the main variables in the silica contamination process in alumina. The results show the great influence of soluble silica in green liquor, which should be controlled below 1.8 g/L to obtain a silica content of 0.011 % on alumina. Another major factor is the alumina concentration in the spent liquor that should not be lower than 115 g/L, because it impacts sharply on silica supersaturation. The remaining variables studied, surface area, temperature and seed storage, show that the procedures and strategies should be reviewed in order to avoid DSP precipitation on hydrate. Therefore, from all results obtained it will be possible to avoid alumina contamination events by silica, and keep it at the level required by the client, only through determination of control limits and strategies review.