Low-temperature sintering of bauxite raw material with alkali as an alternative to the parallel Bayer sintering process

Abstract

The aim is to develop an alternative technology of bauxite raw material processing based on low-temperature sintering of bauxite with caustic alkali, as well as to solve the issue of carbon footprint control at alumina refineries in the Urals. Laboratory tests were carried out by sintering artificial bemite and hematite with chemically pure caustic alkali at temperatures of 300, 500 and 700°C and their further leaching in weakly alkaline solutions. To study the phase, chemical, and particle size distribution of red muds after leaching, various physical and chemical methods of analysis were used, such as X-ray fluorescence, titration method, X-ray phase analysis, scanning electron microscopy, magnetometry with a vibrating sample. The Brunauer – Emmett – Teller method was used to determine the specific surface area and porosity. The study of the kinetics of the solid-phase reaction of the bemite interaction with caustic alkali has shown the kinetic interaction in the temperature range under study. Moreover, sintering of hematite at temperatures of 300 and 500°C and further leaching of the sinter with water resulted in mineralogical changes in the sludge with the production of a new mineral, maghemite, which possesses magnetic properties. When studying the magnetic properties of red mud of lowtemperature sintering of bauxite, we determined that the magnetization was as high as 19–20 electromagnetic units per g (at a sample density of 2.38 g/cm3) at a magnetic field of 10 kE. The specific surface area of these samples was 54.97 and 51.77 m2/g. The performed studies confirm that the proposed technology can be adapted for bauxite to produce highiron red slimes, thus contributing to the integrated processing of bauxite raw materials. In addition, ways to reduce carbon emissions at alumina refineries by eliminating the sintering operation with soda and limestone, which is accompanied by CO2 emission during decomposition of these compounds, can be studied.