The Problem of the Formation of Boehmite and Gibbsite in Bauxite-Bearing Lateritic Profiles

Abstract

The study of a large amount of factual material about the formation conditions of gibbsite or boehmite and their mutual transformations in lateritic bauxites allowed us to solve the problem of boehmite formation and its spatial and genetic relationship to gibbsite. The boehmite formation occurred only during the formation of sedimentary-lateritic bauxites from alluvial and lacustrine sediments that underwent bleaching and resilification at the stage of sediment flooding, as well as on bleached bedrock under sedimentary-lateritic bauxites. The most intense boehmite formation occurred at a depth of 20–30 m from the surface and was accompanied by an alumina input, which was realized here in the form of boehmite along with the gibbsite formation due to the hydrolytic decomposition of kaolinite and partially due to the input alumina. In the upper profiles, the recrystallization of bauxites occurs with the replacement of dissolving boehmite with gibbsite, with a decrease in the total Al2O3 content and an increase in the amount of crystallization water. In classic lateritic bauxites, the boehmite content is highly insignificant; that is, its formation in them practically does not occur or is very much inhibited.