Gibbs free energies of formation for bayerite, nordstrandite, Al(OH)2+, and 067Al(OH)2+, aluminum mobility, and the formation of bauxites and laterites.

Abstract

An internally consistent set of thermodynamic properties are calculated for the monomeric Al-solution species Al3+, Al(OH)2+, 063Al(OH)2+ and 062Al(OH)-4. Some high-molecular-weight organic materials may have a catalytic role in the formation of gibbsite and kaolinite at low pH, whereas low-molecular-weight organic solutes may inhibit precipitation of Al(OH)3. The weathering of primary aluminosilicates proceeds through a series of metastable (irreversible) reactions that progress simultaneously at low T towards the lowest free-energy state. To properly interpret the role of Al in metasomatism, the structure and thermodynamic properties of the Al solution species at >373 K must be determined.-R.A.H.