KAOLINITE AND HALLOYSITE SYNTHESIS IN THE GIBBSITE-SILICA SOLUTION SYSTEM UNDER NORMAL CONDITIONS

Results of physicochemical experiments (carried out during the last 13 years) on the low-temperature synthesis of kaolinite and halloysite, abundant supergene clay minerals, are discussed. The experimental cond itions approach natural bauxite resilification (kaolinization and hall oyzitation), when the bauxite, which is dominated by such alumina mine rals as gibbsite, boehmite, and diaspore, is affected by solutions con taining more than 2-3 mg/l of silica and alumina in concentrations bel ow the solubility of the alumina minerals. The kaolinite and halloysit e synthesis occurred in samples of natural gibbsite treated by Al-free solutions with an initial Si content of 60 mg/l and various initial p H values. In experiments with acid solutions, the behavior of Al shows that after a month equilibrium between gibbsite and solution is attai ned with an insignificant decrease of the Si content in the latter The further synthesis of Al silicates occured at partial equilibrium betw een gibbsite and solution and its oversaturation in Si by more than on e order of magnitude relative to Al silicates. The experimental result s allowed us to estimate the reaction rate constants characterizing Al silicate synthesis from solution and the resilification of Al oxides and hydroxides. An application of these parameters to estimates of the resilification dynamics of gibbsite bauxite is briefly discussed.