The Free Energy of Formation of Gibbsite and Al(OH)4‐ from Solubility Measurements

Abstract Solubility determinations on two particle sizes of crystalline gibbsite, from both undersaturation and supersaturation in the acid pH range, gave a K SO of −34.03 ± 0.05. Using the same gibbsite in the alkaline pH range and extrapolating values from supersaturation to infinite time, a *K S4 of −15.30 ± 0.05 was obtained. From these values a ΔG f 0 (gibbsite) of −274.20 ± 0.06 kcal/mole of Al(OH) 3 and a ΔG f 0 [Al(OH) 4 ‐ aq] of −310.03 ± 0.07 kcal/mole were calculated. The value for gibbsite confirms previous work on the stability of gibbsite and the new Al(OH) 4 ‐ value eliminates a discrepancy between gibbsite stabilities derived from solubility measurements in the acid and in the alkaline pH range.