Conditions in solution during the formation of gibbsite in dilute Al salt solutions. 4. Effect of Cl concentration and temperature and a proposed mechanism for gibbsite formation

Abstract

Experiments were made to determine the effect of conditions in chloride solution on the formation of gibbsite. It was found that the temperature of the systems and the chloride concentration in solution had a marked effect on the rate of all the reactions occurring. In all cases gibbsite was identified as the final product, except when the temperature was 10 °C and when the chloride concentration was about 0.6 N. When the temperature was 10 °C the reactions were very slow, and there was no reason to believe that gibbsite would not have been the final product if sufficient time had been allowed. In the system in which the chloride concentration was about 0.6 N, the final product was an aluminum hydroxychloride. In all systems the concentration of polynuclear hydroxyaluminum ions started at relatively low values, increased with time to a maximum, and then decreased, while with the solids the reverse was true. A mechanism for the formation of gibbsite is proposed.