Mechanisms of Gibbsite Crystallization from Partially Neutralized Aluminum Chloride Solutions1

Hsu Pa Ho
Department of Soils and Crops, Rutgers The State University of New Jersey, New Brunswick, New Jersey 08903
1 New Jersey Agricultural Experiment Station Publication No. D-15420-1-86.

Abstract: To interpret the erratic conditions, rates, and extent of gibbsite crystallization from partially neutralized AlCl3 solution, the following hypothesis is proposed: The initial OH-Al polymers in the freshly prepared solutions were probably unstable and transformed into either gibbsite or stable OH-Al polymers via two different reaction paths. In the presence of nuclei, the OH-Al polymers dissociated into monomeric ions, which then deposited onto nuclei to form gibbsite. In the absence of nuclei, the unstable polymers slowly converted to stable polymers. The erratic stability of OH-Al solutions and gibbsite crystallization are therefore attributed to the relative magnitudes of these two reaction paths which, in turn, are attributed to two key factors: (1) the distribution of unstable vs. stable OH-Al polymers; and (2) the presence or absence of nuclei. The duration of aging of the parent solution governed the distribution of unstable vs. stable polymers. The rate of neutralization resulted in varying localized high alkalinity in OH-Al solution preparation and thus varying development of nuclei.

Key Words: Aluminum hydroxide • Crystallization • Gibbsite • OH-Al polymer • Nucleation

Clays and Clay Minerals; February 1988 v. 36; no. 1; p. 25-30; DOI: 10.1346/CCMN.1988.0360104
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)