A STUDY OF THE MORPHOLOGY OF THE GOETHITE CRYSTALLIZATION PROCESS

Experiments were performed in 1.5- and 150-1 reactors to investigate t he growth process of needle-like goethite crystals under alkaline cond itions. From an analysis of the transmission electron micrographs of t he crystal samples during the reaction process, the nucleation and gro wth processes of the crystal grains were examined. Evidence shows that the nucleation of alpha-FeOOH crystals occurs both on the surface of the Fe(OH)(2) crystal grains and in the bulk liquid, depending on the local concentration of the alpha-FeOOH molecules. The statistical resu lts of the particle size show that the average length and width are bo th basically proportional to R-1/3. The crystals grow in a similar man ner and the size distribution is held roughly constant during the crys tal growth process. The influence of the oxidation rate during the ear ly period of the reaction process on the parameters of the final cryst al grains was examined. The average aspect ratio of the final alpha-Fe OOH grains increases with the decreasing of the oxidation rate in the early period. The particle size changes as a result of aging under cer tain pH and temperature conditions. (C) 1998 Elsevier Science S.A.