The synthesis of goethite by oxidation of Fe 2/ in presence of droxides; it consists of the hydrolysis of Fe 3/ cations. This metallic iron was undertaken in an aqueous medium containing is achieved by pouring freshly prepared ferric solutions into indifferent salts such as Na 2 SO 4 , (NH 4 ) 2 SO 4 , NaCl, and NH 4 Cl. concentrated NaOH or KOH solutions; the aging of the sols Temperature and bubbling air rate were maintained, respectively, takes place at 60-80ЊC for a period of time ranging from 1 at 70ЊC and 1 L/min. The influence of anions and cations on the to several days. Goethite precipitates if the pH of the final kinetics of each step of the process has been followed distinctly, solution is above 12.8; for less basic media a mixture of the iron dissolution rate has been determined by the variation of goethite and hematite is observed (18-20). Matijevic et al. the medium acidity, and the precipitation of goethite has been (21-24) have thoroughly studied the hydrolysis of ferric determined by gravimetric measurements. With respect to Cl 0 , the SO 20 4 anion decreases the rate of the two reactions. NH / 4 acts solutions in acidic medium; b-FeOOH and a-Fe 2 O 3 are the as an inhibitor when it is present at low concentrations and as an end products. Livage et al. (25) gave theoretical consideraaccelerator for higher concentrations; the limit corresponding to tions on the nucleation and germination processes of various the change of NH / 4 behavior depends on the nature of the counter species resulting from the hydrolysis of a variety of metallic ion. The reaction product is composed of pure goethite in the cations. presence of sulfate salts, whereas a mixture of goethite and lepido-
In this paper we have chosen a third synthetic method, crocite, respectively, 60-70 and 40-30%, was observed in the prescontrolled air oxidation of an iron powder suspension in ence of chloride salts.