Kinetic Study of Goethite Formation from Ferrihydrite in Alkaline Medium

• Published in: Industrial & engineering chemistry research 2002-10, Vol.41 (21), p.5226-5231
• Main Authors: Hamzaoui, A, Mgaidi, A, Megriche, A, El Maaoui, M
• Format: Article
• Language: English
• Subjects: Chemistry; Cross-disciplinary physics: materials science; rheology; Earth sciences; Earth, ocean, space; Exact sciences and technology; Growth from solutions; Inorganic chemistry and origins of life; Kinetics and mechanism of reactions; Materials science; Methods of crystal growth; physics of crystal growth; Mineralogy; Non silicates; Physics
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie010931z

The kinetics of goethite formation from ferrihydrite was studied colorimetrically in the initial pH range of 11.00−12.20 and at temperatures varying between 40 and 80 °C. It was shown that the rate of goethite crystallization is significantly influenced by the aging temperature and by the initial pH. The apparent activation energy, calculated from the Barret law, is close to 47.17 (± 2) kJ mol-1. The kinetic data fitting was performed with a heterogeneous reaction model (shrinking core model). It was found that the rate dependence on pH and temperature can be described by the expression r = [7.02 × 10-2 e-5670/T ](a OH − )0.5. The observed fractional-order kinetics was qualitatively described using classical adsorption isotherms. Both the shrinking core model results and the high value of the activation energy favor the hypothesis that the rate of the ferrihydrite transformation process is controlled by the surface chemical reaction.