Abstract
Peptization of ferric hydroxide by hydrochloric acid was examined. Precipitate of ferric hydroxide was added to an aqueous solution of hydrochloric acid and agitated for 30 min at 80° or boiled for 30 min. Efficiency of peptization was evaluated from the concentration of ferric hydroxide in the sol, which was determined by chelatometry after the colloidal particles had changed to ferric ion. It has been found that there is a maximum point of peptization at appropriate amount of ferric hydroxide precipitate added to hydrochloric acid. The degree of peptization increased with the amount of hydrogen ion adsorbed on the particle. The adsorption isotherm of hydrogen ion on the ferric hydroxide particle is well reproduced with Freundlich's equation. The minimum amount of hydrogen ion required to be adsorbed in order to peptize the particle (xmin) depends on ionic strength of the colloidal system (J), and the relation was experimentally determined as follows : xmin=0.95 √(J)+0.03 It has been concluded that hydrogen ion is responsible for peptization of ferric hydroxide as well as for stabilization of colloidal ferric hydroxide particles at about pH 2.5-5, while ferric ion cooperates with hydrogen ion to peptize and stabilize the sols at pH below 2.5.
