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The Kinetics of Gibbsite Dissolution in Nitric Acid¹

ABSTRACT

The kinetics of dissolution of two synthetic gibbsite preparations was studied in nitric acid solutions with pH values that ranged from 1.5 to 3.3. Dissolution rates were determined at 298 K for both gibbsites and additional rate experiments were conducted at 313 K and 328 K with one of the gibbsites. Dissolution was controlled by reactions at the solid-solution interface and not by diffusion. The rate of reaction did not increase monotonically with H⁺ activity; rather, there was a minimum rate of about pH = 2.25. Two different mechanisms with different rate-controlling steps were suggested. At pH < 2.1 the rate-controlling step was probably protonation of positively charged surface sites while at pH > 2.4 the rate-controlling step was probably water attack of surface Al.

¹ Minnesota Agric. Exp. Stn., Univ. of Minnesota, St. Paul. Scientific Journal Series. Paper no. 11847.

² Assistant Professor of Soil Science. Dep. of Soil Science, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication August 3, 1981. Accepted for publication July 23, 1982.