The Hydrolysis of Aluminum Salts in Clay and Soil Systems

Abstract

Aluminum salts undergo more extensive hydrolysis in acid soil and clay systems than in aqueous solutions of the same pH. The “increased hydrolysis” is accompanied by, and presumably is caused by, the sorption of the hydrolysis product which contains Al. As much as 0.2 mmol. of Al was removed from 10‐3M AlCl3 solution by 1 g. of montmorillonite; kaolinite and a soil clay sorbed comparable amounts of the hydrolysis product. During the “increased hydrolysis” reaction, 3 moles of H+ appeared for each mole of Al which hydrolyzed and was sorbed. When clays containing hydrolysis products were treated with dilute mineral acid, 3 moles of H+ were required for each mole of Al dissolved. Although it appears from the above that the sorbed substance is of composition Al(OH)3, the solubility product of gibbsite was not exceeded in many of the acid systems in which the “increased hydrolysis” occurred. It is suggested that the loss of Al(OH)3 from solution occurred through the deposition of Al(OH)3 units on clay surfaces.

Heterogeneity of Montmorillonite Surface and Its Effect on the Nature of Hydroxy-Aluminum Interlayers

“…The hydroxy-aluminum species of basicity 2 has been observed with Dowex-50 resin (Hsu and Rich, 1960) and with Wyoming montmorillonite (Shen and Rich, 1962). In contrast, Ragland and Coleman (1960) favor the composition of AI(OH)3. The significance of the clay minerals surface on the nature of interlayer AI has been emphasized by Thomas (1960).…”

“…A number of workers have endeavored to characterize the nature of the interlayer Al in order to assess its significance to the genesis of gibbsite and other clay minerals in nature Rich, 1963 and1965;Coleman and Thomas, 1964;Frink and Peech, 1963;Hsu and Bates, 1964b;Jackson, 1960 and1963;Kaddah and Coleman, 1967;Ragland and Coleman, 1960;Rich, 1960;Shen and Rich, 1962;Singh and Brydon, 1967;Thomas, 1960;Turner, 1965;Turner andBrydon, 1965 andWeismiller et al 1967). A majority of the workers now believe that Al is present as positively charged hydroxy-aluminum polymers in the interlayer space in the initial stage but have some uncertainty as to its fate during prolonged aging.…”

Hydroxy Interlayers in Expansible Layer Silicates

“…They proposed further, however, that more AI(OH) 2+ than H § ions would be adsorbed by the clay from an aqueous aluminum salt solution. Ragland and Coleman (1960), on the basis of their experiments, concluded that hydrolysis of AI ions increased in the presence of the clay. One important factor appears to be the strong afinity of clay minerals for hydroxy-cations (Barshad, 1960).…”

Acidic Properties of Montmorillonite in Selected Solvents

“…The addition of excess neutral salt favors the continuation of the A13 § hydrolysis reaction by replacing H + from the clay surface. Ragland and Coleman (1960) found that the hydrolysis of A1C13 proceeded further in the presence of clay minerals and soils than in aqueous solution. In their experiments, A13+-saturated clay was leached with dilute AIC13, and AP § served as the replacing cation for H produced during the hydrolysis reaction.…”