The Hydrolysis of Aluminum Salts in Clay and Soil Systems

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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.

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