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Titration of H-Al Bentonite With Tetra-Alkyl Ammonium Bases¹

ABSTRACT

It was postulated that tetra-alkyl ammonium hydroxides would be useful in the titration of acid clay systems because of their base strength and the stability of complexes formed between the tetra-alkyl ammonium cations and clay minerals. Conductometric titrations of H-Al bentonite were performed using tetramethyl- and tetraethanol-ammonium hydroxides; the resulting titration curves were very similar to those obtained with strong inorganic bases.

An improved titration procedure was devised in which a vacuum tube a.c. volt meter was used to determine the null point. Separate small aliquots of clay suspension were titrated with different increments of base equivalent to successive points on a titration curve. This technique permitted an examination of the magnitude and rate of resistance change after the addition of any given increment of base. For lithium hydroxide and tetramethyl ammonium hydroxide, 2 to 3 hours were required for the resistance of the suspensions to become essentially constant. It is concluded that conventional titrations, even with strong inorganic bases, may be subject to considerable error.

An explanation of the time dependency of the conductometric titration of H-Al bentonite systems was offered in terms of differences in diffusion rates of cations in the system. A postulated mechanism for the conversion of an H-bentonite into an H-Al bentonite was presented.

¹ Journal Paper 1703, Purdue University Agr. Exp. Sta., Lafayette, Ind. Contribution from the Agronomy Department. Appreciation is expressed to the National Science Foundation for a grant (NSF G2157) made through the Purdue Research Foundation (PRF 1254) for partial support of this research.

² Assistant Professor of Soils, North Carolina State College, c/o P.C.E.A. Edificio Ministerio de Travajo, Lima, Peru, formerly Instructor in Agronomy at Purdue University; and Professor of Agronomy, respectively.

Received for publication December 28, 1960. Accepted for publication February 8, 1961.