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Salt Displacement and Titration of AlCl3‐Treated Trioctahedral Vermiculites
Author(s) -
Kaddah Malek T.,
Coleman N. T.
Publication year - 1967
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1967.03615995003100030014x
Subject(s) - chemistry , vermiculite , saturation (graph theory) , potentiometric titration , titration , ion exchange , dilution , leaching (pedology) , cation exchange capacity , salt (chemistry) , inorganic chemistry , mineralogy , nuclear chemistry , soil water , ion , geology , soil science , paleontology , physics , mathematics , organic chemistry , combinatorics , thermodynamics
Freshly prepared and 45‐day‐aged Al‐saturated trioctahedral vermiculites from Libby, Montana, and northeastern Transvaal, South Africa, were: (i) leached with 1 N and 0.05 N solutions of NaCl, KCl, and CaCl 2 , (ii) subjected to repeated cycles of 1 N NaCl leaching and Al saturation, and (iii) potentiometrically titrated in H 2 O or N NaCl. In the leaching experiments, the exchange acidity, exchangeable H, Al, and Mg, and the CEC after leaching were determined. Salt solutions displaced only part of the adsorbed Al, with less from South African than from Libby samples. Also displaced were H 3 O and small amounts of Mg ions. The exchange acidity (H 3 O + Al), the ratio of H 3 O to Al, the displaced Mg, and the apparent CEC after Al saturation and displacement varied with the kind and concentration of the displacing solution, the source of vermiculite, the aging period, and the number of cycles of Al saturation and displacement. With freshly prepared Libby samples, the exchange acidity varied from about 60 to 80% of the CEC, with Al constituting 60 to 90%. The corresponding ranges for South African samples were 35 to 50% and 30 to 85%. Of the three salts, KCl solutions gave the smallest exchange acidity and the lowest values for Al/exchange acidity; CaCl 2 effected the highest values, with NaCl in between. Dilution of displacing solutions generally increased the H 3 O ion component of exchange actidity. Repeated Al saturation and displacement resulted in decreased exchange acidity. Potentiometric titration curves of Al‐vermiculites in H 2 O did not suggest the presence of appreciable amounts of exchangeable H 3 O. Titration curves in NaCl had buffer ranges interpreted as suggesting the presence of H 3 O, Al, and another component presumed to be mostly monohydroxy‐Al ions. The two Al‐vermiculites manifested by X‐ray analysis different collapsibility on K saturation and heat treatment. The X‐ray data support the conclusion that Al hydrolysis occurs between vermiculite plates, with general correspondence between the amount of nonexchangeable Al and the failure of the minerals to collapse to 10A upon K saturation and drying.