Influence of Hydroxy Aluminum Ions on pH Titration Curves of Hydronium‐Aluminum Clays

Vermiculite (particles 2 to 0.2 microns in diameter), after being treated with H‐Amberlite IR‐120, aged for 97 days, and suspended in 1 N KNO 3 , showed a third buffer range between pH 5.5 and 7.6 on continuous titration with dilute NaOH. This third buffer range is attributed to neutralization of excess protons of Al‐OH 2 groups in positively charged hydroxy aluminum polymers formed on interlayer surfaces of vermiculite under the influence of their negative charge. This conclusion was reached on the basis of observance of the same additional buffer range in titration curves of partially neutralized and aged AlCl 3 ‐solutions (OH/Al ratios ranging from 1 to 2.25) and of vermiculite treated with the aged hydroxy aluminum solutions. The hydroxy aluminum polymers are only partly exchangeable by 1 N KCl, and also are fairly resistant to treatment of the clay with H‐resin. The X‐ray diffractogram of the vermiculite shows an enhanced 7.2Å. (002) peak after H‐resin treatment and aging, indicating more interlayer material. Hydroxy aluminum treated vermiculite and aged acid vermiculite showed reduced collapsibility on K saturation and heat treatment, pointing also to the occurrence of the hydroxy polymers in the interlayer position. Compared with similar reactions with montmorillonite from bentonite previously reported, these compounds form with greater avidity in vermiculite, have a greater stability to subsequent H‐resin treatment, and have a higher resistance to exchange in KCl. These differences presumably arise because of the higher net negative charge of the vermiculite layers. Soil clays which give X‐ray diffraction evidence of interlayer hydroxy aluminum show the third buffer range on treatment with H resin, without aging time or treatment with hydroxy aluminum solutions.