Adsorption of Stearic Acid by Chrysotile1

Vaughn E. Berkheiser
Soil Science Department, University of Florida, Gainesville, Florida 32611
1 Published as Journal Series No. 3343 from the Agricultural Experiment Station, University of Florida.

Abstract: Stearic acid adsorption by chrysotile asbestos in hexane was shown to occur by the formation of a Mg-stearate complex on the mineral surface. Infrared spectroscopy showed no evidence of physically adsorbed stearic acid over the range of concentration employed. Absorption bands at 1560 and 1410 cm−1 in the spectrum of the chrysotile-stearic acid complex correspond with band positions in the spectrum of a synthesized Mg-stearate complex. No evidence of the acid form, which produces a band at 1713 cm−1, was present in the spectrum of the chrysotile complexes. At an equilibrium concentration of 0.8 mg stearic acid/ml, the mineral adsorbed 42 mg stearic acid/g. By heating the mineral in molten stearic acid, additional stearic acid beyond that observed by adsorption from solution was adsorbed in the carboxylate form. Calculations based on the molecular dimensions of stearic acid and the crystal structure of chrysotile indicate that the limiting factor in possible surface occupancy is the molecular size of stearic acid rather than the surface density of Mg-OH adsorption sites.

Key Words: Adsorption • Chrysotile • Infrared spectroscopy • Magnesium • Stearic acid

Clays and Clay Minerals; April 1982 v. 30; no. 2; p. 91-96; DOI: 10.1346/CCMN.1982.0300202
© 1982, The Clay Minerals Society
Clay Minerals Society (www.clays.org)