Determination of the Total Specific Surfaceareas of Soils by Adsorption of Cetyl Pyridinium Bromide

Abstract

Surface areas of soil clays can be determined by adsorption of cetyl pyridinium bromide (CPB) from solution. T h e method is best used with peroxidized, air-dry samples which have been treated with dithionite-citrate-bicarbonate to remove iron and some aluminium oxides, and made homo-ionic with respect to the exchangeable cation. Apparent CPB areas derived from the plateau of the CPB adsorption isotherm agree with nitrogen areas when no expanding lattice material is present in the sample and when no large proportion of oxides of low surface density of charge remain after the dithionite treatment. When expanding lattice material is present CPB can provide an accurate measure of the internal surfaces provided that the external area is determined independently. Real variations in the crystal size, and hence ratio of external to internal area, are found with montmorillonite, and are exceptionally large for Wyoming bentonite. Specific surface areas determined by the ethylene glycol adsorption method agree reasonably well with areas of non-expanding lattice clays determined by CPB and nitrogen provided that the specific surface coverage by each adsorbed ethylene glycol molecule is taken as 23A2. When expanding lattice material is present the agreement is less satisfactory, but is improved in most instances by correcting the area on the basis that molecules adsorbed on external surfaces cover 23A2 but those on internal surfaces cover 46A2. Within the range of surface densities of charge found for mica-type materials the adsorption of CPB is much less sensitive to differences than is ethylene glycol, and therefore enables surface areas to be determined more accurately. CPB is also considerably more convenient to use, since well-defined adsorption plateaux are formed after overnight shaking.

Use of Inorgano-Organo-Clays in the Removal of Priority Pollutants from Industrial Wastewaters: Structural Aspects

“…This value is greater than the 30 A2 derived from solution-phase measurements on CPC micelles (Nagarajan and Ruckenstein, 1984). On the other hand, it agrees well with the 54 A2 value reported by Greenland and Quirk (1964) for the projected area of an endon adsorbed alkyl pyridinium ion. Note that cetyl pyridinium ion adsorption was used by Greenland and Quirk to measure surface areas of clay particles.…”

Determination of the Cation Exchange Capacity of Clays by Surface Tension Measurements

“…In this region the adsorbed surfactant forms a second layer around the clay, in equilibrium with a concentration of free surfactant which tends to its critical micellar concentration. Consequently, a drop in surface tension can be detected easily at the CEC value, the adsorption of CPC exceeding twice the CEC notwithstanding (Greenland & Quirk, 1964).…”

“…The proposed method is based on the strong affinity of hexadecylpyridinium chloride (CPC), a cationic surface-active agent or surfactant, with the clay surface (Greenland & Quirk, 1964). However the tendency of CPC to form a multi-layer on the clay surface is a limiting aspect of the method.…”

Clay Mineralogy of Some Seasonally Flooded Soils of East Pakistan

“…However, well-defined 'swelling chlorite', expanding to give a 17 A reflection after ethylene glycol treatment, and not collapsing to 10 A when wei ht of vermiculite, on t 6 e basis of 750 mz/g for the total internal area oft f i e type mineral (Greenland and Quirk, 1964). From these contents,…”