Boron adsorption characteristics of “allophanic” soils derived from volcanic ash were studied in samples collected in central-southern Chile. he general technique for boron adsorption was based on the use of selected parameters such as 2.50 g of moist soil equilibrated with 25.0 ml of solution, pH 6.0, room temperature, and 24 hr of reaction. In addition, the effects of equilibration time, pH, concentration of boron, and competition with S and P were studied. The equilibrium time for boron adsorption was about 24 hr, though approximately 60 percent was adsorbed in a very short time. Boron adsorption under acid conditions appears to be the result of molecular adsorption of B (OH)3, whereas the adsorption in the alkaline range, reflects in addition, adsorption of B (OH)4- on activated sites by either alkalinization or protons dissociated from boric acid. Competition experiments showed that there was possibly an effect due to the presence of K2SO4, but little or no effect was noted when boron adsorption was studied in the presence of KH2PO4. The high amounts of boron adsorbed by these soils are due to the affinity of boron for amorphous alumino-silicates, as shown by the significant correlation found between boron adsorption and “allophane” content, and not with other amorphous components of the soils such as organic matter and free iron oxides.
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Schalscha et al. (1973) studied this question.