Studies on the adsorption of boron on humic acids

Abstract

The adsorption of B, in the form of boric acid, was studied on three precipitated humic acids (HA), representing three distinct soil types. B adsorption by HA was strongly pH-dependent, being low and relatively constant in the pH range 3.0-6.5, increasing markedly up to a peak at near pH 9.5, and then decreasing at still higher pH values. Adsorption isotherms for pH values near 6.7 and 8.8. conformed well to the Langmuir equation. The adsorption maxima (b values), as calculated with the Langmuir equation, ranged from 73 to 207 mmol kg-1 HA at a pH near 8.8., and from 10 to 42 mmol kg-1 at a pH near 6.7. The considerable variation in B adsorption by these HA samples was attributed to "Fe + Al' contents present as contaminants in the HA. -from Authors