BORON SORPTION ON CALCAREOUS SOILS AND REFERENCE CALCITES

Abstract

Boron sorption on two calcareous soils, one noncalcareous soil, and two reference calcites was investigated in batch systems both as a function of solution pH (5.5–12) and as a function of initial B concentration (1–250 g B m−3). Boron sorption was investigated on untreated soil samples, and soil samples treated with dilute acid to remove soil calcite. Boron sorption on the soil samples increased from pH 5.5 to 9, exhibited a peak near pH 9.5, and decreased from pH 10 to 11.5. Boron sorption on the two reference calcites exhibited an adsorption envelope with maximum sorption occurring near pH 9.5. The magnitude of the B adsorption maximum was significantly lower for the soil samples treated for calcite removal than for the untreated soil samples. This result indicates that calcite plays an important role in B sorption by calcareous soils. Boron sorption as a function of equilibrium B concentration could be described by both the Freundlich and Langmuir adsorption isotherms over the entire concentration range studied on all materials. Goodness of fit of the Langmuir adsorption isotherm equation was much improved over linear transformations by using the program ISOTHERM with its nonlinear least squares optimization routine.