Isotherms of Adsorption on and Desorption from Calcite of Boron: pH and Salt Dependency

The role of calcite as related to the chemical behavior of boron (B) in calcareous soils was investigated through an assessment of B adsorption and desorption reactions on and from calcite in four ratios of solid to solution rate، three levels of ionic strength، and within a pH range of 7. 5 to 11. 5. Experimental data indicated that B adsorption is increased by an increase in the solid to solution ratio and by increase in its equilibrium concentration. Further، an increase in ionic strength strongly stimulated B adsorption، which is likely due to the formation of boron inner-sphere surface complexes and as well shrinkage in the electrical double layer thicknesses. Boron adsorption increased by increase in pH getting maximized at about 9. 2. Any further increase in pH reduced B adsorption. After four successive desorption stages with calcium nitrate as background solution، approximately 20-40% of the initially adsorbed B was released. In general، it could be concluded that even though calcite is the major mineral in calcareous soils، however، boron-calcite adsorption interactions influence B concentration in the soil solution as by weakly.