Boron Adsorption on Biotite: Effects of pH, Ionic Strength and Nature of Background Solution

Knowledge about factors affecting boron adsorption by minerals commonly found in soils of arid and semiarid areas may help us in management and reclamation of boron polluted soils. The main objective of this study was to investigate the adsorption characteristics of biotite for boron in batch experiments. The adsorption of boron on the adsorbent was studied as a function of pH in the range of 6.5-9.0 with two boron concentrations of 5 mg L-1 and 15 mg L-1. To study the effect of cations and ionic strength on boron adsorption, Mg(NO3)2, Ca(NO3)2 and NaNO3 background electrolytes at three concentration levels (0.03, 0.09 and 0.18 M) were used. Adsorption isotherms were derived by adsorption of boron from solutions containing different concentrations in the range of 1-15 mgL-1 using a 24h batch equilibration. Results showed that the amount of boron adsorption increased with increasing equilibrium pH and ionic strength of solution. Boron adsorption increased from 1.28 mmol kg-1 to 2.64 mmol kg-1 as the ionic strength of solution increased from 0.03 M to 0.18 M. Greater adsorption was observed in the presence of Ca2+ and Mg2+ions as compared with Na+ ions at the same concentrations. Adsorption isotherms of boron were well described by the Freundlich and Langmuir isotherms. Maximum boron adsorption capacity (qmax) of biotite was obtained to be 27.2 mmol kg-1. The experimental data showed that less than 6% of initial boron concentration was adsorbed by biotite. Thus, it seems that this mineral has not a reasonable adsorption capacity for B.