ORIGINAL PAPER Surface complexation model of boron adsorption by calcareous soils F. Ranjbar • M. Jalali Received: 8 March 2013 / Revised: 11 January 2014 / Accepted: 10 March 2014 / Published online: 9 April 2014 Ó Islamic Azad University (IAU) 2014 Abstract This study aimed to evaluate boron (B) adsorption and the capacity of a surface complexation model for simulating this process in calcareous soils. Ten surface soils were collected from different land use areas in Hamedan, Western Iran, to characterize B sorption by soils. The mean B adsorbed by the sample soils varied from 8.9 to 32.8 %. Two empirical models including linear and Freundlich equations fitted well to the experimental data. The linear distribution (K d ) values varied from 1.32 to 6.86 L kg -1 , while the parameters of Freundlich equation including n and K Fr ranged from 1.16 to 1.33 and 3.31–16.81, respectively. The comparison of two empirical models indicated that B adsorption followed a nonlinear pattern. The soil organic matter had positive correlations with Freundlich and linear distribution coefficients. How- ever, empirical models were not suitable for explaining the mechanism of B adsorption, so a surface complexation model was used to simulate and predict the B adsorption process. B adsorption modeling was conducted using Visual MINTEQ and PHREEQC, based on the assemblage of major surface components (hydrous ferric oxides, alu- minum hydroxides, calcium carbonate, and humic acids). B adsorption was successfully modeled by surface complex- ation. The significant contribution of organic matter to B complexes was resulted from both experimental data and mechanistic modeling. Keywords Boron  Surface complexation  Adsorption  MINTEQ  PHREEQC Introduction Boron (B) is an essential nutrient that is required by plants in small amounts. The borate concentration in groundwater and surface water is typically low. However, it can be signifi- cantly increased by wastewater discharges, because borate compounds are common components of domestic detergents (ISO 1990). Boron naturally occurs in groundwater due to the leaching of rocks and soils containing borates and borosilicates. Groundwater B concentrations vary widely throughout the world from \0.3 to [100 mg L -1 (WHO 1998). B adsorption reactions and the extent of soil sorption generally control the concentration of B dissolved in the soil. Chemical processes can also affect sorption reactions by controlling the dissolved B concentration, and conse- quently, they restrict B availability for plants. Distribution coefficients can be used to describe the relationship between the amount of B adsorbed by soil and that dis- solved in water. Plants can only utilize or respond to B present in solution of soils, so B adsorbed on soil surfaces is nontoxic (Keren et al. 1985). Important factors that are known to affect B adsorption and desorption in soils include the system pH (Hingston 1964), clay mineralogy (Hingston 1964; Keren and Mezuman 1981), the type of exchangeable ions (Parks and White 1952; Keren and Gast 1981), and wetting and drying cycles (Keren and Gast 1981). There are various B adsorbing components with differ- ent adsorption capacities including clay minerals, Al and Fe oxides, CaCO 3 , and humic particles (Goldberg and Glaubig 1985; Evans 1987; Goldberg and Glaubig 1988). Although Elrashidi and O’Connor (1982) reported no sig- nificant correlation between boron sorption and the soil CaCO 3 content, the highest level of B adsorption was F. Ranjbar (&)  M. Jalali Department of Soil Science, College of Agriculture, Bu-Ali Sina University, Hamedan, Iran e-mail: f_ranjbar1980@yahoo.com 123 Int. J. Environ. Sci. Technol. (2014) 11:1317–1326 DOI 10.1007/s13762-014-0544-9