Boron removal from aqueous solutions using an amorphous zirconium dioxide

Anovel adsorbent, an amorphous zirconium dioxide (ZrO₂), was prepared and characterized for the removal of boric acid from water. The adsorption behavior of this adsorbent for boron was investigated in a batch system and found to obey Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. Due to Langmuir model, boron adsorption on ZrO₂ was monolayer, favorable and irreversible in nature. The adsorption energy value calculated from Dubinin-Radushkevich model corresponds to chemisorption of boron onto ZrO₂. Boron removal occurred both by adsorption on external surface and by formation of sparingly soluble compounds and variable compositions, e.g. Na[ZrO(OH)_x(B₄O₇)_n] following the chemical reaction. The influence of pH, temperature, contact time, initial boron concentration and adsorbent dose on the removal of boron were studied. The results showed that the adsorption was strongly dependent on the pH of solution and was optimum in pH range 8-9. Furthermore, at pH of 8.5 and at contact time of 24 hrs the removal of boron increased while the adsorbent dose increased and the temperature decreased. At optimum conditions, the maximum boron percentage removal from the solution containing 20 mg B/L was 97.5% and the final boron concentration reached under the recommended limit for drinking water (< 1.0 mg/L). The thermodynamic studies indicated the spontaneous and exothermic nature of the adsorption process while the kinetic researches confirmed the chemisorption as a dominating mechanism of boron removal using amorphous ZrO₂. The pseudo-second-order model adequately described the boron adsorption on the adsorbent.