Boron Removal fromAqueous Solutions using anAmorphous ZirconiumDioxide

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.