A new adsorbent for boron removal from aqueous solutions

摘要

A new adsorbent based on natural clinoptilolite and amorphous zirconium dioxide (ZrO_2) was prepared for the uptake of boron from fresh water. The sorption behaviour of this adsorbent for boron was investigated using a batch system and found to obey Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The ZrO_2 loading level, pH, temperature, contact time, initial boron concentration and adsorbent dose, on the removal of boron were studied. It was found that the removal of boron increased while the adsorbent dose increased and the temperature decreased at an optimum pH (pH = 8) and a contact time of 30 min. At optimum conditions, the maximum boron percentage removal was 75%. According to the D-R model, the maximum capacity was estimated to be >3 mg B/g of the adsorbent. The adsorption energy value (calculated as 9.13 kJ/mol) indicated that the adsorption of boron on clinoptilolite modified with ZrO_2 was physical in nature. The parameters of the adsorption models and the pH investigations pointed to the possibility of a chemisorption process. The thermodynamic parameters (standard entropy ΔS°, enthalpy ΔH°, and free energy ΔG° changes) of boron adsorption were also calculated. The negative value of ΔS° indicated a decreased randomness at the solid-solution interface during the boron adsorption. Negative values of ΔH° showed the exothermic nature of the process. The negative values of ΔG° implied that the adsorption of boron on clinoptilolite modified with amorphous ZrO_2 at 25℃ was spontaneous. It was considered that boron dissolved in water had been adsorbed both physically and chemically on clinoptilolite modified with 30% ZrO_2.