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A new adsorbent for boron removal from aqueous solutions

Kluczka, Joanna, Korolewicz, Teofil, Zołotajkin, Maria, Simka, Wojciech, Raczek, Malwina
Environmental technology 2013 v.34 no.11 pp. 1369-1376
adsorbents, adsorption, aqueous solutions, batch systems, boron, energy, enthalpy, entropy, environmental technology, freshwater, heat production, models, pH, temperature, zirconium
A new adsorbent based on natural clinoptilolite and amorphous zirconium dioxide (ZrO₂) 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 ZrO₂ 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 ZrO₂ 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 Δ S°, enthalpy Δ H°, and free energy Δ G° changes) of boron adsorption were also calculated. The negative value of Δ S° indicated a decreased randomness at the solid–solution interface during the boron adsorption. Negative values of Δ H° showed the exothermic nature of the process. The negative values of Δ G° implied that the adsorption of boron on clinoptilolite modified with amorphous ZrO₂ at 25°C was spontaneous. It was considered that boron dissolved in water had been adsorbed both physically and chemically on clinoptilolite modified with 30% ZrO₂.