Arsenic(III) removal from aqueous solution by raw and zinc-loaded pine cone biochar: equilibrium, kinetics, and thermodynamics studies

• Published in: International journal of environmental science and technology (Tehran) 2015-04, Vol.12 (4), p.1283-1294
• Main Authors: Van Vinh, N., Zafar, M., Behera, S. K., Park, H.-S.
• Format: Article
• Language: English
• Subjects: Aquatic Pollution; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Science and Engineering; Original Paper; Soil Science & Conservation; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 1735-1472; 1735-2630
• DOI: 10.1007/s13762-014-0507-1

The potential of raw pine cone (PC) biochar and its modified form (Zn-loaded biochar) was evaluated for the removal of trivalent arsenic [As(III)] from the aqueous solution. The influence of treatment of PC biochar with Zn(NO 3 ) 2 on the physico-chemical properties of biochar was examined using elemental analyzer, surface area analyzer, thermo-gravimetric analyzer, Fourier transform infrared spectroscopy, and scanning electron microscopy. Experimental results revealed that the removal of As(III) was almost consistent (66.08 ± 3.94 and 87.62 ± 3.88 % on raw and Zn-loaded biochar, respectively) over an acidic pH range of 2–4 as a consequence of high affinity between the positively charged biochar surface and the predominant arsenic species (H 3 AsO 3 and H 2 AsO 4 − ), followed by a decrease with increase in pH in the range of 4–12. Langmuir isotherm model was well fitted to the experimental equilibrium data ( R 2  = 0.93) rendering the maximum adsorption capacity of 5.7 and 7.0 μg g −1 on raw and Zn-loaded PC biochar, respectively. The adsorption of As(III) was well represented by pseudo-second order with reaction rate constant ( k 2 ) of 0.040 and 0.282 mg g −1  min on raw and zinc-loaded PC biochar, respectively, and was mainly controlled by boundary layer diffusion followed by some extent of intra-particle diffusion. The adsorption process was spontaneous with Gibb’s free energy (Δ G °, −4.42 ± 0.72 and −11.86 ± 1.78 kJ mol −1 ) and exothermic in nature with enthalpy (Δ H °, 13.25 and 31.10 kJ mol −1 ) and entropy (Δ S °, 0.058 and 0.141 kJ mol −1  K −1 ) for raw and zinc-loaded adsorbent, respectively.