Modeling and evaluation of chromium remediation from water using low cost bio-char, a green adsorbent

• Published in: Journal of hazardous materials 2011-04, Vol.188 (1), p.319-333
• Main Authors: Mohan, Dinesh, Rajput, Shalini, Singh, Vinod K., Steele, Philip H., Pittman, Charles U.
• Format: Article
• Language: English
• Subjects: activated carbon; Adsorbents; Adsorption; Applied sciences; Bark; Bio-char; biofuels; Carbon; Charcoal - chemistry; Chars; Chemical engineering; Chromium; Chromium - isolation & purification; Chromium adsorption; Chromium removal; Coal Ash; Combustion; Continental surface waters; Environmental Restoration and Remediation - methods; Exact sciences and technology; Hexavalent chromium; Hydrogen-Ion Concentration; ions; Kinetics; Low cost adsorbent; Natural water pollution; Oak; Particulate Matter; Pollution; pyrolysis; Reactors; Remediation; sorption isotherms; Surface chemistry; surface water; Temperature; Water Pollutants, Chemical - isolation & purification; water purification; Water Purification - methods; Water treatment and pollution; Wood
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.01.127

Oak wood and oak bark chars were obtained from fast pyrolysis in an auger reactor at 400–450 °C. These chars were characterized and utilized for Cr(VI) remediation from water. Batch sorption studies were performed at different temperatures, pH values and solid to liquid ratios. Maximum chromium was removed at pH 2.0. A kinetic study yielded an optimum equilibrium time of 48 h with an adsorbent dose of 10 g/L. Sorption studies were conducted over a concentration range of 1–100 mg/L. Cr(VI) removal increased with an increase in temperature ( Q Oak wood ° : 25 °C = 3.03 mg/g; 35 °C = 4.08 mg/g; 45 °C = 4.93 mg/g and Q Oak     bark ° : 25 °C = 4.62 mg/g; 35 °C = 7.43 mg/g; 45 °C = 7.51 mg/g). More chromium was removed with oak bark than oak wood. The char performances were evaluated using the Freundlich, Langmuir, Redlich–Peterson, Toth, Radke and Sips adsorption isotherm models. The Sips adsorption isotherm model best fits the experimental data [high regression ( R 2) coefficients]. The overall kinetic data was satisfactorily explained by a pseudo second order rate expression. Water penetrated into the char walls exposing Cr(VI) to additional adsorption sites that were not on the surfaces of dry char pores. It is remarkable that oak chars ( S BET: 1–3 m 2 g −1) can remove similar amounts of Cr(VI) as activated carbon ( S BET: ∼1000 m 2 g −1). Thus, byproduct chars from bio-oil production might be used as inexpensive adsorbents for water purification. Char samples were successfully used for chromium remediation from contaminated surface water with dissolved interfering ions.