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Adsorption of metribuzin from aqueous solution using magnetic and nonmagnetic sustainable low-cost biochar adsorbents

Essandoh, Matthew, Wolgemuth, Daniel, Pittman, Charles U., Jr, Mohan, Dinesh, Mlsna, Todd
Environmental science and pollution research international 2017 v.24 no.5 pp. 4577-4590
Fourier transform infrared spectroscopy, Panicum virgatum, absorption, adsorbents, adsorption, aqueous solutions, biochar, biofuels, energy-dispersive X-ray analysis, iron oxides, metribuzin, models, pH, pyrolysis, scanning electron microscopy, sodium hydroxide, sorption isotherms, surface area, temperature
Switchgrass biochar (SGB) was made by fast pyrolysis in an auger-fed reactor at 425 °C with a solid residence time of 60 s in the pyrolysis zone during bio-oil production. Magnetic switchgrass biochar (MSGB) was prepared by iron oxide precipitation onto the biochar surface using an aqueous Fe³⁺/Fe²⁺ solution followed by NaOH treatment. Both the SGB and the MSGB were characterized by FTIR, SEM, SEM-EDX, TGA, pHₚzc, elemental analysis, and surface area measurements. Batch sorption studies of metribuzin from aqueous solutions were carried out at different pH values, adsorbate concentrations, and temperatures. The adsorption of metribuzin onto both biochars was highest at a pH of 2. Adsorption isotherms were evaluated from 25 to 45 °C using the Freundlich, Langmuir, Redlich-Peterson, Toth, Sips, Koble-Corrigan, and Radke-Prausnitz adsorption models. Langmuir adsorption capacities at pH 2 were Q ⁰ SGB ~ 151, 223, and 205 mg/g and Q ⁰ MSGB ~ 155, 205, and 155 mg/g at 25, 35, and 45 °C, respectively. Low-cost magnetization of the biochar occurred without significant loss of absorption capacity, enabling facile separation of slurried biochar from liquids following contaminate absorption. Graphical abstract ᅟ