Sorptive removal of salicylic acid and ibuprofen from aqueous solutions using pine wood fast pyrolysis biochar

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2015-04, Vol.265, p.219-227
• Main Authors: Essandoh, Matthew, Kunwar, Bidhya, Pittman, Charles U., Mohan, Dinesh, Mlsna, Todd
• Format: Article
• Language: English
• Subjects: Adsorbates; Adsorption; Biochar; Ibuprofen; Salicylic acid; Solution pH; Sorption; Surface area; Surface chemistry
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2014.12.006

•Pinewood biochar was used to remove two pharmaceutical compounds.•Both carboxylic acid adsorbates have pH-dependent equilibria between their acid and carboxylate anion forms.•Adsorption was not limited to the small surface area.•Sorption followed pseudo-second order kinetics with regression of coefficients of 0.98 or greater. Pine wood biochar, prepared at 698K with a residence time of 20–30s in an auger-fed reactor, was used as a 3-dimensional adsorbent to remove salicylic acid and ibuprofen from aqueous solutions. This biochar was characterized by FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, surface area determination, and zero point charge measurements. Batch sorption studies were carried out at pH values from 2 to 10, adsorbate concentrations from 25 to 100mg/L and temperatures from 298 to 318K. The adsorption of both adsorbates was highest at low pH values, dropped as pH increased and then exhibited a second increase related to the pKa of these carboxylic acid adsorbates. This was followed by a further drop at high pH. Conjugate acid/base equilibria of the adsorbates and the phenolic hydroxyl and carboxylic acid biochar sites versus pH dominated the mechanism. Sorption followed pseudo-second order kinetics. Sorption was evaluated from 298 to 318K using the Freundlich, Langmuir, Redlich–Peterson, Toth, Sips, and Radke–Prausnitz adsorption isotherm models. Langmuir adsorption capacities for both salicylic acid and ibuprofen were 22.70 and 10.74mg/g, respectively. This low surface area pinewood biochar (1.35m2/g) can adsorb far more adsorbate compared to commercial activated carbons per unit of measured surface area. Methanol stripping achieved 93% and 88% desorption of salicylic acid and ibuprofen, respectively, from the spent biochar, and 76% and 72% of the initial salicylic acid and ibuprofen adsorption capacity, respectively, remained after four full capacity equilibrium recycles.