Research paper Adsorption of bisphenol A and ciprofloxacin by palygorskite-montmorillonite: Effect of granule size, solution chemistry and temperature Tedros M. Berhane a , Jonathan Levy a , Mark P.S. Krekeler b, ⁎, Neil D. Danielson c a Department of Geology and Environmental Earth Science, Miami University, 250 S Patterson Avenue, Culler Hall, Oxford, OH 45056, USA b Department of Geology and Environmental Earth Science, Miami University-Hamilton, 1601, University Boulevard, Hamilton, OH 45011, USA c Department of Chemistry and Biochemistry, Miami University, Hughes Hall, 651 East High Street, Oxford, OH 45056, USA abstract article info Article history: Received 8 February 2016 Received in revised form 25 July 2016 Accepted 25 July 2016 Available online xxxx Adsorption and desorption studies of the endocrine-disrupting compound, bisphenol A (BPA), and the antibiotic ciprofloxacin (CIP) with palygorskite-montmorillonite (Pal-Mt) granules (0.3–0.6 mm, 1.7–2.0 mm and ≈2.8 mm), were done as a function of solution chemistry, temperature, and particle size. The data best fit the Langmuir adsorption model with the smallest and the largest granule sizes, respectively, exhibiting the highest (in mg kg −1 , q m = 77.3 for BPA; q m = 107,000 for CIP) and the lowest (q m = 41.0 for BPA; q m = 81,000 for CIP) adsorption capacities. CIP adsorption was strongly pH dependent, while BPA adsorption was slightly pH and ionic strength dependent. Thermodynamic parameters indicated BPA and CIP adsorption were spontaneous. Net-adsorption-desorption hysteresis were indicative of irreversible adsorption. FTIR and thermogravimetric analysis (TGA) data corroborate the mechanisms and the level of adsorption for CIP but not for BPA. The smallest and the medium granule sizes, respectively, are appropriate for potential BPA and CIP removal. Capsule abstract: BPA and CIP adsorption-desorption data was granule size, experimental pH, ionic strength, and temperature dependent. Adsorption-desorption hysteresis indicated irreversible adsorption. © 2016 Elsevier B.V. All rights reserved. Keywords: Bisphenol A (BPA) Ciprofloxacin (CIP) Palygorskite Adsorption Langmuir Hysteresis 1. Introduction Contamination of water resources by pharmaceuticals and endo- crine disrupting compounds (EDC) is widespread (Kolpin et al., 2002; Lapworth et al., 2012). Multiple sources of these compounds are known with sewage treatment plants (STP) representing the main gate- way to the natural environment (Lapworth et al., 2012). Treatment technologies are inefficient and consequently STP often fail to remove most of these compounds (Kolpin et al., 2002; Zhang et al., 2008; Lapworth et al., 2012). Once discharged from a STP, contamination of surface water by these compounds poses acute and chronic health risks to aquatic organisms and a potential human health concern through induced infiltration of surface water to municipal groundwater supplies (Lapworth et al., 2012). Bisphenol A (BPA), a petrochemical product and a basic monomer used for synthesis of epoxy and polycarbonates, is one of the four most frequently detected EDC in the environment (Seyhi et al., 2011; Lapworth et al., 2012; Liao et al., 2012). Due to the ineffectiveness of var- ious sewage treatment procedures and a longer half-life than other nat- ural estrogens, the rate of BPA addition to the natural environment far exceeds its degradation rate (Flint et al., 2012; Li et al., 2013). The re- ported concentrations detected in the environment could potentially in- terfere with the endocrine systems of organisms (Mohapatra et al., 2010; Seyhi et al., 2011). Ciprofloxacin (CIP), a fluoroquinolone antibiotic and a metabolite of enrofloxacin used to treat bacterial infection, is another organic com- pound that has been extensively used and widely detected in the envi- ronment (Kolpin et al., 2002; Chen et al., 2013). CIP could have an imminent and a pronounced environmental impact due to its effective- ness in suppressing microbial activities, thereby potentially hindering vital microbial ecosystem functions such as nutrient cycling and con- taminant degradation (Kuemmerer, 2009). Moreover, CIP in the envi- ronment could increase the antibiotic resistance of pathogenic organisms (Kuemmerer, 2009; Wu et al., 2010; Peng et al., 2014). Adsorption is one of the main treatment mechanisms employed in sewage- and drinking-water-treatment plants due to its low cost, sim- plicity and effectiveness (Pan et al., 2008; Zhou et al., 2012). Previous studies have investigated various potential alternatives to achieve higher removal rates at STP (Xu et al., 2012; Li et al., 2014). This includes but not limited to the use of carbon nanomaterials for BPA and estradiol removal where adsorption was significantly specific surface area-de- pendent with higher adsorption capacity for BPA than for estradiol (Pan et al., 2008). Graphene was found to be the most promising Applied Clay Science xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail address: krekelmp@miamioh.edu (M.P.S. Krekeler). CLAY-03933; No of Pages 10 http://dx.doi.org/10.1016/j.clay.2016.07.023 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Berhane, T.M., et al., Adsorption of bisphenol A and ciprofloxacin by palygorskite-montmorillonite: Effect of granule size, solution chemistry and temper..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.07.023