title: Sorptive removal of tetracycline from water by palygorskite.
abstract: Extensive use of pharmaceuticals and growth hormone in farm animal and live stocks has resulted in their frequent detection in soils, groundwater, and wastewater. The fate and transport of these compounds are strongly affected by their sorptive behavior to the soil minerals and humic materials. In this research, we conducted the sorption of tetracycline (TC), a common antibiotic, on palygorskite (PFL-1), a fibrous clay mineral of high surface area and high sorptivity towards organic compounds. The results showed that the sorption capacity of TC on PFL-1 was as high as 210 mmol/kg at pH 8.7. The sorption was relatively fast and reached equilibrium in 2h. Solution pH and ionic strength had significant effects on TC sorption. The sorption of TC by palygorskite is endothermic and the free energy of sorption is in the range of -10 to -30 kJ/mol, suggesting a strong physical sorption. The X-ray diffraction patterns before and after TC sorption revealed no changes in d-spacing and intensity under different pH and initial TC concentrations, indicating that the sorbed TC molecules are on the external surface of the mineral in contrast to intercalation of TC into swelling clays, such as montmorillonite. The small positive value of entropy change suggested that TC molecules are in disordered arrangement on palygorskite surfaces. Surface sorption of TC on PFL-1 is further supported by the derivative of gravimetric analysis and by the calculation of the amount of TC sorption normalized to the surface area. The results suggest that palygorskite could be a good candidate to remove TC from wastewater containing higher amounts of TC.
authors.affiliation: Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Po-Hsiang
authors.initials: PH
authors.lastname: Chang
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Li
authors.forename: Tsai-Luen
authors.initials: TL
authors.lastname: Yu
authors.forename: Sandagdori
authors.initials: S
authors.lastname: Munkhbayer
authors.forename: Tzu-Hsing
authors.initials: TH
authors.lastname: Kuo
authors.forename: Yu-Chiao
authors.initials: YC
authors.lastname: Hung
authors.forename: Jiin-Shuh
authors.initials: JS
authors.lastname: Jean
authors.forename: Kao-Hung
authors.initials: KH
authors.lastname: Lin
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D017616:Magnesium Compounds / Q000737:chemistry*; D009994:Osmolar Concentration; D017655:Silicon Compounds / Q000737:chemistry*; D013752:Tetracycline / Q000302:isolation & purification*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods
chemical_list: D007220:Industrial Waste; D017616:Magnesium Compounds; D017655:Silicon Compounds; D014874:Water Pollutants, Chemical; D013752:Tetracycline; C026325:attapulgite