title: Comparison of adsorption equilibrium models and error functions for the study of sulfate removal by calcium hydroxyapatite microfibrillated cellulose composite.
abstract: In the present study, the adsorption of sulfates of sodium sulfate (Na2SO4) and sodium lauryl sulfate (SLS) by calcium hydroxyapatite-modified microfibrillated cellulose was studied in the aqueous solution. The adsorbent was characterized using elemental analysis, Fourier transform infrared, scanning electron microscope and elemental analysis in order to gain the information on its structure and physico-chemical properties. The adsorption studies were conducted in batch mode. The effects of solution pH, contact time, the initial concentration of sulfate and the effect of competing anions were studied on the performance of synthesized adsorbent for sulfate removal. Adsorption kinetics indicated very fast adsorption rate for sulfate of both sources (Na2SO4and SLS) and the adsorption process was well described by the pseudo-second-order kinetic model. Experimental maximum adsorption capacities were found to be 34.53 mg g-1for sulfates of SLS and 7.35 mg g-1for sulfates of Na2SO4.The equilibrium data were described by the Langmuir, Sips, Freundlich, Toth and Redlich-Peterson isotherm models using five different error functions.
authors.affiliation: a Laboratory of Green Chemistry, School of Engineering Science , Lappeenranta University of Technology , Mikkeli , Finland.
authors.forename: Sanna
authors.initials: S
authors.lastname: Hokkanen
authors.affiliation: b Department of Environmental and Biological Sciences , University of Eastern Finland , Kuopio , Finland.
authors.forename: Amit
authors.identifier: http://orcid.org/0000-0002-3565-9943
authors.initials: A
authors.lastname: Bhatnagar
authors.affiliation: c Department of Mechanical Engineering , Helsinki Metropolia University of Applied Sciences , Helsinki , Finland.
authors.forename: Ari
authors.initials: A
authors.lastname: Koistinen
authors.affiliation: d Research Unit of Sustainable Chemistry , University of Oulu , Oulu , Finland.
authors.forename: Teija
authors.initials: T
authors.lastname: Kangas
authors.affiliation: d Research Unit of Sustainable Chemistry , University of Oulu , Oulu , Finland.|e Unit of Applied Chemistry , University of Jyvaskyla, Kokkola University Consortium Chydenius , Kokkola , Finland.
authors.forename: Ulla
authors.initials: U
authors.lastname: Lassi
authors.affiliation: a Laboratory of Green Chemistry, School of Engineering Science , Lappeenranta University of Technology , Mikkeli , Finland.
authors.forename: Mika
authors.identifier: http://orcid.org/0000-0003-3247-5337
authors.initials: M
authors.lastname: Sillanpää
mesh_terms: D000327:Adsorption; D002482:Cellulose / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013431:Sulfates; D013816:Thermodynamics; D014874:Water Pollutants, Chemical
chemical_list: D012996:Solutions; D013431:Sulfates; D014874:Water Pollutants, Chemical; D002482:Cellulose; D017886:Durapatite
keywords: Adsorption; calcium hydroxyapatite; nanocellulose; sulfate removal; water treatment