Highly efficient adsorption of Cd(II) onto carboxylated camelthorn residues: applicability of three-parameter isotherm models, kinetics, and mechanism

A. Hashem, G. M. Taha, A. J. Fletcher, L. A. Mohamed, S. H. Samaha

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Abstract

A series of malonic acid treated camelthorn (MATC) sorbents were produced via the reaction of camelthorn biomass with malonic acid, and factors affecting the extent of modification were investigated, including malonic acid concentration, dehydration time and temperature. The optimum sorbent, by carboxylic acid content, was subsequently characterised for surface charge behaviour (pHPZC), surface chemical functionalities (FTIR), morphological structure (SEM), and available surface area. The sorbent was subsequently utilised for adsorption of Cd(II) ions from aqueous media, and parameters influencing adsorption at 30 °C, such as sorbent dose, initial solution pH, exposure time, metal concentration, were investigated. Isothermal analyses were performed using eight models, including two and three parameter equations, with appropriateness of fit assessed via non-linear regression analysis. The adsorption data indicated that the Langmuir model gives the most appropriate fit to experimental curves, with the models ordered as Langmuir >Hill > Toth >Sips > Jossens > Khan > Redlich-Peterson >Freundlich. The highest uptake (qmax) of 582.6 mg g-1 was determined at pH 6. The Freundlich constants, KF and n, at 30 °C were found to be 24.94 mg/g and 2.33, respectively. The value of n (2.33), being in the range 0–10, indicates that adsorption of Cd(II) ions onto malonic acid treated camelthorn biomass is favourable. Evaluation of a series of kinetic models, allowed elucidation of the adsorption mechanism, as a pseudo-second order model gave the most appropriate fit, indicating that chemisorption processes are involved. Cd(II) ions adsorption onto MATC is enhanced by a higher level of active surface sites but was show to be independent of surface area. The work presented here indicates that this sorbent offers effective adsorption potential for Cd(II) ions from water, with potential in wastewater processing.
Original languageEnglish
Number of pages13
JournalJournal of Polymers and the Environment
Early online date7 Dec 2020
DOIs
Publication statusE-pub ahead of print - 7 Dec 2020

Keywords

  • camelthorn
  • chemical modification
  • isotherm models
  • kinteic models

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