Adsorptive removal of thorium(IV) from aqueous solutions using poly(methacrylic acid)-grafted chitosan/bentonite composite matrix: Process design and equilibrium studies

https://doi.org/10.1016/j.colsurfa.2010.07.005Get rights and content

Abstract

A novel composite matrix, poly(methacrylic acid) -grafted composite/bentonite (PMAA-g-CTS/B) was prepared through graft copolymerization reaction of methacrylic acid and chitosan in the presence of bentonite and N,N′-methylenebisacrylamide as cross linker. The composite was well characterized using FTIR, XRD, XPS, SEM, TG/DTG, surface area analyzer and zeta potential measurements. The adsorption behavior of the composite towards thorium(IV) from water and sea water was studied under varying operating conditions of pH, concentration of Th(IV), contact time, and temperature. The effective range of pH for the removal of Th(IV) was 5.0–6.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir isotherm model. The equilibrium Th(IV) sorption capacity was estimated to be 110.5 mg/g at 30 °C. For the quantitative removal of 100 mg/L Th(IV) from 1.0 L simulated sea water, a minimum adsorbent dosage of 2.0 g PMAA-g-CTS/B was required. Adsorption–desorption experiments over four cycles illustrate the feasibility of the repeated uses of this composite for the extraction of Th(IV) from aqueous solutions. Counter current process design was done by using operational lines.

Introduction

Thorium is a naturally occurring radioactive element widely distributed over the earth's crust with nuclear significance. The toxic nature of this radionuclide, even at trace levels, has been a public health problem for many years [1]. Some human activities such as exploitation of ores with associated thorium and nuclear fuel reprocessing can also concentrate this element [2]. Thorium is an important model element for tetravalent actinides in natural waters. It is also useful as a tracer when studying environmentally important processes [3]. The effluents containing Th(IV) are known to cause acute toxicological effects and harmful diseases for human such as lung, pancreatic and liver cancer [4]. A number of techniques including chemical precipitation, electro floatation, ion exchange, reverse osmosis and adsorption have been developed to recover thorium from aqueous solutions. At low concentrations, separation/preconcentration through adsorption of long-lived radioactive radionuclides such as thorium from aqueous solution is important in nuclear/radiation chemistry and environmental/waste treatment chemistry [5], [6], [7]. The composite ion-exchangers have been used in several studies for the treatment of low and medium level liquid radioactive wastes [8]. Chitosan (CTS) is a biopolymer obtained by deacetylation of naturally occurring biopolymer chitin, which is abundant in nature, principally in shells of crustaceans, terrestrial invertebrates and fungi [9], [10]. Chitosan is an effective ion-exchanger, with a large number of amino groups which are responsible for the high adsorption property of chitosan, but in its original form, chitosan is a relatively weak base (pKa  6.2) soluble at acidic media at pH < 6.0. Chemical modification of CTS may be used to prevent the solubility when metal adsorption is performed in acidic solutions [11], [12].

The polymer/clay composites with eco-friendly property and biodegradability were developed by earlier workers for various applications [13], [14], [15]. Particularly, the natural materials, such as starch, cellulose and CTS have attracted great attention due to their abundant resources and degradability [16], [17]. The composite matrix based on natural material could be decomposed by microorganisms, and there by compatible to the natural environment. The objective of this work is to prepare a novel adsorbent, poly(methacrylic acid)-grafted chitosan/bentonite composite (PMAA-g-CTS/B) matrix for the recovery of Th(IV) ions from water and simulated sea water. It was proposed to take advantage of the cation exchange capacity of the carboxyl group from the adsorbent surface to recover Th(IV) ions from aqueous solutions.

Section snippets

Materials

Analytical grade chemicals were used through out the investigation. CTS (Sigma–Aldrich, Milwau-kee, WI, USA) was used for the preparation of adsorbent. The stock solution of Th(IV) (1000 mg/L) was prepared by dissolving 2.459 g Th(NO3)4·5H2O (Fluka Chemie AG, Buchs, Switzerland) in distilled water at 1000 mg/L of Th(IV). All the required working solutions were prepared by diluting the stock solution with distilled water. The methacrylic acid (MAA) was obtained from Fluka. Potassium persulfate

Adsorbent characterization

The IR spectra of CTS, PMAA-g-CTS/B, and Th(IV)-loaded-PMAA-g-CTS/B are shown in Fig. 1. The spectrum of pure CTS shows peak around at 3450 cm−1 corresponding to amine N–H symmetrical vibration and H bonded –OH group in CTS. The peaks present on the range 3400–3800 cm−1 were also indicate the –OH and –NH2 moieties in the CTS backbone. The intense peaks at 2890 and 2320 cm−1 are assigned to the symmetric and asymmetric –CH2 vibrations of carbohydrate ring. The CTS spectrum also shows the

Conclusions

In the present study, a novel adsorbent, poly(methacrylic acid)-grafted chitosan/bentonite composite (PMAA-g-CTS/B) was prepared and characterized. Its efficiency in removing Th(IV) was tested by batch adsorption technique. The pH 6.0 was found to be optimum for the adsorption of Th(IV) on PMAA-g-CTS/B. The kinetic experiments showed that the adsorption follows a pseudo-second-order kinetic model which indicates that adsorption involves chemical reaction in addition to physical adsorption.

Acknowledgements

The Financial support of the major research project (F.No. 37-425/2009 (SR)) received for the study from the University Grants Commission, New Delhi is gratefully acknowledged. Mr. Rijith S. expresses his sincere thanks to the University Grants Commission, New Delhi for the financial support in the form of Research Fellowship to carry out this work. The authors also thank Dr. Shripathi T. at the UGC-DAE consortium for scientific research, Indore, Madhya Pradesh for providing the XPS

References (31)

  • A.K. Arof et al.

    Evidence of lithium–nitrogen interaction in chitosan-based films from X-ray photoelectron spectroscopy

    Mater. Sci. Eng. B

    (1998)
  • D. Langmuir et al.

    The mobility of thorium in natural waters at low temperatures

    Geochim. Cosmochim. Acta

    (1980)
  • T.S. Anirudhan et al.

    Amine-modified polyacrylamide–bentonite composite for the adsorption of humic acid in aqueous solutions

    Colloids Surf. A: Physiocochem. Eng. Asp.

    (2008)
  • G.R. Choppin

    Actinide speciation in the environment

    Radiochim. Acta

    (2003)
  • M.G. Salinas-Pedroza et al.

    Thorium removal from aqueous solutions of mexican erionite and X zeolite

    J. Radioanal. Nucl. Chem.

    (2004)
  • Cited by (158)

    View all citing articles on Scopus
    View full text