Immobilization of heavy metals from aqueous solutions using polyacrylamide grafted hydrous tin (IV) oxide gel having carboxylate functional groups

doi:10.1016/S0043-1354(00)00234-7

Water Research

Volume 35, Issue 1, January 2001, Pages 300-310

https://doi.org/10.1016/S0043-1354(00)00234-7 Get rights and content

Abstract

A new adsorbent containing a carboxylate group has been prepared by the surface modification of a polyacrylamide grafted hydrous tin (IV) oxide gel. The product exhibits a very high adsorption potential for Pb(II), Hg(II) and Cd(II). The effect of initial metal ion concentration, adsorbent dose, pH, concentration of light metal ions, and temperature on metal removal has been studied. The process follows a first-order rate kinetics. The intraparticle diffusion of metal ions through pores in the adsorbent was shown to be the main rate limiting step. The equilibrium data fit well with the Langmuir adsorption isotherm. The selectivity order of the adsorbent is Pb(II)>Hg(II)>Cd(II). Adsorption rate constants and thermodynamic parameters were also presented to predict the nature of adsorption. The method was applied on synthetic wastewaters. Acid regeneration has been tried for several cycles with a view to recover the adsorbed metal ions and also to restore the sorbent to its original state.

Introduction

The presence of heavy metals in the environment is of major concern because of their toxicity and threat to human life and the environment. Lead, mercury and cadmium are examples of heavy metals that have been classified as priority pollutants by the US Environmental Protection Agency (USEPA). Therefore, the elimination of these metals from water and wastewaters is important to protect public health. The treatment methods such as chemical precipitation, membrane filteration, reverse osmosis, ion exchange and adsorption have been practiced for the removal of heavy metals; each has its merits and limitations in application. The adsorption of heavy metals has been studied by a variety of materials such as activated carbons (Tan and Teo, 1987), Clays (Bolto and Pawlowski, 1987), polymeric synthetic resins (Harland, 1994) and metal oxides (Schultz et al., 1987). Studies have been reported on the use of hydrous tin (IV) oxide (Inoue et al., 1985) and hydrous titanium (IV) oxide gels (Abe et al., 1989) as adsorbents for the removal of certain metals from aqueous solutions.

Surface modification by chemical treatment of the adsorbent materials usually increases the adsorption capacity. Thus the chemistry of the sorbent surface rather than the extent of its surface area controls the adsorption in many applications. Silica gel modified with pyridinium ions (Iamamoto and Gushikem, 1989) and clay impregnated with 2-mercaptobenzothiazole (Dias Filho et al., 1995) have been developed for the adsorption of heavy metals such as Pb(II), Hg(II), Cd(II), Cu(II) and Zn(II) and can be employed for the preconcentration of these metals from aqueous solutions. A limited study indicated the potential of surface modification of onion skin (Kumar and Dara, 1981) tree bark (Deshkar et al., 1990) and sawdust (Raji and Anirudhan, 1996) through polymerization in immobilizing the coloured water soluble polyphenols and improving physical characteristics of the adsorbents. The use of polymer grafted metal oxides for the removal of toxic heavy metals from wastewaters has continued to attract considerable attention in recent years, particularly because they are capable of binding heavy metals by adsorption and ion exchange even at higher temperatures (Shigetomi et al., 1980, Suzuki et al., 1987, Shubha, 1996). Carboxylate functional groups substituted on the backbone of the polymerised materials increase the number and change the nature of sites capable of adsorbing metals in solutions (Saucedo et al., 1992). The present work explores the possibility of using the polyacrylamide grafted hydrous tin (IV) oxide gel containing carboxylate functional group to remove Pb(II), Hg(II) and Cd(II) from water and wastewaters by studying its metal removal properties in a series of laboratory experiments. Desorption studies have also been carried out.

Section snippets

Sorbent preparation

The starting material, hydrous tin (IV) oxide gel (HySnO) of relatively uniform and narrow particle size distribution, was first prepared by the reported method (Inoue et al., 1985). The gel was precipitated from a solution of tin (IV) chloride (0.5 M) by adding ammonia (10–20%) solution. The air dried gel was identified as SnO(OH)₂ 1.96 H₂O (Inoue et al., 1985). The gel was grafted with polyacrylamide using the procedure described by Shigetomi et al. (1980) and then functionalized with

Results and discussion

The possible assignments of the functional groups to the important bands of IR spectra of the HySnO and PGHySnOCOOH are shown in Table 1. HySnO shows the broad asymmetric adsorption band at wavenumber range 3300–3450 cm⁻¹, which is attributable to the sum of the contribution from water and hydroxyl groups bonding to tin, the former at the lower and the latter at the higher wavenumber sides. The adsorption band near 1639 cm⁻¹ is due to the bending mode of water and the adsorption at 734 and

Conclusions

The results show that PGHySnOCOOH can be used as an adsorbent for the effective removal of heavy metals from aqueous solutions. The pH of the medium is the controlling master parameter of this separation process. The adsorption densities in general decreases as the adsorbent dose is increased from 5 to 50 g/l. The process had been found to be endothermic. Complete removal of Pb(II), Hg(II) and Cd(II) from its synthetic wastewaters containing 50 mg/l metal ions could be achieved at pH 6.0. The

Acknowledgements

The authors are thankful to the Head, Department of Chemistry, University of Kerala, Trivandrum for providing the laboratory facilities for this study.

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Immobilization of heavy metals from aqueous solutions using polyacrylamide grafted hydrous tin (IV) oxide gel having carboxylate functional groups

Abstract

Introduction

Section snippets

Sorbent preparation

Results and discussion

Conclusions

Acknowledgements

J. Colloid. Interface Sci.

Colloids Surfaces

Wat. Res.

Polymer

J. Colloid. Interface Sci.

Wat. Res.

Wat. Res.

Adsorption and desorption behaviour of heavy metal ions on hydrated titanium dioxide

Analyst

Wastewater Treatment by Ion Exchange

Modified hardwickia binata bark for adsorption of mercury (II) for water

Wat. Res.

Sorption and preconcentration of some heavy metals by 2-mercaptobenzothiazole-clay

Talanta

Statistical Methods

Ion Exchange, Theory and Practice

Metals in aquatic systems

Environ. Sci. Technol.

Studies of the hydrous tin (IV) oxide ion exchanger—IV. The effect of heat treatment

Bull. Chem. Soc. Jpn.