Preparation of an adsorbent by graft polymerization of acrylamide onto coconut husk for mercury(II) removal from aqueous solution and chloralkali industry wastewater

Abstract

Graft copolymerization of acrylamide onto coconut husk (CH), initiated by the ferrous ammonium sulfate/H 2 O 2 redox initiator system, was studied. To determine the optimum conditions of grafting, the effect of the concentrations of ferrous ammonium sulfate, the monomer, and H 2 O 2 and the time and temperature on percentage of the graft yield was studied. A new adsorbent media having a carboxylate functional group was synthesized by the surface modification of polymer-grafted coconut husk (PGCHOCOOH). The mechanism of graft polymerization and surface functionalization is proposed. The material exhibits a very high adsorption potential for Hg(II). The sorption of Hg(II) was found to be dependent on the contact time, concentration, pH, and temperature. Maximum removal of 99.4% with 2 g/L of the sorbent was observed at 125 mol L Ϫ1 Hg(II) concentration at pH 6.0. The slow step which determines the rate of exchange of Hg(II) ions is diffusion through the adsorbent particles. The diffusion coefficients, energy of activation, and entropy of activation were calculated and used to determine the theoretical behavior of the sorption process. The applicability of the Langmuir isotherm established the endothermic character of the adsorption. Acid regeneration was tried for several cycles with a view to recover the adsorbed metal ions and also to restore the sorbent to its original state. The adsorbent efficiency toward Hg(II) removal was tested using synthetic and chloralkali industry wastewaters.

Chromium(III) removal from water and wastewater using a carboxylate-functionalized cation exchanger prepared from a lignocellulosic residue

“…This side group acts as a handle so that the -COOH group is more to protrude with the aqueous solution. Earlier workers have also reported the same spacer effect of the side group present in the carboxylic acid-functionalized synthetic polymers for their unusual binding capacities towards metal ions [22,23]. As such subsequent adsorption experiments with Cr(III) were performed on SDGPMA-SP-COOH.…”

“…The presence of side group [-CONH-(CH 2 ) 2 -NH-CO-(CH 2 ) 2 -] on SDGPMA-SP-COOH can affect the adsorption reaction by its spacer effect [22]. To examine the spacer effect of the side group in SDGPMA-SP-COOH on Cr(III) adsorption, the amount of adsorbent dose required for complete removal of Cr(III) from 50.0 mL of 25.0 mg/L solution for SDGPMA-SP-COOH was compared with that obtained for an adsorbent having -COOH functional group without side group (SDGPMA).…”

Capture of mercury ions by natural and industrial materials

“…This result may be explained by considering the chemical structure of the two materials (Table 2). Pozzolana has a higher concentration of sulphur and phosphate which form mercury complexes and are eventually used to increase the mercury adsorption capacity of sorbents [33][34][35][36]. Similarly the content of iron oxides, which present a good mercury adsorption capacity [37], is higher for the pozzolana rather than for the yellow tuff.…”

Sorption equilibrium of mercury onto ground-up tree fern

“…Several extensive studies have also been performed using activated carbon prepared from agricultural wastes for the removal of mercury from aqueous solutions such as peanut hull carbon [15], olive stones [16], and Sugi wood [17]. In addition, chemically treated sorbents including coconut husks [18], bagasse pith [19], bark [20], and polyacrylamide-grafted banana stalks [21], have been used in attempts to enhance the mercury sorption performance. Most of this work has shown that agricultural products and waste by- * Corresponding author.…”