Chamarthy_et_al-2001-Journal_of_Chemical_Technology_and_Biotechnology

Adsorption of selected toxic metals by modified peanut shells

Srinath Chamarthy,1Chung W Seo 1*and Wayne E Marshall 2

1

Department of Human Environment and Family Sciences,Food and Nutrition Laboratory,North Carolina A&T State University,1601E Market Street,Greensboro,NC 27411,USA 2

United States Department of Agriculture,Agricultural Research Service,Southern Regional Research Center,1100Robert E Lee Blvd,PO Box 19687,New Orleans,LA 70179,USA

Abstract:The objective of this study was to modify peanut shells to enhance their adsorptive properties toward the metal ions cadmium (Cd 2 ),copper (Cu 2 ),nickel (Ni 2 ),lead (Pb 2 )and zinc (Zn 2 ).Milled peanut shells were initially washed with water or 0.1N NaOH or left unwashed.Following these treatments or lack of treatment,the shells were either left unmodi®ed or modi®ed by a heat treatment in the presence of either 1.0M phosphoric acid or 0.6M citric acid.Modi®ed peanut shells were evaluated either for adsorption ef®ciency or for adsorption capacity using the ®ve metal ions listed above.Adsorption ef®ciencies and capacities were compared with ef®ciencies and/or capacities for the commercial chelating or cation exchange resins Amberlite 200,Amberlite IRC-718,Duolite GT-73,and carboxymethylcellulose.For the adsorption ef®ciencies of individual metal ions,modi®ed peanut shells met or exceeded the adsorption values for cadmium,copper,nickel or zinc ions compared with the commercial resins Duolite GT-73and carboxymethylcellulose.In a solution containing all ®ve metal ions,modi®ed peanut shells met or exceeded the adsorption ef®ciencies for cadmium,copper and lead ions compared with Duolite GT-73,Amberlite IRC-718and carboxymethylcellulose.Adsorption capacities of modi®ed peanut shells met or exceeded the adsorption capacity of Duolite GT-73for lead ions only.Citric or phosphoric acid-modi®ed peanut shells showed a preference for Cu 2 and Pb 2 and appear promising as potentially inexpensive adsorbents for selected metal ions.#2001Society of Chemical Industry

Keywords:peanut shells;citric acid;phosphoric acid;metal ions;adsorbents

1INTRODUCTION

Peanut shells are low density,high volume agricultural waste which,in part,are used in animal feed formulations or are burned for energy.These are low value uses for the shells and additional product outlets need to be identi®ed to create higher value products.In order to add value to peanut shells,attention has focused on the utilization of peanut shells as adsor-bents.In this regard,peanut shells have been modi®ed by heat or chemical treatment to improve their ability to adsorb different metal ions or organic compounds.There have been several reports 1±7that have described peanut shell (hull)activated carbon for adsorption of various metal ions and organic com-pounds.In addition to their use as activated carbons,peanut shells have been used as is or undergone different modi®cations to enhance their ability to sequester metal ions from solution.Henderson et al 8reported that untreated peanut shells adsorbed sig-ni®cant amounts of Hg 2 ,Cu 2 ,Ni 2 and Zn 2 at low concentrations of the metals.A 1h exposure of the shells to these metal ion solutions signi®cantly increased their adsorption by decreasing the size of

the peanut shells.Azab and Peterson 9and Wartelle and Marshall 10used alkali treatment to increase Cd 2 and Cu 2 uptake,respectively,by peanut shells.Okieimen et al 11noted that treatment of peanut shells with the chelating agent EDTA improved subsequent Cd 2 and Pb 2 sorption.Recently,Wafwoyo et al 12reacted peanut shells in the presence of either phosphoric acid or citric acid to greatly increase the metal ion binding ability of the shells.

The present study is a continuation of research reported by Wafwoyo et al.12The objective of this study was to extend the results reported by Wafwoyo et al 12including:(1)adding a ®fth metal ion,namely Pb 2 ,to solutions containing the four metal ions,Cd 2 ,Cu 2 ,Ni 2 and Zn 2 ,(2)adding the commer-cial cation exchange resin,carboxymethylcellulose,for comparison purposes and (3)determining adsorption capacities for modi®ed peanut shells and commercial resins.

Phosphoric and citric acids were again chosen as modifying agents in this study because of the promis-ing metal ion adsorption results achieved by Wafwoyo et al 12using these modi®cation strategies.

(Received 26October 2000;revised version received 4January 2001;accepted 13February 2001)

*Correspondence to:Chung W Seo,Department of Human Environment and Family Sciences,Food and Nutrition Laboratory,North Carolina A&T State University,1601E Market Street,Greensboro,NC 27411,USA

Contract/grant sponsor:USDA-CSREES Capacity Building Program;contract/grant number:95-38814-1729Journal of Chemical Technology and Biotechnology

J Chem Technol Biotechnol 76:593±597(2001)

DOI:10.1002/jctb.418