Copper and cadmium sorption onto kraft and organosolv lignins.pdf

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Copper and cadmium sorption onto kraft and organosolv lignins.pdf

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Copper and cadmium sorption onto kraft and organosolv lignins

Bioresource Technology 100 (2009) 6183–6191Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier .com/locate /bior techCopper and cadmium sorption onto kraft and organosolv lignins Hengky Harmita, K.G. Karthikeyan *, XueJun Pan Department of Biological Systems Engineering, University of Wisconsin-Madison, 460 Henry Mall, Madison, WI 53706, USAa r t i c l e i n f o Article history: Received 26 August 2008 Received in revised form 23 June 2009 Accepted 24 June 2009 Available online 29 July 2009 Keywords: Kraft lignin Organosolv lignin Cadmium Copper Ion exchange0960-8524/$ - see front matter 2009 Elsevier Ltd. A doi:10.1016/j.biortech.2009.06.093 * Corresponding author. Tel.: +1 608 262 9367; fax E-mail address: kkarthikeyan@ (K.G. Karta b s t r a c t The relative metal sorption ability of kraft and organosolv lignins was examined as a function of solution chemistry (pH, ionic strength (I), sorbate-to-sorbent ratio) and reaction time. The surface charge charac- teristics and functional group composition of these lignins, especially kraft lignin, are favorable for metal sorption. Sorption of Cu and Cd increased with increasing pH and decreasing I. Description of sorption isotherms required the more complex Sips equation, as compared to the simpler Langmuir and Freund- lich formulations, indicative of the presence of binding sites with varying affinities on these lignin biosor- bents. Sorption capacity varied in the following order: softwood organosolv lignin hardwood organosolv lignin hardwood kraft lignin softwood kraft lignin with sorption maximum of 21.5, 40, 66.7, and 80.6 lmol/g, respectively, for Cu, and 8.2, 18.3, 25.2, and 28.7 lmol/g for Cd. Both Cu and Cd sorption kinetics were rapid with equilibrium levels attained within 80 min and faster uptake was noticed for Cu. Strong competitive effects exhibited by H+ and Na+ in limiting Cu and Cd sorption are sug- gestive of the occurrence of weak ion-exchange type inter