M etal ions such as Fe, Mn and Cu are typically found in kraft process streams where they originate mainly from the wood chips (Jemaa et al., 1999(Jemaa et al., , 2000. These and other metal ions may accumulate in closed cycle kraft mills and create operational problems such as deposits, reduced product brightness and bleaching chemical decomposition (Jemaa et al., 1999;Towers and Scallan, 1996). It is noted that Fe 2+ or Fe 3+ , Mn 2+ and Cu 2+ are considered to be the most harmful metal ions for cellulose degradation (Cardonna-Barrau et al., 2001).Metal ions in an aqueous wood fi bre suspension are either associated with the fi bres or dissolved in the water. The distribution or partitioning of metal ions between the fi bre and the surrounding water (liquor) depends on the amount of negative charge on the fi bre, which is related to the amount of acid groups in the fi bre and their degree of de-protonation. Consequently, the partitioning of the metal ions depends on pH.The prevailing method to model the metal ion partitioning is the Donnan equilibrium model (Towers and Scallan, 1996). Donnan theory was developed to describe the uneven distribution of ions across a membrane separating a solvent and a solution. Thus, a wood fi bre suspension is treated as a liquid-liquid phase equilibrium system with a membrane separating the two liquid phases Ions of Fe, Mn and Cu were introduced into suspensions of protonated or metal-free fi bres and the equilibrium concentration of each metal in the fi bre and surrounding solution was measured. The results were compared with the Donnan equilibrium model. Mn and Cu concentrations on the fi bres were found to be pH dependent and in agreement with the model. An increased amount of Fe on the Kraft pulp fi bres was found and attributed to iron containing precipitates trapped within the fi bres. Precipitates in mechanical pulps had a very small amount (1-2 wt%) of iron.Des ions de Fe, Mn et Cu ont été introduits dans des suspensions de fi bres protonatées ou « sans métaux » et la concentration d'équilibre de chaque métal dans la fi bre et la solution environnante a été mesurée. Les résultats ont été comparés avec le modèle d'équilibre de Donnan. On a trouvé que les concentrations de Mn et Cu sur les fi bres étaient dépendantes du pH et en accord avec le modèle. Une quantité accrue de Fe a été trouvée sur les fi bres de pâte kraft et attribuée aux précipitats contenant du fer retenus dans les fi bres. Les précipitats dans les pâtes mécaniques ont une très petite quantité (1-2% en poids) de fer.

The ability of Brown Stock Washer (BSW) unbleached kraft pulp and Chemi-Thermo-Mechanical Pulp (CTMP) to sequester heavy metals was studied. The BSW pulp is chemically produced while the CTM one is produced by mechanical treatment aided by some chemicals. The two pulps were rendered in their protonated form and then equilibrated with two aqueous solutions of metals. One was ocean water and the other was a laboratory prepared solution of metal ions. Both pulps were able to remove metal ions from the solution in a one-stage procedure. The overall metal removal efficiency of CTMP was in general greater than that of the BSW pulp for the low concentration metals.Reference to this paper should be made as follows: Chandraghatgi, R. and Englezos, P. (2008) 'Sequestering of heavy metal ions from aqueous solutions by using a lignocellulosic material', Int.

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