Adsorption of sodium on [O.sub.2]-prebleached Eucalyptus globulus kraft pulp.

Application: Laboratory research has established the Langmuir isotherm for sodium adsorption on eucalyptus kraft pulp. Mills can use this information to simulate the pulping process and establish a global sodium balance.

European mill ENCE, Pontevedra, Galicia, Spain, producing totally chlorine free kraft pulp from Eucalyptus globulus, wanted to establish a millwide sodium balance and simulate its pulping process. This knowledge is useful in closing the sodium balance in the pulp production process and evaluating the possible closure of water circuits and the recirculation of wastewaters.

WinGEMS software is widely used to model the kraft pulping process. The WinGEMS simulator uses the Langmuir isotherm to represent the adsorption equilibrium of metallic cations on the pulp. Mills producing kraft pulps from pine and birch can refer to the literature to obtain the required Langmuir-model adsorption equilibrium constants for sodium adsorption. However, there is no similar information for eucalyptus kraft pulp.

Objective and results

The research presented here was carried out to determine the sodium adsorption parameters of the Langmuir isotherm for eucalyptus kraft pulp. Because the kraft process involves various stages carried out at different levels of pH, the influence of pH on sodium adsorption was analyzed as well.

Conclusion

Adjustment of the equilibrium data to the Langmuir model revealed the two key isothermal parameters for eucalyptus kraft pulp: Q = 8.26 kg [Na.sub.2]S[O.sub.4]/ovendry ton of pulp and k = 62.8 L/g [Na.sub.2]S[O.sub.4]. Both parameters can be plugged into the WinGEMS simulator to calculate the sodium balance and simulate the pulping process for mills producing TCF eucalyptus kraft pulps.

Vazquez and Antorrena are professors of Chemical Engineering; Goozalez is an associate professor of Chemical Engineering; and Lopez is a PhD candidate. All are affiliated with the Dept. of Chemical Engineering, Faculty of Chemistry, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain. Address correspondence to Antorrena by email at [e-mail]