Most metal ions have negative impacts on pulp mill operations. The
concentrations of metal ions on pulp fibers and in washwaters rise significantly with
increased wastewater recycling. The development of technology to remove these metal
ions requires an understanding of how metal ions are bound to pulp components. It is
also desirable to predict distribution of metal ions between the pulp fibers and the
washwaters.
The adsorption isotherms for eight metal ions (Ca, Ba, Mn, Zn, Pb, Cd, Ni, Na)
were measured on bleached and unbleached (brownstock) kraft pulps at neutral pH and
temperatures ranging from 25 to 75��C. On bleached pulps, the metal ion adsorption
increased rapidly with increasing metal ion concentration in solution and then leveled off.
At neutral pH, the adsorption on bleached pulp was stoichiometric to the carboxylate
sites, whereas the adsorption on unbleached pulp was not, especially at high metal ion
concentration in solution and low temperature.
The pH isotherms specify the adsorption isotherms of sodium and calcium on
wood pulps as pH ranging from 2.5 to 11.0. The pH isotherms on bleached pulp with
only COOH functional groups (pK[subscript a] of 3.77) were saturated at pH 4 and above, whereas
those on brownstock pulp with both COOH and PhOH (pK[subscript a] of 10) functional groups
increased in two steps, at pH 4 and 8.
The brownstock pulp is heterogeneous material. Therefore, only the empirical
Freundlich model was applied to the data. To predict the metal ion adsorption on
bleached pulps, two fundamental equilibrium models were developed: the multi-component
ion exchange and the Donnan equilibrium models. The ion-exchange model
better predicts the metal adsorption at neutral pH, whereas the Donnan equilibrium model
more accurately predicts the pH isotherms.
The adsorption kinetics of Ba����� and Ni����� were measured on wood pulps as a
function of mixing speed, initial metal ion concentration, and temperature. The adsorption
of metal ions reached equilibrium rapidly. The intraparticle diffusion model, based on first
principle with a linear relationship assumption between adsorbed and free metal ion
concentration, satisfactorily predicted the adsorption kinetics at low metal ion
concentration in solution. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33250 |
| Date | 01 May 2001 |
| Creators | Yantasee, Wassana |
| Contributors | Rorrer, Gregory L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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