In this work the adsorption characteristics of paper mill sludge are evaluated for the purpose of
removing metal ions from polluted waters. The Ag(I), Cd(II), Cu(II), Pb(II), and Cr(VI) (as
chromate ion) adsorption mechanism on the sludge is studied by adsorption isotherms in batch
conditions, after paper mill sludge characterization. The effect of several parameters (ionic charge
of metals, pH, and ionic strength of metal solutions) and the competition between different metals
are also considered. For Ag(I), Cd(II), Cu(II), Pb(II), and Cr(VI), the thermodynamic curves fit
the Langmuir model best, whereas experimental data for Cu(II) fit the Freundlich model best.
The nature of ionic charges influences the sorption process: cations are sorbed much more than
chromate ion, and the affinity series for cations is Cu(II) > Pb(II) > Cd(II) ≅ Ag(I). The maximum
amount of sorbed metal (q
max) value is significantly influenced both by the liquid/solid ratio and
by the pH values of metal solutions.
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