I am currently working on the adsorption affinity of copper flotation waste towards heavy metal ions. The desorption tests using 1 mol/L ammonium acetate, which showed that the retention of Cr(III) and Pb(II) onto the adsorbent is somewhat high (nearly 100% for Cr, 70-80% for Pb), indicate that the process could be controlled by chemisorption. On the other hand, the mean free adsorption energy (E), calculated using the Dubinin-Radushkevich constant (β) showed that the energy is less than 8 kJ/mol, and these results suggest that adsorption might be of physical nature. Any ideas why these results are contradictory?
There can be large differences in the rates of the sorption and desorption reactions, e.g. due to sorbed ions causing structural rearrangement of the macromolecular ligands.
Mr Milham, thank you very much for your suggestion. Is there any way to check those rearrangements out?
Mr Ouakouak, that is true. However, in case of Cr(III) the retention was not dependent on adsorbent dose, the dose values being 25, 50, 100 and 200 g/l. In case of Pb(II), 70% retention appeared for 25 g/l dose and 80% appeared for 200 g/l dose.
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