Adsorption of Metal Ions on Crosslinked Lignosulphonic Acid

Abstract

Adsorption gel was prepared by using formaldehyde to crosslink lignosulphonic acid, which is generated in the production of pulp as a by-product of low value or nearly waste. The amount of cation-exchangeable hydrogen ion contained in the gel was measured by titration as 4.83 mol/kg-dry gel, the majority of which was considered to be attributed to hydroxyl groups of phenol moiety of the gel.
Batchwise adsorption tests were carried out to elucidate the pH dependency of the adsorption of some metal ions and adsorption isotherms. Adsorption occurred at pH greater than 2 and increased with increasing pH, suggesting that cationic metal ions are adsorbed on the gel by a cation exchange mechanism. The order of the selectivity was as follows: La(III)>Pb(II)∼Fe(III)>Fe(II)∼Cu(II)∼Al(III)>Cd(II)∼Ni(II)>Mn(II)∼Zn(II). The adsorption isotherms were of the Langmuir-type, and the maximum adsorption capacity was evaluated as 0.86, 0.76 and 0.47 mol/kg-dry gel for copper(II), lead(II) and lanthanum(III).
With a view to practical use of this gel, the separation of lead(II) from zinc(II) was examined using a column packed with the gel. Satisfactory separation was achieved, suggesting the feasibility of applying the gel to, for example, the removal of lead impurity from a zinc plating bath.