A new process for toxic metal uptake by a kraft lignin

A new approach toward removing toxic metals from industrial process water has been investigated using kraft lignin, a by-product of paper production. A detailed study on a kraft pine lignin powder (Indulin AT from MeadWestvaco), which has acid functions that can act as ion-exchange sites, has shown that uptake of divalent toxic metals is accompanied by a release of protons or existing metals from the lignin. Equilibrium constants for displacement of protons decreased with pH, and equilibrium constants for metal-metal exchange showed that binding strengths follow the order (highest to lowest): Pb, Cu, Zn, Cd, Ca, Sr. A demonstrated stoichiometry of one mole Ca displaced for one mole of metal (Sr or Cd) sorbed is fully consistent with a chemical reaction of ion exchange and difficult to explain by frequently used adsorption models (Langmuir adsorption isotherm and biotic ligand model). Since the powder after metal uptake is hard to separate from purified water on a large scale, a novel formulation has been investigated for toxic metal removal. (C) 2003 Society of Chemical Industry.