Ion specific differences in salt induced precipitation of kraft lignin

Kraft lignin (KL) precipitation, measured as turbidity, in alkaline solutions (pH = 10.5) at 70degreesC in presence of various salts was investigated. Special concern was devoted to study ion specific effects on KL from monovalent cations and anions belonging to the so-called Hofmeister or lyotropic series. Thus, in the study the stability of KL solutions containing different inorganic and organic anions as well as various quaternary ammonium bromides were tested. In the case of inorganic anions, Cl- and Br- induced a higher degree of KL precipitation compared to NO3- and SCN-. The effects of the two tested, sodium uronates were found to diverge and, on a short time-scale, galacturonate showed a better KL stabilizing capacity than C1-. The influence of various tetraalkyl ammonium bromides was compared with the effects of different alkali metal bromides. As the length of the alkyl chain was increased, the KL stability was found to be decreasing. However, at equal concentrations, (CH3)(4)NBr was found to induce a lower degree of KL precipitation than NaBr. From the outcome of the investigation it can be seen that the effects of different cations on KL precipitation follows the mutual order stated by the classical Hofmeister series, whereas the anionic effect has a reversed correspondence.