Adsorption of metal ions on humic acids extracted from brown coals

The paper shows results of examination of ion exchange capacity of solid and gel forms of humic acids of brown coals in respect to 17 metal ions. Adsorption of metal ions from single- and multicomponent solutions was carried out in dynamical conditions. The highest affinity to active centers of humic acids proved to have ions of Pb, Ag, Hg, Cu, Ba and Cd. Both types of humic acids selectively adsorbed lead ions, whereas gel forms of humic acids were selective adsorbers of Cr+3 and Al+3. Examination of IR spectra showed that the higher pH solutions, the higher share of the COOH groups in metal ions bonding was involved. The Pb, Ag, Hg and Cu ions are exceptional because even at low pH reaction of the solution (<5) they are bounded with phenolic groups as well. Only these metal ions are able to form complex compounds with carboxylic and phenolic groups of humic acids.