The role of humic substances in chromium sorption onto natural organic matter (peat).
To elucidate mechanisms of Cr3+ sorption onto the unaltered solid natural organic matter, the comparative studies of this ion binding from a solution at pH 4.0 onto three selected particle size fractions: 2000-1000 microm, 630-200 microm and 63-20 microm of markedly different HS content and structure, separated by a wet sieving from an overall sample of peat (Brushwood Peat Humus) were carried out. Comparable patterns of COOH groups and CEC(t) confirmed that for cation exchange capacity were responsible mainly cations connected with COO- functional groups. It was though found that aliphatic acids in the solid state did not take part in Cr3+ binding, thus the finest studied fraction 63-20 microm of the highest contents of functional groups showed the lowest sorption capacity for Cr3+, while similar patterns of sorbed Cr3+, soluble HS content and base CEC(0) indicated that these parameters were directly interrelated. The base ion exchange processes determined by CEC(0) (with Ca2+ as a predominant exchangeable cation) appeared to be not the major mechanisms responsible for Cr3+ sorption. For this metal, strong binding to insoluble large molecular weight organic pool two- to threefold prevailed over the ion exchange processes. Very low acid desorption indicated generally low mobility of Cr3+ -organic compounds.