BINDING AND CHEMICAL FRACTIONATION OF HEAVY-METALS IN TYPICAL PEAT MATTER

Laboratory batch studies were conducted to evaluate the binding capaci ty and the mobility of metal species bound to typical humus peat matte r. The identification of phase composition of mineral fractions and fu nctional groups in the organic matter was assessed, The results showed generally high, but different retention capacity and binding strength , suggesting distinct diversity in binding mechanisms, phases and chem ical nature of binding sites, depending on the metal species and their input concentrations. In general, the binding capacity of peat for th e metal ions studied follows the order: Cr3+ > CU2+ > Zn2+ > Cd2+ and results in the decrease of pH in the same order, due to displacement o f H3O+ from the peat by metal ions. The highest metal enrichment occur s in fractions F1(EXC), F2(CARB), F4(MRO) anti F5(OM) of different bin ding strength adequate to exchangeable, carbonatic, moderately reducib le amorphous Fe-oxide and organic/sulphidic fractions in soils and sed iments. In relation to species distribution in peats, the prevailing p art of Cr3+ is strongly bound in oxidizable organic substrate, while C u2+ is highly enriched in the moderately reducible F4(MRO) and the mos t labile F2(EXC) fractions, Cd2+ and Zn2+ are predominantly bound in t he labile F1(EXC) and F2(CARB) fractions. Diversity of the predominant binding phases for the studied metals suggests rather weak competitio n for binding sites between chromium and copper ions; the strongest co mpetition between the sorbed metal ions is anticipated for F1(EXC) and F2(CARB) fractions.