INTERACTIVE SORPTION OF METAL IONS AND HUMIC ACIDS ONTO MINERAL PARTICLES

摘要

The sorption of metal ions (Pb~2+, Zn~2+ and Cu~2+) and soil humic acids (HA) from aqueous solutions onto mineral particles (sand, calcite and clay) was investigated using a batch equilibrium system. The sorption reactions in two-component systems (heavy metals-mineral par- ticles and humic acids-mineral particles), as well as interactions in three-component system (heavy metals-humic acids-mineral particles) were examined. Results showed that the presence of humic acids, dissolved or bound onto mineral surfaces, considerably influenced the fixation of heavy met- a1s. The various effects, depending on mineral type, humic concentration and specific metal-ion, were observed in three--component system. Sorption of Cu~2+--ions on all minerals studied rapidly increased as the concentration of dissolved HA increased. The amount of Pb~2+--ions sorbed on sand slightly decreased, while on kaolin increased between l5 and 20/100. Sorption of Zn~2+--ion, on all minerals studied decreased at pH 4. At pH 5.5 the sorption of Zn~2+-ion, onto calcite decreased, while on kaolin and sand increased as a function of the humic acid concentration giving the curve with maximum at c(HA) = 2.5 mmol C L~-1. At pH 6.5 sorption onto kaolin and sand increased. This effect occurs as a result of the conditional stability constant of Zn--HA complexes increasing at higher pH which in turn promotes the chelation of Zn~2+--ion, to mineral--bound humic substances. The enhanced sorption of metal ions from the aqueous phase in three--component systems is not only the result of mineral sorption of free metals but also the result of chelation with HA sorbed on the mineral surface.