Uptake of metals on feat moss: An ion-exchange process

Various biomaterials have shown promise as sorbants to remove heavy metals from water. Several advantages of peat moss for such applications include its abundance, low cost, and high metal capacity. A Ca-loaded column of peat moss was therefore studied with mixtures of metals. Metals bind to anionic sites by displacing protons from acidic groups (K-ex(H)) or existing metals from anionic sites at high pH (K-ex). These ion-exchange equilibrium constants were determined in batch experiments by direct measurement of species in solution and sorbed on the solid phase. The same K-ex values of Mg 0.342, Mn 0.862, Ca 1.00, Ni 1.42, Zn 1.88, Cd 2.82, Cu 9.97, and Pb 26.7 relative to Ca were found for a given metal alone or in the presence of a mixture, thus showing that the metals function independently. Under conditions employed for a Mg/Mn mixture, it was found that ion-exchange equilibria were maintained along the column due to very fast rates for metal-metal exchange as measured in a separate kinetic study. A linear relationship for log K-ex(H) vs pH over 10(6) was interpreted as due to metal binding to sites of different acid strengths.