Selective Removal of Toxic Heavy Metals from Contaminated Water Supplies Using Immobilized Humic Substances

The investigation of the competitive binding of metal ions to a biogenic material is described. The material was comprised of organic peat immobilized in a polysilicate matrix and packed into a 5.0 mL bed-volume column. Two separate mixtures of metal ions were studied regarding the concentration of each metal in the effluent as a function of the volume of influent introduced to the material. These mixtures contained 0.157 millimolar Ca(II), Mg(II), and Cu(II) and 0.05 millimolar Cu(II), Hg(II), and Pb(II), respectively. A general order of binding affinities was determined to be Mg(II) < Ca(II) << Cu(II) < Pb(II) < Hg(II). Investigations of binding affinities and capacities for Pb(II) binding to this material indicated the presence of two separate types of interactions. The first, a low-affinity site with a mean affinity of ~501 and a maximum capacity of 73 millimole/gram sorbent was attributed to an electrostatic-driven ion-exchange process. The second distribution of binding sites, with a mean affinity of 56,000 (capacity to 50 millimole/gram sorbent) was proposed to involve the formation of a metal-ligand complex between the Pb(II) and the immobilized humic material.