title: Competitive metal binding to a silicate-immobilized humic material.
abstract: The investigation of the competitive binding of metal ions to a biogenic material comprised of organic peat immobilized in a polysilicate matrix was undertaken. This material was packed into 5.0mL bed-volume columns using 40-60mesh size particles. Two separate mixtures of metal ions were studied by monitoring the solution pH and the concentration of each metal in the effluent as a function of the volume of influent introduced to the material. These mixtures contained either the metal ions Ca(2+), Mg(2+), and Cu(2+) or the ions Cu(2+), Hg(2+), and Pb(2+). A general order of binding affinities was determined to be Mg(2+)<Ca(2+)<<Cu(2+)<Pb(2+)<Hg(2+). Comparisons of amounts of metal ions bound and protons released indicated the initial release of two protons for each divalent metal ion bound. However, prolonged exposure of the material to the metal solutions yielded a molar ratio of 1:1. This suggests the involvement of ion exchange sites followed by that of sites using an alternate binding mechanism. The presence of binding sites with varied mechanisms and metal ion affinities was further illustrated through the initial binding and subsequent release of lower affinity metal ions (e.g., Mg(2+) and Ca(2+)).
authors.affiliation: Department of Chemistry and Biochemistry, New Mexico State University, Box 30001, Department 3C, Las Cruces, NM 88003, United States.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Stark
authors.forename: Gary D
authors.initials: GD
authors.lastname: Rayson
mesh_terms: D000327:Adsorption; D006812:Humic Substances; D019216:Metals, Heavy / Q000032:analysis / Q000737:chemistry*; D008956:Models, Chemical; D017640:Silicates / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D006812:Humic Substances; D019216:Metals, Heavy; D017640:Silicates; D014874:Water Pollutants, Chemical