Heavy Metals Removal from Contaminated Water Solutions

Principal Investigators
Z. Lewandowski, G.G. Geesey, and F.L. Roe, Montana State University

Abstract

Goal: The goal of this project is to quantify the process of heavy metals removal by binding to biopolymers from dilute aqueous solutions containing more than one metal.

Rationale: Extracellular polymers extracted from living microorganisms constitute an attractive alternative for heavy metals removal from dilute aqueous solutions. However, demonstrated technologies do not offer any rational means of predicting the process kinetic s as a function of water chemical composition. Thus far the documented research effort is largely related to binding single metals from aqueous solutions. Such convenient simplification is unacceptable for most technical applications of the process. For e xample, it is a rare exception that a water is contaminated with a single heavy metal. In frequently encountered situations when more than one heavy metal is present in the solution, existing models do not apply, and the result of the process cannot be pr edicted.

Approach: Investigators propose describing the kinetics and thermodynamics of metals binding to biopolymers from solutions of many metals. Relevant parameters for process modeling will be obtained from measurements of binding constants , binding capacities, selectivity coefficients, diffusion coefficients, and rates of metal binding reaction. Predictive value of the models will be experimentally verified.

Status: Biopolymer gel bead binding to heavy metals in water taken from the Berkeley Pit has been studied, and field studies using beads for heavy metal uptake at acid mine drainage sites have been initiated. In order to make use of this technology economically feasible, the beads must be regenerated and reused many times. R egeneration and reuse studies have begun. In mixtures of copper and zinc, binding constants and binding capacities under competition have been determined, and hydrogen ion has been included as a cation. Since concentrations of metals in the solution were relatively high, metal alginate gel beads were formed in situ. The experimental data closely fit the extended Langmuir model, allowing binding group density and stability constants to be determined. A model which predicts final concentrations of di valent cations in solutions comprised of mixtures of the metal ions and protons in the presence of alginate biopolymer gel beads is being developed. The model predicts equilibrium concentrations of copper, zinc, and hydrogen ions in the presence of algina te gel beads. Results show that alginate is much more selective for copper than for zinc. A key finding has been that the maximum binding capacity for alginate is independent of metal type. Investigators are comparing bead regeneration efficacy using equi librium shifting plus electrodeposition to equilibrium shifting alone and to electrodeposition alone. Investigators are preparing to submit a patent application related to biopolymer regeneration. This project is in its third year.

Clients/Users: Results are of interest to other researchers, private industry, and regulatory personnel.

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