Ray H. Crist

Interaction of Metals and Protons with Algae. 4. Ion Exchange vs Adsorption Models and a Reassessment of Scatchard Plots; Ion-Exchange Rates and Equilibria Compared with Calcium Alginate.

Sorption is frequently described in terms of adsorption isotherms (Langmuir, Freundlich), but metal sorption on algae has been recognized to be an exchange process where sorption is accompanied by the release of ions. An experimental ion-exchange constant for Zn displacing Ca from Rhizoclonium was used to calculate concentrations over a wide enough range to assess interpretations given to Langmuir and Scatchard plots. While such plots may be convenient to describe maximum sorption and systematize data, misinterpretations can occur at low metal concentrations in an ion-exchange system. Values of K ex for seven metals displacing Ca from Vaucheria correlated with formation constants of the metal acetates and with K ex of the metals on calcium alginate, a model of cell wall components, indicating the bonding of metals to carboxylate groups of algal cell walls

Interactions of metals and protons with algae

Proton uptake by intact algal cells was found to consist of two processes: (1) a fast (<4 s) surface reaction and (2) a slow (2h) diffusion of protons into cells. A pH titration technique measured only the rapid surface reaction that forms negative sites at higher pH. Adsorption of alkali, alkaline earth, and transition metal ions on algae was quantitatively represented by the Langmuir adsorption isotherm with its two parameters y/sub m/, the maximum amount of metal adsorbed, and K, the equilibrium constant taken as a measure of bond strength. Variations of these parameters with pH and type of metal indicate that metals adsorb to algal surfaces by electrostatic attraction to negative sites, such as carboxylate anions of poly(galaturonic acid) (pectin), as previously suggested.

Use of a novel formulation of kraft lignin for toxic metal removal from process waters

Abstract Kraft lignin, a by‐product in paper production, was converted to a material with high potential for applications in removing toxic metals from process waters. The acid form of kraft lignin in powder form was first converted to Ca‐loaded material by treatment with various amounts of calcium hydroxide and then to a hard solid by combination with a resin in dimethylformamide (DMF) and heating. Strips of these lignin products (LP) were effective in removing Pb and Cd from solutions, with a Pb capacity of ca. 350 µmol/g. One mole of Ca was released to solution for each mole of Pb sorbed, thereby demonstrating that metal uptake was an ion exchange process and not simple adsorption. Advantages to these LP are that 1) they are reuseable with no loss in Pb uptake after eight cycles of uptake/regeneration, 2) their high structural stability is maintained even after immersion in water for 6 weeks, and 3) the DMF used in their preparation can be recovered and recycled.

Ion-Exchange Aspects of Toxic Metal Uptake by Indian Mustard

ABSTRACT Uptake of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) as +2 ions by excised roots of Indian mustard was demonstrated to be an ion-exchange process with existing Ca or protons released to the solution. This initial reaction at the root-aqueous interface is important in the uptake of these toxic metals from contaminated soil. Ethylene diamine tetraacetic acid (EDTA)-amended soil for phytoremediation has Pb in anionic form as [Pb-EDTA]2 −, which was not taken up by excised roots. In nonliving B. juncea, Pb2+ was translocated from a solution through a cut stem to petiole and leaves much more quickly than anionic [Pb-EDTA]2 −. However, in living plants [Pb-EDTA]2 − was more quickly translocated from a solution through roots and petiole to leaves than Pb2+. The final amount of uptake on roots of the living plants was the same for both forms of Pb. The present results are important toward understanding the mechanism of phytoremediation of toxic metal-contaminated soil for two reasons: 1) the initial process, uptake of metal ions by roots, was shown to occur by cation exchange and 2) since [Pb-EDTA]2 − was not sorbed by excised roots, other factors such as transpiration and active transport are important in applications using EDTA-amended soils contaminated by Pb.

Ion Exchange Basis for Biosorption and Bioremediation of Heavy Metals

Abstract An important aspect of mining operations is the extent of sorption of effluent metals to soil and biomass. Of special interest is the partitioning of metal ions in the aqueous-soil-biomass system. The ion exchange relationship of Zn, Cd, Cu, and Pb was found to apply for the metal in the presence of two sorbents: soil with either peat moss, watercress roots, or rye roots. The uptake of Cd from soil by growing rye grass increases with Cd content in the soil, although the per cent uptake is higher for lower amounts. Exchange constants for displacement of protons from limestone soil by Cd decrease by a factor of 105 as pH changes from 4 to 6.6. A linear relationship for log KH exvs. pH can be interpreted as Cd binding to weaker acid sites in more basic media. Comparable results were found for peat moss and the alga Vaucheria. These findings are relevant to agricultural hazards posted by heavy metals as well as the possible use of certain crops for bioremediation.