**2.2. Ionic linkages**

bridge or linkage " the material maintains a high ion-complexation capacity." These workers also demonstrated metal-ion removal capacity for representative metals (transition metal ions, alkali metal ions, etc). The material under dynamic conditions removed 50 mg Cu(II) /g

**Figure 1.** Flow chart for the synthesis of a supported chelating agent. BPEI consists of branched ethylenediimino moi‐

A similar technique was used by Soliman, who also used a silica gel matrix and a covalent linker to tie to a series of amines, mono-, di-, tri-, and tetra-amine [15]. Using a batch equili‐ brium technique, he measured the removal capacities (mmole/g) for divalent forms of cobalt, nickel, copper, zinc, cadmium, and lead. In general maximum removal values (at optimum

El Ashgar used a variation on the technique [16]. Specifically, 3-chloropropyltrimethoxysilane was used to alkylate diethylenetriamine, i.e, reaction with the halide end to produce a precursor of a polymer (I, Eqn. 1). The reaction of I with tetraethylorthosilicate resulted in a

®

(1)

( ) ( ) ( ) ( ) ( ) <sup>3</sup> <sup>2</sup> <sup>2</sup> 2 2 + 33 2 2 4 CH O Si CH NH CH NH CH NH 2 EtO Si Polymer

pH values) were obtained for the tetra-amine species.

"diethylenetriamine polysiloxane immobilized ligand system."

eties [14]

126 Column Chromatography

I

composite. The metal absorbing ability followed the order Cu2+ > Cd2+ > Zn2+.

Examples are available from a number of studies. The authors demonstrated that the use of ion-exchange resins as supports for chelators that can be derivatized or converted to ions is a versatile technique [22]. Examples involving two different ion-exchange resins help indicate the range of the technique.

An *anion-exchange resin* in the hydroxide form RNHOH (e.g., IR-120), can be treated with other chelating agents HCh converted to the anionic forms, NaCh (Eqn. 2).

$$\text{RNH}\_4\text{OH} + \text{NaCh} \rightarrow \text{RNH}\_4\text{Ch} \quad + \text{ Na}^+ + \text{OH}^-\tag{2}$$

A *cation-exchange resin* exists as a polyalkylsulfonic acid, RSO3H and can react with a chelating agent in a protonated form HCh+ (Eqn. 3).

$$\text{RSO}\_3\text{H}^+ + \text{HCh}^+ \rightarrow \text{RSO}\_3\text{H}\text{Ch} \quad + \text{H} + \tag{3}$$

Lee and coworkers [23] used the technique shown (Eqn 2) to load a number of chelating agents, among them chromotropic acid, onto the anion exchange resin Dowex® 1-X8 (chloride form). These composites are easy to prepare, and loading of metal ions on the chromatography columns showed the metal ion loading as a color change.

An anion exchange resin (e.g. Amberlite® R-120) was treated with protonated dithiooxamine, H2NC(S)C(S)NH2. Using the supported ligand, quantitative removal of copper, cadmium, and lead ion solutions at neutral or slightly alkaline solutions of deionized or tap water, but poor results were obtained with sea water [22].

carbon in the pores experienced changed environment, e.g., from hydrophobic to a hydrophilic condition. It was presumed that in the new environment, the form of the long- chain hydro‐ carbon altered, going from a stretched- out to a coiled version (idealized form, Figure 3) as a result of association of London forces. The coiled version would lead to a wedged ligand.

Chromatographic Separations with Selected Supported Chelating Agents

http://dx.doi.org/10.5772/55521

129

**Figure 3.** Idealized depiction of a long chain hydrocarbon coiled by virtue of London forces in a hydrophobic environ‐

Remaining sections of this chapter are concerned with research involving the commercially available supported chelating agent called Octolig® because large quantities were available for a very reasonable cost (a wholesale price prior to 2008 was \$40 per kilogram), and a collaboration was established with Robert Alldredge on the basis of mutual interest in the

Examples of the removal of heavy metal ions by Octolig® may be found in three areas: patents,

Lindoy and Eaglin [14] provided useful information about their experiments demonstrating

A *first exampl*e involved a Colorado plating shop with numerous plating lines, removal of Cr, Cu, Ni, and Zn was a matter of concern. The existing precipitation process did not consistently reduce heavy metal concentrations to less than required limits. By use of an Octolig® column

Several examples are available in literature provided by Metre-General, Inc. [28].

The efficacy of the approach is considered later (*cf*. Table 8).

**3. Removal of heavy metal ions with Octolig®**

the efficacy of removal of representative transition metal ions.

supported chelators, as noted elsewhere [10].

company literature, and refereed journals.

ment. Redrawn from [24]

**3.1. Patent literature**

**3.2. Company literature**

**Figure 2.** Schematic representation of a Dean-Stark Apparatus [21]

### **2.3. London-forces (corkscrew) approach**

On occasion useful ligands are available, but need to be converted to supported ligands.

Examples of such ligands include LIX54 [CH3(CH2)11C6H4COCH2COCH3], LIX860 (*n*-dodecyl‐ saldoximine), oleoylacetone, and *N, N*'-didodecyldithiooxamide (all were once commercially available). A two-step procedure was used [24-27]: First, silica gel (5 g) was mixed with 25 mL of hexane, and the excess solvent allowed to evaporate to produce silica gel with pores loaded with hexane. Next the treated silica gel was mixed with a solution of a chelating agent in hot hexane. After stirring, the hexane was allowed to evaporate. It was hypothesized that a change in environment resulted with the evaporation of the hexane, i.e., that the long-chain hydro‐ carbon in the pores experienced changed environment, e.g., from hydrophobic to a hydrophilic condition. It was presumed that in the new environment, the form of the long- chain hydro‐ carbon altered, going from a stretched- out to a coiled version (idealized form, Figure 3) as a result of association of London forces. The coiled version would lead to a wedged ligand.

**Figure 3.** Idealized depiction of a long chain hydrocarbon coiled by virtue of London forces in a hydrophobic environ‐ ment. Redrawn from [24]

The efficacy of the approach is considered later (*cf*. Table 8).
