Oligoamine Resins

Many of the transition metal cations are strongly coordinated by uncharged nitrogen-containing ligands. Consequently, chelating resins possessing strongly electron-donating nitrogens will selectively remove Cu2 +, for example, from solutions containing alkali and alkaline earth cations. Since the resin is uncharged, the adsorbed cations must be accompanied by mobile counterions to maintain elec-troneutrality. SenGupta has exploited this effect to adsorb anions such as phosphate, selenite, oxalate and phthalate on copper-loaded picolylamine resins (Dow 2N or 3N). These coordinating anions displace anions, such as sulfate, that are associated with adsorbed Cu(II) only by electrostatic attraction. Loss of copper from the resin during ligand exchange is extremely small.

Even conventional weak base resins - usually used as anion exchangers - are capable of separating transition metals from alkaline earths. Uptakes of

Cu(II) have been demonstrated at pH 5 on the phenolic weak base resin Duolite A7 and the acrylic weak base Amberlite IRA35 comparable to their anion exchange capacities (1-2 meq g 1). Uptake of Ni(II) or Zn(II) was smaller. Regeneration with mineral acid was efficient. An aminophenol resin of similar structure to Duolite A7 was found to adsorb Cu(II), presumably accompanied by sulfate ions, from CuSO4 solutions at pH 4-7. Other transition metal ions (Fe2 +, Co2 +, Ni2 +, Zn2 +, Cd2 + and Hg2 + ) were scarcely adsorbed in this pH range, but in the proto-nated form (pH + 2) the resin became highly selective for Fe3 +.

The transition metal affinity of resins having aliphatic oligoamine substituents increases with chain length (number of amino groups in each chelating group). It has been reported that acrylic oligoamine resins (Figure 5) can adsorb significant amounts of Cu2 + , Ni2 + , Zn2 + or Cd2 + from solutions containing ethylenediaminetetraacetic acid (EDTA), provided alkaline earth cations are also present. Transition metal uptakes were highest on resins derived from tetraethylenepentamine or penta-ethylenehexamine.

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Solar Panel Basics

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