COPPER-SELECTIVE CHELATING RESINS .2. COLUMN EXTRACTIONS

Two chelating resins based on poly(glycidylmethacrylate-co-ethyleneglycol dimethacrylate) and two based on poly(styrene-co-divinylbenzene) have been used in small-scale column extractions of Cu(II) from sulphate solutions containing 1.0 mg l-1 of metal ion at pH 5. Two of the resins bearing 2-aminomethylpyridine residues with saturation capacities up to ∼ 15 g Cu(II) l-1 resin showed sharp breakthrough profiles and rapid exchange kinetics. The other two with higher ligand loading displayed shallow profiles and did not reach saturation capacity, indicating a significant proportion of the ligand groups to be inaccessible under the conditions employed. For a column of 10 ml bed volume, increasing the flow rate of the feed solution from 1 ml min-1 progressively to 30 ml min-1, using one of the more efficient resins, showed that above a rate of ∼ 5 ml min-1 the bulk movement of ions through the column was too fast for all the resin-bound ligands to be accessed. As a result breakthrough moved to lower volumes and the working capacity dropped. No difference was found in the elution of all four resins with 1 M H2SO4 at a flow rate of 1 ml min-1. In all cases Cu(II) was rapidly and efficiently eluted from the column. The selectivity properties of the two efficient resins in extracting Cu(II) ions from a solution containing a large excess of Zn(II) ions were also investigated. The effect of a 250-fold excess of Zn(II) proved negligible in both cases, and Cu(II) was rapidly and selectively extracted with a separation factor of ∼ 900: 1 in the case of the polystyrene-based resin, and ∼ 500: 1 in the case of the methacrylate-based species. In terms of kinetic performance and metal ion selectivity (in both loading and elution) the results of the batch extraction experiments were confirmed in these column tests, hence proving the predictive value of careful batch testing. On considering kinetic factors, capacity factors and metal ion selectivity factors, a resin carrying a 2-aminomethylpyridine group attached to a polymethacrylate backbone proved to be the optimum one. © 1990.