Metal ion binding properties of novel wool powders

Abstract

Wool fibres have shown potential for the removal and recovery of toxic chemical and metal ions; however, their slow kinetics of binding has limited their widespread application. In this study three wool powders have been prepared from chopped wool fibre using various milling operations. Brunauer, Emmett, Teller analysis (BET) showed negligible change in surface area and Positron annihilation lifetime spectroscopy indicated no change in nanoporosity of the powders on processing. Binding of the transition metal ions, Co2+, Cu2+, and Cd2+ was investigated over the pH range 3-9 at ambient temperature (23°C) using their respective radioisotopes (i.e.57Co,64Cu, or109Cd). The optimum pH for binding of Cu2+ and Cd2+ was in the range 6-8, while Co2+ absorption peak was sharp at pH 8. The rate of uptake of Cu2+ for each of the wool powder was dramatically faster (∼ 42 fold) than that of the wool fibre. In comparison with commercial cation exchange resins, the wool powders showed significantly higher (two to nine fold) metal ion loading capacity. Selective binding of the metal ions could be enhanced by varying pH and/or incubation times. The use of radioisotopes to monitor the metal ion binding allowed the development of a highly sensitive and rapid high-throughput analysis method for assessing wool powder binding properties. The ability to produce large quantities of wool powders and their ease of handling indicate that they have potential for application in separation and recovery of metal ions from industrial effluents and environmental waterways.