Metal ion binding properties of novel wool powders

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, or ¹⁰⁹Cd). 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.