Wool powders used as sorbents to remove Co²⁺ ions from aqueous solution

The Co²⁺ sorption of two wool powders was investigated using its radioisotope ⁵⁷Co (T_1/2 = 271.8 days and γ = 122.1 and 136.5 keV) as a tracer. The effects of the type of buffer, the pH value, the contact time and the initial concentration of Co²⁺ on the sorption behaviour of wool powders were studied. The Co²⁺ releasing ability of wool powders and the re-use of wool powders to sorb Co²⁺ were also examined. The optimum sorption of Co²⁺ by the powders occurred at pH 8 in phosphate buffer and pH 10 in ammonium sulphate buffer. Fourier-transform infrared spectroscopy (FTIR) was used to study the changes in chemical structure of the wool after exposure to both buffer solutions. Compared to the untreated wool fibre, the fine wool powders showed rapid sorption rates and high sorption capacities for Co²⁺. Co²⁺ ions were recovered after exposing the Co²⁺ loaded wool to HCl (0.1 M) and buffer at pH 3 (glycine/sodium chloride). After releasing Co²⁺ ions from wool powders, the efficiency of wool powders re-used to sorb Co²⁺ was 80% of that of the fresh wool powders. It is concluded from this study that wool powder can be used as an efficient sorbent to remove and release Co²⁺ from solution.