Nitrate removal from aqueous solution by way of adsorption on modified sheep wool

Acid modification of sheep wool changed the surface charge from a negative to a positive one as demonstrated by means of zero-charge point determination. The positive surface facilitated the adsorption of nitrate (NO₃ ⁻) anions. The amount of nitrates in solution within 20–100 mg/dm³ was determined applying a home-developed ultraviolet spectrometry method. A little more effective modifier was 0.01 M hydrochloric acid (HCl) than the 0.1 M one. In the case of citric acid concentration, the effect was opposite. Wool modified with hydrochloric acid showed higher nitrate adsorption (up to 5 mg/g) compared with the sample modified with citric acid, (up to 1.7 mg/g of nitrate and 3, respectively). Testing eight adsorption isotherm models indicated inhomogeneity of the adsorbed layer from chemical as well as physical aspects. The Freundlich, Temkin and Halsey models fitted best. The study demonstrated that biopolymer modified using a suitable acid has the potential to remove nitrates from an aquatic environment.