The study dealt with the investigation of the effect of an acidic chemical modifier on the surface properties and sorptivity of sheep's wool as an adsorption material. The adsorption of nitrate anion (NO3-) from aqueous solutions onto sheep's wool modified with organic acid (oxalic acid; c = 0.2 mol dm-3) and inorganic acid (hydrochloric acid; c = 0.01 mol dm-3) was studied. It was shown that the chemical modification of the adsorbent has a significant effect on its surface properties. The acidic treatment resulted in a shift of the pH point of zero charge (pHPZC) by 4-5 units to lower values and an increase in the number of active sites capable to bind anion. The chemical modification increased the number of functional groups with the necessary affinity towards NO3-. At an initial concentration of 100 mg dm-3 of NO3- ions in the solution, the removal efficiency was of 50 % for the sample modified with HCl, whereby the limit of nitrate concentration permitted for drinking water (50 mg dm-3) was met. The results showed that the sorptivity of the modified wool depends on the initial concentration of the solute in the solution (with increasing concentration of NO3- ions, the sorptivity increases) and on the type and concentration of the modifier used. The efficiency of adsorption on organic acid activated wool was only 30 %. Student's t-test showed significant differences in the sorptivity between the sheep wools modified with inorganic and organic acid. The adsorption process for all modified samples was independent on the initial pH of the solution, as the sorptivity was mostly constant in the range of pH values 3-8. A decrease in sorptivity was observed only at very low (1.4 and 2.1) and high (9.1) pH values, which are practically unrealistic in drinking water. The experimental results showed that sheep's wool with acid surface modification has some potential to be an alternative filter medium in the treatment of drinking water contaminated with nitrates.
This work was supported by Slovak Research and Development Agency (APVV-19-0087). The authors wish to thank Zuzana Branišová from Trnava University, Department of Fine Art Education, for the pictures creation.Porubská M., Cvik M., Jomová K., Branišová Z., Braniša J. (2022) Surface Innovations. 10(1), p. 68 – 75.
Elemile O., Akpor B. O., Ibitogbe E. M., Afolabi Y. T., Ajani D. O. (2022) Cogent Engineering. 9(1), p. 1 – 19.
Xu X., Gao B., Yue Q., Li Q., Wang Y. (2013). Chemical Engineering Journal. 234, p. 397–405.
Viglašová E., Galamboš M., Danková Z., Krivosudský L., Lengauer Ch. L., Hood-Nowotny R., Soja G., Rompel A., Matík M., Briančin J. (2018) Waste Management. 79, p. 385 – 394.