Sinteza katjonskih ligno-celuloznih sorbenata i primena za uklanjanje anjonskih polutanata iz vode

Abstract

Тhe aim of this dissertation was the development of new cationic sorbents, based on a modified lignocellulosic precursor (shell of L. vulgaris as a cheap and easily available plant material), intended for the removal of anionic pollutants from water, primarily phosphate and nitrate as the causative agents of eutrophication. Two original cationic sorbents (KALV and LVAT-CTAC), obtained by the developed procedures (chemical synthesis and surfactant grafting, respectively), were characterized using different methods (CHNS/O, pHPZC, FTIR, SEM-EDS). Sorption tests have shown that both sorbents can be used to remove phosphate and nitrate from the aqueous solutions. Sorbent LVAT-CTAC (based on surfactant) resulted in a maximum removal efficiency of 46% for phosphate, and 22% for nitrate. Sorbent KALV (based on ammonium agent) showed greater removal efficiency of investigated anions (88% for phosphate, and 79% for nitrate). Under optimal conditions, the maximum sorption capacity of KALV for phosphate was 17.85 mg/g, and 16.53 mg/g for the sorption of nitrate. The sorption process is complex in nature (ionic exchange and physical sorption), and takes place in a mixed reaction-diffusion regime. The kinetics of the anions sorption indicates that the results are the best fitted with the non-linear pseudo first-order model. The equilibrium study shows that the phosphate sorption can be best described by Freundlich and Sips isotherms, while the nitrate sorption is better described by Langmuir and Sips models. Thermodynamic parameters confirm that the anions sorption is exothermic and spontaneous in the temperature range of 20-40 oC. At higher temperatures, desorption of the anions from the sorbent surface is favored. The effect of coexisting anions in the solution on the sorption capacity of KALV decreases in the order of: H2PO4->NO3->SO42->Cl-. The possibility of regeneration and reuse of KALV sorbent was confirmed through five consecutive cycles of the sorption/desorption process. The exhausted sorbent with accumulated phosphates and nitrates can be used as a fertilizer to improve soil fertility.