Abstract: | There are two main objectives of this work: (a) to obtain fundamental data regarding the electrochemical behavior of some mononitrophenols [2-nitrophenol (2-NP), 3-nitrophenol (3-NP) and 4 nitrophenol (4-NP)] and dinitrophenols [2,4-dinitrophenol (2.4-DNP), 2,6 dinitrophenol (2,6-DNP)], influence of electrode nature, pH, concentrations on the electrochemical behavior and (b) to use these fundamental data (a) for the applied electrochemical reduction processes in order to reduce the nitrophenols concentration in synthetic wastewaters. We investigated both the wastewaters containing a single nitrophenol and a mixture of nitrophenols (4-NP and 2,6-DNP in different volume ratios), using different laboratory experimental plants: two compartment reactor type filter-press, an undivided electrochemical reactor and a two compartment reactor, all with electrolyte recirculation. The experimental processes were pursued by different methods: cyclic voltammetry (BAS100 and AUTOLAB PG-STAT12), and spectrophotometry in UV-Visible (Unicam Helyos B and DR/2000 HACH). The first peak potential, Ep1 for 2,6-DNP, shows two linear regions with different slopes, corresponding to an acid behavior specific to nitro phenols values (pKa = 4-5). The first peak height reaches the maximum value in acidic media.
The applied electrolyses demonstrated practically 90-99% removal yield for the both nitro derivatives, depending on the experimental conditions. The best result have been obtained, in the case of 4-NP, in two compartment reactor type filter-press with nickel cathode (94% of 4-NP removal), and in the case of 2,6-DNP the final removal was of 99% in two compartment reactor with graphite cathode. |
