Adsorpcja fenoli z roztworów wodnych na pylistych węglach aktywnych

The adsorption process by solid adsorbents is one of the most efficient methods for the removal of organic pollutants from water. Adsorption is attractive for its relative flexibility and simplicity of design, low cost, ease of operation and regeneration. Activated carbons are now the most commonly used adsorbents of proven adsorption efficiency for organic compounds due to their physicochemical properties including specific surface area, pore volume, pore size distribution and surface chemistry. For water treatment on a commercial scale granular activated carbon is most commonly used. In this paper the adsorption of phenol (Ph) and 4-cresol (4K) from aqueous solutions on powdered activated carbons (PAC) was studied. As adsorbents, two activated carbons L2S and SX2 with similar physicochemical properties were used. The adsorption was studied in a batch adsorption system, including both kinetics and equilibrium. The kinetics was fitted with the pseudo-first order and pseudo- second order models. The adsorption kinetics was found to follow the pseudo-second order model with the coefficient of determination values greater than 0.99. The adsorption isotherms were determined and modeled with the Freundlich and Langmuir equations. The equilibrium data obtained for both adsorbates were better described by the Langmuir model than by the Freundlich isotherm model. It was found that the 4K was adsorbed better than Ph on both adsorbents. The adsorption capacities of the L2S and SX2 activated carbons towards phenols were comparable. The values of the Langmuir adsorption capacity qm for phenol were 1.634 and 1.591 mmol/dm³ for the L2S and SX2 activated carbons, respectively. The qm values for 4-cresol were 1.885 and 1.844 mmol/dm³ for the L2S and SX2, respectively. The influence of solution pH on the adsorption was also investigated. The adsorption of the Ph and 4K was almost constant from the pH 2 to 8, and decreased significantly with further increase in the pH (above the pK_a of the adsorbates and pH_PZC of the adsorbents).

W pracy porównano właściwości adsorpcyjne dwóch pylistych węgli aktywnych (L2S i SX2) o zbliżonych właściwościach fizykochemicznych jako adsorbentów do usuwania fenolu i 4-krezolu z roztworów wodnych. Zbadano kinetykę adsorpcji, adsorpcję w warunkach równowagowych oraz wpływ pH roztworu. Adsorpcja obydwu adsorbatów przebiegała zgodnie z modelem kinetycznym pseudo 2. rzędu, a w warunkach równowagowych była dobrze opisana równaniem izotermy Langmuira. W każdym przypadku 4-krezol adsorbował się szybciej i z większą wydajnością niż fenol. Różnice w pojemnościach adsorpcyjnych poszczególnych pylistych węgli aktywnych były niewielkie. Adsorpcja utrzymywała się na stałym poziomie w środowisku o pH od 2 do 8, jej znaczny spadek był obserwowany w wysokich wartościach pH (> 8), powyżej wartości pK_a adsorbatów i pH_PZC adsorbentów.