Adsorption test of methylene blue onto porous powdered ceramics obtained from mixtures of kaolin–bauxite and kaolin–oyster shell

Two mixtures, respectively, F1 [kaolin (K) and bauxite (B)) and F2 (kaolin (K) and oyster shell (C)] were prepared and fired in order to get ceramics which were along with raw materials (kaolin, bauxite and oyster shell) utilized for adsorption of methylene blue (MB). Thus, two sets of F1 were prepared and fired, respectively, at 1100 and 1200 °C to obtain porous products denoted as KB1 and KB2. Also, two sets of F2 were prepared and fired, respectively, at 950 and 1050 °C to obtain ceramics denoted as KC1 and KC2. Depending on raw materials and powdered products, the following analyses were achieved: chemical analysis, X-ray diffraction, FTIR, SEM and N2 adsorption/desorption isotherms. Also, tests including contact time, pH of MB and concentration of MB onto powders of raw materials and porous ceramics were investigated. Adsorption of MB by all adsorbents was very fast. At ambient temperature and pH = 5.3, equilibrium time was 10 min and MB was removed as follows (mg/g): oyster shell (14), kaolin or bauxite (16), KB1 (57), KB2 (56), KC1 (54) and KC2 (50), respectively. In terms of maximum adsorption, effect of pH showed that KB1 and KB2 adsorbed more at pH = 4, while KC1 and KC2 adsorbed better at high pH (6–7). According to adsorption data obtained, Langmuir isotherm model described well the adsorption process of all porous ceramics. Also, pseudo-second-order model correlated well with kinetic data obtained from adsorption of MB onto the porous ceramics.