ADSORPTION ISOTHERMS AND KINETICS STUDIES OF THE REMOVAL OF METHYLENE BLUE FROM AQUEOUS SOLUTIONS USING Chrysophyllum albidum SEED SHELL

Methylene blue (MB) adsorption from aqueous solution onto activated carbon prepared from Chrysophyllum albidum seed shell under various experimental conditions was investigated. The Steam Activated C. albidum Shell (SACAS) carbon was characterized using Fourier Transform Infrared (FTIR) Spectrophotometry and Scanning Electron Microscope (SEM). Batch mode experiments were conducted to assess the potential of SACAS for the removal of MB from aqueous solution. Equilibrium isotherm studies were conducted by varying initial concentration of MB solution, pH of solution, contact time and SACAS dosage to study the uptake of MB from the solution. High removal efficiencies of SACAS were obtained at the following optimum conditions: Initial MB concentration of 100 mg/L (96.8%), adsorbents dose of 1.5 g (95.4%), contact time of 120 min (94.76%) and pH of 9 (95.3%). The adsorption of the MB by the adsorbent was found to increase with increasing initial concentrations of the MB solution. Also, the adsorption rate increased with pH. Equilibrium data of the adsorption MB onto SACAS were analyzed using Langmuir and Freundlich models. The data fitted the Langmuir adsorption isotherm model (R2 = 0.942) than the Freundlich model (R2 = 0.925). The Langmuir dimensionless constant, RL, for the adsorption of MB ranges from 0.012-0.053. The RL result favours adsorption of the MB. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. Adsorption of the MB could be described by the pseudo-second-order kinetics (R2 = 0.99). The FTIR bands at 3745.45 cm-1 3427.61 cm-1, 2926.06 cm-1, 1637 cm-1 and between 1197.59 cm-1 and 1124.75 cm-1 were identified as hydroxyl, amine, alkyl chain and amide and phosphate, respectively and P-O vibration of C-PO32- moiety at 1041.32 cm-1, amine R-NH2 at 3030 cm−1, carboxylic acids at 2822 cm−1, and phosphates at 1709.05 cm−1 before MB adsorption. Scanning Electron Microscopy (SEM) analysis showed that the average pore size on the activated carbon was 20 and 50 μm before and after MB adsorption, respectively. It can be concluded that activated carbons derived from C. albidum Shell (SACAS) showed good potential for removal of MB from aqueous solutions, and can be employed, therefore, as a low cost alternative to commercial adsorbents in the removal of dyes from textile wastewater.