Modeling and optimization of process parameters in elucidating the adsorption mechanism of Gallic acid on activated carbon prepared from date stones

We make use of chemical activation with phosphoric acid to prepare an activated carbon from date stones (DSAC). After characterization for surface area and pore volume, it was tested as an adsorbent for gallic acid (GA) removal from aqueous solutions: Operating variables including contact time (410 min), adsorbent dosage (0.1 g in 150 mL), GA concentration (10 mg/L) and solution pH (4.5) were optimized using the Box-Behnken design (BBD) under response surface methodology (RSM) approach. Adsorption of GA onto DSAC may be described by the pseudo-second-order kinetics model equation suggesting that the process is chemisorption. The equilibrium data fitted the Langmuir isotherm model with a maximum capacity of 156 mg/g (25°C, pH 4.5). The GA adsorption process was found to be exothermic, while ΔG° was negative implying that the reaction is spontaneous.