A comparative study of using barberry stem powder and ash as adsorbents for adsorption of humic acid.

In the present research, investigation of the practical utility of barberry stem powder (BSP) and barberry stem ash (BSA) for humic acid (HA) removal from an aqueous medium by adsorption was carried out. The adsorption process was tested by varying of pH (3-11), reaction time (5-20 min), initial HA concentration (5-40 mg/L), adsorbent dosage (1-4 g/L), and temperature (15-35 °C). The isothermal results revealed that the adsorption process is favorable for both used adsorbents and it is highly described using the Freundlich and Langmuir models (R2 > 0.960). Also, the maximum uptakes of BSP and BSA for HA were 20.220 and 16.950 mg/g at the abovementioned optimized conditions (pH = 7, reaction time = 10 min, temperature = 15 °C, initial HA concentration = 40 mg/L, and adsorbent amount = 1.0 g/L), respectively. The results achieved from the fitting of the experimental data with Dubinin-Radushkevich isotherm model showed that the HA molecules are adsorbed onto the BSP and BSA by physiosorption process. From the thermodynamic study, it appeared that the biosorption process of the HA onto two studied adsorbents was of exothermic nature. The kinetics of the adsorption process of HA has been found to be pseudo-second-order model (R2 = 0.930-0.999). Thus, the results obtained from this paper elucidated that the BSP exhibited higher adsorption capacity in comparison to BSA, for HA removal up to permissible concentrations.