Removal of anthraquinone dye from wastewaters by hybrid modified activated carbons

Dyes are among the main environmental pollutants, due to the high amount of discharge of wastewater, lost in the dyeing process, without any further treatment. Anthraquinone dyes are stable and resistant in the aquatic system. Among the methods that have been applied to remove these dyes from wastewaters, adsorption on activated carbon has been reported as a very effective technique, and its modification with oxides and hydroxides of metals have been used to increase its surface area. In the present study, the production of activated carbon was originated by coconut shells, and a mixture of metals and metalloids, such as magnesium, silicate, lanthanum, and aluminum (AC-Mg-Si-La-Al), was used for its subsequent modification and applied to Remazol Brilliant Blue R (RBBR) removal. AC-Mg-Si-La-Al surface morphology was studied by BET, FTIR, and SEM methods. For the evaluation of AC-Mg-Si-La-Al, several parameters, such as dosage, pH, contact time, and initial RBBR concentration were studied. According to the results, in pH 5.0 ± 0.1, the dye percentage rate reached 100% by applying 0.5 g/L. Therefore, the optimal dose of 0.4 g/L and pH 5.0 ± 0.1 are selected, which leads to 99% removal of RBBR. The experimental data found to better fit to Freundlich isotherm (R² = 0.9189) and pseudo-second-order kinetic (R² = 0.9291) models and 4 h were the sufficient time for adsorption. According to thermodynamics, a positive value of ∆H⁰ (19.661 kJ/mol) suggests the endothermic nature of the process. The AC-Mg-Si-La-Al adsorbent was able to regenerate after 5 cycles of use, showing only a 17% decrease in its efficiency. Because of its effectiveness in full RBBR removal, AC-Mg-Si-La-Al could be further examined for the removal of several other dyes, even anionic or cationic.