Adsorption of anionic wood dyes on KOH-activated carbons from Pinus radiata sawdust

Chemically activated carbons synthesized from pine sawdust were applied efficiently for the elimination of wood dyes from aqueous solutions. Different proportions (1:2 and 1:4) of activating agent (KOH) and activation temperatures (600 and 850 °C) were used. Carbon surface morphology was characterized. The effect of pH (2–12), initial adsorbate concentration (5–500 mg L−1), and carbon dosage (0.1–0.5 g L−1) on dye adsorption were studied in batch mode. Langmuir model described well the adsorption equilibrium. The maximum found adsorption capacities were 1221.58, 1673.03, and 240.38 mg g−1 for blue and red at 500 mg L−1 and black at 100 mg L−1, respectively, using activated carbon at 850 °C and 1:4 (ACPS-4–850); at 25 °C, adsorbent dose 0.4 g L−1 for blue and black and 0.3 g L−1 for red dye and without change the pH for blue and red and at pH = 2 for black dye. The pseudo-second-order model explained the kinetics of adsorption except for the black dye at 100 mg L−1 using ACPS-4–850 for which it was the pseudo-first-order model. Desorption studies performed with ACPS-4–850 revealed that the adsorption was irreversible by chemical regeneration, whereas for the black dye, regeneration was efficient using H2O2 as desorbing agent.