Preparation of activated carbon from pine (Pinus radiata) sawdust by chemical activation with zinc chloride for wood dye adsorption

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Wastewater containing dyes are released into water bodies generating serious problems in human health and marine life. To contribute to the solution of this problem, a novel activated carbon was prepared from untreated pine (Pinus radiata) sawdust by dry chemical activation with ZnCl2 and was used for wood dye adsorption. The carbon was characterized by point of zero charge, N2 and CO2 adsorption isotherms, SEM-EDX, and FTIR. N2 and CO2 surface areas were 471.4 and 319.5 m2 g−1, respectively, with 91% of micropores. Wood dye adsorption was studied in function of pH (2–12), adsorbent dose (0.1–4 g L−1), time (up to 48 h for blue and red and 12 h for black), and initial concentration (5–500 mg L−1). The equilibrium data for the blue and black dyes were satisfactorily fitted to the Freundlich model while those for the red dye to the Langmuir model. Kinetic data were explained by the pseudo-second order (chemisorption process) and intraparticle diffusion models. At 5 mg L−1, a 100% removal efficiency was achieved at all pH for the blue dye, whereas for the red and black, natural pH (5.1) and pH = 2, respectively, led to the best removal efficiencies, 96 and 56%. Increasing concentration above 25 mg L−1 significantly reduced adsorption efficiency for blue and red dyes. For the black dye increasing the dose to 1 g L−1, the adsorption efficiency reached 82% at 25 mg L−1. High removal efficiencies were achieved for all dyes at 25 mg L−1 and 4 g L−1.