: 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.

In this paper, an activated carbon obtained from Pinus radiata sawdust is applied to remove blue, red, and black wood dyes from aqueous solutions in a fixed-bed column. The flow rate (7.7–30.8 mL min⁻¹), initial dye concentration (25–500 mg L⁻¹), and bed height (2–4 cm) highly influence the breakthrough-curves’ features. The results indicate that the adsorption capacity increased by decreasing the flow rate and increasing the initial dye concentration, except for the black dye, and increasing bed height, except for the red dye. In addition, the breakthrough time changed by modifying the studied variables. The curves became steeper as the flow rate increased and as the bed height decreased. Also, by increasing the inlet dye concentration, the breakthrough time decreased significantly, and sharper breakthrough curves were obtained. The activated carbon with a surface area of 2826 m² g⁻¹ led to high values of the adsorption capacity between 150 and 1300 mg g⁻¹. The Yoon–Nelson and Thomas models were the ones that best described the adsorption data. The activated carbon saturated with black dye could be used in three successive cycles after regeneration with H₂O₂.

This research explores the synthesis and application of carbon-based adsorbents derived from olive stones and almond shells as low-cost biomass precursors through carbonization at 600 °C combined with chemical activation using KOH, H₃PO₄, and ZnCl₂ with carbon/activating agent (C/A) ratios of 1:2 and 1:4 (w/w) at 850 °C for the removal of Cu²⁺ and Pb²⁺ ions from aqueous solutions. The carbons produced were characterized using different techniques including SEM-EDX, FTIR, XRD, BET analysis, CHNS elemental analysis, and point of zero charge determination. Batch-mode adsorption experiments were carried out at adsorbent doses of 2 and 5 g L⁻¹, initial metal concentrations of 100 and 500 mg L⁻¹, and natural pH (around 5) with agitation at 350 rpm and 25 °C for 24 h. KOH-activated carbons, especially at a 1:4 (w/w) ratio, exhibited superior adsorption performance mainly due to their favorable surface characteristics and functionalities. Pb²⁺ was entirely removed (100%) at the highest initial concentration of 500 mg L⁻¹ and an adsorbent dosage of 5 g L⁻¹, while for Cu²⁺, the maximum adsorption efficiency was 86.29% at an initial concentration of 100 mg L⁻¹ and a dosage of 2 g L⁻¹. The results of this study will help advance knowledge in the design and optimization of adsorption processes for heavy metal removal, benefiting industries seeking green technologies to mitigate environmental pollution.

The present work analyzes the behavior of an activated carbon fabricated from almond shells for the removal of cationic dyes (methylene blue, MB, and malachite green, MG) by adsorption from aqueous solutions. The carbonized precursor was activated with KOH at a 1:2 (w/w) ratio with the objective of increasing both the surface area and the pore volume. Both non-activated and activated carbon were characterized in different aspects of interest in dye adsorption studies (surface structure, point of zero charge, specific surface area, and pore size distribution). The effect of the dye’s initial concentration and adsorbent dosage on dye removal efficiency and carbon adsorption capacity was studied. Adsorption kinetics were analyzed under different experimental conditions, and different models were assayed to determine the adsorption mechanism. Dye adsorption in the adsorbent surface could be considered the rate-limiting step. Different adsorption equilibrium models were evaluated to fit the experimental data. This adsorbent allowed us to reach high Langmuir adsorption capacity for both dyes (MB: 341 mg·g⁻¹, MG: 364 mg·g⁻¹ at 25 °C and 0.5 g·L⁻¹). Moreover, kinetic and equilibrium adsorption data have been used to simulate breakthrough curves in a packed-bed column using different conditions (bed length, liquid flowrate, and dye initial concentration). The simulation results showed that almond shell activated carbon is a suitable adsorbent for methylene blue and malachite green removal from wastewater.

This research explores the synthesis and application of carbon-based adsorbents derived from olive stones and almond shells as low-cost biomass precursors through carbonization at 600°C combined with chemical activation using KOH, H3PO4 and ZnCl2 with carbon/activating agent (C/A) ratios of 1:2 and 1:4 (w/w) at 850°C for the removal of Cu2+ and Pb2+ ions from aqueous solutions. The carbons produced were characterized using different techniques including SEM-EDX, FTIR, XRD, BET analysis, CHNS elemental analysis and point of zero charge determination. Batch-mode adsorption experiments were carried out at adsorbent doses of 2 and 5 g L-1, initial metal concentrations of 100 and 500 mg L-1 and natural pH (around 5) with agitation at 350 rpm and 25°C for 24 h. KOH-activated carbons, especially at a 1:4 (w/w) ratio, exhibited superior adsorption performance mainly due to their favorable surface characteristics and functionalities. The greatest adsorption efficiency reached 100% (101.41-101.68 mg g-1) for Pb2+ at 500 mg L-1 and 5 g L-1 dosage, and 84.63-86.29% (41.69-42.52 mg g-1) for Cu2+ at 100 mg L-1 and 2 g L-1 dosage. The results of this study will help advance knowledge in the design and optimization of adsorption processes for heavy metal removal, benefiting industries seeking green technologies to mitigate environmental pollution.

The present work analyses the behaviour of an activated carbon fabricated from almond shell for the removal of cationic dyes (methylene blue and malachite green) by adsorption from aqueous solutions. The carbonized precursor was activated with KOH at a 1:1 (w/w) ratio with the objective of increasing both surface area and pore volume. Both non-activated and activated carbon were characterized in different aspects of interest in dye adsorption studies (surface structure, point of zero charge, surface area, pore size distribution). The effect of dye initial concentration and adsorbent dosage upon dye removal efficiency and carbon adsorption capacity has been studied. Adsorption kinetics was analysed under different experimental conditions and different models were essayed to determine the adsorption mechanism. Dye adsorption in the adsorbent surface could be considered the rate-limiting step. Adsorption equilibrium isotherms have also been obtained, and Langmuir and Freundlich equations showed the best fitting to the experimental data. Moreover, Adsorption kinetic and equilibrium data have been used to simulate breakthrough curves in a packed-bed column using different conditions (bed length, liquid flowrate, dye initial concentration). Simulation results showed that almond shell activated carbon is a suitable adsorbent for methylene blue and malachite green removal from wastewater.