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The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R L , from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (ΔG 0 ), standard enthalpy (ΔH 0 ), standard entropy (ΔS 0 ) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation. Nomenclature AActivation energy of adsorption (kJ/mol) C f Final metal ion concentration, ppm (mg/l) C 0 Initial metal ion concentration, ppm (mg/l) C t Metal ion concentration at time t, ppm (mg/l) D Diffusion coefficient (cm 2 /s) ΔG 0 Gibbs free energy change (kJ/mole) ΔH 0 Enthalpy change (kJ/mole) ΔS 0 Entropy change (J/k mole) k 1 Pseudo-first-order rate constant (min −1 ) k 2 Pseudo-second-order rate constant (mg/g min) K f Freundlich adsorption constant (mg/g) K idIntra-particle rate constant [(mg/g) min 0.5 ] MMass of adsorbent per unit volume (g l −1 ) m Amount of adsorbent added (g) n Freundlich constant q Amount of adsorbate per gram of adsorbent (mg/g) q e Amount of adsorbate per gram of adsorbent at equilibrium, (mg/g) q tAmount of adsorbate per gram of adsorbent at any time, t q m Equilibrium adsorption capacity using model q max Maximum adsorption capacity (mg/g) R 2Linear correlation coefficient Water Air Soil Pollut (2011) 218:499-515

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In this study, the adsorptive effectiveness of sustainable and cost-effective eucalyptus bark biomass in the removal of methylene blue (MB) dye from its aqueous solution has been tested using a packed bed up-flow column experiment. A series of column experiments using raw eucalyptus bark was performed to determine the breakthrough curves with varying inlet MB dye flow rate (10-15 mL min -1 ), initial MB dye concentration (50-100 mg L -1 ) and adsorbent bed height (10-15 cm). High bed height, low flow rate and high initial dye concentration were found to be the better conditions for maximum dye adsorption. To predict the breakthrough curves and to determine the characteristic parameters of the column dynamics for industrial applications and for process design, Thomas model, Yoon-Nelson model and bed depth service time model were applied to experimental breakthrough data. All models were found suitable for describing the dynamic behaviour of the column, with respect to MB flow rate, initial dye concentration and adsorbent bed height. The findings revealed that eucalyptus bark biomass has a high adsorption potential for the removal of MB dye from aqueous solutions in a column system, and that it could be used to treat dye-containing effluents. List of symbols ACross sectional area of bed in column (cm 2 ) A 1 Used bed area (cm 2 ) A 2 Unused bed area (cm 2 )pollutant concentration (mg/L) C o Inlet pollutant concentration (mg/L) H Height of bed in column (cm) H B Used bed length up to break point (cm) H T Bed height of column (cm) H UNB Unused bed length (cm) K o Rate constant in BDST model (L/mg min) K T Thomas rate constant (mL/mg min) K YN Yoon and Nelson rate constant (min -1 ) MTZ Mass transfer zone (cm) m Amount of adsorbent in the column (g) m p Mass of pine cone (g) m total Total amount of methylene blue dye sent to column (g) N o Adsorption capacity (mg/L) Q Volumetric flow rate (mL/min) q total Total adsorbed methylene blue dye quantity (g) q o Equilibrium adsorbate uptake (mg/g) t Breakthrough (sampling) time (min) t t Total time (min) t total Total flow time (min) t b Usable capacity of bed up to the breakthrough point time (min) t u Time equivalent to usable capacity (min) U Influent linear velocity (cm/min) V Effluent volume (ml) V eff Total effluent volume (mL) s Time required for 50 % adsorbate breakthrough (min)

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