The sorption characteristics of citric acid modified wood to remove copper and lead ions from aqueous solution under batch conditions have been investigated. Sorption was pH dependent with increasing uptake at higher pH values. The kinetics of sorption for both ions was rapid with 90% sorption taking place within the first 60 min regardless of its initial concentration. Sorption can be explained by a second-order kinetics model from which the rate constant, the equilibrium sorption capacity and the initial rate were calculated. From these parameters, the predictive models for Cu and Pb sorbed (qt) in time t and at an initial concentration (Co) are given by qt = Cot[0.31 Co-2.29 + (0.04C o + 5.19)t] and qt = Cot/[0.06C o-6.59 + (0.01 Co + 4.48)t] for Cu and Pb, respectively. Using these models the predicted and experimental uptakes of Cu and Pb were compared and discussed. Maximum sorption capacities of modified wood under present experimental conditions were 23.70 and 82.64 mg/g for Cu and Pb, respectively. However, for untreated wood the corresponding values were 2.56 and 7.71 mg/g indicating a tenfold increase in sorption upon citric acid modification. Ethylene diamine tetraacetic acid and nitrilotriacetic acid complexed with both ions render sorption less favorably. However, salicylic acid had little influence. In a binary system, Pb ions were more favorably sorbed than Cu ions which could be due to the larger ionic radius of the former ions.

The adsorption behaviour and the micro-and mesopore size distributions of commercial palm kernel shell activated carbons (PKSAC) and other commercial activated carbon are characterized. The results showed that PKSAC are predominantly microporous materials, where micropores account 68-79% of total porosity. On the other hand, commercial activated carbons: Norit SX Plus, Calgon 12 × 40, and Shirasagi "A" activated carbons contained high mesopore fraction ranging from 33 to 52%. The analysis showed that the degree of mesoporosity of PKSAC is increased steadily with the decrease of particle size. This is due to the presence of channels interconnect the smaller pores in the interior of smaller particle size PKSAC. The smaller size PKSAC particle that is highly mesoporous has preformed better on the adsorption of larger molecules such as methylene blue. On the other hand, bigger size PKSAC particle has better performance on the adsorption of smaller adsorbates such as iodine. Nomenclature q tAmount of methylene blue ions adsorbed at time t (mg/g) Q 0Number of moles of solute adsorbed per unit weight of activated carbon (mol/g) A MCross sectional area of one MB ion (m 2 ) bEnergy of adsorption constant of Langmuir model C e Solute concentration in the aqueous phase at time t (mg/L) C 0 Initial solute concentration in the aqueous phase (mg/L) D meso Average mesopore diameter determined by BJH model (Å) D micro Mean micropore diameter determined by HK model (Å) K F Freundlich isotherm equation constant [mg/g(1/mg) 1/n ] k f Rate constant of pseudo-first-order equation defined in (4) (min −1 ) k i Rate parameter of intraparticle diffusion defined in (6) (mg L −1 min −1 ) k s Rate constant of pseudo-second order equation defined in (5) (L mg −1 .min −1 ) N a Avogrado's number (6.023 × 10 23 ) 1/n Freundlich isotherm equation constant (dimensionless) q e Amount of methylene blue ions adsorbed at equilibrium (mg/g) R 2Regression factor of sorption kinetic plots S BET BET specific surface of activated carbon (m 2 /g) S MB Surface coverage of methylene blue ions within activated carbon (m 2 /g) S micro Surface area of activated carbon due to micropores (m 2 /g) t Time (min) 508 Adsorption (2009) 15: 507-519V meso Mesopore volume obtained by BJH model (cm 3 /g) V micro Micropore volume obtained by DR model (cm 3 /g) V t Total pore volume of activated carbon (cm 3 /g) X MB Fraction of surface coverage of methylene blue ions over BET surface area (S MB /S BET )

56 cm 3 g −1 ). The mesoporosity of naturally occurring activated carbons is observed to increase with decreasing particle size. Mechanical grinding was therefore performed to investigate its effect on the mesoporosity and microporosity of OPSA.