Adsorption characteristics of silver ions onto activated carbon prepared from almond shell

The adsorption of Ag(I) ions from aqueous solutions by almond shell activated carbon (ASC) was studied in a batch adsorption system. The BET surface area, total pore volume, and mesopore volume of ASC produce were found to be 893.62 m(2)/g, 0.472, and 0.293 cm(3)/g, respectively. Factors influencing Ag adsorption such as initial Ag ion concentration (170-680 mg/l), pH (2-12), contact time (10-180 min), and temperature (298-308 K) were investigated. The adsorption process was relatively fast and equilibrium was established about 60 min. Maximum adsorption of Ag(I) ions occurred at around pH 4.5. A comparison of the kinetic models on the overall adsorption rate showed that the adsorption system was best described by the pseudo second-order kinetics. The adsorption equilibrium data fitted best with the Langmuir isotherm and the monolayer adsorption capacity of Ag(I) ions was determined as 59.52 mg/g at 308 K. Thermodynamic parameters were calculated for the Ag(I) ion-ASC system and the positive value of Delta H (28.446 kJ/mol) showed that the adsorption was endothermic and physical in nature.