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 m2/g, 0.472, and 0.293 cm3/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 ΔH (28.446 kJ/mol) showed that the adsorption was endothermic and physical in nature.