Competitive Adsorption of Heavy Metal Ions from Aqueous Solutions onto Activated Carbon and Agricultural Waste Materials

Agricultural waste materials (peanut shell and sawdust) were used as replacements for activated carbon to remove heavy metal ions from aqueous solution. Batch adsorption experiments were conducted in single, and competitive systems. The adsorption efficiencies of different heavy metal ions were, in descending order: lead, copper, cadmium. Activated carbon showed best adsorption efficiency (lead: 14.01 mg/g; copper: 13.1 mg/g; cadmium: 5.5 mg/g), followed by peanut shell (lead: 9.5 mg/g; copper: 49.1 mg/g; cadmium: 5.07 mg/g), and sawdust (lead: 5.5 mg/g; copper: 5.3 mg/g; cadmium: 3.99 mg/g), which showed the worst efficiency. The amount of heavy metal ions adsorbed onto activated carbon, peanut shell and sawdust increased with the increase of adsorption time and then reached equilibrium values. As the initial concentration of heavy metal ions increased, the amount of heavy metal ions adsorbed increased while the removal ratios thereof decreased. The adsorption processes in both single and competitive systems followed a Langmuir isotherm model and pseudo second-order kinetic model. The intraparticular diffusion process can be divided into two stages for the adsorption process of heavy metal ions. There were antagonistic effects among three kinds of heavy metal ions in a competitive system.