A Comparative Study: Adsorption Properties and Mechanism of Different Character Residual Sludge for Heavy Metal

The removal of Cu²⁺ and Cd²⁺ of aqueous solution by residual sludge from four type sewage treatment plant was investigated. Effect of adsorption time, kinetics and thermodynamics of adsorption was researched. The study indicated that all of the sludge can absorb mono-component Cu²⁺ or Cd²⁺ but the sludge from Petrochemical Wastewater plant had deposition rather than adsorption on Cu²⁺ or Cd²⁺. The equilibrium time of the sludge from Maize Processing and Machining Wastewater plant was achieved after 2 hours and that of the sludge from Urban Sewage and Petrochemical Wastewater plant was 1 hour. Sludge type was the decisive factor of equilibrium time rather than solution concentration, metal ion type. The adsorption process was found to follow a first-order rate mechanism and rate constant was evaluated. The Langmuir and Freundlich adsorption isotherm models were used to represent the experimental data. The Langmuir models was fitted better. The sludge from Maize Processing Wastewater plant had best binding affinity with Cd²⁺ and the sludge from Urban Sewage plant had best binding affinity with Cu²⁺.