Adsorption of Cd(II) ions from aqueous solutions onto activated carbons
Advancing the chemical engineering fundamentals
Electrochemical Engineering (T2-14P)
Keywords: Cadmium, adsorption, isotherms, breakthrough curves, desorption
Heavy metals are considered among the most toxic substances for both human beings and the environment. They are constantly released into the aquatic environment from natural processes such as volcanic activity and weathering of rocks as well as anthropic sources which in the last twenty years have become of leading importance in the worldwide emission balance of these substances.
For example, cadmium containing wastewaters derive from several industrial applications and represent relevant environmental hazards. Hence, appropriate water treatments for cadmium removal are required to reduce their concentration in wastewaters before they are discharged into the environment as well as to recover polluted natural water bodies. Activated carbon adsorption has been widely used to remove pollutants from wastewaters. However, commercially available activated carbons may be expensive and the optimization of the operating conditions for adsorption processes is of the greatest importance.
This paper documents the results of experimental study on cadmium removal from model aqueous solution by adsorption onto a commercially available granular activated carbon (Aquacarb 207EA). Process aptimization requires the analysis of both adsorption thermodynamics and kinetics.
Adsorption isotherms have been carried out at different pH, salinity and temperature levels, highlighting a strong influence of these parameters on cadmium capture by the activated carbon. In particular, cadmium adsorption is strictly related to solution pH while temparature and salinity have more limited effects. In particular, cadmium adsorption is the highest at neutral pH levels while it strongly decreases by decreasing pH. Moreover, due to cadmum hydroxide precipitation, the adsopiton becomes unrelevant in alkaline systems.
Kinetic tests have been carried out in fixed bed columns, by vaying cadmium solution concentration and flow rate at neutral pH. Moreover, desorption tests have been conducted with 0.1 M nitric acid solution, showing that the complete regeneration of the column can be obtained with limited amounts of the acid solution and suggesting a possible recovery of cadmium ions.
Presented Wednesday 19, 13:30 to 15:00, in session Electrochemical Engineering (T2-14P).
