Study On Heavy Metals Adsorption By Marine Algae

The accumulation of heavy metals by algae has been studied extensively for biomonitoring or bioremediation purposes. It is found that the accumulation of heavy metals by algae is one of the most effective methods and the research on this has been performed more than fifty years. With the advantages of low cost raw material, big adsorbing capacity and no secondary pollution etc., the algae are promising to be used in treating industrial water containing heavy metals. A series of marine algae were tested for their adsorption properties. The mechanism studies illustrated that the non-living algae might have the same or even greater adsorption capacity. From the study of marine algae抯 adsorption kinetics and thermodynamics, it is found out that: The adsorption process lasted about 24 hours, in which the complexation between the metal ions and the functional groups on the surface of and inside the biological material played a major role. During the adsorption processes there are mainly three kinds of parallel reactions that are respectively very fast. fast, or very slow. The process. that contains several first order reactions, may be expressed by the following function: C~ 1 c1C~1 e~lt+Co2e42t+Coiek3t, where ~, k2 and k1 are the reaction constants of these three kinds of reactions. Freundlich equation fitted very well the adsorption isotherms. II It is demonstrated that the principal mechanism of metallic cation sequestration involves the formation of complexes between a metal ion and functional groups. These functional groups are present on the surface or inside the porous structure of the biological material, in which carboxyl groups of alginate play a major role in the complexation of heavy metals. The optimal pH, which was the major factor influencing the adsorption of the metals, was around 6.4; and the higher the ionic strength, the lower the sorbing capacity. Different species of algae and the algae in the same species have different adsorption capacity. The selection affinity for heavy metals and the retention of physical integrity are two major criteria for the screening of a biologic adsorbent to be used in water treatment. The removal rate and sorbing capacity were relative to the chemical properties of the ions. In a co-existing ions system, the ions compete one another during the sorption, and the competition can be explained by 搕he principle of hard and soft acids and bases? Our study performed on the adsorption mechanism has significantly increased our understanding of the adsorption between algae and heavy metals. To get a thorough understanding of this, we still need further intensive studies. It is also need to carry out more on the immobilization of algae. The modification of algae can improve their mechanical properties. Immobilization of whole cells of microorganisms is one of the most commonly used methods both in fundamental research and industrial processes.