Abstract

The removal of heavy metals from our environment especially wastewater is now shifting from the use of conventional adsorbents to the use of biosorbents. The presence of heavy metals in the environment is of major concern because of their toxicity, bioaccumulating tendency, and threat to human life and the environment. In recent years, many low cost sorbents such as algae, fungi bacteria and lignocellulosic agricultural by-products have been investigated for their biosorption capacity towards heavy metals. In this comprehensive review, the emphasis is on outlining the occurrences and toxicology of heavy metals and the biosorption capacity of biosorbents compared to conventional adsorbents. A detailed description of the adsorption properties and mode of action of these biosorbents is offered in order to explain the heavy metal selectivity displayed by these biosorbents. The role of cell structure, cell wall, micropores and macropores is evaluated in terms of the potential of these biosorbents for metal sequestration. Binding mechanisms are discussed, including the key functional groups involved and the ion-exchange process. Quantification of metal-biomass interactions is fundamental to the evaluation of potential implementation strategies, hence, sorption isotherms, sorption kinetics, intraparticle diffusivities as well as models used to characterize biosorbent sorption are reviewed. The sorption behavior of some biosorbents with various heavy metals is summarized, their relative performance evaluated and a bioseperation process flow diagram for heavy metal removal from  wastewater using biosorbents was proposed.

Key words: Biosorption, heavy metals, biosorbents, kinetics, wastewater.