Sustainable approach for recycling seafood wastes for the removal of priority hazardous substances (Hg and Cd) from water

Monteiro, Rui J. R.; Lopes, Cláudia B.; Rocha, Luciana S.; Coelho, João P.; Duarte, Armando C.; Pereira, E.

http://hdl.handle.net/10400.1/9576

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Mercury and cadmium are considered by the water framework directive priority hazardous substances. In this work, the capacity of crab carapace and clam shell wastes to remove mercury and cadmium from water was evaluated under batch conditions, for realistic contamination scenarios in monometallic and binary solutions. The results evidenced that in monometallic solutions and under studied operational conditions, both biosorbents can achieve Hg2+ removal efficiencies higher than 80% and the kinetic process is well described by two of the most widely used equations, the pseudo-second order and the Elovich model. In terms of biosorption equilibrium, crab carapace and clam shell wastes displayed very distinct behaviours. While clam shells achieve the complete monolayer coverage and the isotherm is well described by the Langmuir model, crab carapace powder display a more unusual behaviour, that is well described by the BET isotherm, and is characterized by an almost convex shape to the concentration axis, with an infinite slope for an Hg2+ concentration in solution around 25 mu g/L. In binary solutions, both wastes are able to uptake simultaneously Hg2+ and Cd2+, however the uptake of Hg2+ was inhibited in some extent, attributed to the high kinetic and equilibrium selectivities of the bio-wastes for cadmium. (C) 2016 Elsevier Ltd. All rights reserved.