Grapefruit biomass as a chelating agent in contaminated water
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A description of the experience
Environ Technol. 2012 Apr-May;33(7-9):761-72. The use of native and protonated grapefruit biomass (Citrus paradisi L.) for cadmium(II) biosorption: equilibrium and kinetic modelling. Bayo J1, Esteban G, Castillo J.
This paper describes the use of native and protonated grapefruit biomass, a by-product of the food industry, as an effective and low-cost biosorbent for cadmium removal from aqueous solutions.
The biomass composition was analysed by high-performance liquid chromatography, scanning electron microscopy coupled with energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy, showing that hydroxyl and carboxylic groups were the main functional groups implicated in Cd(II) biosorption.
The effect of different parameters affecting the biosorption process were studied. The optimum removal of cadmium ions was at pH 4.5.
Elution of alkaline-earth ions proved to be related with cadmium uptake, aiming for an ion-exchange mechanism. Protonated biomass showed higher adsorption affinity, binding strength and irreversibility for cadmium than native grapefruit, although the optimum metal uptake and high reaction rate was for the native form of grapefruit.
Biosorption experimental data fitted Freundlich > Langmuir > Temkin equilibrium adsorption models. Data for both types of biomass were better fitted by a pseudo-second-order kinetic model, with an excellent correlation between calculated and experimental values. Because of these experimental results, and taking into account that both types of biomass displayed an exothermic and spontaneous physical adsorption process, native grapefruit can be proposed in further experiments as a cheap, effective, low-cost and environmentally friendly natural sorbent for the removal of cadmium from industrial wastewater effluents, avoiding chemical pretreatment before its use.