Single and binary biosorption of cerium and europium onto crab shell particles

The ability of crab shell to biosorb two rare earth elements (REE), namely cerium(III) and europium(III) from single and binary systems has been studied. Crab shell majorly comprised of calcium carbonate, protein and chitin. Experiments to identify the role of these constituents in REE biosorption revealed that calcium carbonate was mainly responsible for REE removal. Microprecipitation of REE by carbonate ions and subsequent settling on the surface of crab shell was identified as major mechanism responsible for crab shell biosorption performance. At optimum pH of 6, in single component system, crab shell exhibited maximum Ce(III) and Eu(III) uptakes of 144.9 and 49.5 mg/g, respectively, according to the Langmuir model. In binary systems, both Ce(III) and Eu(III) compete with each other resulted in decreased uptake. In an attempt to model the binary biosorption data, Sheindorf–Rebhun–Sheintuch equation provided more accurate prediction of isotherm data compared to extended Langmuir model with constant interaction factor. Kinetic experiments revealed that equilibrium was attained in 60 min, followed by complete saturation in 2 h, for both Ce(III) and Eu(III). Pseudo-first order model better predicted the kinetic data with high correlation coefficients and low % error values than pseudo-second order model.