Efficiency of eggshell as a low-cost adsorbent for removal of cadmium: kinetic and isotherm studies

Eggshell (ES) is an alternative source of calcium carbonate that efficiently removes heavy metals in aqueous solution. The adsorption capacity of ES depends on their physico-chemical properties and the influence of experimental conditions, but in the majority of reports, not all the reaction parameters related to adsorption process of heavy metals are available, and the adsorption mechanism is not systematically studied. In this contribution, the use of ES waste is reported to establish an overall performance trend of the experimental parameters on cadmium ion (Cd2+) adsorption from an aqueous solution. Different physicochemical techniques Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) are used to characterize the physico-chemical properties of ES and the adsorption performance is studied as a function of contact time, pH, concentration, and adsorbent dosage. The highest adsorption capacity, 217.4 mg.g(-1), obtained in 10 min at an initial pH = 5 with an adsorbent dose of 0.8 g.L-1, is mainly attributed to the high specific surface area of the eggshell used in this work. Adsorption kinetics are described by the pseudo-second-order model, in good agreement with the experimental data, and the sorption mechanism follows the isotherm model of Langmuir, characterized by the chemical adsorption of a homogeneous monolayer of Cd2+ on the surface of ES adsorbents. The desorption efficiency of cadmium ions is efficient in the presence of nitric acid. The outcomes provided by the study confirm the use of eggshell as an effective and inexpensive material, offering high efficiency for cadmium removal.