Ginkgo biloba L. shells-based adsorbent for the removal of Cu^2 + and Cd^2 + from aqueous solution: Kinetics, isotherm, thermodynamics and mechanisms

A large amount of Ginkgo biloba L. shells are produced from the well-developed Ginkgo biloba L. industries in China. The shell can be exploited as a low-cost and renewable adsorbent for the removal of heavy metals. In this work, physicochemical properties of Ginkgo biloba L.-based adsorbent (GS) were firstly characterized using composition analysis, proximate analysis, ultimate analysis, N₂ adsorption-desorption isotherm, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The adsorption of Cd^2 + and Cu^2 + using the produced GS was tested under various process conditions and the mechanisms studies were carried out. GS exhibited a typical feature of lignocellulosic biomass, containing 38.92% of cellulose, 26.14% of hemicellulose and 28.34% of lignin. Surface functional groups such as C[dbnd]O, [sbnd]OH, [sbnd]NH, [sbnd]C[dbnd]N and C[dbnd]C were observed and exposed on the rough and irregular surface of GS. In addition, minerals such as alkali and alkaline earth metals were discovered in the matrix of GS. The adsorption of Cu^2 + and Cd^2 + could be well fitted by the Langmuir isotherm model and the pseudo-first order model. The maximum adsorption capacity of Cd^2 + and Cu^2 + was estimated to be 21.58 and 42.59 mg/g, respectively. Thermodynamic analysis demonstrated that the adsorption was spontaneous and endothermic. Ion exchanges and complexation driven by minerals and surface functional groups were significantly responsible for the adsorption of Cu^2 + and Cd^2 + using the prepared GS.