Potential application of Curtobacterium sp. GX_31 for efficient biosorption of Cadmium: Isotherm and kinetic evaluation

In this study, the adsorption capacity and mechanism of Cd 2 + ${}^{2+}$ by both live and dead Curtobacterium sp. GX_31 biomasses were evaluated using a batch experiment, adsorption isotherm and kinetic models, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) analysis. The optimal pH, dosage, and contact time were 6.0, 1.0 g/L, and 60 min, respectively. Under optimal conditions, the removal efficiency was >90% for the live biomass and close to 100% for the dead biomass at an initial Cd 2 + ${}^{2+}$ concentration of ≤ $\le$ 10 mg/L, and the maximum adsorption capacities were 37.04 and 40.16 mg/g for the live and dead biosorbents with 200 mg/L Cd 2 + ${}^{2+}$ . The R 2 ${\mathit{R}}^2$ values of the isotherm models indicated that the Temkin isotherm model was best fitted for both the live and dead biomass. The parameters K L ${\mathit{K}}_L$ (0.3998 vs. 5.1066), n (4.0177 vs. 6.0205), and b T ${\mathit{b}}_T$ (507.7947 vs. 675.3512) implied that the dead cells had a higher affinity, stronger adsorption, and higher binding energy than the live cells. The kinetic study showed that the pseudo-second-order model was more suitable for depicting the biosorption process, demonstrating that the rate-limiting step might be chemisorption and more than one step, which was confirmed by the intra-particle diffusion model. SEM analysis identified Cd 2 + ${}^{2+}$ adsorbed onto the cell surface. FT-IR spectra suggested that hydroxyl, amino, carboxyl, sulphate and carbonyl functional groups might be involved in Cd 2 + ${}^{2+}$ adsorption. Based on the results obtained, Curtobacterium sp. GX_31 might be a promising novel biosorbent for Cd 2 + ${}^{2+}$ -contaminated soil or water, especially at lower concentrations.